the masterbuilder_november 2012
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Contains two articles written by me: - Backhoe Loader Industry in India - Fire Safety in High Rise Buildings (www.masterbuilder.co.in)TRANSCRIPT
48 The Masterbuilder - November 2012 • www.masterbuilder.co.in
Optimal Thermographic Procedures for Moisture Analysis in Buildings Materials
Thermal scanning is applied to buildings to collect information regarding component elements, their shape, their physical characteristics, and their state of
decay. Is based on analysis of the thermo-hygrometrical anomalies that affect structures. Thermovision is mainly used for investigation of surface defects (0-3 cm). One of the most frequent applications on historical building deals with moisture diffusion. Moisture damage is secondary only to structural damage as cause of decay in ancient buildings. The presence of water in structure and its changes of state (vapour-liquid) are responsible for the damage of materials, for damage of supplies inside the buildings and even for sickness of people who lives in. Same materials can be damaged differently depending on environmental conditions and, particularly, to the level of water contained inside the wall. Water content in walls is a fundamental information regarding the decay analysis in cold climatic condition; usually water content is a key factor when temperature stays below zero for several months. In those cases the water volume grows as frost and generates pressure within porous of the wall materials, therefore generating cracks in the structure. In northern Europe and America, the temperature stays below zero for long period
during winter: in addition to the damage already described the water in the insulation material coating causes thermal bridge the building. In temperate climatic area during winter, the thermal inertia, due to the thickness of the ancient walls (usually more then 50 cm), prevents the frost of water content inside the wall. Damage is concentrated on the surface (few cm depth), due to the continual cycles of frozen-defrost. An additional issue related to moisture is the water transition between the wall and the surrounding environment.
The investigation of moisture in walls is one of the more unreliable application of Thermography IR applied to Cultural Heritage preservation. The temperature of the damp areas are colder then dry ones (a), because of surface evaporation, or warmer (b), because of the higher thermal inertia of water versus building materials. The apparent discrepancy between the two results of detection (a) and (b) is due to the different microclimatic condition of the scanningi.
Aim of the paper is to define optimal procedures to obtain the reliable map of moisture in building materials, at different environmental and microclimatic conditions. Other goal is the description of the related energetic phenomena
Elisabetta Rosina1, Nicola Ludwig2 1Dipartimento di Conservazione e Storia dell’Architettura, Politecnico di Milano2Institute of Applied General Physics, Università degli Studi di Milano
The presence of moisture in building materials causes damage second only to structural one. NDT are successfully applied to map moisture distribution, to localise the source of water and to determine microclimatic conditions. IR Thermography has the advantage of non-destructive testing while it allows to investigate large surfaces. The measures can be repeated in time to monitor the phenomenon of raising water. Nevertheless the investigation of moisture in walls is one of the less reliable application of Thermography IR applied to cultural heritage preservation. The temperature of the damp areas can be colder then dry ones, because of surface evaporation, or can be warmer, because of the higher thermal inertia of water content versus building materials. The apparent discrepancies between the two results are due to the different microclimatic conditions of the scanning. Aim of the paper is to describe optimal procedures to obtain reliable maps of moisture in building materials, at different environmental and microclimatic conditions. Another goal is the description of the related energetic phenomena, which cause temperature discontinuities, and that are detected by thermography. Active and passive procedures are presented and compared. Case studies show some examples of procedures application.
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causing the temperature discontinuities, which are detect-able by thermography. In the contribute passive and active thermography are compared in order to define best application of each modality.
Thermography Process
Thermography works well to localise damp zones (ii), either in the passive way (no external heating) or in the active one (heating from outside of the building) (iii).
Active approach
Localisation of Major Thermal Capacity Areas
In temperate climatic area during winter, the thermal inertia, due to the thickness of the ancient walls (more then 50 cm), prevents the water content inside the wall to ice. Damage is concentrated on the surface (few cm depth) because of both the continual cycles of frozen-defrost and the growing salts deposits on the sub-superficial layers. On the other hand, in northern Europe and North America, the temperature stays below zero for long periods during winter: in addition to the damage already described the water in the insulation coating causes thermal bridge in the building. Finally, wetted building materials may cause healthy problems in a longer run. The water content in the building materials keeps the heat in case of protracted heating – e.g. solar radiating(iv). The damp areas have a higher thermal capacity than dry ones. So warmer areas can be detected without performing any artificial heating.
Water Content and Thermal Properties of the Materials
Moisture in porous materials (like construction ones) spreads into the pores to their filling. Water has higher specific heat (4-5 times) and higher thermal conductivity (20 times more then the air content in the empty pores) than common building materials. Water radically modifies density , specific heat cp and thermal conductivity k. All these three factors increase according to the water increasing. Thermal inertia (effusivity e) is a physical parameter that contains all the three factors. It can be easily determined by means of active thermographic tests.
(1)
Materials with different values of cp k could be characterised by measuring surface transient temperature in the heating process. The “active method” is based on the measure of the energy input and the temperature increase on the heated surface. The test supplies a constant energy flux by radiation to the sample surface. The surface temperature is measured by a long wave thermocamera that acquires thermal images at a rate of 0.2 Hz.
An adequate theoretical model of heat transfer allows processing the temperature increase of the surfaces during the test. In the case of building materials both low conductivity and thickness (some cm) allow to use a simple solution of the heat transfer equation in the approximation of adiabatic and semi-infinite medium. The sample is considered homogeneous and isotropic, with a uniform superficial temperature T0 at initial time. A uniform heating flux Q for a short time (few minutes) has performed. That heating allows to consider adiabatic (without significant heat losses) the temperature evolution. In this conditions the expression of the surface temperature is(v):
(2)
where the thermal inertia can be singled out and represents the angular coefficient of the square root of the time versus the temperature increasing ( T).
(3)
Nevertheless only the measured value of thermal capacity allows to obtain the water content
(4)
where Cpw is the specific heat of water, Cpd of the dry material and Cp (referred to the moist material) can be determined, according to (1), only if the thermal conductivity of moist materials is known.
The measure of thermal diffusivity a allows to obtain k, the conductivity of moist material, that can not be measured directly.
and in this way (5)
Nevertheless , at the present state can be obtained only in lab, on specimens. Therefore the method is unlikely used on the field, to determine the water content.
The Reference Method
The test can be simplified using dry materials as reference if the absorbed energy is constant both in time and in space. In this case (called “reference method” vi) the measure of the energy absorbed is not required. A major absorbivity due to the water content in damp materials allows to evaluate their thermal inertia. Therefore the value of thermal inertia of a sample, of unknown water content, gives good indication about its water content if compared with the thermal inertia of a dry sample.
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Materials and Methods
Five brick cores with different water content were the samples under test. The bricks had homogeneous characteristics of weigh, volume and thermal properties (emissivity and absorption). The samples (30 cm3) were dampened and placed in airtight containers for 48 hours. The specimens were heated by lighting (two halogen lamps, 500W, colour spectrum 3300°K), at under control conditions. The lamps were set symmetrically at 60 cm from the surface. The power of the heating on the surface was around 800 W/m2. The heating was long 2 minutes, and the frequency of the recording images was 5/sec. The measures were repeated changing the displacement of the samples, to survey differences of heating due to the lamps. The absorption gap due to water content was estimated in about +20%.
Further lab measures were carried out to test the method on a large scale model. The model of an ancient wall was built in the lab of DCSA, Politecnico di Milano. Pebbles, bricks, lime mortar as materials for the inner structure. A double layer of lime mortar plaster coats the surfaces. A 3D survey supplied the irregular thickness of the not plane plaster. A pipe system, insert in the wall during the building, allowed to fill with waters the wall in a short time. The same measure procedure was repeated. Many cycles of heating have been performed on the model and on five brick cores -at different water content – to compare reference and passive methods (fig. 1-3). The devices employed were: thermocamera -AGEMA 900, Humbug environmental probes - RH%, T°C.
Graphs 1, 2 show the results. The values of angular coefficients related to graphs are in tab. 1
Graph 1: Reference Method Applied on Solid Brick Cores
Graph 2: Reference Method Applied on Wall Scale Model
Water Content Dry 17,8% 17,6% 8,7% 7,7%
Angular 0,85 0,42 0,47 0,48 0,45
Coefficient
Tabel 1: Values of Angular Coefficients Related to Graphs 1
The ratio of e between the dry specimen and the wet one is 0.45, rather near to the literature value 0,66 (iii), when Q increases of 20% (due to the major absorption of radiation, above all in the infrared range).
The method does not survey the differences of water content if more then 7%, as it appears in the graph 1. The differences of angular coefficient of the lines may depend on not homogeneous radiating. As verification the position of the specimens have been changed, at the same heating condition: actually the variations of angular coefficients changed, related to the new position of the specimens.
The dependence of effusivity on the water content is not clearly defined (theoretically and from lab tests), nevertheless the data obtained by lab tests and specific literature allow to point out that the change from dry to wet condition (saturation) increases effusivity of about 80% (brick). Effusivity changes are not enough remarkable to indicate the variation of water content, above all on the field, where the margin of uncertainty ranges 20-30%.
Passive Approach
Localisation of Surface Evaporative Flux
In the case of evaporation, so frequent at less then 45°Latitude(vii), the high value of latent vaporisation heat,
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causes the cooling of the moistened surfaces(viii). The evaporation most of all depends on Relative Humidity (RH) of the air near the surface, on its Temperature (T°), on the water content in the material, on its chemical-physical characteristics and on soluble salts content. The influence of T° and RH on the evaporation speed can be studied only keeping microclimatic conditions under control.
The Evaporative Flux in Wall Energetic Balance
The measure of wall surface temperature allows to obtain a precise and quantitative indication of the evaporative rate when an opportune model is defined for the energetic balance on the wall surface in dependence of air temperature, environmental radiation, the speed of the wind and the relative humidity. In dry building materials the energy loss caused by the evaporation is insignificant compared with the total energy transferred over the surface. Conduction from the inner wall is neglectable when determining its superficial temperature in the time characteristic of the thermographic scan of the wall (few minutes).
This effect is amplified in the ancient wall because of its thickness and the use of solid bricks. Regarding the energy associated with the mass transfer within the wall (water and salts) it is less significant then the energy lost by evaporation. In fact the amount of heat carried by a certain quantity of water from a point to another of the wall is approximately two orders of magnitude less then the energy required to evaporate the same quantity of water.
If we take into account the effect of a forced evaporation in the energetic balance of the wall surface it causes a thermal imbalance Q, which can be observed as a decrease of some degree of temperature. This is essentially compensated by the increase of convection and conduction. If the heat loss caused by the evaporation is constant the cooling effect of the wall can be calculated knowing the equilibrium temperature among the different kinds of heat exchange.
Furthermore in the aforesaid conditions of strong evaporation the energy loss causes a decrease of temperature dT in a time dt upon all the evaporating surface according to the inverse proportion to its mass on superficial unit (superficial density of mass m) and to its specific heat.
(6)
Water content may be evaluated in function of thermal capacity of the damp masonry cpm. The solution of (6) gives cpm, if all the kinds of thermal exchange on the surface are defined (viii).
Evaporative Flux Computation
The evaporative flux is obtained at the balance between
the kinds of thermal exchanges This happens when the temperature assumes the equilibrium value T . The expression of the flux assumes therefore the form:
(7)
where: and a = mean emissivity of the sample in its existence range and environmental efficacy emissivity; = Stefan- Boltzmann constant ( 5,57 x 10-8 W/m2K4); =
absorption coefficient of the wall surface, Ta= environment temperature; Tint = inner temperature of the wall; h= convective exchange coefficient; k* conductive coefficient;
ev= water heat vaporisation ; ev= evaporative flux (kg/m2s).
Where the terms due to the radiation exchanges can be estimated with good precision considering zones lacking in evaporation, but in the same conditions of radiation. Temperature reaches T in times of the order of 102-103 sec for the brick samples of small dimensions (30 cm3) under investigation.
Material and Methods
The tested samples were the same brick cores as above (paragraph 2.1.3) with different water content (17.8% 17.6% 8.7% 7.7% and dried in hot air). The samples (30 cm3) were dampened and placed in airtight containers for 48 hours. For the continuation of experiments we used a climatic chamber (fitotrone) that allows to range environmental variables: temperature (10-40 C), RH (20-98%), air speed (0.1-5m/s) and lighting (0-5000 lux). The environmental conditions chosen for every experiment were 0 lux, air speed 0.1 m/s (which would minimise the convection’s effects), air temperature of 25° C, and relative humidity kept constant at 50%. The samples were subsequently isolated on the bottom and lateral side with a waterproof membrane. A balance (precision 10-3 gr) in a climatic room measured their weight drop in continuos. In order to estimate the conditions of radiation inside the room some dry samples were put beside the damp samples, with same shape and emissivity.
The cooling due to evaporation was recorded by a thermocamera (AVIO 2000 SW) (Graph 3). The evaporative flux of each sample was measured continuously by a precision balance connected to PC. The samples achieved balance temperature in about 5 minutes. The flux values were calculated according to (7), using the temperature measures, and keeping in account the environmental radiation and convection. The comparison between data is shown in tab 2. The same experiment has been carried out on the model of wall (see previous paragraph). Graph 4 shows the thermal curves of cooling. In this case the evaluation of evaporative flux is more difficult because
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of the unknown coefficient of environmental convective exchange and non-homogeneous surface of the wall, even if it is possible to identify the balance temperature of the areas with different water content.
Graph 3: Evaporative Cooling on Brick Cores
Graph 4: Evaporative Cooling on Scale Wall Model
Thermographic Procedures and Optimal Condition of Shot
The application of thermography to buildings is scarcely supported by specific rules in force. In Italy ISO 9252/88 is the only recommendation edited, and specifically regards Thermography employed to detect energetic loss. The standard is based on the results of IRIS-CNR research group (1985) and it refers to procedures relative to out of date device. The authors present a first report on the procedure in use, based on their experiences, to improve and to contribute to the debate in course in the international committee and research groups devoted to NDT procedures. The approach is exclusively functioned to moisture detection by the presented method.
Generality
The examination of all the documents available regarding the project and the components of the structure is a mandatory prerequisite. A survey of the materials, of their damage is required, in order to know the actual state of the surface to investigate. These data allow to localise the inquiring areas on which the operator will apply the specific modality of investigation (see following paragraphs) and even the integration with other testing. The investigation of damp areas is based on the comparison between the thermal behaviour of dry and damp areas: therefore in the same shot there can be both zones, at the same condition (of heating or, in passive method, of the environment surrounding).
Spot heating (e.g. hot pipelines, electric cables, plaster delaminations, stains or coloured parts) may affect the results. Winter heating inside the building could prevent to detect moist areas:
- The heating tends to dry the wall in case of residual low-medium water content,
- Thermal bridges due to thin walls, their non perfect connection, windows and doors, etc, may cause false alert
A preliminary scanning requires to shot all the surface of the wall, to set camera parameters and to detect the most evident anomalies. Further shots, closer to the surface, allow to analyse the investigated defects.
Active Thermography
Reference Method
In case of surface not exposed to sun radiation, the operator has to provide artificial heating on the field, as like above mentioned about lab test. In this case the reference method supplies experimental data.
- Plan of the scanning
17,8% 17,6% 8,7% 7,7% Dry
Weighed flux 4,76*10-5 4,40*10-5 0,98*10-5 1,06*10-5 0,00
Calculated flux (eq. 7)
4,55*10-5 4,50*10-5 0,80*10-5 0,82*10-5 0,00
Tabel 2
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- The thermal analysis has to be applied on small but homogeneous zones.
- LW thermocamera provide best results (the scanning has to be shot during the heating).
- Frequency of images not less then 1/sec
- Reference and investigated areas have to be shot in the same pictures.
- The surfaces have to be as homogeneous as possible: same materials, colour, roughness, reflectance, etc, for both the reference and the damp areas.
- Accuracy during the heating is mostly required.
Heating Set Up
- The heating has to be mostly homogeneous both on the wet and on the reference areas. Lighting is the best modality. The operator has to dispose even number of halogen lamps, symmetrically to the investigated areas.
- The camera has to be settled perpendicularly to the surface, and the sequence of recording depends on the speed of heating. Slow and low heat transfer is possible, due to their low conductivity. Differences of the thermal behaviour (revealing damp and dry zones) have to be pointed out in a short time, before reaching the energetic balance between radiation from lamp/environment and the wall. Powerful heating (1000 W/m2) is required to increase the temperature of surface at least of 4-5 degrees in the time as short as possible (few minutes).
Post Process
Adequate software allows to analyse the sequence of the thermal image during heating. The thermal curves support the comparison between damp and dry surfaces. In lab data process the curve is obtained from the average values of small areas chosen inside the investigated surface. In case of not homogeneous surface the choice of these areas may affect the final results, because the optical characteristics of the surface alter the heating absorption due to water content.
Outside Shot (Without Artificial Heating)
- High air RH% and wind pressure do not affect the reliability of the test; anyway optimal environmental conditions, as like clear sky, no rain, T° not below 0°C, are favourite.
- In case of the source of the heating is natural (sun), the orientation of the surface is fundamental to plan the scanning. Depending on the disposition even the same external elevation could be radiated in different hour and for different time.
- Shadow due to other buildings or to projections may
affect the thermal images. All these factors have to be recorded before scanning, in order to calculate the best time of the shot.
- The scanning has to be shot in emissive phase, after the end of the radiation.
- No artificial heating is required.
Post Process
Thermal analysis software may supply qualitative analysis and the study of the thermal profiles of the areas investigated.
Passive Thermography
- Plan of scanning
- Thermal scanning has to be applied at steady state condition.
- The surface has to be kept out of direct heating for approximately 12 hours before the scanning.
- Environmental or microclimatic condition may prevent a reliable scanning: the operator has to measure microclimatic and environmental T° and RH% continuatively during the scanning.
- In case of critical condition some solutions are possible to increase the level of transpiration so to improve measurements (e.g.: increase the temperature, so to decrease RH; dry air close to the surface, etc.)
Environmental Conditions
The most appropriated environmental conditions required to increase the level of transpiration so to improve measurements are:
- Low RH in the air layers in contact with the surface (lower then 80%)
- Air temperature not below 6-7 C°.- Strong draught generating air movement
Post Process
After Thermal analysis supported by specific software, further image elaboration improves the qualitative results. In every case a specific palette of colours or grey levels has to be studied in order to point out the differences between damp and dry zones.
Case Studies
The following examples show applications of active and passive thermography. Integrative tests were carried out in most of the cases, e.g. gravimetric tests, to quantify the water content in the areas where surface temperature was anomalousix. Integration of these tests gives advantages of the mapping speed of moist distribution, obtained without touching the walls (by thermography), and the quantitative
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knowledge of the water content on the surface and inside the wall (by gravimetric method). The results of weighting test are not only related to the dried specimen but, if the results of the thermography show an homogeneous surface temperature distribution, also to all the investigated areas. The strict connection with lab tests allowed to perform the most adequate technique on the field.
In the first of the case presented, the damp areas were pointed out by both of the two different phenomena (thermal inertia and evaporative flux) acting at the meantime and at the same microclimatic condition. All of these cases are settled in northern Italy
Donizetti Institute of Music, Bergamo
The historical building is settled in the centre of the city. The actual shape is due to the progressive joint of close buildings. The differences of elevation of the same floors denounce that the original structures (made of different buildings) remained under the restructure of the facade. The major damage is related to the presence of water at the ground floor and in the cellar, and its distribution follows the anomalies of the building.
Objective of the analysis: map of moisture diffusion, evaluation of water content in the walls, finding the source of infiltration or rising damp.
Results
Passive thermography was applied. It revealed that the major concentration of water was in the first room of the cellar. Both the walls under the main street and the inner yard were damp. A curious difference may be noted: the wall (fig. 5, wall “A”) presents a constant water diffusion from the bottom to the top, and the damp areas appear warm. In the opposite wall (fig. 6, wall “B”), the moisture is localised above all in two large spots, colder then the surrounding surface.
According to the distribution mapped by thermography in “A” wall the plaster’s water content resulted 8.9%-12.2% (saturation value: 19%), limestone’s 9.6% (saturation value =25% ) brick’s 6-13% (saturation value = 19%). In “B” wall water content achieves higher values: 17.5-27% plaster; 24% limestone, clay 28%, brick 24%. The microclimatic condition were critical during the scanning: 13°C, RH 76%. At this condition evaporative flux is quite inhibited, it is detectable only where “running” water is emerging at the surface.
The conclusion was that the “A” wall was affected by damp coming from the contact with the earth (under the street level), while in the “B” wall, additionally to the damp due to the earth, two main infiltrations were localised, due to two leakages in the old pipelines.
Santa Maria Delle Grazie, Milano
The walls of the famous cloister (home of Leonardo’s Last Supper fresco) were affected by rising damp. The cement-lime mortar of the plaster, applied during the last restoration, prevents evaporation of water content. Nevertheless the damage affects the basis of the wall (below 80-100 cm from the ground).
Objective of the analysis: identify the line of rising damp, verify the correspondence between visual state of damage and moisture distribution.
Results
The images were shot at critical condition (T°8-9°C; RH 89%, clouds): evaporative flux was furthermore inhibited. Active reference method has been applied. The light but continuous heating inside the rooms was evident in the damp part of the wall even in the preliminary passive shot. Following graphs show the thermal curves obtained during the heating. The curves of the two zones have clear differences (Dry area = squares, damp = crosses). Weighing test, performed on samples from the surface, resulted 6.5% (area 1, at the bottom)- 5.6 % (area 2, 1.2 m up to the floor) of water content (plaster, saturation value = 14%).
Santa Maria in Cantuello, Ricengo (Cremona)
A colder strip was detected at 2.5 m up to the floor, in the niche of Angel’s statue. Optimal microclimatic conditions allowed to detect the areas where evaporative flux were acting (T=15°C, RH=60%). In that point the brick wall was affected by an infiltration, due to a solid deposit of earth on the edge of the roof. A sod overgrown with moss coats the roof of the little niche and it is responsible for the infiltration.
SQ time [s^0,5]
Martinengo Parrish (Bergamo)
This church is settled in the Po plane, it presents damages due to raising damp: all the frescoes up to 1-1.5 m from the ground level were destroyed. A thermographic campaign
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was carried out in May ‘98 to detect the situation of the actual level of the rising damp. The zones interested in the rising damp coincided with the most damaged ones. The thermographies were shot in a dry sunny day with 28° C outdoor temperature and 22°C inside, during the measure the relative humidity varied between 55% and 68%.
Discussion
The comparison between the methods appears in the following tab. The authors compared the results obtained only on the investigated materials (plaster and brick)
Active Method(detection of major
inertia areas)
Passive Method(detection of
surface interested by evaporative flux)
Advantages Direct measure of the water content (on labsamples)
Direct relation between evaporative flux anddamage of the surface. No heating required.Applicable on wide surface
Limitations Difficulty to obtain high and homogeneousheating. Reference Method: the measures are relative to a dry area.
