coursework

HEALTH MONITORING AND REHABILITATION OF SURFACE STRUCTURES [2012]

QUESTION 1

The section of the motorway is approximately 60 years old reinforced concrete pavement overlaid around fifteen years ago by hot rolled asphalt (HRA). The road is 7.3m wide three-lane carriageway and carrying approximately 33,000 vehicles per day in each direction. The dimension of the concrete slab is approximately 14.5mX3.7m with thickness of 250mm. Your firm has been commissioned by a major contractor to undertake a non-destructive evaluation of the joints using the Falling Weight Deflectometer (FWD). The principal aims of the pavement investigation are to:

to evaluate the joint performance of the existing pavement using FWD, to identify the joints that might require treating just to keep the road in full service

until the improvement begin to provide engineering data to the improvement scheme developer

The FWD joint deflection data is given in File name CW brief1.xls

Provide required analysis and interpretation of data for joint evaluation and recommends necessary treatment programmes for these joints.

SOLUTION:

Fig. 1. Falling Weight Deflectometer (FWD)

In principle the FWD generates a load pulse by dropping a mass onto a spring system. The mass and drop height can be adjusted to achieve the desired impact loading. Peak vertical

|N0369400 MSc Structural Engineering with Materials

1


deflections are measured at the centre of the loading plate and at several radial positions by a series of geophones.The Fig. 2 & 3 shows the position of geophones for approach and leave testing.

Fig. 2. FWD Setup for Approach Testing

Fig. 3. FWD Setup for Leave Testing

From analytical calculation,

1. APPROACH SLAB

While considering,

a. LTE (%)


2


65% is good and have no dowel problem, 13% is of poor and required long term treatment and 22% have moderate trouble and required short term treatment.

b. Slab Curvature

55% is good and have no foundation problem. 9% have moderate problem in foundation and required short term treatment and 36% is having poor foundation and required long term treatment.

2. LEAVE SLAB

While considering,

a. LTE (%)

49% is good and have no dowel problem, 36% is of poor condition and required long term treatment and 15% have moderate trouble and required short term treatment.

b. Slab Curvature

27% is good and have no foundation problem. 54% have moderate problem in foundation and required short term treatment and 19% is having poor foundation and required long term treatment.

CONCLUSION

Overall results say that 38% of approach slab is of good condition. Meanwhile, remaining 62% is of poor condition due to dowel problem or voiding or poor foundation and these remaining 62% required short/long term treatment to sustain its design life.


3


38%

62%

Approach Slab

goodbad

30%

70%

Leave Slab

goodbad

Chart 1. Approach Slab Chart 2. Leave Slab

QUESTION 2

A 1Km long failed in situ C28/35 concrete pavement section in NTU port has previously been strengthened by the application of a hot rolled asphalt (HRA) surfacing course which is still intact. The port is, however, shortly to take delivery of heavier handling plant and wishes to upgrade the pavement further. During the first strengthening operation, photographs were taken of the concrete, which showed it to be substantially cracked (corner cracking and mid-slab cracking) but not spalled or crazed. Slight reflective cracking has occurred in the HRA overlay. The visual survey has identified 15mm rutting in the first 400m of the tested section, but the remaining 600m with only 5mm rutting. The construction of existing pavement is as Shown in Fig. 4.

Fig. 4. Typical Section of Existing Pavement

GIVEN There are two criteria,

a. 15mm rutting in the first 400m of the test section.


4


b. 5mm rutting on the remaining 600m.

The tables and charts used for solving,

Table 1. Condition Factor for cracking and spalling

Table 2. Condition Factor for maximum degree of localised Rutting and localised settlement


5


Table 3. Material Equivalence Factors relating C8/10 CBGM to other materials

SOLUTION:

a. 15mm rutting in the first 400m of the test section.

Course Actual Thickness

Material Conversion

Factor

CF1 CF2 Effective Equivalent

Thickness of C8/10 CBGM

(mm)Insitu Concrete

310 0.62 0.5 0.9 225

Crushed Rock

150 3 1 0.9 45

Total 270mm


6


Thickness

b. 5mm rutting on the remaining 600m.

