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International Journal of Research and Innovation (IJRI)

International Journal of Research and Innovation (IJRI)RESIDUAL COMPRESSIVE STRENGTH OF TERNARY BLENDED CONCRETE AT

ELEVATED TEMPERATURES

N.Somanath Reddy1, Venkata Ratnam 2,

1 Research Scholar, Department of Civil Engineering, Aurora Scientific Technological and Research Academy, Hyderabad, India.2 Associate professor , Department of Civil Engineering, Aurora Scientific Technological and Research Academy, Hyderabad, India.

*Corresponding Author:

N.Somanath Reddy , Research Scholar, Department of Civil Engineering, Aurora Scientific Technological and Research Academy,Hyderabad India.

Published: July 25, 2015Review Type: peer reviewedVolume: II, Issue : II

Citation:N.Somanath Reddy ,Research Scholar (2015) "RESID-UALCOMPRESSIVESTRENGTHOF TERNARY BLENDED CON-CRETE AT ELEVATED TEMPERATURES"

INTRODUCTION

General

Concrete containing industrial by-product/mineral ad-mixtures is used expensively throughout the world. Con-crete is generally to be fire sustaining material at moder-ate temperatures. In most of the fire incidences, it has been found that concrete structures remain intact with minor damages. The reasons being attributed to low ther-mal conductivity of concrete, which limits the limits, the depth of penetration of fire in a structure. During the fire, no toxic fumes are emitted by concrete. Developments during the last decade have seen a marked increase in the number of structures involving the long time heating

of concrete. The extensive use of concrete as a structural material for the high-rise buildings, nuclear reactor pres-sure vessels, storage tanks for hot crude oil and hot wa-ter, coal gasification and liquefaction vessels increase the risk of concrete being exposed to high temperature. This has to a demand to improve the understanding of the ef-fect of temperature on concrete. Hence the extensive use of concrete as a structure material in all the above men-tioned structures necessitated the need of the study of the behavior of concrete at high temperature.

The main factors determine strength in concrete are the amount of cement and mineral admixture used and the water-cement ration. Numerous studies have been con-ducted on the strength development of fly ash concrete and the following major conclusions are drawn. Many variables influence the strength development of fly ash concrete.

The most important being the properties of fly ash, chemi-cal composition, particle size, reactivity and temperature and other curing conditions. Also a number of research-ers in various countries have investigated the effect of el-evated temperatures on the residual strength of concrete. In most of these investigations the main variable as far as the heating regime is concerned, has been maximum level of temperature to which temperature on the residual strength of concrete. The gravel aggregate being thermally stable up to 250oC, the incompatibility is mainly because of cement paste. The shrinkage of cement paste is due to

Abstract

The extensive use of concrete as a structural material for the high rise buildings, storage tanks, nuclear reactors and pressure vessels increase the risk of concrete being exposed to high temperatures. This has led to a demand to improve the understanding of the effect of temperature on concrete. The behavior of concrete exposed to high temperature is a result of many factors including the exposed environment and constituent materials.

Concrete structures are exposed to fire when a fire accident occurs. Damage in concrete structures due to fire depends to a great extent on the intensity and duration of fire. The distress in the concrete manifests in the form of cracking and spalling of the concrete surface.

The objective with the study was to examine the Residual Compressive Strength of Ternary Blended Concrete when sub-jected to elevated temperatures. To investigate the effect of temperature and to evaluate structural safety an attempt has been made to study the Compressive Strength of Ternary Blended Concrete when subjected to elevated temperatures.The study concentrates mainly on studying the properties of Residual Compressive Strength of Ternary Blended Con-crete for various w/b ratios at 2000C, 4000C and 6000C.

In the present investigations, the effect of high temperatures of Residual Compressive Strength of Ternary Blended Concrete when subjected to elevated temperatures are studied. The main test parameters involved in this study are Temperature ranges, the time of exposure.