Dependence on environmental andmicroclimatic condition
Dependence on Soluble Salts
Yes; soluble salts may change surfaceabsorption
Yes; flux evaporation decreases wheresoluble salts are present
Speed of the Test Speedy measures on the field, quantitativeresults requires post processing phase
Speedy measures on the field, quantitativeresults requires postprocessing phase
Sensibility to the Water Content
Low-Medium: 10% for porous materials
Low-Medium: 10% for porous materials
Dependence onEnvironmental Conditions
No Yes
Cost Low Low
Conclusions
Both the systems allow to map the moist areas. An advantage of the passive system has an easier extension to large surface. It connects directly the evaporative flux and the damage. It allows early diagnosis of the zones more to risk for the degradation identifiable thanks to the presence of high evaporative flux. Those zones, where moisture even if not still rendered evident from connected pathologies, will be manifested with certainty in case not take part to modify the variable that determine it. Moreover the illustrated methods can be used also to monitor and to test the restoration intervention on buildings.
The unsolved problems are linked to the on field application (reference method) and the dependence on the environmental and microclimatic conditions (passive method). Particularly in the active procedure on the field: the heating modality (homogeneity), the measures of thermal diffusivity (without collection of samples) and the limitation of math model applied.
In the passive modality the study of influence of environ-mental condition has to be carried out, to find a direct correspondence between the variables, and to obtain a valid measure of evaporative flux.
In that way experimental set up will be disposed to measures environmental variables mainly affecting thermographic process.
Figures
Thermographs of the five brick cores, placed in a insulating frame.
Fig.1: During Lighting
Fig. 2: Without Heating During Evaporative Cooling
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References
i E. Rosina, N.Ludwig, L. Rosi, “Optimal Conditions to Detect Moisture in Ancient Buildings. Study Cases from Northern Italy”, Thermosense XX-An International Conference in thermal sensing and imaging, diagnostic applications, Orlando (USA), April 1998
ii M. La Toison, “Infrared and its Applications”, Philips Technical Library, N.V. Gloeilampenfabrieken, Endhoven (The Netherlands), 1964, pg. 83-100
iii E. Grinzato, G.P. Bison, S.Marinetti, V.Vavilov, “Thermal Infrared Non Destructive Evaluation of Moisture Content in Building: Theory and Experiment”, CNR Congress on Moisture, Varenna (Italy), September 1994
iv A. Colantonio, “Thermal Performance Patterns on Solid Masonry Exterior Walls of Historic Buildings”, Thermosense XIX, SPIE vol. 3056, Orlando (USA), April 1997
v M. Phillipson, A. Stupart, “Temperature and moisture conditions in masonry: frost performance”, Proceedings of Int. Symposium on Moisture Problems in Building Walls, Porto (Portuga1,) September 1995, l, pp.405-415
vi E. Grinzato, G.P. Bison, S.Marinetti, “Moisture evaluation by dynamic thermography data modelling”, Thermosense XVI, SPIE vol. 2245, Orlando (USA), 1994
vii L. Binda, G. Baronio, “Studies of the Durability of Brick and Stone Masonry and Their Components”, Selected Papers 1979-1996, vol., II, DIS, Politecnico di Milano, Milano (Italy),1996
viii N Ludwig, M.Milazzo, G.Poldi, “Misura di umidità superficiale nelle murature mediante termografia”, 9° AIPND National Congress, Padova (Italy), September 1997 pgg.163-172
ix G.Cruciani Fabozzi,E. Rosina, M.Valentini: La valutazione del regime termoigrometrico della muratura: integrazione di termografia e prove ponderali. 20° Congr. Naz. AICAT-GICAT, Workshop : Metodi chimici , fisici e biologici per la salvaguardia dei Beni Culturali. Roma 18-12-1998
Fig 3: Active Thermography: Moisture Diffusion During Heating, the Damp Areas are Colder Because of the Major Thermal Inertia
Fig 4: Music Institute Donizetti, Bergamo. Wall “A” in the Cellar; Passive Thermography, the Rising Damp Affecting the Bottom of Wall Corresponds to the Warmer areas. Fig 5-6, Thermocamera AGEMA 570 LW
Fig 5: Music Institute Donizetti, Bergamo. Wall “B” in the Cellar; Passive Thermography. Despite of the Critical Microclimatic Condition (13°C, 76%RH) two Infiltrations (Due to Pipeline Leaks) are Evident as Colder Areas.
Fig. 6: Santa Maria Delle Grazie, Milano. Passive Thermography of the Damp Bottom of the Wall. The Major Thermal Inertia of Water Content Kept the Light Heating of the Room After its Turning off. Thermocamera AGEMA 900 LW
Fig 8: S.ta Maria in Cantuello, Ricengo (Cremona): passive thermography reveals a colder strip (40 cm large) behind the Angel Statue, 2.50 m up to the floor. A sod overgrown with moss coats the roof of the little niche and it is responsible of the infiltration. Thermocamera AGEMA 489 LW
Fig 7: Martinengo Parish (Bergamo).The Rising Damp Corresponds to the Colder Zones at the Bottom of the Walls. Thermocamera AVIO TVS- 2000 SW
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Construction of Underground Metro Stations and Associated Tunnelling
The population of Chennai in 1639 was 40000 and today the city is estimated to have a population of 7.5 million, which gives a population density of about 6482
per sq. km. The city, with its present population generates about 11 million trips in a day, with about 6million vehicular trips. The ever growing vehicular and passenger demands coupled with constraints on capacity augmentation of the existing network have resulted in chaotic condition during peak hours of the day.
A number of transportation studies were carried out in the past for Chennai Metropolitan Development Authority (CMDA). These studies discussed travel pattern, network characteristics and the degree of traffic saturation on the existing roads in the Study Area. The proposed high capacity, high frequency metro will not only be a cheaper mode of transport but also provide for a safer, reliable and better customer service. A feasibility study was carried out in 2003 to select and priorities the corridors for Chennai metro. Based on detailed traffic surveys seven corridors were identified.
The Metro rail will wind its way at a speed of 80 km/hr through the city over a distance of 45.1 kms of which 24 kms will be entirely underground. Total area of land required for the construction of Metro is approximately 50 hectares equivalent to 100 football fields. The project is estimated to cost 14000 Crores INR of which 41% will be contributed by the Central and State Governments. The remaining amount will be funded by a loan from Japan International Cooperation Agency (JICA).
L&T has been one of the leading construction company having prior experience working in similar projects however, the Chennai Metro construction comes with its share of challenges and difficulties. In the construction industry each site is unique in various aspects and the features of the site should be analysed and incorporated right from the tendering stage of the project. In case of
metro construction, even though the basic methodology remains same for Delhi and Chennai Metros, the variation in the soil and climatic conditions of the two cities will result in variation of project duration and equipment and labour deployment.
The contract value of the project is 930.8 crores. Chennai Metro Rail Limited (CMRL) is the client for the project and they have nominated M/S Embye as the general consultant for the project. The design consultant for the project is the award winning consultants: M/s Mott MacDonald Pvt. Ltd.
After successful completion of many stations in Delhi Metro Project, L&T in a JV with Shanghai Urban Construction Group (SUCG) is now executing the project comprises of the design and construction of all works and services necessary to complete the underground section from the west end of Egmore station (Egmore station not included in UAA-04) to the south end of Shenoy Nagar station (Shenoy Nagar station not included in UAA-04) in Corridor 2, i.e. Nehru Park Station, Kilpauk Medical College Station and Pachaiappa’s College Station each of 228m .Design and construction specifications, include the following: - Survey and Handing over of the project land and
associated site clearances. - Traffic Diversion for undertaking station works with
alternate roads and steel decking - Diverting utilities from the station zone. - Construction of Diaphragm wall including temporary
& permanent plunge columns as station retaining structures and load bearing columns respectively.
- Construction of launching shaft for TBM Drive. - RCC Slabs Construction at three different levels i.e. at
roof level, concourse level and base level. - Selection of tunnel Boring Machine (TBM- Earth Pressure
Balance type) manufacturing and shipment to site. - Construction of TBM launching chamber - Lowering, Assembly and commissioning of TBM for
R G SainiProject Director Metro Tunnelling Chennai, L&T SUCG JV
Ground Engineering
www.masterbuilder.co.in • The Masterbuilder - November 2012 61
construction of tunnel. - Segment Ring Casting at precast yard for feeding as
liner to tunnel. - Tunnel Drive for down line till next shaft and
relaunching. - Tunnel Drive for up line till next shaft and relaunching. - Construction of TBM retrieval chamber - Cleaning of tunnel and installing accessories including
walkways and cross passages.
8. Interface and support for various system works like track laying, the overhead catenary for power, passenger gates, signalling and telecom, VAC and AHU systems along with lifts and escalators
9. Architectural works matching with heritage structure nearby for main station box and entrances including signages.
10. Electrical & Mechanical works including plumbing, drainage, fire fighting and electrification.
11. System integration and trial testing.
12. Provision of station and substation structures, utility diversion and relocation etc.
13. All works necessary to provide inter-modal transfer facilities for pedestrians & road user of ground level and access into station.
14. All temporary and permanent utilities including foul drainage to be connected into public services.
Major quantities
Diaphragm wall 55,0000 sqm
Piles 4250 rmt
Excavation 3,40,000 cum
Concrete 1,35,000 cum
Reinforcement Steel 18,600 mt
Structural steel 1850 mt
Waterproofing 41,000 sqm
Tunnel Segments 5670 Nos
Major Plant and Machinery Availability
We cannot imagine Metro without machineries, as it presents many civil engineering challenges at sites involving greater heights and deeper depths. Many challenges have been met successfully through deployment of new expertise, sophisticated machinery and equipment at the site to execute any work. So we have mobilised many high capacity cranes like TFC-280 and QUY-80 , medium capacity cranes of make P&H 335, P&H 440,EOT cranes, casagrande rigs BH 180, DG’s of various capacities ranging from
250 Kva to 62.5Kva ,and many excavator including long arm excavators, overhead gantries for executing various activities of the project. This is in addition to tunnel boring machine and related specialised equipment required for tunnelling with 5 nos. of silent diesel generators of 1012 Kva capacity each and batching plant for concrete and grout production.Cranes are provided with Safe Load Indicators (SLI) and tools & tackles are all inspected by an external agency before implementing at work.
Tunnelling by Tunnel Boring Machine and Related Instrumentation
Since tunnelling can result in a significant range of vibrations to the adjacent buildings, instrumentation in all locations adjacent to the tunnelling areas is required. Monitoring instruments which are given below and many more are installed to monitor the movement and of structure on a daily basis.
1. Settlement Points used for monitoring vertical settlement on horizontal and vertical surfaces of a building or a structure.
2. Piezometer which is used for measuring magnitude and distribution of pore water pressure and its variation with time.
3. Inclinometer which is designed for measurement of lateral movement of any structure.
4. Load Cell used for measuring and monitoring forces on a modular structural strutting.
The Tunnel Boring Machine is a huge, incredible piece of equipment that can forge its way through hard rock, sand or soil, hollow out tunnels without any disturbance to the surroundings. In CMRL UAA-04 project, two nos. TBM is being used for the project to match with the project speed. The TBM have been especially design for encountering mix strata and accordingly the cutter disk and other components are design by specialist with various design parameters which took nearly six months of manufacturing and two months of shipment from Shanghai to Chennai.
Major Components of TBM
1. Cutter Disc- To excavate rock or soft ground by the rotation of an assembly of teeth or cutting wheels under pressure against rock face.
2. Shield Skin- keeps the soil from getting into the machine and to provide a safe working space for the workers.
3. Pushing Jack- To be in full contact with the erected segment and hydraulically extend as the cutter disk turns and thrusts forward.
4. Main Drive- To provide a force in rotating the cutter disc.
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62 The Masterbuilder - November 2012 • www.masterbuilder.co.in
5. Screw Conveyor- To move the spoil at the cutter disc and feed onto a conveyor system.
6. Erector- To erect the segments to form a complete ring after shifting upto the tail of the TBM.
7. Backup facilities- To travel with the TBM and to service the operation of annulus grouting, welding, extension of ventilation, power and track etc.
TBM commissioned by L&T-SUCG JV
The TBM can work continuously for 10,000 hours and can bore at an average speed of 8mm/min. The total weight of all the components of the TBM is more than 400 tonne with
maximum weight of one of the component is 120 tonne which requires a great deal of logistics to handle from the port to the project site and lowering into the 20m deep shaft.The TBM while in operation exerts a maximum force of 45,184 kN. The TBM will operate at an average speed of nearly 6m/day in rocky strata and of an average speed of 10m/day in soil strata and the boring will continue at depths of 22 to 27 m below ground level.
The length of the TBM is 78 metres in total and the outer diameter of the cutter head is 6.3 m. The initial drive of the TBM will be to a distance of 10 m which is equal to the length of the cutter head and associated accessories. We are providing every safety measures for the tunnelling as the TBM alignment passes below many high buildings. The ring consisting of 6 segments of 1.2 m width,275mm thickness and 3.7 m length for each of the 5 segments and 1.3 m for key segment used for lining of the tunnel which is being cast at the casting yard in Vayalanallor. The surface logistics for the transportation of the segments has been planned in such a way that the segments can be brought to site with minimum hindrance to the public while minimising the travel time of the segments from the casting yard to site. One 40 tonne trailer can carry 2 segments and each shift will be requiring 6-8 trailers of delivery depending upon the progress of the tunnel.
TBM Launching from
TBM Retrieval at Distance between two location(m)
Nehru Park Station Egmore Station 939
Nehru Park Station Kilpauk Medical College Station
562
Pachaiappa’s College Station
Kilpauk Medical College Station
804
Pachaiappa’s College Station
Shenoy Nagar Station 1036
The TBM goes in four sections, both up line and down line through the tunnel alignment.
Planning for the Construction
Considering the complex nature of project involving various disciplines and interface with many system wide contractors spreading over more than 4000 activities interlinked to each other hence a Detailed Works Programme (DWP) required to be prepared in the beginning of the project considering base line and key dates, target dates of the contract. The programme is updated regularly based on the actual site condition and land availability and other parameters. The construction team follows the programme and update regularly based on various inputs from time to time.The micro schedule which has been prepared is regularly updated. The scheduling is being maintained in Primavera for easy updating and monitoring.
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64 The Masterbuilder - November 2012 • www.masterbuilder.co.in
Project Details
Our Project Construction Mainly Consist of
The project mainly consists of the construction of Diaphragm wall, which act as a retaining structure and boundary for our station. The diaphragm wall is constructed for every 5 meters of the station length and goes upto the depth of the station. Koden test and sonic logging test are done for checking the verticality and D-Wall integrity respectively. Some of the chemicals like Geosoil Polymer are used in the trench for its stability during 25 m of trenching work before putting the reinforcement cage inside.
Launching shaft is constructed to launch and retrieve the tunnel boring machine. For Launching Shaft construction excavation has to be done depending on the Top Down Construction (excavation from top to base with the use of struts to retain the structure) or Bottom Up Construction (excavation from base to top with the construction of slabs). Dewatering is also being done before the excavation for removal of the water through dewatering wells. The excavated muck is transported to the dumping yard situated at 35 km away from project site at night time ensuring the cleaning of each dumper on wheel washing bay to prevent the dust accumulation on road.
Metro station slabs are to be constructed in three levels; viz. base slab, concourse slab and roof slab level having 6m vertical clearances in each level. The slabs will be constructed using a combination of top down method at the shaft locations and bottom up method at the station areas. Waterproofing above and below slabs wherever necessary is being done to prevent the water leakage.
Cross Passage
Cross passages(CP) are connecting tunnels and are to be provided at regular intervals to evacuate passengers in case of any emergency. The cross-passages will be provided at 250 m intervals. Before starting the cross passage excavations, it is necessary to improve the soil characteristics around CPs. High pressure jet grouting method will improve the soil stabilization.28 days later,
Bottom Up Constructed Launching Shaft
Station Model
there will be a core test to confirm the soil is strong and stable.The cross passage will be constructed using NATM method with suitable waterproofing measures having a provision of sump at the deepest location of the tunnel
Internal Activities and Finishing Inside Tunnel
Location Area in m2
Nehru Park 17522
Kilpauk Medical College 12460
Pachiyappa College 13328
The Total Area Required for the Construction in the Three Sites of UAA-04 Package is
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www.masterbuilder.co.in • The Masterbuilder - November 2012 65
The segment lining will provide the required architectural finish for the tunnel. Dimples have been provided in the segments at the time of casting for drilling and cable laying. The rail will be placed over a base support with adequate drainage.
Walkways
- Ensuring cleanliness of the road. Deployment of separate housekeeping workers
Provision for environmental impacts of this Metro corridor has been made to cover various protection works, additional compensatory measures, and compensation for loss of trees, compensatory afforestation and fencing, monitoring of water quality, air/noise pollution during construction is done. For every one tree cut 12 trees are planted and maintained.
The safety department conducts regular pep talks and training sessions for workers and engineers. Regular audits are conducted on site and the safety issues are addressed immediately. The project is certified by BSI-ISO and OSHAS and recently was conferred with the ROSPA award.
Walkway will be provided for service personnel and emergency rescue. It is also known as Escape Walkways which provides continuous access from the train to the cross passages and station platforms and having a width of 966 mm at train floor level.
Quality initiatives
The Metro work has to be executed with full quality control and guaranting the overall life of the project as 120 years following all the codes and specification laid. Many varieties of test are conducted for ascertaining the quality of activities in hand like Sonic logging test for D-Wall integrity, Pull out test for couplers, adiabatic test for temperature control, Proctor test for compaction. The quality team work towards ensuring proper quality standards of the raw materials such as cement, sand, aggregates, admixture, as well as concrete of M20, M35 & M50 and fabricated steel. The quality laboratory is well equipped with scientific instruments calibrated to conform to Indian Standards and to test the materials at the required testing frequencies.
Safety Health & Environment
- Barricading the construction zone - Diversion boards are all placed at frequent intervals for
proper vehicular traffic diversions - Medical test were carried out for all labours before
induction. - Traffic marshals are provided to manage traffic. - Noise proof power generators are used - Internal underground columns are marked with
fluorescent paint for easy visibility during excavation
Past Metro Project executed by L&T
L&T’s association with Metro Business started a decade back when it bagged the first elevated package of Delhi Metro followed by 6.6 km of underground metro corridor including construction of six underground stations. Sub-sequently for DMRC Phase2, L&T has completed 4.65km twin
RoSPA award by L&T SUCG JV
Hauz Khas Metro Station
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66 The Masterbuilder - November 2012 • www.masterbuilder.co.in
tunnel and 3 stations by cut & cover method on standalone basis and with joint venture companies have completed 10.72km twin tunnel by TBM & two number of stations.
Udyog Bhawan Metro Station
Benefits of Metro to commuters
1. Time saving for commuters 2. Reliable and safe journey 3. Reduction in atmospheric pollution 4. Reduction in accident 5. Reduced fuel consumption 6. Reduced vehicle operating costs 7. Increase in the average speed of road vehicles 8. Improvement in the quality of life 9. More attractive city for economic investment and growth
10. The Chennai metro is very conscious of the needs of disabled people and will make all efforts so that they do not face any difficulties. All our stations will have ramps from the streets so that wheelchair-bound persons can directly roll up to the lifts. The lifts will move to the concourse level where the ticketing counters are located. From the concourse level, other lifts will take them to the platform level. Signs have also been put up outside all lifts that these are exclusively for the use of disabled persons
The control panels inside all the lifts are placed at a low level so that persons on wheelchairs can access these without having to strain themselves. Disabled commuters can also expect accessible seating on the trains, as well as Braille instruction signs and audio announcements.
Operational Logistics
The metro users will have access to trains after every 5 minutes to 15 minutes for peak and lean time respectively. The trains will travel at an average speed of 30 km per hour. Hence accordingly that it will take only 30 minutes for passenger to travel from Chennai Central to St. Thomas Mount, a distance of 22 kilometres. Initially CMRL will be placing four-car trains having a capacity to carry 1,250 passengers which will be subsequently replaced by six-car trains.
The above facilities will be available to the commuters by 2015.
Ground Engineering
The Masterbuilder - November 2012 • www.masterbuilder.co.in68
Triangular Polyestor Fibers asSecondary Reinforcement in Concretefor Flexure / Split Tensile Strength
KRS. Narayan, BE.Civil, M.Tech
Leeds University - U.K., F.ICI., F.ACCE
"Fiber Reinforced Concrete" is relatively a new construction
material developed through extensive research and
development work during the last two decades. Fiber
Reinforced Concrete (FRC) is defined as composite
material which consists of conventional concrete
reinforced by randomly dispersed short length fibers of
specific geometry, made of steel, synthetic (polymeric) or
natural fibers.
Plain cement concrete has very low tensile strength and
causes formation of micro cracks in stressed and
unstressed states of concrete. Also, it has a low strain at
fracture and brittleness with less ductility especially in
case of High Performance Concrete. Fiber Reinforced
Concrete is the answer to modify these properties of Plain
Concrete.
Advantages of Frc
Various advantages of Fiber Reinforced Concrete are,
- Resistance to Micro-Cracking.
- Toughness and Post-Failure Ductility
- Impact & Abrasion Resistances.
- Resistance to fatigue.
- Improved strength in shear, tension, flexure and
compression.
- Reduced permeability
The interaction between the Fiber and Concrete matrix is
the fundamental property that affects the performance of
a cement based fiber composite materials. An
understanding of this interaction is needed for forecasting
the fiber contribution and for predicting the behavior of
such composites. The following are the major parameters
affecting the fiber interaction with the matrix.
- Condition of the matrix--Uncracked or Cracked.
- Matrix composition.
- Geometry of the Fiber-Triangular or Circular.
- Type of fiber--steel, polymeric, mineral or naturally
occurring fiber.
- Surface characteristics of the fiber.
- Stiffness of the fiber in composition with matrix
stiffness.
- Orientation of the fibers--aligned versus random
distribution.
- Volume fraction of fibers.
- Rate of loading.
- Durability of fiber in the composite and the long term
effect in the Concrete matrix.
Experimental Investigation
The behaviour and strength of Conventional and Fiber
Reinforced Concrete are ascertained by testing the
specimens in the laboratory. This chapter deals with the
mix design, preparation of the specimen, and casting,
testing and test results of the specimens.
Materials
It is necessary to get the maximum performance out of all
of the material involved in producing a concrete. The
materials involved in this project are Portland cement,
coarse aggregate, fine aggregate and super plasticizers.
The additional material involved in this project is
Triangular Polyestor Fiber-Synthetic Fiber.
Cement
The cement used for this investigation was OPC53 grade
Birla cement. The specific gravity of the cement was found
Concrete Fiber Reinforced
www.masterbuilder.co.in • The Masterbuilder - November 2012 69
to be 3.11 and it is conforming to IS 269-1979.
Fine Aggregate
The fine aggregate used for all the specimens was
complying with IS 383- 1970. The specific gravity of fine
aggregate was 2.52, sieve analyses were conducted and
it was found that the sand used was conforming to zone II
grading. The fineness modulus of fine aggregate was
2.074
Coarse Aggregate
The coarse aggregate used was hard broken stone drawn
from an approved quarry. Mean size of 20mm was used.