Course Actual Thickness

Material Conversion

Factor

CF1 CF2 Effective Equivalent

Thickness of C8/10 CBGM

(mm)Insitu Concrete

310 0.62 0.5 1 250

Crushed Rock

150 3 1 1 50

Total Thickness

300mm

The analysis shows this pavement to be equivalent to 270mm for first 400m and 300mm for remaining 600m.

To calculate actual thickness of new layer, CBGM thickness corresponding to SEWL - Single Equivalent Wheel Load (KN) and number of passes for the road is required. This can be obtained from Chart 3. Base Thickness Design Chart.


7


Chart 3. Base Thickness Design Chart

Scenario 1:

Assumption

SEWL = 1100 KN

Number of passes = 250,000

CBGM thickness = 680mm

Thickness of new layer

For first 400m

= 680 – 270

= 410mm

For second 600m

= 680 – 300

= 380mm


8


Fig. 5. Layout of new pavement

Scenario 2:

Assumption

SEWL = 600 KN

Condition 1




For first 400m

= 530 – 270

= 260mm

For second 600m

= 530 – 300


9


= 230mm

Fig. 6. Layout of new pavement according to condition 1 (Scenario 2)

Condition 2:

Number of passes = 1,500,000



For first 400m

= 610 – 270

= 340mm

For second 600m

= 610 – 300

= 310mm


10



Condition 3:




For first 400m

= 660 – 270

= 390mm

For second 600m

= 660 – 300

= 360mm


11



Scenario 3:

Assumption

SEWL = 300 KN

Condition 1




For first 400m

= 300 – 270

= 30mm

For second 600m

= 300 – 300


12


= 0mm


For this condition only first 400m required an overlay of new layer.

Condition 2




For first 400m

= 530 – 270

= 260mm

For second 600m

= 530 – 300

= 230mm


13



Condition 3




For first 400m

= 630 – 270

= 360mm

For second 600m

= 530 – 300

= 330mm


14



CONCLUSION

From analytical result, the economical Scenario for new layer are Scenario 2 (condition 1) and Scenario 4 (condition 2) because both have same thickness for new layer and can be operated at two different SEWL load and of different number of passes for road.

SEWL (KN)

No. of passes on

road

CBGM Thickness

(mm)

Thickness of new

layer for first

400m (mm)

Thickness of new layer for remaining 600m (mm)

Scenario 1 1100 250,000 680 410 380Scenario 2 Condition 1 600 250,000 530 260 230

Condition 2 600 1,500,000 610 340 310Condition 3 600 4,000,000 660 390 360

Scenario 3 Condition 1 300 250,000 300 30 0Condition 2 300 8,000,000 530 260 230Condition 3 300 12,000,000 630 360 330


15


QUESTION 3

Your firm is commissioned by a client to carry out a pavement investigation of approximately 1km of a major trunk road. The road is a two-lane dual carriageway. The survey works were undertaken during a night time static lane closures on 2nd April. All surveys were carried out in accordance with the procedures outlined in the Design Manual for Roads and Bridges (DMRB) Volume 7. The surveys were conducted in lane 1 of and comprised a Falling weight deflectometer survey. You are required to analyse FWD deflection profiles to identify homogeneous sections from a CUSUM plot and perform a back-analysis to calculate the layer moduli. The data is given in excel format in Supplied data.

SOLUTION:

In principle the FWD generates a load pulse by dropping a mass onto a spring system. The mass and drop height can be adjusted to achieve the desired impact loading. Peak vertical deflections are measured at the centre of the loading plate and at several radial positions by a series of geophones. The fig. 12 shows a typical deflection bowl.

Fig. 11. FWD deflection bowl

There are two goodness of fit parameter that is commonly used for indicating how well the program has matched the data. These are the Absolute Mean Deviation (AMD) and the Root Mean Squared Deviation (RMS), defined as:


16


Absolute Mean Deviation (AMD) = |Σ (dci - dmi)/n|

Root Mean Squared Deviation (RMS) = √ (Σ(dci - dmi)2/n)

Where: dmi are the measured deflections in microns at positions i =1 to n;dci are the calculated deflections in microns at positions i =1 to n;n is the total number of sensor positions used in the analysis (normally seven).