The tests were conducted for a total of 180 cubes on various w/b ratios ternary blended concrete by exposing them at different temperatures like Room Temperature, 2000C, 4000C and 6000C and 4 Hours, 8 Hours and 12 Hours duration. The results indicate that the ternary blended concrete is effective in resisting the effect of temperature on the compres-sive strength.

1401-1402

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dehydration of Cao/SiO2 H2O (C-S-H gel) at high tempera-ture causing, the loss of its cement ability. This C-S-H gel bond mainly depends on Cao/SiO2 (C/S ratio). Hence for the above reason the class F fly ash having low c/s ratio is used as high volumes to cement in this study. The project gives the result of residual strength of high volume fly ash concrete with fly ash as a partial replacement and addi-tional material after exposing it to elevated temperature.

In both developed and developing countries recent re-searchers amide at the energy conservation in the ce-ment and concrete industry, focused on the use of less energy intensive materials such as Fly-ash, slag and nat-ural pozzlolanas. Later some attention has been given to the use of pozzolana, Micro silica as partial replacement to Portland cement. Unlike natural pozzolanas and fly ash, the silica reaction involving Micro silica is rapid and therefore, a long curing period is not necessary.

FLY ASH

Fly ash is divided into three classes depending on its cal-cium content, in recognition of the difference in behavior between low and high lime fly ashes. These classes are as follows:

Type F, low calcium, 8% CaOType CI, intermediate calcium, 820% CaOType CH, high calcium, .20% CaOLow CaO fly ashes generally provide good resistance to alkali-silica reaction (ASR) and sulphate attack. Howev-er, strength development at early ages is typically slower than that in conventional Portland cement content, espe-cially at higher levels of replacement. High CaO fly ashes, on the other hand, are less efficient in suppressing expan-sion due to ASR or sulphate action, but generally react faster than low CaO fly ashes and have less negative im-pact on the early strength of concrete and are less sensi-tive to inadequate curing.

Most fly ashes, regardless of composition, tend to reduce the water demand of concrete and increase its resistance to fluid flow and the ionic diffusion. The beneficial effects of fly ash on permeability and diffusivity tend to become more apparent with time especially in the case of the more slowly reacting low CaO fly ashes.

Advantages of fly Ash in concrete

The technical benefits of using fly ash in concrete are nu-merous. The various advantages found by different inves-tigators in India are summarized bellow 1. Superior pozzalonic action 2. Reduced water demand (for fly ash low carbon content and high fineness) 3. Improved workability 4. More effective action of water reducing admixtures5. Reduced segregation and bleeding 6. increases setting time but remains within limits 7. Less heat of hydration 8. Less drying shrinkage 9. Higher ultimate compressive strength, tensile, flexural and bond strength 11. Higher ultimate modulus of elasticity.12. Reduced alkali-aggregate reaction 13. Improved freezing and thawing

Micro Silica

During the last three decades, some new Pozzolan materi-als have emerged in the building industry as an off shoot of research aimed at energy conservation and strict en-forcement of pollution control measures to stop dispers-ing the materials into the atmosphere. Micro Silica (other names have been used are silica dust, condensed silica fume) is one such Pozzolan, which has been used as a partial replacement of Portland cement due to its versatile properties. The availability of high range water-reducing admixtures (superplasticizers) has opened up new ideas for the use of Micro Silica as part of the cementing mate-rial in concrete to produce very high strength cement (> 100 MPa/15,000 psi).

Micro Silica is a by-product from the reduction of high purity quartz with coal in electric arc furnaces in the manufacture of silicon and ferrosilicon alloys. The Micro Silica, which has a high content of amorphous SiO2 and is consisted of very fine spherical particles, is collected from the gases escaping from the furnaces. Micro Silica is also collected as a by-product in the production of other silicon alloys such as ferrochrome, ferromanganese and ferrovanadium.