The specific gravity of coarse aggregate was 2.73. And it
was confirming to IS 383 - 1970
Water
Portable water available in the laboratory was used for
casting all the specimens in this investigation. The quality
of water was found to satisfy the requirements of IS 456-
2000.
Synthetic Fiber (Triangular Polyestor Fiber)
The fiber used is a 12mm long VIRGIN TRIANGULAR
MONOFILAMENT Polyestor, with an Aspect Ratio of <
360. For a mean sized aggregate of 20mm, 12mm Fiber
length is adequate. Young's Modulus of Triangular
Polyester Fiber was found to be >6500MPa
Super Plasticizer
Commercially available super plasticizer having a specific
gravity of 1.2 at 25 degree centigrade. Desired Slump
was 75mm + - 25mm for better workability.
Material Properties
Mix Design
In this study, Indian standard recommended method
(IS 10262-1982) has been adopted for the mix design.
S.No
1
2
3
4
Material
Cement OPC
-53 grade
Fine aggregate-
sand
Course
aggregates-
20mm size
Fibers--
Triangular
Polyestor Fiber
Name of the property
Specific gravity
Fineness of cement
Initial setting time
Standard consistency
Final setting time
Specific gravity
Grading
Water absorption
Fineness modulus
Specific gravity
Water absorption
Length (mm)
Crossection
Specific gravity
Aspect ratio
Diameter
Density
Experimental results
3.106
8%
141 min
32%
265 min
2.52
II
2%
2.074
2.73
1.50%
12mm
Triangular
1.34-1.39
350
0.035mm
0.90 Kgs / Cu.M
The mix proportion adopted for concrete is 1:1.238:2.917
with w/c ratio of 0.4 for a desired Slump of 75mm + -
25mm. All the samples are prepared from the desired
mix. The volume of fiber added is 0.25% of weight of
cement. Concrete Mixer was of 0.1 Cu.M batch capacity
and to prepare a Concrete with a Slump of 75mm + -
25mm, 420Kgs C/c has been considered after sufficient
Trial mix preparations.
Details of mix
Testing Procedure
- Cube Compressive Strength
The test was conducted as per IS 516-1959. The cube of
standard size 150 mm x 150 mm x 150 mm were used to
find the compressive strength of concrete specimen after
28 days curing, and were placed at the compressive
testing machine of capacity of 300 tons with out
eccentricity. At failure, the maximum load was noted and
compressive strength was calculated. The average of
three values is taken as the compressive strength.
- Cylinder Compressive Strength
The specimens used for the test were of 150 mm diameter
S.No
1
2
3
4
5
6
Material
Cement 53grade OPC
Fine aggregate
Coarse aggregate (20mm size)
Water
Fiber
Super plasticizer
Quantity per m3 in kg
420
540
1200
170
0.25% by weight of cement
0.4% by weight of cement
Concrete Fiber Reinforced
The Masterbuilder - November 2012 • www.masterbuilder.co.in70
and the height of 300 mm. Tests were conducted using
compressive testing machine of 300 tones. The test was
carried out at a uniform stress after the specimen had
been centered in the testing machine.
Compressive Strength Test Set Up
- Split Tensile Strength Test
The test was conducted as per IS 5816-1970. The test
was carried out by placing the cylindrical specimen of
diameter 150 mm and height 300 mm, horizontally
between the loading surface of a compressive testing
machine and the load was applied until failure of the
cylinder along the vertical diameter. The maximum load
applied was noted down.
- Flexural Test
The test was conducted as per IS 516-1959. Beams of
size 100 x 100 x 500 mm were used for the determination
of flexural strength. The test was conducted using the
universal testing machine adopting two points loading.
The specimen was positioned in the testing machine and
a steel I section beam for transferring the concentrated
load as the two point load (1/3 each other) was kept over
the concrete beam. The supporting length of the prisms
was fixed at 400 mm and load was applied Up to final
failure of the specimen.
- Young's Modulus Of Concrete Cylinder
The test was conducted using compressometer as per
IS516 - 1959. The cylinder of standard size 300 mm height
and 150 mm dia were used to find the modulus of elasticity.
Specimens were placed on UTM of 100 tons capacity
without eccentricity and uniform load was applied till the
target load failure of the cylinder. The target load and
deflection were noted and modulus of elasticity was
obtained. The original length of the compressometer is
150mm. The deflection readings are change in length,
from that the strain was calculated For finding young's
modulus of concrete, the deformation of various loads
was observed and the results are plotted graphically
against the stress. Using the stress strain curve tangent
in drawn and modulus of elasticity is found.
Compressive Strength Test Set Up (Stress- Strain Relationship Test Arrangement)
Test Results
Split Tensile Strength
The cylinder specimens are cast and tested for split
tensile strength as per IS 5816-1970 using compression
testing machine of capacity 300 tons.
Flexural Strength
This test was conducted as per IS 516-1959 on prisms of
standard size 100x100x500 mm. Tests were carried out in
Universal Testing machine. The supporting length of the
prisms was fixed at 400mm with two points loading at 1/
3rd distance with each other. Two uniform point loads were
Flexural Strength Test Set up
S.No
1
2
Description
Normal concrete (N)
Fiber concrete (F)
Sample No
1
2
3
1
2
3
Loaded Area (mm2)
141372
141372
Ultimate Crushing Load
(KN)
190
170
200
210
250
270
Split tensile Strength
(N/mm2)
2.68
2.41
2.83
2.97
3.54
3.82
Average split tensile
Strength (N/mm2)
2.64
3.44
Concrete Fiber Reinforced
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applied and the maximum failure load was noted. The
modulus of rupture was calculated.
Compressive Strength
The cube and cylinder specimens are tested for
compressive strength using compression testing machine
of capacity 300 tones.
Modulus Of Elasticity (Or) Young's Modulus OfConcrete
The cylinder specimen is casted and tested for young's
modulus, using UTM of capacity of 100 tons.
Comparison of Results and Discussions
Test results of the specimens are compared and the
discussion is made from the test results. The fibers
concrete are compared with the conventional concrete.
Split Tensile Strength
The split tensile strength is increased by 30.3% for
Triangular Polyestor Fibre reinforced concrete over plain
concrete.
Flexural Strength
The flexural tensile strength is increased by17.93% for
S.No
1
2
Description
Normal concrete (N)
Fiber concrete (F)
Sample No
1
2
3
1
2
3
Loaded Area (mm2)
150x150
150x150
Ultimate Crushing Load
(KN)
860
940
910
1080
960
1040
Compressive Strength
(N/mm2)
38.22
41.78
40.44
48
42.67
46.22
Average split tensile
Strength (N/mm2)
40.15
45.63
Compressive Strength of Cube
S.No
1
2
Description
Normal concrete (N)
Fiber concrete (F)
Sample No
1
2
3
1
2
3
Loaded Area (mm2)
17671.46
17671.46
Ultimate Crushing Load
(KN)
570
610
540
610
710
Compressive Strength
(N/mm2)
32.26
34.52
30.55
34.52
40.18
Average split tensile
Strength (N/mm2)
32.44
37.16
Compressive Strength of Cylinder
S No
1
2
3
4
5
6
Description
N 1
N 2
N 3
F 1
F 2
F 3
Young's modulus (N/mm2)
26578.95
24531.79
25250
28300
26439.25
24969.1
Average (N/mm2)
25453.15
26569.45
S No
1
2
Description
Normal
concrete
Fiber
concrete
Average split tensile
Strength (N/mm2)
2.64
3.44
Increase in Compres-
sive Strength (N/mm2)
30.3
Triangular Polyestor Fibre reinforced concrete over plain
concrete.
Young's Modulus of Cylinder Specimen
The young's modulus is increased by 4.38% for Triangular
Polyestor Fibre reinforced concrete over plain concrete.
Comparison of Young's Modulus
Conclusion
- Addition of Triangular Polyestor Fiber in Concrete
Concrete Fiber Reinforced
S.No
1
2
Description
Normal concrete (N)
Fiber concrete (F)
Sample No
1
2
3
1
2
3
Ultimate Crushing Load (KN)
11.5
11.25
11.7
13.5
14
13.1
Flexural Strength (N/mm2)
4.6
4.5
4.68
5.4
5.6
5.24
Average flexural Strength
(N/mm2)
4.59
5.41
www.masterbuilder.co.in • The Masterbuilder - November 2012 73
S No
1
2
Description
Normal
concrete
Fiber
concrete
Average flexural
Strength (N/mm2)
4.59
5.41
Increase in flexural
Strength (N/mm2)
17.86
increases the Split Tensile Strength at 28 days by
30.3% at a fiber dosage of 0.25% by weight of cement.
- Due to addition of Triangular Polyestor Fiber, the
Flexural Strength is increased by 17.86% compared
with Conventional Concrete.
S No
1
2
Description
Normal concrete
Fiber concrete
Average
25453.16
26569.45
% of increase
4.38
- The Young's modulus of FRC is increased slightly when
compared with Conventional concrete. This is due to
the contribution of young's modulus of Fiber in
Concrete.
- Stress-Strain Curve for Cylinder specimens-Normal
V/s Fiber Concrete.
Fig -1 Specimen 1
Fig -1 Specimen 1
Stress strain curve for cylinder specimen - Fiber concrete
Fig -2 Specimen 2 Stress strain curve for cylinder specimen - normal concrete
References
- Dr.A.R.Santha Kumar-Emeritus Professor-IIT-Madras and Former
Dean-Anna University.
- Mr.Johnson and Mr.Kanaga Sabapathy-Project In partial fulfillment
of the requirements for their M.E-Degree.
- Asad Esmaily and Yan Xiao. "Behaviour of reinforced concrete
column under variable axial loads". ACI structural journal, sept -
oct 2005.
- Balasubramanian.K, Bharat kumar.B.H, Gopalakrishnan.S and
Paremeswaran .V.S. "Flexural behaviour of steel fiber reinforced
concrete beams under static load". Journal of structural engg,
vol.25.no.3, oct-1998,pg 28-36.
- Barr.B, Asghari.A and Hughes.T.G, "Tensile strength and
toughness of FRC materials".The international journals of cement
composite and light weight concrete. Vol 10, no 2. Pg 101-107
- Baskar.S, Leung.C, Li.V.C,Wang Y and Yamanobe.K " Tensile
flexure mechanism and mechanical and properties of fiber
reinforced concrete".Proceddings of the international symposium
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on fibre reinforced concrete Dec 16-19, 1987 Madras, India pg
1.163-1.171
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experiments on size effect in shear of members without stirrups".
ACI structural journal Nov - dec 2005
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strength of steel fiber reinforced concrete beams". ACI journal
Nov 1972 pg 673-678.
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concrete beams in shear". The international symposium on fiber
reinforced concrete.Dec 16-19, 1987, Madras, India pg 1.133 -
1.147.
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"Compresive strength and bearing stress of steel fibre reinforced
concrete" ICJ, vol 51, june1977, pg 183-188.
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concrete under compression". ICJ vol 70 July 1998 pg 353-356.
- Paremeswaren .V.S, "Research and application of FRC in Indian
scenerio". ICJ, vol 70 oct 1996,pg 553-557.
- Swamy R.N, AL-Tann.S.A and Ali.S.A.R. "Deformation and
ultimate strength in flexure of reinforced concrete beams made
with steel fibrous concrete" ICJ, vol 78, Sep - Oct 1981,
pg 76-82
- Shetty M.S "Concrete technology theory and pratice (First edition
1982) Publisher, S.chand and company. New Delhi.
- Bansal.R.K. "A text book of strength of materials (Third edition
1996) publisher lakshmi publications (p) Ltd .New Delhi.
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for concrete mix design"
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aggregate for concrete"
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strength of concrete cylinders".
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Streamlining Energy Analysis of Existing Buildings with Rapid Energy Modeling
Scalable Energy Assessments
The implementation of efficiency measures and renewable energy generation in existing buildings represents a significant opportunity to reduce energy costs and hedge against energy price risk. In light of this, there are an increasing number of national and regional building directives to promote better performing buildings. These mandates and other factors such as energy security, global climate change and economic stimulus programs are driving energy efficiency retrofits of commercial buildings around the world.
To respond to these economic and energy challenges at the scale, speed, and efficiency needed, the building industry must be able to quickly and cost effectively prioritize, mobilize, and focus its retrofitting efforts. However, we face major challenges in determining the potential energy savings in existing buildings—data that is essential for identifying retrofit and renovation candidates.
Many of the current methods of performing energy assessments are expensive and laborious. The types of assessments that achieve the greatest savings are those based on whole building energy analysis and follow the steps below:
- Data collection of existing conditions – Design (geometry) of the building, utility history, performance of equipment and materials, weather data, operating schedules, etc.
- Energy model creation – Using above data develop whole building energy model.
- Calibration – Modify unknown parameters in energy model to ensure energy results match utility history within acceptable threshold
- Energy efficiency measures – Modify energy model to estimate energy and cost savings for various energy efficiency measures. Estimate costs for implementing measures and prioritize list based on simple payback.
These assessments require a high level of technical expertise and sometimes the assessments are inaccurate due to a lack of data, time, or budget. In short, they are not scalable.
Autodesk
Improved building performance is critical for decreasing greenhouse gas emissions and reducing energy costs. However, identifying potential candidates for energy efficiency retrofits poses significant challenges. Building professionals, developers, owners, facility managers, insurers, financiers, and regulators are all struggling to get the information they need to support their building decisions. To systematically evaluate and update existing building portfolios, the building industry needs a scalable process to assess building performance quickly, cost-effectively, accurately and efficiently. Rapid energy modeling is a streamlined process that helps you analyze and estimate building energy consumption using Building Information Modeling (BIM) solutions. With a smaller budget, shorter timeframe, and less initial data, building professionals can evaluate expected building performance and identify areas for improvement. This paper outlines rapid energy modeling workflows using Autodesk solutions and documents results from real-world validation.
Figure 1: Rapid energy modeling is a streamlined process to move rapidly, and with minimal data, from existing building conditions to energy and carbon reduction analysis through a simplified simulation process.
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Rapid Energy Modeling for Existing Buildings
Rapid energy modeling is a streamlined, scalable approach for performing energy assessments of existing buildings. While the umbrella term can represent a number of solutions, a typical workflow consists of three steps: capture, model, and analyze.
Step 1: First, you capture existing building conditions. Starting from as little as photos, satellite images, aerial images, or laser distance meters, you collect basic information about a building such as geometry, location, orientation, and structural or operational anomalies.
Step 2: This digital information is calibrated and converted into a simplified 3D building model. Your model can be a:
- Conceptual massing model that defines the internal volumes of the building (which is all that is necessary for basic energy modeling), or a
- Detailed model using design elements such as walls, floors, windows, roofs, and rooms or spaces.
Step 3: In this step, you analyze the building model by performing energy analyses to assess expected building performance.
The core value proposition of rapid energy modeling is the democratization of the portfolio energy assessment process. It makes energy assessments quick and cost-effective, and results in easy to understand and actionable conclusions based on building science, the building’s geometry, and local climate conditions.
Uses for Rapid Energy Modeling
Rapid energy modeling can accelerate the initial steps of an energy assessment process that is used to:
- Screen a building portfolio for high potential retrofit candidates. Building owners, property managers, and tenants with large portfolios can use rapid energy modeling to estimate the energy consumption and carbon footprint of an entire set of buildings. They can use it to assess factors such as energy costs and carbon emissions across several buildings, and identify outliers as well as buildings with high potential for improvement and ROI.
- Prioritize retrofit investments and energy efficiency measures. Developers, building owners, facility managers, or tenants can use rapid energy modeling to quickly understand and compare potential retrofit and renovation options, and drill down into the energy model of existing buildings to make post-analysis recommendations on energy efficiency upgrades.
- Evaluate the lifecycle impact of retrofit decisions. Designers, architects, contractors, and construction companies can use rapid energy modeling to quickly evaluate various design alternatives for intended retrofits and identify solutions that optimize lifecycle impact.
- Streamline asset rating. Insurers, financiers, regulators, and real estate brokers may find rapid energy modeling valuable in getting the information they need to support their asset rating process in a cost-effective manner.
Autodesk Software for Rapid Energy Modeling
A broad selection of Autodesk software solutions can be used to support rapid energy modeling, including:
- Autodesk® Revit® Architecture or Autodesk® Revit® MEP software.
- Autodesk® ImageModeler™ software (available to Revit Architecture and Revit MEP Autodesk Subscription customers during the term of their Subscription).
- Autodesk® Revit® Conceptual Energy Analysis features (available to Revit Architecture and Revit MEP Autodesk Subscription customers during the term of their subscription).
- Autodesk® Green Building Studio® web service. - Workflows can also take advantage of technology
previews available on Autodesk Labs including Project Photofly1 (to help capture existing conditions), Project Vasari (for modeling), and Globe Link (for importing information from Google Earth™ mapping service to your Revit application).
- In addition, some of the workflows described in this Figure 2: Rapid energy modeling includes three key elements: capture, model, and analyze.
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document can use non-Autodesk software, including Pictometry Online (POL) from Pictometry International Corp., PKNail from PointKnown, and Google Earth from Google.
The table below shows how the various software options are used in the three-step rapid energy modeling process.
The combination of these various software options translate into a series of distinct rapid energy modeling workflows. Your particular workflow for rapid energy modeling will depend on the method of capturing existing building conditions and the desired level of analysis. The next section describes the three key steps of the workflow—capture, model, and analyze.
additional information about the building from the facilities manager. For example, if not all the sides of your building are visible in aerial photographs, you will need some other source of information to fill in the missing building surfaces. Orthogonal satellite images can also be insufficient and require you to, at a minimum, obtain the building’s height and number of levels.
Regardless of how you capture your existing conditions, you will need some minimal information about your building and its operations, such as:
- Square footage
- Operating schedule (12/7, 10/5 etc.)
- Information on structural anomalies not visible in pictures (such as atriums, basement, and storage areas)
- Operational idiosyncrasies such as inefficient HVAC, simultaneous heating/cooling, or high server load
- Utility bills (for comparison)
Step 1: Capturing Existing Conditions
The first step in the rapid energy modeling process is to capture the existing conditions of your building(s). The format of the existing conditions (i.e. digital photographs, aerial or satellite images, or laser distance meter measurements) will dictate the exact steps and software needed to help capture and process those existing conditions:
Digital Photographs
ImageModeler is image-based modeling and photo grammetry software that helps you generate models from digital photographs. Alternatively, Autodesk Project Photofly is photogrammetry software that converts pictures to 3D point clouds and meshes.
Both solutions enable you to stitch together the photographs of your building, set the coordinate system and scale, and then model over the images to create a 3D wireframe model of your building.
Once the wireframe model is complete, you then export it as a DWG™ and use it in your BIM solution to help create a full 3D model of your building (see the “Creating a Building and Energy Model” section below).
Satellite Images
If you use satellite images to help capture your existing building conditions, you can use Globe Link for Autodesk Revit Architecture or Autodesk Revit MEP to download the image from Google Earth and pull it into Revit Architecture 2012 or Revit MEP 2012. You can also import a scaled Google Map satellite image directly into Project Vasari. Because the satellite image only displays the building footprint, you
Key Elements of Rapid Energy Modeling Existing Conditions
The most common forms of existing building conditions are:
- Digital photographs: These are photographs of your building taken specifically for rapid energy modeling.
- Aerial images: You can download oblique aerial images from Internet sites such as Google Earth or Microsoft® Bing™ mapping services. Alternatively, you can use images from commercial providers of geo-referenced aerial and oblique image libraries such as Pictometry.
- Satellite images: Like aerial images, you can download orthogonal images of your building from sites such as Google Earth.
- Laser distance meters: These low-cost laser meters are common surveying tools, and you can also use them onsite to capture key measurements of your building.
There are advantages and disadvantages to using these various formats. For example, you can create sufficiently detailed buildings models based on digital photographs, but the photographs must be taken from different points of view and have as many common points as possible between them to enable the capture software (Project Photofly2 for example) to calculate their 3D coordinates. As such, it requires an onsite resource. The same is true for measurements from a laser distance meter, which also requires training on the device and the capture software.
Aerial and satellite images are much easier to obtain and need minimal training, but they do require you to obtain
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will need to know (at a minimum) the approximate height of the building and/or floor-to-floor height per floor as well as the approximate window-to-wall ratio (i.e. the glazing percentage) before proceeding with modeling.
Aerial Images
You can download oblique aerial images from Internet sites such as Google Earth or Microsoft Bing and process them in a manner similar to satellite images. However, a “birds-eye view” of your building may not always be available or the quality of the pictures may be insufficient.
Alternatively, you can also use aerial images and software from Pictometry (fee required, see www.pictometry.com). In addition to providing the aerial images, the software enables you to extract building information that you can use for modeling such as distance and area measurements, number of windows, orientation of the building, and coordinates of the building location. Pictometry’s Pictometry Online software outputs a KML file that can be imported directly into Revit Architecture or Revit MEP to create a full 3D model of your building.
Laser Distance Meter
If you plan to capture existing conditions using a laser distance meter, you can use PKNail software from PointKnown (www.pointknown.com) to process those measurements and create a Revit model of your building. By inputting a few simple field measurements PKNail will build a Revit model of the existing structure, in the field, in real time. This approach involves trained survey personnel that walk around the perimeter of a building and measure key points on the building.
The PKNail software utilizes Bluetooth®-enabled laser
distance meters to capture dimensional data in the field and send it directly to a laptop loaded with the Revit Architecture or Revit MEP. By capturing data in a specific sequence, the PKNail software creates a Revit model representing the skin of your building as it is being measured. Once the measurements are finished, you then complete the modeling processing by manually adding floors, zones and roofs.
Step 2: Creating a Building Model
After capturing your existing building conditions, you then use the data from Step 1 to create either a conceptual massing model or a more detailed model that incorporates building elements such as walls, floors, windows, roofs, and rooms/spaces.
For a first-pass energy assessment, a conceptual massing model is often sufficient. To create the conceptual model, you can use either Revit Architecture or Revit MEP software. Both solutions offer conceptual design tools that can help you quickly create building forms using the geometry captured in Step 1. However, if you know in advance that you may need a more detailed building model for further engineering driven analysis, for design, or for facility management purposes, you may want to create a detailed model.
If you use digital photographs or aerial images to help capture the existing conditions of your building, you simply import the DWG or KML file into Revit Architecture or Revit MEP and use the wireframe model as a reference to create your conceptual model. If you use satellite images, you start the modeling process by tracing over the building footprint in Revit Architecture or Revit MEP and then use additional information about your building (such as its height and number of floors) to create a model. If you used a laser distance meter to help capture existing conditions, you use Revit Architecture or Revit MEP to complete the model created by the PKNail software.
Another option for creating conceptual models is to use Project Vasari3, which is currently available as a technology preview on Autodesk Labs. Project Vasari is a standalone conceptual modeling and energy analysis tool, designed to increase accessibility for early design phase conceptual energy analysis. The software includes the Conceptual Energy Modeling features described below.
Step3: Analyzing Energy Consumption and Carbon Emissions Once your building model is complete, you are ready for energy simulation and analysis. You can use the Revit Conceptual Energy Analysis features for your initial analysis and/or use Green Building Studio for more detailed whole building analyses.