The AMD indicates whether or not there is an overall bias to the calculated deflection bowl relative to the measured bowl. The RMS indicates how well, on average, the calculated bowl matches the measured bowl. Although a good fit does not in itself indicate that a correct solution has been obtained, a poor fit does indicate that the solution found is suspect.

Number of layers Maximum Values (microns)

AMD RMS2 4 113 2 5

Table 4. Guide value for AMD and RMS

The values that exceed the guide value shown in Table 4 should be treated with caution.

CONCLUSION

From the analysis, 65% of load stations are good and remaining 35% is in poor condition and

should be treated with caution.


17


65%

35%

Overall Pavement Performance

goodpoor

Chart 4. Overall performance of Pavement

QUESTION 4

Write a report on concrete hydrophobic protection for highway structures. The maximum

word limit is 1000 words


18


INTRODUCTION

Highway is any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a "highway transportation system". Highway structures include bridges, culverts, subways, footbridges, pipes greater than 600mm diameter and retaining walls.

The most commonly construction used materials for highway structures are concrete and steel. All these materials need protection against environmental effects mainly water, temperature, wear and tear and abrasion. The above mentioned highway structures should be protected from the environmental effect, in-order to sustain its durability. Because the above mention structures are constructed for a certain design life.

Most of the highway structures are hydrophobic, because they are directly exposed to environment. So that structures need protection against hydrophobic threats. Most of the highway structures are made of concrete and one of the most commonly built highway structures are bridges. Despite concrete’s durability, serious concrete damage that endangers a structure’s existence frequently occurs. The main cause of concrete damage is reinforcement steel corrosion due to environmental influences. Concrete has two arch-enemies: water-soluble salts and gases.

Concrete Deteriorations are due to

Permeability to moisture, chlorides, gases Lack of properly entrained air Exposure conditions

Concrete Absorbs Water


19


When building materials come into contact with water, they absorb an amount which depends on their porosity. This causes various forms of damage:

Concrete destruction by corrosion of the reinforcing steel (chloride induced) Chemical corrosion, e.g. binder transformation by acidic gases (SO2, NO2, CO2) Cracks by swelling and shrinkage Frost damage and freeze/thaw damage by road salts Efflorescence and salt damage by hydration and crystallization Lime leaching Rust stains Dirt pick-up and stains Fungal, moss, lichen and algal growth

To avoid these damages:

Concrete needs effective and long-lasting protection. Water-repellent treatment enhances concrete’s durability.

In this report I have discussed about different materials and products of various brand used for concrete hydrophobic protection of highway structure.

DIFFERENT TYPES OF CHEMICAL, MATERIALS AND PRODUCTS USED FOR CONCRETE HYDROPHOBIC PROTECTION OF HIGHWAY STRUCTURES

1. Silanes (Chemical)

Silanes for concrete impregnation must possess two specific properties: they must penetrate well into the relatively dense concrete and resist degradation by the high alkalinity found especially in fresh concrete. Organosilicon compounds have been recognized as the ideal active agents for the hydrophobic impregnation of absorbent mineral building materials for over 40 years now. The compounds work by binding strongly to the building material to form extremely stable Si-O-Si structures, similar to silicone resin.


20


Fig 1. The silane docks onto the concrete to develop the water-repellent effect

2. SEALERS (materials)

Concrete sealers work in two ways. First they prevent the absorption of moisture. Depending upon the exposure condition of the unprotected deck, the average internal moisture is about 50 to 80 percent of the saturation level. Secondly, they allow the progressive internal drying of concrete to a 30 to 40 percent level by reducing the rate of moisture gain from the environment. The most important property the sealer must have is that it must protect the concrete and at the same time it must be breathable.