Figure 3: Project Photofly converts pictures to 3D point clouds and meshes, and creates 3D wireframe models that you can use for rapid energy modeling.
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The Revit Conceptual Energy Analysis features generate an energy analysis from your Revit Architecture or Revit MEP conceptual model and give you results based on user-defined parameters such as building location and type, and hours of operation. You view the results of the analysis in a separate window via graphs, charts, and tables.
Green Building Studio web service uses the DOE-2 simulation engine for energy analysis and offers options to fine-tune your analyses and perform whole building analysis if needed. The user also has the ability to continue analysis in other software by using gbXML files that can be exported from both Revit Conceptual Energy Analysis features and Green Building Studio.
Findings from Preliminary Trials
The various rapid energy modeling workflows have been given preliminary road tests by Autodesk, its customers, and professional services firms, such as URS-Scott Wilson, a globally integrated design and engineering consultancy for the built and natural environments in the United Kingdom, and DPR Construction, a leading general contractor in the United States, specializing in technically complex and sustainable projects.
Results
The project teams conducting these pilot trials modeled existing building conditions and performed building energy analysis in just a few days, and in many cases with no previous experience using Autodesk tools, all of which led to encouraging insights.
The results of these trials were comparable to actual building performance data and deemed reasonably satisfactory by the stakeholders. Even deviations from actuals pointed to useful insights:
- Incorrect or inadequate assumptions can be easily changed in the software.
- Deviations can uncover important operational insights or even inefficiencies that are in need of fixing. These rapid energy modeling studies have been encouraging from a number of perspectives.
Time (“Rapid”)
Time (and hence cost) saving is one of the most obvious and significant benefits of rapid energy modeling. The process promises to drastically bring down variable costs associated with modeling for energy analysis and hence allow large-scale assessments in a shorter time. Figure 6 below demonstrates this point, presenting the results of rapid energy modeling experiments carried out with the help of Autodesk software.
As a case in point, Autodesk performed rapid energy modeling for six Autodesk facilities on three continents in a matter of days for each facility (and in some cases only hours) without any project team members needing to travel to the building sites and with no previous experience using the Autodesk tools. (Photographs of the buildings were taken by local onsite resources.)
Given these results, the word “rapid” in rapid energy modeling takes on different connotations. The modeling process itself is streamlined and does not require specialized energy personnel. In addition, learning the process is fast due to simplified modeling and analysis software. Finally, the process can be a quick screening method to identify buildings in need of a deeper energy assessment.
for other workflows assumes the use of non-Autodesk
Figure 4: Use Revit Architecture or Revit MEP software to more quickly create building forms for rapid energy modeling.
Figure 5: Autodesk Revit Conceptual Energy Analysis features help you simulate your building performance.
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software and is based on informal surveys of resident subject matter experts. Designated yellow area represents rapid energy modeling workflows that use Autodesk software at the core and also 3rd party solutions such as PointKnown and Pictometry.
schedules in most commercial buildings. On the other hand, natural gas consumption has a higher sensitivity to occupant behavior and climate fluctuations, making it harder to predict. Nevertheless, natural gas consumption for a number of buildings is a significant utility cost. It may even outweigh electrical costs for certain building types and geographic locations. Hence more due diligence needs to be conducted to determine the root cause of these deviations.
Electricity and Fuel Consumption (“Energy”)
Electricity consumption often represents the bulk of a commercial building’s energy use and therefore is a key criterion for energy assessment. The various rapid energy modeling workflows tested by Autodesk and its customers were found to be reasonably accurate in this regard, again considering the amount of time and effort expended.
For all the workflows tested, the estimated electricity intensity numbers were found to be quite close to the building’s real energy consumption (as determined by actual utility bills). A chart showing results from one of the workflows is shown below in Figure 7. The only outlier was the facility in Manchester, New Hampshire. After the rapid energy modeling process was complete, the team discovered that the building has a data center that wasn’t modeled and that significantly drove up electricity consumption.
These results underscore the importance of learning beforehand about a building’s structural anomalies (such as atriums) or operational idiosyncrasies (such as large data centers) before drawing conclusions about the building’s performance.
The fuel estimates, on the other hand, were not found to be close to the actuals for two of the three Autodesk facilities that were able to supply fuel data. It should be noted that the fuel consumption costs took up a relatively small percentage of these buildings’ overall utility bills (ranging from approximately 13-17%). Electricity use is often more predictable because it is based upon set operating
Figure 6: The benefits and tradeoffs of different rapid energy modeling, workflows, based on accuracy, cost, and time.
Figure 7: Rapid energy modeling is a reasonably effective predictor of actual electricity consumption.
Geometry (“Modeling”)
The building geometry and the corresponding square footage calculations resulting from in-house experiments and customer pilots were also quite close to the actuals. Figure 8 below shows the results from one of the experiments. The calculated areas of all of the buildings were within 7%, with the exception of the San Rafael, California facility.
That outlier was due to a modeling error—a structural anomaly that was not visible from photos but could be seen when looking at building floor plans. To keep the study double blind, the researchers purposefully avoided looking at available floor plans during the rapid energy modeling process.
While it is very easy to go back and fix the model, this error again brought to light the need to augment building images
Figure 8: Project teams successfully modeled existing building conditions and performed building energy analysis of these facilities in just a few days.
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with additional information on structural anomalies.
Validating Other Key Parameters
It should also be noted that the team took pains to validate other structural and operational parameters such as glazing percentage, floor heights, and loads, as well as square
footage and energy consumption, in an attempt to reduce the risk of false positives or false negatives. Results from one such validation exercise are illustrated in the table below.
Conclusion
Rapid energy modeling has been shown to reduce the time needed for the initial steps of an energy assessment, which can help professionals perform building energy assessments and carbon reduction analysis faster and more economically. A range of stakeholders from building owners and tenants to real estate brokers and financiers stand to benefit from this approach.
Rapid energy modeling can bring down the variable costs associated with energy assessments. This enables large-scale assessments in a short time—leapfrogging traditional modeling methods for energy analysis and building audit techniques, and thus helping the building industry create a low-carbon built environment.
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Improve Workmanship in the Block Work
There are various ways to improve the workmanship in block work construction. These steps will hot only help us to overcome the defects in block work but
also control thermal cracks. Thermal cracks are in most of the cases unavoidable, yet can be controlled. The following are a few step suggested for the same.
- Ensuring uniform mortar mix- Ensuring uniform mortar thickness- Optimum moisture levels in contact surfaces- Vertical joint positions- Ensuring proper line & level- Proper curing
Ensuring Uniform Mortar Mix
The mortar mix plays a major role in avoiding thermal cracks in the masonry. Variation in the uniformity of mortar mix may affect the wall. Ensuring proper and equal mix for entire building is not a practical one. Yet ensuring for a single or a set of few interconnected walls is practically possible and also very important.
If in case the mortar mix batches are not proper in any given wall, the crack may appear at the junctions.
For example, in a wall half portion is constructed with X% water content & another half with Y%. The junction where both portions meet will get cracked easily. So for a given single wall or a set of interconnected walls has to be done with same kind of mix, in terms of
- Same brand & type of cement- Single source aggregate- Single source water- Mix ratio – quantities of ingredients in every batch of mix
The above listed points can be varied for separated walls. But for a single or a set of interconnected walls, maintaining the requirements is very important.
Ensuring Uniform Mortar Thickness
In any given single or a set of interconnected walls maintaining uniform thickness will avoid unnecessary thermal cracks at unwanted places.
First 4 courses of block work is constructed with 8mm thick mortar, another 4 courses are constructed with 10mm thick.
The working nature of first 4 courses will be different than the next 4 courses for the temperature variations. As these two areas working differently the crack may appear at the junction.
Nirmal Ganesh MSenior Manager - Sobha Developers Ltd
This may happen due to varying experience of laborers, changes in mortar mix, block dimensions & environment conditions. Some proper planning is required to ensure the uniform thickness of joints in a wall. Following steps may be adopted,
Step 1: By considering wall dimensions calculate the number of blocks per layer & total number of layers.
Step 2: Mortar thickness has to be planned as follows.
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If the X < 3.27 or X> 3.31, then a cut block need to be introduced.
Step 3: The step 2 is applicable to calculate the thickness of the mortar in horizontal bed by considering the height of the wall
Optimum Moisture Content at the Contact Surfaces
Varying moisture content in the mortar, concrete blocks & other concrete surfaces will affect the quality of masonry work. In practical site conditions measuring the moisture content at various surfaces & fixing the standards are very difficult. So common knowledge and the experience of the masons are required to set the things right. For example, a wall is constructed in two days. At the first day environment is dry, blocks & mortar kept and used under sun. The next day is a rainy day & work started when there is a little drizzling. Now in first day premoitening the contact surfaces are very important. In the second day water should be used as less as possible in all the places. This will ensure that in a single wall the moisture content is maintained approximately equal to entire wall.
Ensuring Proper Vertical Joint Laps
If you observe the picture you can note that the vertical joints are staggered. Proper load distribution is ensured by staggering the vertical joints. In the normal practice the vertical joints are fixed to the middle of the block in the next course. But it is not easy in all type of walls in the practical conditions.
The above discussed example is the junction of two walls. But some more complicated three wall junctions in ‘T’ shape & four wall junctions in ‘+’ shape are also available.
For example, if the block length is 400mm, ideal vertical joint lapping will be at 200mm, i.e., middle of the block in the next course. But in a construction site you may see the laps of 80mm / 100mm / 120mm / 150mm. But the minimum requirement is not understood properly.
The minimum requirement is l/4. So if you use the blocks of length 400mm, the minimum lap is 100mm. take the following example of two 4” walls meeting at ‘L’ shape.
We get the lap of 100mm. this is one of the major reason why it is not achieved in practical conditions. By introducing 300mm length of cut blocks at the junction this issue can be resolved. At the junction you can achieve the minimum requirement of 100mm & other areas you achieve 200mm.
Ensuring Proper Line & Level
In the usual practice the bottom most courses takes more importance than any other course. This course is checked
extensively for line, level, room dimensions, beam plumb & etc, Other courses are left with less importance. Giving more importance to other layers has the following advantages,
a. Level is maintained for entire wallb. Fixing adjustable course & last course will be easy &
properc. Fixing the sill & lintel will be very easy.
For example observe the lintel fixing in the below pictures,
Proper Curing Requirement
The concrete blocks supplied to the sites are already cured for minimum number of days in the block making factories. So when you do curing for the block masonry, you need to cure only the mortar. If you do the curing for entire wall, the water observing nature of the blocks will create unnecessary issues. So you need to do small spray curing in the mortar joints only.
Fixing of lintel is easy as the levels in both the sides of the window are maintained properly
Fixing of lintel requires more work since the levels in both the sides of the window are not maintained properly
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Challenging Design: Foundations for Tall Buildings
In the design of foundations for tall buildings, engineers face a challenging task as a conventional design approach may not be able to address all the key design issues. The
foundation design team has to employ innovative approaches to tackle the problem. Due to the size of the tall building, it is necessary to design a cost-effective foundation system that meets the long term performance requirements.
This paper will describe the involvement of female engineers in tall building projects. Details of the design approach and its application to the Incheon Tower in South Korea and Nakheel Tower in Dubai will also be discussed.
Foundation Design Team
Organisation Chart
The major tasks of the tall building geotechnical designers are to provide professional recommendations for the foundation design, undertake geotechnical review services and independent analysis of foundation performance. The tall building design team will often comprise a project principal, a project manager and design engineers as shown in the organisation chart in Figure 1.
The major roles for each member of the team are outlined below:
- Project Principal–supervision of the design team and review process and providing technical advice to the design team and the clients.
- Project Manager–preparation of proposal and cost esti-mation of the design services, liaison with the clients and supervision of design process.
- Design Engineers – development of geotechnical models and parameters and undertaking foundation analyses.
Roles and Responsibilities of Authors
Coffey Geotechnics have been appointed as the geotechnical
Helen Chow1*, Frances Badelow1 1Coffey Geotechnics Pty Ltd
The design of foundations for tall buildings is a challenging task for geotechnical engineers as they are required to consider all geotechnical aspects of the project, with the aim of identifying and managing the geotechnical risks. In the design of foundations for tall buildings, lateral loadings are of great importance as are the vertical loadings. A small rotation at the foundation will be magnified to a very large magnitude at the top of the structure due to the height of the building, which will affect the serviceability and functionality of the building. This paper presents the foundation design process for two cases - the 1km high Nakheel Tower in Dubai and the 151 storey Incheon Tower in South Korea. The role of the authors as an internal reviewer of the analyses and an engineer undertaking the numerical analyses during the different project phases will be discussed. Analyses of the proposed foundation were carried out by computer programs using the boundary element method and 2D & 3D finite element methods based on the limit state approach. Key issues, in particular the overall performance of the foundation, will be addressed. The paper concludes with a summary of the design processes and the basic design criteria for tall buildings.
Fig. 1: Organisation Chart for Tall Building Foundation Design Team
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designer for Incheon Tower and as geotechnical peer re-viewer for Nakheel Tower.
The second author, Frances Badelow, was acting as the project manager for the Incheon Tower and also the peer reviewer for Nakheel Tower. The first author, Helen Chow, was acting as the design engineer for Incheon Tower and the peer reviewer for Nakheel Tower.
Project Manager – Frances Badelow
As a project manager, Ms Badelow was involved in the preparation of the proposal and estimation of the design and peer review services costs based on the scope of services provided by the clients.
For Incheon Tower, she set out the design steps for the design process, provided guidance to the design engineers in the development of geotechnical models and parameters, which were then used to carry out the design and reviewed the foundation design at various stages of the design process. She also liaised with the client and the structural engineers. As the superstructure and the foundation are interacting components of a single system, it is important that the geotechnical design engineers work closely with the structural design engineers to provide an effective design of the foundation for the client.
For Nakheel Tower, she set out the steps for peer review process and was part of the geotechnical peer review team for the foundation design provided by the foundation designer.
Design Engineer– Helen Chow
As a design engineer for Incheon Tower, Ms Chow was involved in the interpretation of ground conditions and assessment of foundation performance for different pile layouts and load combinations using different numerical methods. For Nakheel Tower, she undertook independent analyses of the foundation system proposed by the foundation designers.
Prior to becoming a design engineer, Ms Chow carried out extensive research and developed a computer program for numerical analysis of piled raft foundations at the University of Sydney. The computer program employs the finite layer and finite element methods in the analysis. Upon the completion of this research, Ms Chow began work as a design engineer and has been involved in projects such as foundation design for bridges, buildings and embankments, soft soil ground treatment design, and retaining wall and slope stability analysis which allowed her to apply the knowledge she acquired through research to design work and further developed her design skills through the exposure to different kinds of project.
Foundation Systems and Design Issues
Piled raft foundations are a cost-effective form of foundation for tall buildings and have been extensively used by geotechnical engineers in the past two decades. For most piled raft foundations, the primary purpose of the piles is to act as settlement reducers. The proportion of load carried by the piles is considered to be a secondary issue in the design.
Unlike the conventional piled foundation design in which the piles are designed to carry the majority of the load, the design of a piled-raft foundation allows the load to be shared between the raft and piles and it is necessary to take the complex soil-structure interaction effects into account.
The performance of a piled raft can be influenced by several factors such as the conditions of the supporting soil, relative stiffness between piles and soil, loading conditions, size and length of the piles, and pile arrangement. Therefore, the design has to take account of these factors to achieve the objective of economic construction with satisfactory performance.
In the design of foundations for tall buildings, design engineers have to understand the mechanism of load transfer from the raft to the piles and to the soil and then to address the following issues (Poulos, 2009):
- Ultimate capacity of the foundation subjected to vertical, horizontal and moment loading combinations.
- Influence of the cyclic nature of wind and earthquake on foundation capacity and movements.
- Overall settlement of the foundation.
- Differential settlements, both within the high-rise footprint and between high-rise and low-rise areas.
- Load-sharing between raft and piles and load distributions along the piles.
- Possible effects of externally - imposed ground movements on the foundation system, for example movement arising from excavations for pile caps or adjacent facilities or movements arising from ongoing consolidation settlement of soft soils.
- Earthquake effects, including the response of the structure-foundation system to earthquake excitation and the possibility of liquefaction in the soil surrounding and/or supporting the foundation.
- Dynamic response of the structure–foundation system to wind-induced forces.
Design Process
Prior to the commencement of a project, it is necessary to
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have a well planned design process. The design process should include several phases as follows:
- Phase 1 – Subsurface exploration
- Carry out a ‘desktop’ study of all the geotechnical engineering data and work available from previous investigations and geotechnical engineering recommen-dations in the vicinity of the site.
- Perform site specific geotechnical investigation to explore the soil strata profiles and groundwater conditions across the site and carry out in-situ and laboratory testing to obtain the properties of each soil strata.
- Phase 2 – Foundation Design
- Develop geotechnical models and parameters based on the available geotechnical information obtained from Phase 1.
- Preliminary selection of a foundation system using simplified geotechnical profiles and analysis methods.
- Detailed design of a foundation system based on detailed geotechnical models and structural loads provided by the structural engineers to predict the performance of the foundation including the ultimate capacity of the foundation and anticipated settlement of the foundation under loading combinations.
- If excavation is required, design the retention system. The design has to consider a system of controlling groundwater inflow during construction and for the completed project.
- Assessment of seismicity of the site including changes in soil and rock conditions during earthquakes and possible effects on the foundation system.
- Assess the effects of construction on adjacent properties and on other facilities within the site.
-Phase 3 – Foundation testing and monitoring
- Perform a pile load test for the verification of design assumptions in Phase 2. If necessary, refine the foundation design based on the interpreted test results.
- Monitor the performance of the foundation and compare the measured performance with the predicted performance.
Incheon Tower, Korea
Incheon Tower is a super high rise twin tower, where each tower consists of 151 storeys with a height of 601m and is connected by three skybridges as illustrated in Figure 2. The tower is proposed to be constructed on reclaimed land underlain by soft marine clay in Songdo, Korea. Coffey Geotechnics was appointed as the geotechnical designer.
Ground Conditions
The Incheon site is located within an area of reclaimed land and as such is subjected to variable ground conditions. Detailed geotechnical aspects of the site are described by Badelow et al (2009).
The reclaimed land is comprised of approximately 8m of
The rock materials within about 50m from the surface have been affected by weathering which has reduced their strength to a very weak rock or a soil-like material. This depth increases where the bedrock is intersected by closely spaced joints, and also sheared and crushed zones that are often related to the existence of the roof pendant sedimentary / metamorphic rocks. The geological structures at the site are complex and comprise geological boundaries, sheared and crushed seams - possibly related to faulting movements, and jointing.
The inferred contours of the ‘soft-rock’ surface within the tower foundation footprint were developed based on the available borehole data. It was found there was a variation in level of the top of soft rock of up to 40m across the foundation as presented in Figure 3.
To take into consideration the variation of ground conditions, the footprint of the tower was divided into eight zones with the appropriate geotechnical models and parameters developed based on field and laboratory tests and experience of similar soils on adjacent sites. As the performance of the UMD under vertical and horizontal loadings is of great importance in the design of the tower foundation, the selection of parameters for this stratum has to be carefully considered. Table 1 presents the typical parameters adopted for the foundation design.
Foundation Layout and Load Combinations
The tower foundation consists of a 5.5m thick raft supported by 172 no. bored piles socketed into the ‘soft rock’ stratum. The pile arrangement and pile sizes were obtained from a
loose sand and sandy silt which is constructed over approximately 20m of soft to firm marine silty clay (Upper Marine Deposits – UMD) underlain by approximately 2m of medium dense to dense silty sand (Lower Marine Deposits – UMD), followed by residual soil and a profile of weathered rock.
The lithological rock units present under the site comprise granite, granodiorite, gneiss (interpreted as possible roof pendant metamorphic rocks) and aplite.
Fig. 2: 151 Incheon Tower (artist’s impression)
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series of trial analyses conducted by the geotechnical and structural engineers.
The primary purpose of the piles is to control settlement of the foundation. The pile lengths were determined by the geotechnical designers based on the pile settlement performance as the first priority and pile capacity as the second priority.
provided by the structural engineers. The typical loads of the tower are summarised as follows:
The final design adopted a diameter of 2.5m as the pile diameter with a minimum socket length of two pile diameters into soft rock. The pile lengths vary from 36m to 66m, depending on the depth of the founding soft rock stratum. The raft is embedded into the ground with the base of the raft located at about 14m below the ground surface level. The pile layout of the foundation is presented in Figure 4.
Load combinations used for the foundation design were
- Vertical Load (Dead Load + Live Load): Pz(DL+LL) = 6622MN
- Horizontal Load (Wind Loads): Px(WL) = 146MN, Py (WL) = 112MN
- Horizontal Load (Earthquake Loads): Px(EQ) = 105MN, Py (EQ) = 105MN
- Moment due to Wind Loads: Mx(WL) = 12578MNm, My (WL) = 21173MNm
- Torsional Moment: Mz(WL) = 1957MNm
Foundation Performance
The performance of the foundation has been assessed using the following computer programs:
- CLAP (Combined Load Analysis of Piles)–for the assessment of overall stability under ultimate load combinations
- GARP (General Analysis of Rafts with Piles)–for the assessment of foundation settlement under vertical and moments loading
- PLAXIS 3D – for the assessment of the foundation under vertical and horizontal loading
Vertical Loading
Computer program GARP was used as the main design tool. In the GARP assessment, the piled raft is in contact with the underlying soil but not with the surrounding soil. The predicted maximum settlement for the load combination of dead load + live load was about 67mm with a differential settlement of 34mm. In the analysis, the resistance provided by the soil surrounding the raft has been ignored.
Fig. 3: Inferred Contours of Soft Rock Surface
Stratum Ev (MPa) Eh (MPa) fs (kPa) fb (MPa)UMD 7 - 15 5 -11 29 – 48 -
LMD 30 21 50 -
Weathered Soil
60 42 75 -
Weathered Rock
200 140 500 5
Soft Rock (above EL-
50m)300 210 750 12
Soft Rock (below EL-
50m)1700 1190 750 12
Ev = Vertical Modulus fs = Ultimate shaft frictionEh = Horizontal Modulus fb = Ultimate end bearing
Tab.1: Summary of Adopted Geotechnical Parameters
Fig. 4: Pile layout Plan for Tower Foundation
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The commercially available program PLAXIS 3D Foundation was used to provide an independent check of the foundation settlement. Analyses have been carried out for two
cases
(a) Case 1: Similar to the GARP analysis, the piled raft is in contact with the underlying soil.
(b) Case 2: The piled raft is in contact with the underlying soil and the soil surrounding the raft and basement walls is included (the soil above the base of the raft).
The finite element mesh used in PLAXIS 3D for case 2 is shown in Figure 5 with basement walls supporting the sides of the excavation. The soil layers are modelled as
Mohr-Coulomb materials to allow for non-linear behaviour. Figure 6 presents a plot of percentage of applied load versus vertical displacement at the centre of the raft which shows that the deflection of the foundation is reduced when the resistance provided by the surrounding soil is considered.
Horizontal Loading
The performance of the foundation under lateral loading is a critical issue in the foundation design for tall buildings. Computer program CLAP was used to assess the lateral stiffness of the pile group (assuming no contact between the raft and underlying soil) and a separate calculation was carried out to assess the lateral stiffness of the raft and basement walls. The predicted lateral deflection of the pile group from CLAP was about 22mm.
PLAXIS 3D was used to assess the overall lateral stiffness of the piled raft foundation. Three cases were analysed by PLAXIS which included cases 1 and 2 as above and an additional case 3 that is similar to the CLAP analysis which considers the pile group only.
The lateral displacement predicted by PLAXIS 3D agreed well with the CLAP results. Figure 7 presents a plot of percentage of applied load versus horizontal displacement of the raft which shows that the lateral deflection decreases when the raft is in contact with the underlying soil and decreases further when the surrounding soil resistance is considered. In this case, because of the large number of piles, the effect of the raft burial on lateral deflection is small.
The Nakheel Tall Tower
Nakheel Tower, one of the multi-billion dollar projects in Dubai, will be one of the centre-pieces of Nakheel Harbour. The tower is proposed to have a height in excess of 1 kilometre with more than 200 floors and will be the tallest structure in the world when completed.
Golder Associates have been appointed as the foundation designer and Coffey Geotechnics appointed as the geotechnical peer reviewer.
A brief summary of the foundation design is described
Fig. 5: Finite Element Mesh for PLAXIS 3D
Fig. 6: Load Deflection Behaviour at Centre of Piled Raft (Vertical Loading)
Fig. 7: Load Deflection Behaviour at Centre of Piled Raft (Horizontal Loading)
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below, detailed analyses have been presented by Haberfield et al (2008)
Ground Conditions
The geotechnical profile consists of a 20m thick sand layer, underlain by cemented carbonate siltstone (calcisiltite) with gypsum layers up to 2.5m thick occurring at depths in excess of about 75m below ground level. Laboratory and in-situ tests were carried out to estimate the properties of the soil materials.
One of the features of the foundation materials was the existence of a ‘bond yield strength’ which controls the compressibility of the materials. If the imposed stress on the ground is less than the ‘bond yield strength’, the soil will behave as a very stiff material, otherwise, the compressibility would increase by an order of magnitude. In the foundation design, it is necessary to limit the stresses on the ground to be below the bond yield strength to avoid excessive settlement.
Foundation Layout
The foundation system consists of a raft with a thickness that varies up to a maximum of 8m supported by a total of 392 barrettes. The barrettes have sizes of 2.8m x 1.2m and 2.8m x 1.5m and extend to depths of 37m, 42m and 72m below the carbonate cemented siltstone where the base of the raft is to be founded. Figure 8 presents the foundation layout for Nakheel Tower.
Geotechnical Peer Review
Geotechnical peer review involves the tasks of reviewing the geotechnical designers’ report and the foundation design method, and then developing independent geotechnical models based on the available geotechnical information and then undertaking independent analyses for the foundation for different loading conditions.
The independent geotechnical model adopted for the foundation design was developed based on the available
information and the barrette test results. Computer programs PIGS and CLAP were used to assess the overall stability of the foundation under the ultimate limit state load combinations in which the foundation capacities were reduced by a factor of 0.65. The assessment has shown that the foundation satisfied the ultimate state limit design criterion.
Computer program GARP was used to carry out the settlement assessment of the foundation system. Simplified finite element analysis using the commercially available PLAXIS 2D was carried out to check the GARP results. As the pile layout is symmetrical, a quarter of the foundation was modelled in GARP and an asymmetric model was used in PLAXIS 2D. The barrettes were modelled as equivalent circular rings in PLAXIS 2D.
From the GARP analysis, the maximum settlement was 95mm which was in good agreement with the computed settlement of 92mm obtained by Golder (designer) using a three-dimensional finite element analysis (PLAXIS 3D).
Conclusion
In the past few decades, there have been an increasing number of females choosing engineering as their career. Female engineers have been involved in many different aspects of engineering works from academic research to working in industry. They are often given the opportunity to undertake different roles in major projects.
This paper outlines two of the super-tall building projects that the two authors have been involved with. Key design issues and design processes have been discussed. Ground conditions should be well understood in the development of geotechnical models and parameters. In the design, the performance of a foundation under lateral loadings is a critical issue, therefore special consideration has to be given in the evaluation of parameters for the assessment of lateral response.
For the Incheon Tower where the raft is embedded, it is necessary to consider the resistance provided by the soil beneath and surrounding the raft in the design.
References
- Badelow, F., Kim, S., Poulos, H.G. and Abdelrazaq, A. (2009). “Foundation design for a tall tower in a reclamation area”. Proc. 7th Int. Conf. Tall Buildings, Hong Kong, Ed. F.T.K. Au, Research Publishing, 815-823.
- Haberfield, C.M., Paul, D. and Ervin. M. (2008). “Case History – Geotechnical; Design for the Nakheel Tall Tower”. ISSMGE Bulletin, Vol. 2, Issue 4, 5-9.
- Poulos, H.G. (2009) “Tall buildings and deep foundations – Middle East challenges”. Proc. 17th Int. Conf. Soil Mechs. Goet. Eng., Alexandria, (Hamza M, Shahien M, and El-Mossalamy Y (eds), IOS Press, Armsterdam, 4: 3173-3205.Fig. 8: Foundation Layout for Nakheel Tower
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Foundation for High Rise Buildings
In the design of foundations for large buildings on deep deposit of cohesive soils it is generally seen that if raft foundation be chosen the foundation will have sufficient
factor of safety against shear failure but corresponding settlement will be very high to permit. In such cases pile foundations are generally selected causing very large cost for such foundations. The settlements are successfully controlled in such foundations. However in the late, it has
been recognized if few number of piles are installed at suitable locations below the raft foundation for such structures, the resultant settlement under such structures will be much smaller and will be within permissible limits compared to that below the raft without provision of piles. Use of raft in conjunction with some piles will be costlier than in case where only raft is used if possible but much less than the case when only piles are used. As a result in
MB Bureau
Due to increasing economic development, rapid industrialization and decreasing availability of land for construction in thickly populated countries like India, scope for extending construction in horizontal direction is becoming increasingly lesser resulting in construction of high-rise building with increasing number of floors. In such cases if raft foundations are proposed it is generally observed allowable bearing capacity of such rafts are quite high so that such foundation can withstand the applied loads due to high-rise buildings to a great extent without causing shear failure but the major problem of such foundation is that the total settlement below the foundation at different locations will be very high beyond permissible limits.
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the past decades there has been increasing recognition to use some piles with raft to reduce the total and differential settlement of raft leading to considerable economy without compromising the safety and performance of the foundation structure system. Such a foundation system is called piled-raft. One of the most important buildings constructed with such system is for the foundation system of the world’s tallest building the Burj Dubai. Similar foundations are also being adopted in India for twelve storey buildings in Chennai. The adoption of piled-raft foundation for high-rise buildings is also very common in European cities. Thus it seems on the context of increasing construction of buildings of large heights in metropolis in India and other countries, piled-raft foundation will be increasingly adopted as a most economic safe foundation system. In this paper an attempt has been made to describe the concept of load transfer mechanism for piled -raft foundation from superstructure to the foundation.
- The safety and stability of nearby buildings and services must not be put at risk => ultimate limit state (ULS) / serviceability limit state (SLS)
The three common types of foundation system that are adopted for High-Rise buildings are-
- Raft Foundation- Pile Foundation- Combined Pile-Raft-Foundation (CPRF)
With increasing height of building respectively increasing loads the depicted raft foundation is not suitable to transfer the loads properly into the ground. Therefore a pile foundation is often used. The main function of a pile foundation is to transfer all loads with piles to lower levels of the ground which are capable of sustaining the load with an adequate factor of safety (ULS). The innovative combined pile-raft-foundation (CPRF) is nowadays often used to transfer the loads into the ground. In comparison to a pile foundation, the combined pile-raft foundation both the piles and the raft transfer the loads into ground. The loads are transferred by skin friction and end bearing as well as contact pressures of the raft foundation (bearing pressure) (See in Figure 1).
Piled Raft Foundation: Burj, Dubai
The present paper is on customary foundation systems for high-rise buildings such as raft and pile foundation as well as the innovative foundation system of combined pile-raft-foundation. Where piles are primarily used to reduce settlements and where an adequate factor of safety against failure is provided, the innovative combined pile-raft foundation (CPRF) has been put forward in the past. Some case study of few high rise buildings is included for better understanding.
Foundation systems
Every design will have to satisfy the following conditions-
- The factor of safety against failure of the foundation and of the supporting soil has to be adequate => ultimate limit state (ULS)
- The settlement of the foundation as a whole and in particular differential settlements under working load should not be so large as to affect the serviceability of the structure => serviceability limit state (SLS)
Figure 1: Load Transfer Mechanism in Combined Pile-Raft-Foundation
The piles are used up to their ultimate bearing capacity (load level) which is higher than the permissible design value for a comparable single pile. The combined pile-raft-foundation represents a complex foundation system, which requires a qualified understanding of the soil-structure interactions.
The foundations system of the CPRF can lead to the following advantages in comparison to a raft or pile foundation:
• Reduction of settlements and differential settlements of structures.
• Reduction of tilt in consideration of eccentric loading or inhomogeneous soil conditions.
• In case of hybrid foundation it is possible to avoid joints in the raft.
• Reduction of number of piles and pile length in comparison to a pile foundation.
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- Reduction of forces, stresses within the raft in case of an optimal position of the piles.
Due to the complexity of this foundation system no valid calculation method has yet been implemented in national or international technical codes and standards. Recommendations exist though for CPRF. Therefore the combined pile-raft-foundation must be monitored by means of the observational method with a monitoring programme.
Case studies
- Main Tower – Frankfurt, Germany
The building reaches a height of 200 m. The building is founded on a combined pile-raft foundation. The thickness of the raft within the tower is between 3 to 3.8 m. A total of 112 piles with diameter of 1.5 m were installed. The length of the piles varies from 20 m to 30 m (Figure 2).
The ground encountered consists of quaternary sands down to 10 m below the surface where it is underlain by tertiary sediments of the Hydrobien. These sediments (Frankfurt clay) consist of clay interbedded with sands and limestone bands (Figure 2). The ground layers of the Inflaten (Frankfurt limestone) and Certithien (marl) were encountered beneath the Hydrobien.
To ensure an economic design of the Main Tower three innovative ideas were put forward:
1. The bored piles of the retaining wall are part of the foundation system (combined pile-raft foundation). They transfer the loads in addition to the 112 foundation piles into the ground. Figure 3 shows the position of the piles of the foundation and of the retaining wall.
2. The building pit and the first floors of the main tower were constructed in top-down-technique to reduce construction time and to provide a pit which observe stability and serviceability of neighboring structure. By using this technique it is possible to construct the basement floors and the upper floors at the same time (Figure 3).
3. Apart from their static function the piles of the foundations and partly of the retaining wall are used for the environ-mental-friendly heating and cooling of the building. For this, the piles were additionally installed with heat exchanger tubes (Figure 4), so that the piles work as heat exchanging elements to create a closed system. Energy is transferred to the ground from the exterior (outside air) and stored until it is needed (Figure 4). The energy piles can load and unload the seasonal storage. In winter energy can be withdrawn, thus a cooling of the ground arises. In summer the cooled down ground can be used for cooling the building through the ceilings.
Figure 2: Main Tower: Ground model /combined pile-raft foundation
Figure 3: Plan view of the foundation system / top-down technique
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Figure 4: Seasonal storage of energy with a closed system / energy pile
For this, a very low groundwater velocity is essential. The monitoring shows that the foundation piles of the Main Tower carry approx. 37 % of the total load of the building whereas the piles of the retaining wall carry approx. 26 %.
Figure 5: Sony Center: Ground model / aerial view
- Sony Center – Berlin, Germany
The building reaches a height of 103 m. The building was constructed directly next to an existing railway station. The geometrical position of the high-rise building on the overall area of the raft causes a large eccentricity of the loads (Figure 5). Due to this fact as well as the geological conditions a combined pile-raft foundation was constructed to transfer the loads into the ground. The thickness of the raft within varies between 1.5 and 2.5 m. A total of 44 bored piles with diameter of 1.5 m were installed.
the piles. Beneath the raft a total of 5 earth pressure cells were installed. Additionally 13. The settlements of the building are monitored by geodetical points. The maximum settlement of the building add up to 2.8 cm. The tilting is smaller than 1/2000. These results cause no negative effect on the serviceability of the building. The measured mean value of pile resistance was measured to 15 MN for piles for a centre pile.
- QIPCO Tower - Doha, Qatar
The QIPCO Tower is situated at the coastline of the West Bay in Doha, Qatar. The building reaches a height of 200 m (Figure 6). A ground investigation is currently in progress, which has been planned by the authors. It consists of drillings, geophysical methods, field and laboratory tests are the basis for a successful planning and construction of such a structure. The combination of different investigation methods makes it possible to detect relevant geological conditions such as the phenomena of cavities. This innovative application of geophysical methods offers the possibility to screen the ground three-dimensionally in the affected zone. This method in combination with drillings can offer savings in both time and costs. The qualified interpretation of all obtained data serves as a basis for the numerical simulations to design an optimised foundation system as well as to evaluate all necessary design parameters for the structural engineer. For the transfer of the loads into the ground, a combined pile-raft foundation for the tower area is in planning.
Figure 6: Animation picture and ground model without foundation system
- The Commerzbank , Frankfurt Germany(Pile Foundation)
The building is founded on a pile foundation. The building was constructed directly next to an existing high-rise building. The existing building reaches a height of 103 m and is founded on a raft. A total of 111 telescopic piles with diameter of 1.8 m within the first 20 m beneath the
The ground and groundwater conditions were explored by boreholes. Up to a depth of 4m beneath the surface fillings and organic soils were encountered underlying by loose to medium dense sands of the Pleistocene. Dense sands were encountered in depth beyond 15 m. A layer of boulder clay with a thickness of 5 - 10 m was found. For the verification of the carrying behaviour of the combined pile-raft foundation a monitoring programme was installed. A total of 4 piles are instrumented with measuring devices, such as pressure cells at the top and bottom as well as strain gauges within
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raft, followed by a diameter of 1.5 m were installed. All piles were constructed with a jet grouted shaft as well as jet grouting 10 m underneath the piles in the cavernous limestone.
The maximum settlements of the building add up to 2.1 cm. The minimum settlements were encountered with 1.5 cm. This leads to a tilting of smaller than 1/2000. These results cause no negative effect on the serviceability of the building. The monitoring shows that the 111 piles of the Commerzbank carry approx. 96 % of the total load of the building. This indicates that not all loads are transferred by the piles into the ground.
Conclusion
On the basis of an extensive ground investigation and a detailed description of the ground, the foundation of high-rise buildings can be planned in an economic and safe manner. The report shows customary foundation systems for high-rise buildings such as a pile foundation as well as the innovative combined pile-raft-foundation. The choice of the adequate system is often depending on the proof of the serviceability of the high-rise building and / or neighbouring structures. Pile foundations have been constructed to reduce the settlements and to satisfy the ultimate limit state and what is more the serviceability. For the design of a pile foundation it is often required that each pile must individually satisfy an according factor of safety. If a pile foundation is just designed to reduce settlements, the required and known geotechnical proofs are a conservative design approach.
Where piles are primarily used to reduce settlements and where an adequate factor of safety against failure is provided, the innovative combined pile-raft-foundation (CPRF) has been put forward in the past. The essence of the combined pile-raft-foundation is to employ piles so that settlements are reduced to an acceptable amount. The successful design and construction has been verified by many structures including many high-rise buildings. For an even more efficient use of foundation piles, the use of geothermal energy with help of these piles has been lately carried out. For this, the foundation piles have been additionally equipped with heat exchanger tubes to use the ground as an seasonal storage. Many more applications to use geothermal energy are possible. More effort should be put into this field of geothermal foundation system to provide and improve new possible innovative ideas for an environmental-friendly use of energy.
References
- Braja, D. (2004): Principal of Foundation Engineering, 6th Edition
- BS (British Standard) 8004 (1986): Code of practice for foundations
- BS 5930 (1999): Code of practice for site investigation
- Bajad, S.P. and Sahu, R.B (2009), “Optimum design of piled raft in soft clay – A model study.” Proce. IGC Conf., Guntuy, page 131-134.
- Balakumar, V. and Ilamparuthi, K. (2007), “Performance monitoring and numerical stimulation of a 12 storey building.” Indian Geotechnical Journal 37(2), page 94-115.
- Conte, G., Mandolini, A. & Randolph, M.F. (2003), “Centrifuge Modelling to investigate the performance of piled rafts.” Proc. Of the 4th Int. Seminar on Deep Foundations on Bored and Auger Piles, Millipress, Rotterdam, page 359- 366.
- Cooke, R.W. (1986), “ Piled raft foundation on stiff clays, a contribution to design philosophy.” Geotechnique, 36(2), page 169-203.
- Poulos, H.(2008), “ The piled raft foundation for the Burj Dubai –design and performance” IGS - Ferroco, Terzaghi Oretion – 2008,Indore.
- Randolph, M.F. (1994), “Design methods for piled roofs and piled rafts.” Proce. 13th Int. Conf. on SMFE, New Delhi, page 61-82.
- Russo, G., and Viggiani, C. (1998), “Factor controlling Soil-Structure interaction for piled rafts.” Int. Conf. on Soil-Structure Interaction in Urban Civil Engineering, Ed. Katzenback, R. and Arslan, V., Darmstadt.
- Terzaghi, K., and Peck, R.B.(1967), “ Soil Mechanics in Engineering practice.” 2nd Ed., John Weley and Sons, New York.
- Innovative foundation systems for high-rise buildings, Prof. Hubert Quick, Simon Meissner, Dr. Joachim Michael, Technische Universität Darmstadt, Institut für Werkstoffe und Mechanik im Bauwesen, Darmstadt, Germany (Proceedings of the 1st Intelligent Building Middle East Conference 5-7th, December 2005, Bahrain).
Figure 7: Commerzbank in Frankfurt, Germany
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Machines for Concrete Placement Through Concrete Pumps
Concrete is one of the most common building materials. Its use in construction applications has expanded in both the equipment and scientific sides
of the business with improved mix quality and placement technology. There are two ways of concrete placement concrete dumping and concrete pumping.
Concrete is a fantastic building material but it’s not always the easiest to handle. Dumping of concrete at any construction site is hard and labor-intensive, it is a slow process and reduces the concrete quality. Pumping concrete is probably the best way to improve the construction time, reduced cost, and allow more aggressive engineering projects to be accomplished. The concrete pump placing method also allows for quicker return on investment for companies and for the individuals hiring the concrete work as efficiency is greatly improved.
Other benefits associated with pumping include the fact that it keeps the concrete mix from segregating and the aggregate evenly distributed. Getting concrete wherever needed is now simplified with a pumping system. The many cost-saving benefits have made concrete pumping a popular, economical and efficient ways of handling and placing concrete.
Concrete pumps are hydraulically operated powered by diesel driven engines or Electric motors. It works on tandem concrete pumping pistons which alternate suction and delivery to create a continuous flow of concrete through the pipeline.
Concrete pumps are classified in following ways
Trailer-Mounted Concrete pump
The first type of concrete pump is placed on a trailer, and it is commonly referred to as a stationary pump or trailer-mounted concrete pump. These pumps require truck for towing to transport it to any construction sites. These pumps require steel pipes and rubber concrete placing hoses to be manually attached to the outlet of the machine. The hoses are linked together and lead to wherever the concrete needs to be placed. Trailer pumps normally pump concrete at lower volumes than boom pumps.
Trailer-mounted concrete pumps are widely used in RMC and all infrastructure projects. These pumps have two types of output based on applications,A) high pressure
John Kennan, Rahul SharmaSchwing Stetter
Trailer-Mounted Concrete pump
pumping (Piston Side) for high-rise projects of vertical pumping or longer distance pumping and B) high volume pumping (Rod Side) for projects like dams, Power projects, Airports etc.
Truck Mounted Boom Concrete Pump
The second type of concrete pump is attached to a truck. It is known as a truck-mounted boom concrete pump because it uses a wireless remote-controlled articulating robotic arm (called a boom) to place concrete with pinpoint accuracy. Boom pumps can be found in various sizes range from (17m to 62m) and are used on most of the larger construction projects such as high rise buildings as they are capable of pumping at very high volumes and because of the labor saving nature of the placing boom. They are a revolutionary alternative to the truck-mounted concrete line pumps.
Boom trucks are self-contained units consisting of a truck and frame, and the pump itself. Boom trucks are used for concrete pours for everything from slabs and medium high-rise buildings, to large volume commercial and industrial projects. They range from double-axle truck mounted
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pumps used for their high maneuverability, suitability for confined areas, and cost/performance value, to huge, six-axle rigs used for their powerful pumps and long reach on high-rise and other large-scale projects.
Booms for these trucks can come in configurations of three and four sections, with a low unfolding height of about 16 feet. This low unfolding height is ideal for placing concrete in confined areas. Longer, five-part booms can reach up or out more than 200 feet. Because of their reach, boom trucks often remain in the same place for an entire pour. This allows ready mix trucks to discharge their loads directly into the pumps hopper at one central location and helps to create a more efficient jobsite traffic flow. Most manufacturers offer a variety of options, from chassis and pump size, to boom configurations, remote control, and outrigger options.
Truck Mounted Boom Concrete Pump
Stationary Placing Boom
The third type of machine for concrete placing is known as a placing boom and basically has the same type of boom as on the truck-mounted machine. These types of booms are used on jobs where the confines of the construction site will not permit the movements of trucks mounted boom or line pump.
Placing booms are usually placed on the jobsite with a large crane or on a mast with a self climbing mechanism. Mostly the placing booms are mounted on the top of multi-story building as its being constructed and moving up into the sky. They are generally erected in the middle of the construction site or along the passage for the elevator, which help to provide maximum reach.
Stationary Placing booms are the ideal method of choice for placement of concrete during multi-story building projects like high rise buildings. Separate concrete placing booms can be used in situations where the boom truck may not be able to conveniently access the pour site. Combined with the right concrete pump, these placing booms provide a
Stationary Placing Boom
systematic method of concrete distribution. Typically, the boom is remounted on a pedestal, which can be located hundreds of feet from the pump and connected with a pipeline.
Truck-Mounted Line Concrete Pump
The fourth type of concrete machine is mounted on a flatbed truck and known as a truck-mounted line pump. It is used in the same fashion as a trailer-mounted concrete pump. These pumps require steel or rubber concrete placing hoses to be manually attached to the outlet of the machine. Those hoses are linked together and lead to wherever the concrete needs to be placed.
Line pumps are mobile compared to trailer pump and it is widely used in projects like Road construction, RMC’s project sites where concrete pours are spread at different locations.
Truck-Mounted Line Concrete Pump
Skid Mounted Line and Shotcreting Concrete Pump
Skid Mounted Line concrete pumps is skid or rail mounted
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pumps usually transported and moved around by forklifts or cranes. These pumps are used the same as trailer mounted concrete line pumps. These pumps normally used for smaller volume concrete placing applications such as underground concrete pumping, shotcreting, and grout pumping.