Types of concrete surface sealing products:

a. Penetrating Sealers

Penetrating sealers are products that are absorbed into the surface of the concrete and react with the concrete to form a hydrophobic (or water repelling) surface. No film is formed; therefore pores in the concrete are not blocked.

b. Coatings Coatings (coloured or clear) are products that bond to the surface of the concrete and form a film. The waterproofing properties of the coating are generally independent of the concrete properties, although the coating must remain adhered to the concrete for the coating to function.

3. HYDROPHOBIC AGENTS (materials)

Defence against Water and Harmful Substances


21


Creating a water-repellent zone at the surface of the concrete considerably reduces the uptake of water and aggressive substances. The masonry remains drier, and is consequently less prone to the kinds of damage mentioned. However, this is only true of capillary water uptake, which is the water uptake by building materials – when an exterior wall is exposed to rain, for example.

Silanes Can Rescue Concrete Structures

The most efficient way of protecting concrete is to prevent water uptake. The past decades have shown that highly alkylated silanes (iso-octyl) are the ideal product class for this. Their current dominance in masonry protection stems from their outstanding water-repellency and durability. Silanes outperform rival product classes in their resistance to physical, chemical and microbiological attack. Provided that the right product is chosen, impregnation with silane will preserve a structure for a long time.

The commercially available hydrophobic product for concrete consists of silanes/siloxanes. Silane contains 100% active substance or they are dissolved in alcohol or hydrocarbons (about 10 to 20% active substance). Three commercially available hydrophobic products which comply with all test criteria are used:

- Product A, 99% silane (no solvent) - Product B, 100% silane (no solvent) - Product E, 20% silane/siloxane dispersed in water

In standard concrete, these products penetrate to such depth and amount, that the hydrophobic zone is at least 2mm and typically up to 5mm depth.

Fig 2. water-repellent zone at the surface of the concrete


22


Much of the damage caused by moisture can be prevented, or at least reduced or kept at bay for longer, by means of hydrophobic impregnation.

4. WACKER CHEMIE AG (product)

Wacker Chemie AG has been a leader in masonry protection with silicones for decades. Its broad series of masonry protection agents covers an extensive range of applications, from preservation of historic buildings and highway structures to concrete protection. Ongoing product development ensures that products are continually adapted to meet market requirements. One of the commonly used products for water repellent treatment

SILRES BS Creme C

SILRES BS Creme C is an aqueous, solvent-free, water-repellent cream based on silane. It’s a high-quality specialty product for the hydrophobic impregnation of concrete and reinforced concrete.

SILRES BS Creme C’s thixotropic consistency is unique among water repellents and its properties are excellent for the impregnation of high-quality concrete and reinforced concrete. Unlike conventional liquid products, SILRES BS Creme C can be applied to the required extent in just one or sometimes two steps. Depending on porosity and thus concrete quality, the silane active ingredient penetrates into the substrate within a short space of time (30 minutes to a couple of hours) and there it reacts, liberating alcohol with the silicate matrix of the capillaries and pores of the concrete. The creamy layer that was initially white disappears completely. Since the active ingredient is the same as in conventional liquid water repellents, water- repellent treatment with SILRES BS Creme C also allows the pores and capillaries of the substrate to remain open, leaving the substrate breathable.

SILRES BS Creme C is designed so that the active ingredient penetrates as deeply into the concrete as possible and thus optimally protects against the absorption of water and aggressive substances, as well as against damage from freeze/thaw cycles.

5. HYCRETE (product)

Hycrete is a water-based additive to concrete that is used to counter rust and corrosion. It was developed by the eponymous American company Hycrete and is certified as a Cradle to Cradle nutrient Because of the water repelling properties the placement of water repelling materials after pouring hycrete is not needed anymore.


23


Regular concrete absorbs water and anything dissolved in it. With Hycrete's solutions, regular concrete becomes hydrophobic concrete, keeping water out. And protective barriers are formed around rebar, resulting in highly effective concrete corrosion inhibition.

Some of the commonly used HYCRETE products for water repellent treatment

Hycrete W1000 (For maximum waterproofing protection in concrete)

Superior product offering hydrophobic integral concrete waterproofing. Low-odour, water based product. Dosed at one gallon per cubic yard.