Skid Mounted Line concrete pumps
These pumps has ability to reach where truck and trailer mounted pumps cannot. These types of pumps perform well in mines and tunnels because of their compact nature. These pumps are uncommon except on specialized jobsites such as mines and tunnels.
Over the past century, sprayed concrete has replaced the traditional methods of lining tunnel profiles and has become very important in stabilizing the excavated tunnel section. Modern tunneling without sprayed concrete is inconceivable. Sprayed concrete was used for the first time in 1914 and has been permanently developed and improved over recent decades. Advantages of wet mix sprayed concrete pumps are low re-bond higher output, less wear & tear in pump hoses and nozzles.
Valve Technology
A concrete pump should be reliable, robust, powerful and
Shotcreting Concrete Pump
with less wear and tear in order to successfully complete the tough operations at any construction site. The pumping characteristics of a concrete pump are essentially determined by the valve system used. It should be able to pump a great variety of material, beginning with plasticized mortar all the way up to construction concrete with large-grain, crushed material and low consistency, with a minimum of wear. There are 3 kinds of concrete valves widely used;
- The Flat Gate Valve: Rugged in its ability to handle inconsistent, low grade or big aggregate concrete. However due to its design though operation cost is higher this valves can pump concrete produced by drum mixers also.
- The S- valve: Used for regular pumping jobs, however due to its shape there is reduction in size leads to pressure built up & it’s bearing surface on one side.
- The Newest Rock Valve: The SCHWING patented Rock Valve gives best efficiency for pumping concrete today. The Rock valve has sliding action on both sides ensuring minimum wear and due to its conical shape it enable access for hard facing internally.
Flat Gate Valve
Schwing’s Rock Valve Technology
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Equipment for Diaphragm Wall Construction
Underground space creation has gained importance in the Indian cities to help release scarce land resulting from rapid growth in population. Underground space
structures are thus becoming common for deep basements of residential buildings and shopping malls; underground Metro Rail Transit Systems for both roads and railways. Further, underground power houses, water curtains below dams are some of the underground structures in the heavy infrastructure facilities.
Open excavations for construction of such underground structures quite often becomes impossible due to closely spaced structures in the vicinity of excavation, very high water table conditions, difficult soil conditions, existing underground utilities in close proximity, stringent restrictions to lateral ground movements, etc. Excavation support systems under such conditions become necessary. However, provision of proper excavation support system has always suffered from commercial considerations rather than from a careful techno-commercial consideration. A key factor to careful techno-commercial consideration can be through awareness about the availability and proximity to various methods, technologies and equipment for construction of excavation support systems.
Common Types of Earth Support Systems
Depending on excavation depth, ground conditions, ground water level, allowable vertical and horizontal displacements of adjacent ground, water tightness requirements of support system, availability of construction know-how, cost factors, subsequent construction methodology, working space limitations, etc., the following types of deep support systems are commonly used.
- Diaphragm walls- Secant / contiguous Pile walls- Sheet pile walls- Soldier pile with wooden lagging walls
Piled walls (b. to d. above) use rotary piling equipment which are common in India now a days. However, the Diaphragm wall and related equipment are yet to gain popularity and understanding amongst the stack holders. The following sections, construction of diaphragm walls and the related equipment are discussed.
Diaphragm Walls
Diaphragm wall is an underground wall constructed from the ground level to support excavation sides from lateral earth pressure and water pressure, and to provide water tightness to the underground structure. Diaphragm walls can be temporary if they only support the sides until construction below ground level is completed. They can also be permanent if they form part of the main wall of the underground structure.
Diaphragm walls find the following applications: earth and water retention walls for deep excavations, basements, and tunnels; High capacity vertical foundation elements; seepage control walls under dams, etc. These are also used as a permanent basement walls for facilitating Top-down construction method.
Typical wall thickness varies between 0.6 to 1.5m. The wall is constructed panel by panel in full depth. Panel width varies from 2.5m to about 6.5m or even more depending on various conditions. Short widths of 2.5m are selected in less stable soils, under very high surcharge or for very deep
J Jeyson SamuelL&T GeoStructure, Larsen & Toubro limited, Manapakkam, Chennai
Inadequate space in urban settings has set forth a challenging trend to go deeper into the ground and to increase the space required for providing public amenities, parking, housing utilities, industrial mass storage, etc. The space constraints necessitate the deep excavations to have earth retaining systems. One of the important earth support system is Diaphragm wall. This paper is an attempt to increase the awareness on latest Diaphragm wall systems, equipment and technologies available in India.
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walls. Different panel shapes other than the conventional straight section like T, L are possible to form and used for special purposes. Traditionally, panel excavation is carried out using cable supported Grab. Hydraulic grabs with Kelley arrangement have recently been introduced in India on large Infrastructure projects. More recently developed hydraulic cutter type machines have also entered few projects in India. Apart from the Diaphragm wall excavation equipment, other equipment involved are cranes for reinforcement lowering, pumps, tanks, de-sanding equipment, air lifts, mixers etc.
Steps involved in the construction of diaphragm wall can be broadly listed as follows:
- Guide wall construction along alignment- Trenching by crane operated Grab/ hydraulic grab or
trench cutter- Bentonite flushing- Lowering reinforcement cage- Concreting using tremie
The sequence of diaphragm wall panel construction is schematically illustrated as below.
It must be remembered that Diaphragm walls are constructed as a series of alternating primary and secondary panels. Alternate primary panels are constructed first which are restrained on either side by stop-end pipes. Before the intermediate secondary panel excavation is taken up, the pipes are removed and the panel is cast against two primary panels on either side to maintain continuity. Water stoppers are sometimes used in the construction joints between adjacent panels to prevent seepage of ground water.
Equipment for Diaphragm Walls
Diaphragm wall construction involves heavy construction equipment. These equipment can be grouped based on three major activities viz. trenching, reinforcement lowering, concreting.
Trenching activity involves a network of equipment consisting the trench excavation equipment, desander or decanter and slurry handling pumps. A typical network for trench excavation is illustrated in the sketch below.
Equipment for Trench excavation are of the following type.
Reverse mud circulation rig are the first generation equipment used for Diaphragm wall trench excavation. They use a percussion chisel connected to a powerful mud pump to excavate soils and soft rocks. This system is almost obsolete in India.
Mechanical clamshell grabs are generally about 10 to 20 MT in weight, 6 to 10m long and suspended on a crane with double winch with free fall arrangement with sufficient line pull. One winch holds the grab body and the other winch operates the grab bucket through sheaves to give closing forces ranging up to 120 MT. The above features help these
Trench Excavation Equipment
Suitability Not Suitable for Productivity*
Trench CutterSoil, rock &
Boulders200 Sqm / Day
Mech. / Hydraulic grabs
Soil Rock & Boulders 75 Sqm / Day
Reverse Mud Circulation
Soil & Rock Boulders 30 Sqm. / Day
* Very Approximate and depends on various factors
Reverse Mud Circulation Rig Mechanical Clamshell Grab
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mechanical grabs excavate the panel trench through all types of soils with fairly good verticality control.
Hydraulic grabs (Fig below) are generally rope suspended or Kelly guided with sufficient weight and length and mounted on a suitable hydraulic crane or mechanical crane with power pack. The closing forces of 180 MT is quite common. The above features help these mechanical grabs excavate the panel trench through all types of soils and hard formations with good verticality control and higher productivity.
Trench cutter (Fig above) which is otherwise called as Hydromill or Hydrofraise is a latest development. The features in this equipment enables trenching through all types of soils and rocks with greater verticality control and speed. The cuttings of the trench excavation is carried by trenching slurry and removed at a desander. The desanded slurry is circulated back in the trench. Verticality of the excavation can be controlled by using hydraulic flaps available in the cutter frame. This way, the trenching is continuous, fast, straight and clean.
Prefabricated diaphragm wall reinforcement cage is inserted, once the trenching is completed. This requires one or two cranes for lifting and lowering activities as shown in picture below. Reinforcement cages of lengths varying from 12m up to even 25m with weights ranging between 10T to 25T can be lifted and lowered in single piece. However, depending on the availability of space and crane capacity, reinforcement cages can be lifted and lowered in pieces and lapped during lowering.
Hydraulic Grab Trench cutter
Diaphragm wall concreting is done by tremmie method and hence the concrete must have adequate workability to ensure smooth flow from bottom of panel to top of panel, completely replacing the slurry without mixing. Typically, each diaphragm wall panel would require about 50 to 200 cum of concrete in a span of 4 hours. Hence, production of diaphragm wall concrete is a careful decision to be made considering the availability of Ready Mix Concrete
(RMC) plants in the closer vicinity and the logistics. A typical concrete pouring operation is shown in the picture below.
Summry & Conclusions:
In the foregoing sections, diaphragm wall as earth retaining system of deep excavations was out lined with brief method description and major equipment required for the same. While many of the minute details of diaphragm wall construction are not discussed here, the author would like to bring the attention of the readers the following.
Diaphragm wall structurally resist and protect the life and facilities of underground structures from the soil and water pressures and the leakages. In achieving this, concrete and the method of concreting assumes greatest importance and throws many challenges such as logistics through metros to bring concrete to the tune of about 200cum within 5 hours and without compromising quality. Hence, the author would like to appeal the readers to research better methods of in situ concrete production and placing for Diaphragm wall construction.
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‘Equipment for Evaluation, Testing and Maintenance of Concrete Structures’
It is often necessary to test the concrete structure after the concrete has hardened to determine whether the structure is suitable for its designed use. It is important
to carryout tests without damaging the concrete. The tests available for testing of concrete range from the completely non-destructive, where there is no damage to the concrete, through those where the concrete surface is slightly damaged, to partially destructive tests, such as core tests and pullout and pull off tests, where the surface has to be repaired after the test. Another purely non-destructive way of estimating the in-situ strength of concrete is by “Maturity method”. The maturity method is a technique that allows the in-place concrete strength to be estimated using the time and temperature history of freshly placed concrete.
The range of properties that can be assessed using non-destructive tests and partially destructive tests is quite large and includes such fundamental parameters such as density, elastic modulus and strength as well as surface hardness and surface absorption, and reinforcement location, size and distance from the surface. In some cases it is also possible to check the quality of workmanship and structural integrity by the ability to detect voids, cracking and delamination. Non-destructive testing can be applied to both old and new structures. For new structures, the principal applications are likely to be for quality control or the resolution of doubts about the quality of materials or construction. The testing of existing structures is usually related to an assessment of structural integrity or adequacy. In either case, if partially destructive testing alone is used, for instance, by removing cores for compression testing, the cost of coring and testing may only allow a relatively small number of tests to be carried out on a large structure which may be misleading. Non-destructive testing can be used in those situations as a preliminary to subsequent coring.
Typical situations where non-destructive testing may be useful are, as follows:
- Quality control of pre-cast units or construction in situ- Removing uncertainties about the acceptability of the
material supplied owing to apparent non-compliance with specification
- Confirming or negating doubt concerning the workmanship involved in batching, mixing, placing, compacting or curing of concrete
- Monitoring of strength development in relation to formwork removal, cessation of curing, prestressing, load application or similar purpose
- Location and determination of the extent of cracks, voids, honeycombing and similar defects within a concrete structure
- Determining the concrete uniformity, possibly preliminary to core cutting, load testing or other more expensive or disruptive tests
- Determining the position, quantity or condition of re-inforcement
- Increasing the confidence level of a smaller number of partially destructive tests
- Determining the extent of concrete variability in order to help in the selection of sample locations representative of the quality to be assessed
- Confirming or locating suspected deterioration of concrete resulting from such factors as overloading, fatigue, external or internal chemical attack or change, fire, explosion, environmental effects
- Assessing the potential durability of the concrete- Monitoring long term changes in concrete properties- Providing information for any proposed change of use
of a structure for insurance or for change of ownership
NDT Equipments
A wide range of Non-Destructive Testing (NDT) equipments are available for testing of concrete structures. They are classified as follows:
Dr. R NagendraTechnical Director, Civil-Aid Technoclinic Pvt. Ltd.
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- Concrete rebound hammers- Ultrasonic Pulse Velocity testers- Profometers or Cover meters- Corrosion analyser- Permeability apparatus- Impact echo testers- Semi/partial destructive testing- Core extraction Pull-
out tester, Pull-off tester- Devices for Non-destructive testing of piles- Concrete Maturity meter- Penetration resistance testing- Windsor probe- Instrumentation of structures
Concrete Rebound Hammer
Rebound hammer test is a quick method for assessing the quality of concrete based on surface hardness indicated by the rebound number. A higher rebound value indicates higher strength / surface hardness of concrete.
Technical Reference
IS 13311-(part-II)-1992-(reaffirmed in 2004), ASTM C 805
The equipment consists of a pair of transducers (probes) of same frequencies, electrical pulse generator, electrical timing device and cables.
Cover meters
Cover meter is used for assessing the cover and mapping of rebars. It can also be used for estimating the size / diameter of rebars most popular equipment used is pro-fometers from M/s. Proceq, Switzerland.
The equipment works on electromagnetic principles. The equipment consists of a display unit coupled with universal probe
Technical reference: BS :1881 (part 204)
a) Original Schmidt Concrete Rebound Test Hammer
b) Digi-Schmdt Hammer c) Schmdt Rebound Hammer – P, L, L9 Types
Ultrasonic Pulse Velocity testers
Ultrasonic pulse velocity test method is extensively used to assess the quality and strength of in-situ concrete in members. This test is generally used to check the compaction, uniformity of concrete, determination of cracks, presence of honeycombs, and also strength estimation (qualitatively). Most popular equipment used for ultrasonic pulse velocity test is ‘PUNDIT’ (portable ultrasonic non-destructive digital indicating tester) from U.K, ust (ultrasonic tester) from U.K and ‘TICO’ meter from Switzerland.
Photos of Ultrasonic Pulse Velocity Tester
Profometer-5 (Cover Meter) Profometer-5+ (Cover Meter)
Profoscope Ferroscan
Corrosion analyser
Corrosion of embedded steel is the major cause of deterioration of concrete structures. This may lead to structural weakening due to loss of steel cross-section, surface staining and cracking or spalling.
Half-cell potential measurement test the half-cell potential measurement test essentially consists of measurement of absolute potential at the concrete surface with a reference electrode.
The measured absolute potential is considered to be the best criterion for assessing the corrosion status of the embedded rebars.
The most popular equipment used for the above test is
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‘CANIN corrosion analyser’ from Proceq, Switzerland. The equipment consists of digital mili - voltmeter and copper - copper sulphate half-cell.
Impact-Echo can also be used to determine the location and extent of flaws such as cracks, delaminations, voids, honeycombing and debonding in plain, reinforced and post-tensioned concrete structures. It can locate voids in the subgrade directly beneath slabs and pavements, measure the depth of surface-opening cracks, and determine thickness or locate cracks, voids and other defects in masonry structures where the brick or block units are bonded together with mortar. Impact-echo is not adversely affected by the presence of steel reinforcing bars.
Semi / Partial Destructive Test:
The most common semi / partial destructive testing methods adopted to evaluate structural members are:
a.Extraction of cores & carrying out compressive strength test.
- Pull out test (lok test).
Photos of Corrosion Analyser
Permeability Tester
In-situ permeability test is conducted on the concrete surface. Gas / water under pressure is allowed to diffuse into the concrete media. The reduction in pressure with time is an indication of porosity in concrete.
Based on the rate of reduction in pressure permeability can be calculated. This serves as a measure to evaluate concrete quality.
Photos of Water Permeability Test Set-Up
Initial Surface Absorption Test
Initial surface absorption is defined as the rate of flow of water into concrete per unit area at a stated interval from the start of the test at a constant applied head and temperature. Results will be expressed as ml/ml2/s at a stated time from the start of test. This method is detailed in BS 1881: Part 5 (207)
Impact Echo Tester
Impact-Echo is a method for nondestructive evaluation of concrete and masonry, based on the use of impact-generated stress (sound) waves that propagate through the structure and are reflected by internal flaws and external surfaces. Impact-Echo can be used to make accurate, nondestructive, measurements of thickness in concrete slabs and plates, following an ASTM C 1383-98a Standard.
Torrent: Permeability Tester
Photos of Initial Surface Absorption Test
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- Capo test.- Pull-off test - Load test on structures.
the strength and homogenity of in-situ concrete. Most popular equipments used for core extraction are HILTI from Germany, ELE from U.K., Bosch from Germany. The equipment consists of diamond tipped core barrels fitted to the electrically driven motor with water as a coolant.
Echo Impact Tester
Pistol Grip Transducer
Intrument Components
a.Extraction of cores & carrying out compressive strength test.
Core test is one of the most appropriate method to assess
Photo of Core Cutting Machine
Pull out test
Pull out test is also known as lok test. A specially shaped steel insert with enlarged end will be cast while concreting at the proposed test location. The extended end of the steel insert above concrete is pulled through a pulling device and insert is pulled out with a cone of concrete. The force required to pull the insert is measured. Pull out tests fall into two basic categories; those which involve an insert which is cast into the concrete, and those which offer the greater flexibility of an insert fixed into a hole drilled into the hardened concrete. Cast-in methods must be preplanned and will thus be of value only in testing for specification compliance, whereas drilled hole methods will be more appropriate for field surveys of mature concrete. In both cases, the value of the test depends upon the ability to relate pull-out forces to concrete strengths. Although the results will relate to the surface zone only, the approach offers the advantage of providing a more direct measure of strength and at a greater depth than surface hardness testing by rebound methods, but still requires only one exposed surface.
An appropriate calibration chart shall be established in the laboratory to correlate the pull out force with estimated compressive strength of concrete. Most popular equipment used for the above test is pull out tester from German equipments. The equipment consists of specially designed inserts, pulling device with a load indicator.
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Capo Test
Capo test is an improved version of pull out test. At the test location, special inserts are introduced in the driven hole and pulled out. The required force to pull the inserts along with concrete is measured and co-related with the calibration chart developed for the above test in the laboratory.
to the concrete surface with an epoxy resin and jacked off to measure the force necessary to pull a piece of concrete away from the surface.
Lok Test Apparatus
Pull-off Test
This approach has been developed to measure the in-situ tensile strength of concrete by applying a direct tensile force. The method may also be useful for measuring bonding of surface repairs and a wide selection of equipment is commercially available with disk diameters typically 50 mm or 75 mm. Procedures are covered by BS 1881: Part 207 and it should be noted that the fracture surface will be below the concrete surface and will thus leave some surface damage that must be made good A disk is glued
Load Testing of Structures
Load test is conducted on the identified members to check the behaviour of members under design loads. Dial gauges / deflectometers are placed under the member to measure the deflection & deflection recovery during load test. If the measured deflection and deflection recovery are within the permissible limits then the tested members can be accepted.
Technical reference IS 456-2000
Devices for Non-Destructive Testing of Piles
The quality of pile can be tested using low strain Pile Integrity Tester (PIT). The equipment comprising of hammer, accelerometer and data collector. This equipment is used to find out change in cross section of pile (bulging or necking), quality of concrete and length of pile.
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High strain equipment: This consists of heavy hammer, strain gauges, accelerometers and data collector. This equipment is meant for arriving at load carrying capacity of pile, settlement of pile and integrity of pile.
Accoustics Concrete Tester
The Acoustic Concrete Tester (ACT) is a concrete thickness gauge that measures the concrete thickness of pavements, slabs, retaining walls, foundation footings and tunnel linings. This nondestructive testing instrument also identifies flaws such as delaminations, voids, and spalls.
The ACT is precise, light, battery operated and rugged for field use in all weather conditions. It works for concrete structures from 75 to 900 mm thick.
The ACT uses Ultrasonic Echo Technology. It electronically generates a broadband pulse that includes all frequencies required to accurately determine the thickness of the structure. Measuring thickness with the ACT consists of placing two small probes on the structure to be tested and touching the ACT screen. A telescoping pole helps test hard to reach structures. As the structure responds to its natural frequency, its thickness is displayed on the high visibility ACT screen. The ACT also calculates the wave speed of structures of unknown thickness.
The ACT eliminates coring or excavation, and easily self calibrates the concrete wave speed prior to the test. It only takes seconds to measure the thickness of the concrete.
Concrete Maturity systems
The Maturity Method of estimating in-place concrete strength has been studied for more than 50 years, and as a result, the science of concrete curing is well understood. Since 1987, it has been an ASTM Standard Practice (C1074). When concrete hardens, it gives off heat proportional to its curing rate. By learning how much heat is released, an accurate estimate of the strength can be determined. Generally, concrete in a structure cures at a much faster rate than concrete in a test cube. This is due to the much larger mass of the structure, and better hydration which aids curing.
When determining the early-age strength of cast-in-place concrete, reliance on test cubes can lead to problems. For example, if test cubes are cured at a lower temperature than the structure, the cubes would underestimate the strength of the slab, which means that critical construction operations are delayed unnecessarily. Or conversely, if the deck is cooler than the cubes, the cubes would overestimate the strength, a clear safety concern. Maturity testing monitors the curing of the structure and compares it to the cube, to more accurately track strength gain in the structure, improving both safety and construction operations.
Photo of Pile driving Analyzer Photo of Sensors for Pile driving analyzer
Photo of Accoustic Concrete Tester
Allows you live access to your data from any computer, 24hrs a day
Penetration Resistance Testing
The technique of firing steel nails or bolts into a concrete surface to provide fixings is well established, and it is known that the depth of penetration is influenced by the
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strength of the concrete. A strength determination method based on this approach, using a specially designed bolt and standardized explosive cartridge, was developed in the USA during the mid 1960s and is known as the Windsor probe test. It has gained popularity in the USA and Canada, especially for monitoring strength development on site, and is the subject of ASTM C803.
Although it is difficult to relate theoretically the depth of penetration of the bolt to the concrete strength, consistent empirical relationships can be found that are virtually unaffected by operator technique. The method is a form of hardness testing and the measurements will relate only to the quality of concrete near the surface, but it is claimed that it is the zone between approximately 25 and 75 mm below the surface which influences the penetration. The depth is considerably greater than for rebound or any other established ‘surface zone’ tests.
Instrumentation of structures for stresses and strains:
Strain Gauges for Steel: Weldable strain gauges measure strain in steel. Typical applications include:
Photo of Windsor HP Probe - ASTM C-803
Testing Being Conducted
- Monitoring stresses in structural members of buildings, bridges, tunnel linings and supports during and after construction.
- Monitoring the performance of wall anchors and other post-tensioned support systems.
- Monitoring loads in strutting systems for deep excavations.
- Measuring strain in tunnel linings and supports.
- Monitoring areas of concentrated stress in pipelines.
- Monitoring distribution of load in pile tests.
Strain Gauges for Concrete: Embedment strain gauges measure strain in concrete. Typical applications include:
- Measuring strains in reinforced concrete and mass concrete.
- Measuring curing strains.- Monitoring for changes in load.- Measuring strain in tunnel linings and supports.
Conclusion
It can be said that wide range of NDT equipments are available for testing, evaluation and analysis of concrete structures. It is the expertise available to interpret the test results plays a very important role in deciding acceptance or otherwise of a structural member from the point of view of quality control or in resolving a dispute.
References
- Bungey J.H., Millard S.G., Testing of Concrete in Structures, Third Edition, 1996, Blackie Academic & Professional, an imprint of Chapman & Hall,
- ACI 228.1R-03, In-Place Methods to Estimate Concrete Strength
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Concrete Batching Plants Some Cost and Quality Issues
Preamble
Indian Standard Plain and Reinforced Concrete- Code of Practice (Fourth Revision) IS 456: 2000 incorporated number of changes. A Clause on “Quality Assurance Measures” has been incorporated to give due emphasis to good practices of Concreting. Proper limits have been introduced on the accuracy of measuring equipments to ensure accurate batching of concrete. Design Mix Concrete Has been made obligatory for grades M25 and above. The accuracy of the measuring equipment shall be within +/- 2% of the quantity of cement being measured and within +/- 3% for other materials. These can be realized only by proper batching and mixing Plants. Many Organizations have made it obligatory to use batching plants. Thousands of batch plants are in operation in India. However, their supply, installation and operation in practice raises some cost and quality issues, these are also examined in the paper
Type of batching plant
A wide variety of configurations are available to suit space restrictions particularly in urban locations. Star type aggregate bins with scraper boom are common in India. They require large space, not always available in Cities.
Bin-Fed batching plants are transportable, fully automated, have their own hydraulic off-loading legs and are capable of producing outputs of up to 40m3 per hour. These batch plants can be custom made to suit construction industry specifications, with accessories added such as: ad-mixture plants, low-level or upright cement silos, aggregate feeders and water chillers.
Tower Batching Plant
The concrete batching plant Tower-type, in addition to having the integrated features of the horizontal type plants, has the added benefit of larger storage capacities and the benefit of gravity batching Considerable reduction of mechanical elements used in the batching process results in considerable power savings and the simplification of the system. Decreases the cycle timings for the production due to the absence of conveyor belts or skip for aggregates movements.
Besides, the vertical disposition of the aggregate storage allows big volumes on a small base surface. All parts of mixing tower are connected by bolts and nuts structure. It is easy and fast to install and dis-install the whole plant, and it saves the time and cost to install and test the plant greatly; The tower, with compact structure, is made of
S A ReddiFormer MD, Gammon India Ltd.
In The Last Decades, India witnessed quantum jump in mechanization of concrete construction, thanks to National Development and Construction Exports. Organizations of all shades have been involved in supply and operation of construction equipment. The writer has been witness to the selection, installation and operation of concrete construction equipment in India and elsewhere. The Paper attempts to detail some of the quality issues being experienced in the process
Fig 1 Modular Batch Plant
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external closed steel plates, which are anti-noise, anti-dust, and heat preserved; Has maintenance and repair platforms and stairs with comfortable space; Washing system has high-pressure pumps, with automatic control and manual control; Closed structure design, closed aggregates conveyor, and external 360°lighting allow all-weather operation.
Aggregates Batcher
The batcher, with 3-5 aggregate hoppers, can be assembled as per individual requirements. There are independent weighing hoppers and belt conveyor under the aggregate hoppers that could be designed as steel structure type, underground and half-underground types. The aggregates can be fed into the aggregate hoppers by loader or belt conveyor. The hopper discharging gates and discharging speed are controlled by computer via cylinder. After aggregates scaling, the aggregates will be conveyed into the transitional hopper. . Each and every aggregate is weighed individually or accumulatively, and the weighing accuracy is guaranteed. The accuracy of aggregates proportional ratio is realized through computer control system, which automatically re-feeds the aggregates if there is shortage of weight, warns if there is overweight.
Location Of Batch Plant: Location should be such that minimum time elapses between mixing and placing concrete It should preferably be close to pour point. For construction of 23 bridges in Nepal. In the Nineties, the author had mounted a batch plant on a Trailer which was hauled by a tractor to wherever concreting was planned. In contrast, for a project in Orissa, space for batch plant was allotted kilometers away, beyond security gate manned by CISF, involving delays of hours! Concrete Quality suffered.
For a cooling Tower Project, Batching Plant was located at the foot of the tower, discharging concrete into the pump directly, minimizing travel time. With longer time interval in moving concrete, quality suffers.
Fig 2 Tower Batch Plant
Fig 3 Star Bin Aggregate Storage
Fig 4 Tower Batch Plant
Batch Plant Components
Quality Assured concrete requires the following minimum batch plant components in addition to the mixer:
- Weighing system periodically calibrated - Moisture Probe for fine aggregates- Program Logic Control for all quality requirements- Silos for cement, mineral admixtures- Aggregate handling system
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- Bulk/Bagged Cement Feeding System- Water Weighing System
However, purchase dept of the user delete some items on grounds of economy!
Most common omissions include Moisture Probes, Slump Meter, inadequate PLC, adequate number of Silos, Inadequate Calibration arrangements etc. Majority of Batch Plants in India are not fitted with moisture probes. Fitted at the entry point of fine aggregates into batch hopper, the probe monitors moisture content, quantifies the value and via the PLC automatically adjusts water content in each batch, ensures the designed water content in each mix. Even many RMC Plants in India are not fitted with moisture probes!
Fig 5 Automatic cement bag feeding Machine
In the absence of moisture probes, the moisture content in sand is checked once or twice a day by using stove or oven; neither method monitors moisture continuously, results in variation of water content in the mix, and concrete quality. The mix design assumes aggregates, cement and water are present in the correct proportions, according to the dry material weights. If sand contains 10% moisture, when you weigh out 1000 kg, only 900kg is sand; the rest is water. You can allow for this by estimating or measuring the moisture of the sand and increasing the amount that you weigh in proportion. If your sand moisture decreases by 2% without being noticed, however, the batching system will weigh out 2% more sand than you require and will add appreciably less water than needed, making a dry batch. Moisture Content varies thro the Day. Traditional methods of using frying pan to assess moisture once or twice daily are not good enough. Batch Plants should be fitted with Moisture Probes at the sand feed point. Probe is connected to the computer, which will continuously adjust the mix water accordingly. The aggregate moisture sensor ensures that the batch is proportioned according to the DRY WEIGHT MIX DESIGN.
Moisture probe is unique; it can continuously adjust the load
Fig 6 Moisture Probe
water as the material flows over the probe, a method that ensures consistent slump predictability in high specification concrete and concrete product manufacturing. The probe can be installed and calibrated in a matter of hours. Moisture Probe continuously adjusts the load water as the material flows over the probe; method ensures consistent slump in concrete. Probe is accurate to within ±0.3%; achieves this consistency through self adjusting circuitry that detects and corrects changes caused by time, housed in a one-piece stainless steel casing. Mounted directly above the feed gate, the probe collar makes it unnecessary to drain the bin when installing, the probe can be installed and calibrated to the material in a matter of hours
Mixer Water Dosing System: There are two ways to add water to concrete. The first is to meter the water volumetrically, based on the mix design. This method neglects the error in batched weights, adding the same amount of water regardless of the weight of cement or aggregates in the batch. Variations in slump are the result .The second is to monitor the moisture of the mix and add the quantity of water required to produce the correct slump or water/cement ratio. We need this to eliminate the variations and produce consistent product
What is a slump meter? The water content is controlled by monitoring the effort required to turn the mixer. As water is added to the dry ingredients, the effort increases. Any further increase in water results in a drop in the effort as the mix starts to liquefy. This drop is very rapid and is a sensitive measure of the slump . This is measured with a wattmeter in the motor’s electrical circuit. Slump metering
Fig 7 Precision water control system
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gives good results when the same mix design and batch size are used for long periods.
Batch Plant Accessories Required For Quality Concrete
- Program Logic Control- Vibrator for sand compartment- Compressor, Screw conveyor support pipe- Control cabin with locking arrangements- Additional feed line for cement screw repair- Cement silo filter controls- Radial scrapper with distribution box (specify jib length,
bucket cap) - Earth leakage control- All connecting cables - Complete wire of units, limit switches and valves- Terminal box, Block connections between parts to
terminal box- Lighting for machine platform, traveling path- Tropicalization of electric parts to resist temp: 50o C,
relative humidity: 90%
What is Program Logic Control (PLC)? PLC programs run in an endless loop like a wheel turning, repeating hundreds of times every second. Every time around, they check all the inputs, make decisions based on the program in the loop and set all the outputs. It is possible for a programmer to make a mistake in the program, but no mistake can halt the operation of the PLC; it keeps on running. Because it cannot freeze, it performs reliably throughout its long life, requiring little if any maintenance
Batch Plant Erection Time: Case -Tripoli West Thermal Power Station, Libya : Batch Plant was ordered from ELBA Germany. Contracting Company’s Engineer was exposed for one week in the German plant, before delivery. The supplier had committed to erect & commission the Batch Plant in 24 Hours. Foundation for the batch plant was ready before its receipt at site. Batch Plant was delivered in two modules. Tools and tackle were kept ready. The batch plant was actually commissioned in one day!!! This was in 1976. Today in India it takes two to four weeks to erect and commission a batch plant by the contractor. Supplier is in a position to erect and commission faster. Mobile batching plants are now manufactured in India. In Some cases, the plant has actually been commissioned in four hours
Diesel Generating Sets: Due to uncertain electricity supply from the Power Utilities, provision of diesel Gensets is common in India. However the capacity provided is far in excess of requirements. When the author started operations in Libya in 1976, the German supplier had recommended 35kW standby Gensets, worked successfully. Thirty years later Indian equipment suppliers recommend up to 125kW, being provided by contractors as standby for 30 cum batch plant.
Batch Plant utilization in India Case: 30 cum PlantRated output: : 30 cum per HourRealizable output : 20-22 doActual output : 10-12 do Average
Reasons: The Mixer is not loaded to capacity, Batch Plant mixed concrete waiting for Truck Mixers, low placement rate, finishing delayed, condition of access road, inadequate no of truck mixers, cement feed delay, aggregate feed delay etc. Low output affects the quality of concrete
Batching Plant Location & Layout
Location should be as near to the center of gravity of Job to minimize haulage cost and product quality variations due to variations in haul distances. Aggregate stock pile floor should be in concrete, with drainage slopes. Control cabin should be in a commending position so that the operator can observe the return of empty trucks and positioning. Concrete laboratory should be located on the exit route.
Location of Ready Mix Plants: In India Most of the RMC Plants are located outside the city, resulting in long travel up to 3 hours or more due to city traffic congestion. Large space is required for on-site installation due to type of plant Chosen. RMC Plants in Europe are located within the two hour limit of travel. In Case of space constraint, Tower type plants are chosen. The author had visited an RMC plant in Scotland with Tower type unit. There was no space earmarked at ground level for materials. The Tower unit had vertical radial storage above ground for materials. Continuous stream of trucks feed the tower via below ground hopper and vertical bucket conveyor. Land used for the batch plant was hardly about 600 sqm. Elsewhere the RMC supplier strictly follows the two hour maximum time between mixing and delivery of concrete, a quality requirement.
Access to Truck Mixers
Layout of road should allow unidirectional truck mixer movement for loading, dispatch. Provide paved access road, drainage and ensure fast movement of loaded truck mixers. Avoid Steep Grade in access road. Cleaning Truck Mixers after every load is discharged, and provide for disposal of dirty water
During construction of JNPT terminal in the eighties, Concreting operation as mechanized, but no attention was paid to proper maintenance of access roads. Concreting was frequently interrupted due to truck mixers bogged down in poor service road; many truck mixer loads were rejected due to delayed delivery. Truck tyre consumption was very high. In retrospect, it was concluded that it would have been cheaper to provide concrete paved service road!!!
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Concreting starting time, working hours, night work, impact on quality
During a Korean Visit, it was observed that concreting activities are restricted to daylight working hours, primarily as a quality assurance measure. Workers were unwilling to work at night as it affected their social life.
In India, concreting on major projects generally start late evening due to variety of reasons : attraction of overtime, delayed pour card clearance, unplanned operations etc. The main casualty has been quality. Senior supervision is difficult to ensure at night. Lighting can never match daylight. Most accidents happen at night, interrupting concrete pour, cold joints etc. Work at night is more expensive. Quality Assurance is poor during night. There is less output during night.
Recently in Bangalore, concreting an RC flat slab of large span was started at 0100 hours in the night and continued for 30 hours. It is difficult to control quality in such cases. It would have been preferable to start such major pour in the morning.
The author was involved in management of precast yard for Delhi Metro contract. Initially, activities were carried round the clock for certain monthly output. Work during night required huge expenses towards running diesel generators, besides indifferent quality. Work was reorganized so that concreting was done during the day only. The productivity was same, though the work period was reduced by half, but of improved quality.
Qualified / Trained Operators: Irrespective of the level of sophistication of the batch plant, it is necessary to employ
trained operators with elementary knowledge of concrete quality. The author had visited RMC plants in Germany extensively. Every RMC operator is required to undergo one week course dealing with quality requirements prior to employment. There are institutions offering such courses.
We do not have such institutionalized system in India. Some Batch Plant manufacturers do offer training facilities, but not very popular as there is no compulsion to get trained. Majority of batch plants in India are operated by persons promoted from helper category! There are exceptions: some expatriate Companies had employed diploma holders as operators.
Quality is not free. Quality is like buying oats. If you want nice, fresh, clean oats, you must pay a fair price. However, if you can be satisfied with oats that have already been through the horse ..... that comes a little cheaper!
“It is unwise to pay too much, but it is worse to pay too little. When you pay too much, you lose a little money ..... that is all. When you pay too little you sometimes lose everything, because the thing that you bought was incapable of doing the things it was bought to do. The common law of business balance prohibits paying a little and getting a lot .... it cannot be done. If you deal with the lowest bidder, it is well to add something for the risk that you run. And if you do that you will have enough to pay for the something better” John Ruskin (1819 - 1900)
John Ruskin’s Dictum applies equally to buying batch plants. In India, a typical 30 cum batch plant cost ranges from ` 25 to ` 50 lakhs depending on quality parameters and range of accecories. Buyer Beware!!!
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Application of GIS-BIM Integration for Mega Project Construction Equipment Management
With the advances in the field of information techno-logies, construction industry has started taking advantages some of these developments. GIS &
BIM are the tools used to manage construction projects and can improve the construction planning and design efficiency by integrating locational and thematic information in a single environment. There is huge potentials of using 3D-GIS and BIM by integrating together.in managing construction project activities. All mega construction equipments can be optimally used and controlled using integrated GIS-BIM technology.
About GIS and 3D GIS& BIM
Geographic Information Systems (GIS) is an appropriate technology for managing construction projects and can
improve the construction planning and design efficiency by integrating locational and thematic information in a single environment. It provides capabilities to solve problems, involving creation and management of data, integration of information, visualization and cost estimation to which most of the construction management software is lacking. In construction management, GIS leads to the improvement in collective decision-making among planners, designers and contractors. A large number of data involve in planning and design phases of construction projects are usually stored in various forms such as drawings, tables, and charts. These data need to be sorted out properly to ensure it can be retrieved and manipulated by related parties when needed. Database in GIS environment can provide a wide range of information to construction industry with a mechanism for
MB Bureau Report
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rapid retrieval and manipulation capabilities. Integration of schedule and design information makes it easier for the project manager to monitor and control the construction progress. Several tools for construction industry using GIS as suggested in many literatures and their applicability has been demonstrated with suitable case study. However, the practical usefulness of these developed tools in construction industry is still doubtful and the implementation on real world project in the industry is rare. Further, most of the reported works uses different software in combination with GIS software. Although, CAD technologies provide visualization capabilities, but three dimensional (3D) GIS technologies could not only provide advance visualization techniques (e.g. fly-through with query on-demand and way-finding) but also stores geometry’s topological infor-mation and being able to perform true 3D analysis, which is not yet possible in CAD technologies.
Whereas, Building Information Modeling (BIM) represents the process of development and use of a computer generated model to simulate the planning, design, construction and operation of a facility. The resulting model, a Building Information Model, is a data-rich, object-oriented, intelligent and parametric digital representation of the facility, from which views and data appropriate to various users’ needs can be extracted and analyzed to generate information that can be used to make decisions and to improve the process of delivering the facility. Refer Figure 1 for BIM modeling.
been gradually utilized in many disciplines. 3D-GIS provide several benefits to the construction industry, in which most of the construction management software are lacking. It may improve the construction planning and design efficiency by the integration of 3D spatial and attribute information in single environment. In general, managing construction is quite demanding and needs rapid spatial information on the spot even using the conventional 2D GIS. It would be great if a construction project is managed by decision makers using 3D-GIS where the required information is in the form of 3D display of a dynamic 3D spatial query and analysis. Geographic information systems (GIS) facilitate the analysis of large amounts of spatial data used in the process of location optimization for various construction equipments such as tower cranes. In addition, integrating analysis results from GIS with 3D visual models enables managers to visualize the potential conflicts with all such mega equipments in great detail. Building Information Modeling (BIM) helps managers to visualize buildings before implementation takes place through a digitally constructed virtual model. Hence, the integrated GIS-BIM model starts with the identification of feasible locations for defined mega construction equipments. The method presented is based on previous works using “geometric closeness” and coverage of all demand and supply points as key criteria for locating a group of mega equipments. Once the geometry of the construction site is generated by the BIM tool, the model determines the proper combination of tower cranes in order to optimize location. The output of the GIS model includes one or more feasible areas that cover all demand and supply points, which is then linked to the BIM tool and generates 3D models to visualize the optimum location of all the mega construction equipments. As a result, potential conflicts are detected in different 3D views in order to identify optimal location.
Use of GIS and BIM technology in managing Tower Crane- A mega construction equipment
Tower cranes are considered as the centerpiece of construction equipment in building projects. They play a key role in transporting a variety of materials vertically and horizontally. The efficiency of tower cranes largely depends on their type, number and location. As the number of work tasks and the demand for tower cranes increase, planners may experience difficulties in making an appropriate decision about the optimum layout of tower cranes. A poor decision, however, is likely to have significant negative effects, which will lead to additional costs and possible delays.
On typical construction projects, the selection of the appropriate crane can have a significant influence on the cost, time and safety of construction operations. Due to this role, many models have been developed over the past 20 years for solving tower crane problems, generally
(a) 3D Architectural Model (b) Integrated Sturcutral and MEP Model
(c) Site Logistic Planning Model (d) Quantiy Estimates
Why 3d-Gis and BIM integrationin Construction Management
To-date, two dimensional (2D) GIS is still being utilized in various engineering projects especially in managing construction industry but its complete potential to expand into another dimension, the 3D-GIS for better data manipulation, analysis and visualization using 3D data sets has not been realized yet. 3D-GIS, known as an ideal tool for representing 3D geometry, semantic as well as topology, has
Figure 1: Different Components of a Building Information Model
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related to financial and operational efficiency. Some of the literature addresses safety issues associated with tower cranes, whereas others rely on improving the crane operation, or involve cost forecasting models. Most crane location-related studies relied on the use of mathematical programming formulations. Some of these methods were designed to minimize the total crane transportation cost. Researchers have also developed mathematical models in an attempt to decrease total crane transportation time.
The location and type of tower cranes are closely related to the shape, position and spatial characteristics of the loads and obstacles. This spatial data is mainly used in the process of location optimization for tower crane(s), which is possible to be analyzed in large amounts by geographic information systems (GIS). The optimal number of tower cranes is a function of their locations and the geometric layout of loads. On the other hand, GIS support the wide range of spatial data that can be used to support location problems. The advantage of GIS-based methods is that they directly use spatial aspects of the construction site and display output in a suitable form to the user. For these reasons, GIS is found to be useful for such purposes. In addition, visualization techniques can be used to further enhance the functionality and integrity of GIS models.
However, due to the limitation of GIS tools in automated drafting and lack of semantic information about buil-ding elements, one can utilize different visualization tools. Regarding the distance between the crane’s cab and load location, finding an optimal place for the tower crane plays an important role in improving operator’s view. To respond to this need, it is appropriate to model the operator’s viewpoint through the use of Building Information Modeling (BIM). Furthermore, visual representation can be extended to monitor the crane’s movements and to prevent the collision of tower cranes operating in a shared work zone. In reality, the number of structural elements (obstacles) increases with construction progress. Cranes must not only avoid collisions with these elements that have previously been installed but also need a collision-free path for each
subsequent element to be installed. The snapshots generated by BIM are capable of appropriately representing the changing construction environment.
Integration Of GIS And BIM
While BIM systems focused on developing objects with the maximum level of detail in geometry, GIS are applied to analyze the objects, which already exist around us, in most abstract way. Therefore, to visualize existing topography and a new facility to be developed together we need more research on integrating the data models of BIM and GIS. Several studies have been conducted to explore the application of GIS technology in BIM environments and BIM models in the geospatial domain. For instance, some researchers investigated the application of BIM in a geospatial context in order to improve the transfer and representation of information between these two domains. Another research established a prototype system to demonstrate the feasibility of BIM models to support indoor GIS applications. Researchers on the other hand, recognized the need to integrate different IT technologies, such as GIS, RFID and digital building information, in one reliable platform for emergency response management.
However, aforementioned research efforts have focused on either BIM or GIS. Real integration of BIM and GIS is achieved by using the strengths from both the BIM and GIS world in the context of the other, which has been recently proposed. Before integration approach is developed, the advantages and differences between BIM and GIS should be considered. To develop a BIM-GIS model, it is essential to bring the benefits of both technologies together into a single comprehensive model. GIS builds upon existing information and objects; so, BIM should be used to create the building information. On the other hand, the lack of spatial analysis capabilities in BIM underlines the need for utilizing GIS. The major incompatibilities that exist between the technologies have been provided in Figure 2. Integrating these two technologies depends on the assumption that there are applications from both domains, which can maximize the value of both.
GIS BIM
Modeling Environment Mainly focus on outdoor environment. An outdoor activity may need to be positioned in GIS.
Focused mainly on indoor environment. Outdoors applications are limitd to the outside of buildings. 3D modeling of site untilities and terrain modeling are also available in BIM.
Referance System Geopatial data is always georeferenced. Objects are defined in a physical world with global coordinate systems or map projections.
BIM objects have their own local corrdinate system, for example at the left comer of the building.
Details of Drafting GIS builds upon existing information and objects. It covers a large area with less detail and in smaller scales.
Drafting capabilities of BIM are utilized to develop large scales with higher level of details.
Application Area GIS is focused on urban and city areas. BIM is rooted in the building and its attributes.
3D Modeling GIS capabilities are limited to simple 2D shapes, Experimentation with 3D in GIS is in an early stsge.
BIM is unique in its ability to work in full 3D environment. BIM has a rich set of spatial features and attributes.
Figure 2: Incompatibilities between BIM and GIS
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Figure 3: Flowchart of GIS-BIM optimization location model
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Enabling interoperability at the semantic level is an important issue for the link between BIM and GIS. The key to conducting interoperability at the semantic level is to make sure that the relationship between two different disciplines is maintained during data transfer. To solve this problem, one researcher suggested a mechanism that automatically transforms the relationship from one discipline to the other. Efforts to enhance interoperability within the AEC industry and GISs have been made during the last two decades. Among the most prominent of these models are the Geographic Markup Language, GML, and the Industry Foundation Classes, IFC. The Open Geospatial Consortium (OGC) introduced the GML for data interoperability in the geospatial commu-nity. GML allows complete data transfer between different databases and application software, which results in application scheme.