Application

a. Precast componentsb. Architectural water features and fountainsc. Bridges, dams and highway infrastructure

Hycrete W500 (For Waterproof Concrete)

Integral hydrophobic waterproofing product used when reducing absorption is critical but achieving less than 1% absorption is not essential. Low-odour and water-based product. Dosed at one gallon per cubic yard.

Applications

a. Precast componentsb. Architectural water features and fountainsc. Bridges, dams and highway infrastructure

6. TAM (product)

Tam is a hydrophobic pore-blocking admixture for concrete. One of the commonly used products for hydrophobic protection

TamSeal Hydroproof

TamSeal Hydroproof is a hydrophobic pore-blocking admixture for concrete. It provides protective and integral permeability reduction, which ensures dense, structurally sound concrete. Capillary absorption is dramatically reduced, preventing


24


the ingress of potentially harmful soluble salts such as chlorides and sulphates, resulting in concrete which is waterproof and durable.

Key Benefits

Reduced Permeability Can be used in concrete in contact with potable water Can be used with all types of concrete and with all types of cement binders Cost effective Simple design Drilled fixings can be made without loss of waterproofing performance Reduced excavation cost Faster construction time Insensitive to delays caused by inclement weather Corrosion protection Integral protection against soluble salts Improved chemical resistance

Typical Applications

Below ground structures, basements, piles and pile cap, foundations, services ducts etc.

Reinforced concrete in marine environments subject to tidal and wet/dry cycling. Water retaining structures, water tanks, swimming pools, reservoirs and water

towers. Highway structures in contact with spray or from directly applied de-icing salts. Land drainage, manholes and silage pits.

CONCLUSION

This report contains a brief description of various materials and products used for concrete hydrophobic protection of highway structures. The commonly used construction materials for highway structures are concrete and steel. All these materials need protection against environmental effects mainly water, temperature, wear and tear and abrasion. The highway structures should be protected from the environmental effect, in-order to sustain its durability. Concrete Deteriorations are due to, permeability to moisture, chlorides and gases, lack of properly entrained air and Exposure conditions. Much of the damage caused by moisture can be prevented, or at least reduced or kept at bay for longer, by means of hydrophobic impregnation. Creating a water-repellent zone at the surface of the concrete considerably reduces the uptake of water and aggressive substances. Most commonly sealers are used for concrete hydrophobic protection of highway structures. The most important property the sealer must have is that it must protect the concrete and at the same time it must be breathable. Moreover, silanes plays an important role in the


25


hydrophobic protection of concrete highway structure due its water repellent property, most of the product (HYCRETE, TAM and WACKER CHEMIE AG) available in the market for hydrophobic protection is of silanes.

REFERENCE

Heron, 2001. Prevention of reinforcement corrosion by hydrophobic treatment of concrete,TNO Building and Research, 46, 227. Netherland:

WACKER SILICONES, 2012. Available at: <URL: http://www.wacker.com/cms/en/wacker_group/divisions/silicones/silicones.jsp>

Design manual for roads and bridges: volume 2 highway structures: design (substructures and special structures) materials, section 4 paints and other protective coatings, part 2, bd 43/03, the impregnation of reinforced and prestressed concrete highway structures using hydrophobic pore-lining impregnants

HYCRETE, 2012. Available at: <URL http://www.hycrete.com/>

TAM SEAL Hydroproof, 2012. Avaiable at < www.taminternational.com>


26

http://www.taminternational.com/


Michael M., Angela R., 1993, Rapid Concrete Bridge Deck Protection, Repair and Rehabilitation, Concrete Bridge Protection and Rehabilitation: Chemical and Physical Techniques, Washington, DC: Strategic Highway Research Program

Jennifer l., Darwin d., and Carl e., 2000. Evaluation of corrosion protection methods for reinforced concrete highway structures. University of Kansas centre for research

The structural design of heavy duty pavements for ports and other industries, by John Knapton, Edition 4, 2007, Interpave

Design Manual for Roads and Bridges (DMRB), volume 7, 2008, Highways Agency


27

coursework

Documents

silres bs

subin babu

falling weight

hot rolled

wacker chemie

peak vertical

desired impact

architectural