An Approach for Optimised GIS-BIM Model- A Case Study
The methodology outlined above was employed to determine the needed tower cranes and their optimal locations for a commercial building project. The project is a commercial complex located in Tehran, Iran, consisting of 6-story shopping mall, entertainment complex, underground parking, and recreational facilities with a site area of 8 acres (32000 m2) and a total gross floor area of 128,200 m2. The location in an urban area with limited workspace and its proximity to congested throughways are factors that require the contractor to utilize tower cranes. In order to demonstrate the model’s capabilities, three different types of tower cranes are taken into account when identifying the optimal locations. Although the crane’s prices are not included in the table, the model is capable of considering different combinations of tower cranes to minimize the total cost. In this case, after grouping the tasks based on different types of cranes, the process starts with assigning a tower crane to a task group and generates the remaining task groups based on different types of cranes. The process is repeated for all tower cranes, until the best crane combination that has the minimal cost is reached. Figure 3 shows the flow chart for the model and Figure 4 shows the optimal location of tower cranes achieved through integration of GIS-BIM concept vis a vis with the proposed one. It can be seen that how application of this technology
helped in efficient management of the mega construction equipments in this case it is tower cranes. Figure 5 gives a general view of the case study project under construction.
Figure 4: Comparison of actual and optimal locations for tower cranes
Figure 5: General view of the case study project under construction
Conclusion
This article shows the new approach for integrating GIS and BIM that enables managers to visualize the 3D model of tower cranes and other mega construction equipments in their optimal locations. Identifying minimal number and optimal location of such mega equipments, especially when they operate with overlapping work zones, can create a challenge for managers. This process comprises a variety of spatial data that can be presented in the 3D visualization model. Thus, there is a need for a new tool with spatial analysis and visualization capabilities within a single environment. Integrating GIS with BIM seems to be an appropriate approach to solve such problems.The implementation of the proposed model reveals the feasibility and practicality of using GIS for managers who have access to a BIM model with the full range of material information. This model can be applied as part of a site layout process and, using scheduling functionality provided by many BIM tools, allowing visualization of the sequential construction of the building. The practical application of the model will become even more useful in the future, as software applications support data standards and various information exchange efforts such as IFC. Integration of GIS and BIM, however, still comes with some limitations. The developed method suffers from a certain lack of interoperability between GIS and BIM. Although the use of commercially available tools in the model enables the user to exchange data between the BIM and GIS domains, it still requires him or her to have knowledge about both systems and their functionalities. In order to fully integrate GIS and BIM, future work should focus on providing more interoperability at the semantic level. The employment of mobile computing technologies is another potential area for future studies. This will extend the applicability of the model to real projects.
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Reference
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Polymer Modified Asphalt – A Solution to Many Asphalt Problems
In the past, unmodified asphalts were able to cope with the traffic volumes and loads exerted on them. Nowadays, the burden placed upon road system has reached a
critical stage in many developed and developing countries where the increased volume in heavy vehicles coupled with an appreciable increase in allowable axle weights for these vehicles has lead to a dramatic increase in level of stresses exerted on asphalt surface. Due to the sharp increased of stresses exerted on asphalt surface, most of the road system experience distress and deteriorate before it can achieve the design service life. The use of polymer modified
asphalt offer a promising way to improve pavement perfor-mance hence it can prolong the service life of the road system even though the road experience unexpected increasing number of traffic volume. Polymer modified asphalt pavement exhibits greater resistance to rutting and thermal cracking and decreased fatigue damage, stripping and temperature susceptibility. Typically, polymer modified asphalt are more viscous compare to unmodified asphalt and tend to show improved adhesive bonding to aggregate particles. Asphalt emulsion consists of small asphalt drop-lets suspended in water. It can be produced by mixing
Sonjoy Deb, B.Tech,’Civil’
Associate Editor
“Today, many problems are arising due to the increased aging of our current asphalt. This aging process causes major structural deteriorations on our roadways. In order to fix this major problem, civil engineers have to find a solution, the answer to this burning problem is polymer modified asphalts (PMA)”
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hot asphalt with water containing emulsifying agent in a colloid mill. Asphalt emulsion that normally used for cold application has several advantages compared to normal asphalt or asphalt cutback such as eco-friendly, easy to handle at ambient temperature and energy saving material because it does not need any heating process in its use. Currently, polymer modified technology is used in asphalt emulsions to improve its physical properties, performance, and durability. Polymer modified asphalt emulsions offers improvements in mitigation of pavement distress and reduced life cycle costs when compared to unmodified asphalt emulsions. In addition, polymer modified asphalt emulsions also exhibit reduction in rutting and thermal cracking related problem and increased resistance to many forms of traffic-induced stress.
Basics of PMA:
PMA has two materials viz. (a) polymer and (b) asphalt emulsions leading to what is called (c) polymer modified asphalt (PMA). So a brief basics about all these three is discussed below:-
(a) Polymer - Either natural or synthetic, polymer consists of a small, simple, and repeating chains of organic compounds called monomers. Compound jointing of two or more different monomers is called copolymer. Refer Figure 1.
The polymers enhance the asphalt properties by forming a continuous network within the binders. There must be compatibility between polymers and binders in order to create a uniform connected network. In the incompatible case, the polymers will group themselves and are not connected. Refer Figure 3.
Types of Polymer Modifier
The polymer modifiers are
Figure 1: Example of Copolymers
(b) Asphalt Emulsions - Asphalt emulsions are produced by a mixing of asphalt and emulsifying agent (surfactant) creating micro-asphalt droplets dispersed in water. Asphalt emulsions are classified by the types of surfactants which can be anionic, cationic, and nonionic.
(c) The Polymer Modified Asphalt (PMA) - Polymer modifiers make changes in the structure of asphalt binders resulting in the modification of key physical properties which are:
- Elasticity- Tensile strength- High temperature susceptibility- Low temperature susceptibility- Viscosity- Adhesion and cohesion
firstly classified into two general groups based on their characteristics at low temperature.
1. Elastomeric polymers - having very highly yield property.
2. Plastomeric polymers - having very highly strength property.
Both are again separated into two another classes by their temperature-rearranged structural characteristics.
1. Thermoset polymers - linked network cannot be reversed upon reheating.
2. Thermoplastic polymers – linked network can be reversed upon reheating.
Figure 2: Type of emulsions
Compatible Incompatible
Types of Commonly Available Polymer
There are six types of polymer available in the market which includes the following:
- Natural rubber and latex is an elastomeric hydrocarbon polymer found in many plants.
- Synthetic rubber and latex is a thermoset elastomeric polymer whose particles are dissipated in water.
- Block copolymers are styrene polymers polymerized with small molecules.
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- Reclaimed rubber is a used scrap tire rubber.- Plastics are typically thermoplastic plastomers consisting
of polyolefins or copolymers of ethylene.- Polymer blends are polymers created by blending of
different polymer additives.
Summary of all types of commonly available polymers with their market product name is listed down in the Figure 4.
commonly used for asphalt binder modification. These are as discussed below-
- Preblending - The polymer modifier is added to the binder before the emulsification process.
- Soap Pre-batching - The polymer modifier is added to the soap solution (water and emulsifier) before the emulsification process.
- Co-milling - The polymer modifier is added to the colloid mill during the emulsification process.
- Post-Modification - The polymer modifier is added to the final asphalt emulsion (at the plant or in the field).
From the study, Forbes et al found that, pre-blending method produce a monophase emulsion where a single phase of polymer modified asphalt droplets can be seen. The other methods produce bi-phase emulsions which are a combination of two phases of asphalt droplets and polymer droplets. However, in bi-phase emulsion manu-facture, the polymer is not exposed to temperatures above 85 - 90 °C while in monophase emulsions the pre-blended asphalt and polymer is processed at temperatures up to 180°C to allow adequate dispersion of the polymer in the asphalt. At high temperatures approaching 200°C there is an increased risk of both polymer and asphalt degradation occurring. This may cause an adverse effect upon the quality of the polymer modified asphalt residue and presents a major advantage with bi-phase emulsions.
Figure 5 below shows a typical Asphalt modification process in the form of a flow diagram.
Polymer Type Examples Classification
Natural Rubber (Homopolymers)
Natural Rubber (NR), Polyisoprene (PI), Natural Rubber Latex (NRL)
Thermoset Elastomers
Synthetic Latex / Rubber (Random Copolymers)
Styrene-Butadiene (SBR) Thermoset Elastomers
Polychloroprene Latex (Neoprene)
Thermoset Elastomers
Polybutadiene (PB, BR) Thermoset Elastomers
Block CopolymersStyrene-Butadiene-Styrene (SBS)
Thermoplastic Elastomers
Styrene-Isoprene-Styrene (SIS)
Thermoplastic Elastomers
Styrene-Butadiene Diblock (SB)
Thermoplastic Elastomers
Reclaimed Rubber Crumb Rubber Modifiers Thermoset Elastomers
PlasticsLow/High Density Polyethylene (LDPE/HDPE), Other polyolefins
Thermoplastic Plastomers
Polyvinyl Chloride (PVC)Thermoplastic Plastomers / Elastomers
Ethylene-Propylene-Diene-Monomer (EPDM)
Thermoplastic Elastomers
Combinations Blends of Above Varies
Figure 4: Type and Classification of Polymer Modifiers
Various Polymer Modification Method
Polymer modified asphalt emulsion is a product made from asphalt emulsion that has been modified with polymer emulsion or a product made by means of emulsifying asphalt that has been modified by polymer. Several techniques can be used to produce polymer modified asphalt emulsion. The polymers or modifiers may be added into hot asphalt before emulsification process take place, added to the finished emulsion product or “co-milled” at the colloid mill with the various component streams during production. The blending method to add polymer has important influence on polymer network distribution and will affect the performance of polymer modified asphalt emulsions. Forbes et al studied the effect of polymer modification techniques on asphalt binder microstructure at high temperatures: Four general techniques are
Figure 5: Typical Emulsion Modification Process
Polymer Dosage Rates
The dosage rates of polymer vary but are generally one to five percent polymer by weight asphalt, two to three percent is the most common dosage rates for chip seal and slurry seal application. Johnston and Gayle stated that the range of polymer content dosing recommended for most applications generally varies between about 2 percent and 10 percent by weight of the residual asphalt content with most research, standard, and manufacturer specifications calling for a polymer concentration of approximately 3
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percent to 5 percent. The optimal percent depends upon the specific polymer, specific asphalt and their interaction. Study conducted by Anderson et al shows that the addition of polymer between 2.8% - 3.0% had little effect on the stress-strain response of the emulsion residue at low temperatures and had moderate increases in stiffness of the emulsion at temperatures above 25 °C. Takamura use 3.0-3.5 percent of SBR latex for microsurfacing formulation that consist of 100 parts of aggregates, 8-15 parts of water and 0.5-2 parts of Portland cement
Increased Durability with PMA
A study was completed for the Affiliate Committee of the Asphalt Institute on the use of PMA for reducing distress in asphalt. The results from this study found that the use of certain PMA mixes reduced deformation and increased the life of asphalt by 2 to 10 years. This is very promising for PMA for it to be used on a more massive scale; however 2 to 10 years is a wide range. The cost of a modified binder can be anywhere from 50 to 100% larger per ton than that of conventional asphalt cement. Obviously PMA, if implemented properly can improve on standard asphalt in terms of sustainability as shown in figure 1.
A typical application of PMA is shown in Figure 6, where in it is justified that PMA offers durable roads than conventional asphalt based roads.
will increase every nation’s reliance on foreign oil. However, with Polymer-Modified Asphalt, it can be manufactured from current asphalt that is fatigued, damaged, rutting, or cracking and is incapable of performing on roads to a reasonable standard. By doing this it will use fewer resources to make new asphalt that is stronger and better suited for our roadways. Recycling of old asphalt can be easily done. The process can be completed on site by heating and melting the asphalt to its liquid state, and then adding the additives to the asphalt. Since PMA involves polymer additives such as styrene-butadiene-rubber and complex polymers previously mentioned which contain rubber element engineers can recycle old tires. Tires are usually improperly disposed of by being burnt to ashes which pollutes the air even more or they are placed in garbage dumps which clearly is not desired. However, if engineers recycle these resources and utilize them properly, it will allow production of new generations of asphalt. This new generation will use even less natural resources, which will not be as abundant in the future. Since PMA can be created using mostly recycled elements, which can reduce costs of asphalt, it could also potentially become cheaper to manufacture than creating new asphalt from petroleum. Creating new asphalt requires a lot of different process, which also costs a lot of money. Obtaining and distilling petroleum is a very long and dirty process that can cost millions, not to mention the additional costs to actually lay it down on the roads. With the rise in oil prices every year, eventually it will become too costly to create asphalt. This is why with PMA, using recycled materials it will be sustainable on its own without the need of massive amounts of nonrenewable resources. Sustainability must be a factor in all engineering products in the future. With the realization that our resources we depended upon for two centuries are becoming scarce it must be a priority for every new technology and project today. Polymer-Modified asphalt already is a technology engineers can easily make sustainable all we must do is be willing to try it.
Conclusion
Overall, the use of polymer modified technology has been proven that it can improve the physical properties, performance, and durability of asphalt emulsion. For example, the used of polymer can improve the temperature susceptibility and rutting performance of cold mix. Certain polymer can be added at higher dosage level in asphalt emulsion compared to hot modified asphalt which means the improvement of polymer modified asphalt emulsion is better than hot polymer modified asphalt. The method to add polymer is depends on the physical properties of the polymer. The cost of the polymer modified emulsion is around thirty percent higher than unmodified emulsion, however the total cost (materials, construction, traffic control,
Figure 6: A residential road in Bradford County where polymer modified asphalt was used (left) and Conventional asphalt was used (right)
Sustainability the Striking Adavantage Achived through Polymer Addtion to Asphalt
Sustainability, when it come roadway engineering mostly deals with the environmental and economic impact of asphalt production, implementation, and lifespan. Since asphalt is the main material used for roads, Polymer-Modified Asphalts will have to improve upon our current roadway durability and environmental impact. PMAs ability to improve on the durability of asphalt is just one part of sustainability as a whole. As knows to all, one of the main problems with asphalt production is that it is made from petroleum which is obviously, not a renewable resource and
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and user delay) is only slightly increased or even the same. This happens because the higher initial cost is offset by the longer in service life. Also quick drying aspect of PMA though tend to provide difficulty yet it is countered by the benefits that it brings to the road it would be applied on. In order for PMA to be more widely utilized, more research must be conducted to find ways to bring down costs, and counter it’s quick cooling characteristics to still be further advanced than the existing asphalt.
Reference
- J. Johnston and K. Gayle, “Polymer Modified Asphalt Emulsions: Composition, Uses and Specifications for Surface Treatments,” FHWA Publication No.FHWA-CFL/TD-08-00x, April 2009.
- A. Forbes, R. G. Haverkamp, T. Robertson, J. Bryant and S. Bearsley, “Studies of the microstructure of polymermodified bitumen emulsions using confocal laser scanning microscopy,” Journal of Microscopy, Vol. 204(3), pp. 252-257, 2001.
- R. Zhang and Y. He, “An Asphalt Emulsion Modified by
Compound of Epoxy Resin and Styrene-Butadiene Rubber Emulsion,” International Journal of Mathematical Models And Methods In Applied Sciences, Vol. 1(4), pp. 232-238, 2007.
- Anderson, D. A., Christensen, D. W., Roque, R., and Robyak, R. A. “Rheological Properties of Polymer- Modified Emulsion Residue” American Society for Testing and Materials, ASTM, Philadelphia, 1992
- FHWA (2009). “Field guide for polymer modified asphalt emulsions.
- K. Takamura, “SBR Synthetic Latex in Paving Applications,” presented at the Bitumen Asia 2000, Singapore, 2000.
- Brown, Daniel C. “Asphalt Producer: Working with Polymer Modifiers.” Better Roads June 2004: 78-81. Black Lidge Emulsitions. Web. 20 Feb. 2011. <http://www.blacklidgeemulsions.com/images/ap06-04polymer.pdf>.
- Mallela, Jagannath, and Quintus L Von Harold. REDUCING FLEXIBLE PAVEMENT DISTRESS IN COLORADO THROUGH THE USE OF PMA MIXTURES. Rep. no. 16729.1/1. Round Rock: Applied Research Associates Incorporated, 2005. Web. 14 Feb. 2011. <http://www.co-asphalt.com/documents/Asphalt-FinalReport_PMAinColorado.doc>.
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Cracks Repair in Pavement Quality Concrete
As we have experienced a tremendous growth in Infra-structure of India and National Highways specifically, the construction of pavement quality
concrete highway has been the preferred option compared to the bituminous highway due to its low maintenance and long life.
However there are various types of cracks which PQC pavements develop post construction and during the service life. This article has highlighted the repairs of two types of cracks which are most common and develop either post construction and during the service life.
The structural defects are highlighted in the form of various types of cracks in the slab. The settlement at joints may also occur and if the remedial action is not taken it may also lead to development of cracks.
The structural cracks are classified according to their severity which is defined in terms of width of the cracks.
Different types of cracks
1. Narrow Cracks – If the width of crack is 0.5mm it is considered as narrow crack. It is assumed that there is full aggregates interlock and full load transfer is taking place within the slab at the crack.
2. Medium Crack - If the width of crack is 0.5 -1.5mm it is considered as medium crack. It is assumed that there is partial aggregates interlock and partial load transfer is taking place within the slab at the crack. These types of cracks permit ingress of water.
3. Wide Crack – If the width of the crack is greater than 1.5 mm it is considered as wide crack. It is assumed that there is no aggregates interlock and no load transfer is taking place within the slab at the crack. These types of cracks permit ingress of water and fine detritus.
Transverse and Longitudinal Cracks
Transverse Crack
Narrow transverse cracks are a normal feature of all slabs.
They are considered to be structurally insignificant. They are not expected to deteriorate further and consequently are not likely to require any remedial treatment.
Medium Transverse crack may be because of following reasons
a. Excessive bay lengthb. Dowel bar restraintc. Late sawing of Joint grooves
The remedy for the above is to form a groove and seal with elastomeric sealant.
Wide transverse cracks which will be greater than 1.5mm and generally approximately half to full depth of slab and may attain full depth if not treated in time.
The wide transverse crack will be due to following reasons:
a. Inadequate reinforcement lapb. Sub base restraint (Lack of separation layer or excessive
irregularity of sub base)
The remedy is stitching.
Longitudinal Cracks
The longitudinal cracks are not expected and may well deteriorate and develop further unless some remedial action is taken.
Reasons for longitudinal Cracks
a. Excessively wide bays
b. Compression failure
c. Settlement
Narrow and medium cracks in unreinforced slab are to be remedied by means of stitched crack repair.
Stitching
There are two methods of stitching the cracks of concrete i.e. Cross bar stitching and Staple pin stitching. This type of stitching is limited within a panel only and not between the
Anil TiwariManager, UltraTech Cement Ltd
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www.masterbuilder.co.in • The Masterbuilder - November 2012 201
two panels as both the panels are made independent by saw cutting and are to kept independent from adjacent panels for free horizontal and vertical movements. If the crack continues beyond the saw cut groove then the stitching of the extended crack is to be done independently.
Cross Bar Stitching
Cross Bar Stitching is used for repairing the Transverse cracks.
- The Depth of the crack is ascertained before the treatment and the marking is done with black paint.
- Drilling points are marked at a distance from the crack equivalent to the depth of slab at 600mm intervals along the crack with alternate points on opposite side of cracks.
- Drill holes (min 16mm dia) at approx 26- 30 degrees to the surface of the slab to a depth which allows 50mm cover at the bottom of the slab.
- These slots are cleaned out by compressed air/water jet. The slots should be completely dry before further treatment.
- Cartridges of epoxy resin type adhesive are placed in the holes and are inserted through the cartridges.
- The tie bars are rotated for about one minute to ensure that adhesive is well mixed.
- The tie bars are pre-cut before insertion so that the end is approx. 50mm below the surface.
- Alternatively, the length of the tie bars may be predetermined by measuring down the hole and notching the bars at a point 50 mm below the surface.
- After the bars have been driven in, and mortar has set the surplus can be broken off by twisting.
- Any bars which continue to twist after the mortar should
have set shall be deemed to be unbounded. They shall be withdrawn and the holes redrilled.
Plug the remainder of the hole with epoxy resin mortar. The road may be opened to traffic as soon as the mortar in the holes has set.
(Refer figures of Cross Bar Stitching)
Minimum 16mm diameter holes drilled at approx 26- 30 degrees to the surface of the slab at 600 mm c/c
Typical Transverse Crack
Closer view of the drilled hole at the Transverse Joints
12mm diameter deformed tie bars placed inside the drilled holes
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Staple pin Stitching
Staple Pin Stitching is used for repairing the longitudinal cracks.
- The longitudinal joint is marked with black paint and slots are chased out 25-30mm wide by 470mm long at 600mm c/c at right angles to the line of the crack.
- The depth of slots shall be such as to ensure that when bedded the tie bars lie between 1/3 to ½ the depth of the slab below the surface.
- Holes are drilled 25-30mm diameter by 50mm deep at each end of the slots. These slots are cleaned out by compressed air/water jet.
- The slots should be completely dry before further treatment. When in dry state the slots are primed and the staple tie bars of 16 mm dia. are placed into the beds of epoxy resin mortar and cover to a minimum depth of 30 mm with the same material.
- The rest of the slot is filled with thoroughly compacted
resin mortar/micro concrete.
- A groove is sawn along the line of the crack and sealed with elastomeric sealant only after the micro concrete is cured.
The road may be opened to traffic as soon as the sealant in the groove has set (After 48 hours).
(Refer figure of Staple Pin Stitching)
Conclusion
These types of repairs are carried out within the panel. If the crack wider than 1.5 mm is experienced within 1 -1.5 metre at the transverse or longitudinal joint it is always necessary to carry out full depth repair i.e. to cut the panel to the full depth and redo the concreting after removing the old concrete.
Staple pin and cross bar stitching helps in arresting the cracks and avoid further deterioration of the panel and the sub-base. The reason for carrying out stitched crack repair is to convert the crack into a tied warping joint which will allow the slab to “hinge “at that point whilst preventing the crack from becoming wide thereby enhancing the life of slab.
Acknowledgement
Author acknowledges the experiences shared by Mr S. B. Kulkarni AVP Technical Services, Ultratech Cement Ltd, Mumbai and Mr. Anil Trivedi, Proprietor, M/s Efftech Marketing Services, Thane (Mumbai).
References
- “Specifications for Highway Works”- Department of U.K.- IRC-15- Specifications of Ministry of Road Transport and Highways
(MORTH)
Typical Longitudinal cracks
Staple tie bars of 16 mm dia. are placed into the beds of epoxy resin mortar and cover to a minimum depth of 30 mm with the same material.
Slots are chased out 25-30mm wide by 470mm long at 600mm c/c at right angles to the line of the crack
Concrete Highways