Micro Silica is predominantly silicon dioxide. Its prime characteristic is particle size which would be as low as 0.2 micron, which is about 100 times smaller than Port-land cement grains. The extremely small grain size of Mi-cro Silica is responsible for its high reactivity with free lime in the concrete to form a strong and non-permeable paste. The other important properties which established Micro silica as a formidable building material are its im-perviousness to water, low permeability to chloride ion and resistant to sulfate and acid attack. Because of high surface area and high contents of amorphous silicon in Micro silica, the latter acts as a highly active Pozzolan and reacts more quickly than ordinary Pozzolans.

The Pozzolanic reaction may begin as early as 2 days after cement hydration and the main Pozzolanic effect of Micro Silica in concrete takes place between the ages of 3 and 28 days for curing at 20o C. The presence of Micro Silica provides increased internal cohesion of fresh concrete. As a result, local areas of weakness such as bleed water channels and voids under coarse aggregate particles can be eliminated. The transition zone between cement paste and coarse aggregate particles is an especially critical re-gion in most concrete. It is frequently the weakest part because of bleed-water voids, so it is under the greatest stress because of the elastic bond between the cement paste and the relatively stiff aggregate material.

The presence of Micro Silica brings reduction of bleed-ing in fresh concrete and in consequences, significant improvements in the density of the transition zone and in the mechanical behavior of hardened concrete. The strength of the transition zone can be further enhanced by a Pozzolanic reaction.

Triple-Blends (Ternary cement system)

It means Micro Silica or other cement replacement ad-ditives are to be used with OPC only. That is not strictly true and ternary mixtures comprise efficient -systems. The primary incentive of adding limited amount Micro Silica for example 5 percent with Fly-ash cement mixes was to ensure high early strength research has however, shown that Ternary mixtures of OPC, Micro Silica and Fly-ash result in synergic action to improve the micro

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structure and performance of concrete. When both silica fume and fly-ash are used, the resultant enhancement of strength or pozzolanic activity was greater than super position of contributions of each, for the respective pro-portions. Such synergic effect results from strengthening the weak transition zone in aggregate cement interface, as well as segmentation and blocking of pores.

Depending upon the service environment in which it is to operate, the concrete structure may have to encounter different load and exposure regimes. In order to satisfy the performance requirements, different ternary com-pounds required. Such as cement, fly-ash, silica fume. Greater varieties are introduced by the corporation of ad-ditives like pozzolana, granulated slag are inert fillers this leads to different specifications of cements in national or international.

Effects of Ternary cement system

The combination of Micro Silica and Fly ash in a Ternary cement system (i.e., Portland cement being the third com-ponent) should result in a number of synergistic effects, some of which are obvious or intuitive, as follows: Micro Silica compensates for low early strength of con-crete with low CaO fly ash. Fly ash increases long-term strength development of Mi-cro Silica concrete. Fly ash offsets increased water demand of silica fume. Micro Silica reduces the normally high levels of high CaO fly ash required for sulphate resistance and ASR pre-vention. Very high resistance to chloride ion penetration can be obtained with ternary blends. Fly ash due to presence of spherical particles that easily rollovers one another reducing inter partial friction (call bearing effects) leads to improved workability and reduc-tion in water demand.

AIM OF PRESENT STUDY

The main aim of the present experiment investigation is to study and examine the Residual Compressive Strength of Ternary Blended Concrete when subjected to Elevated Temperature.

The Residual Compressive Strength of Ternary Blended Concrete specimens made with locally available fine ag-gregates i.e., river sand and crushed angular granite of 20 mm size as coarse aggregate, Fly ash and Micro silica for various water/ binder ratios.

In the Present investigation tests were conducted on Ter-nary Blended Concrete by exposing them at different tem-perature like 200oC, 400oC, 600oC at 4 hours, 8 hours, and 12 hours duration after 28 curing. The specimens are tested for compressive strength, percentage weight loss and non destructive test to measure velocity of con-crete.

The result reveal that Ternary Blended Concrete is more effective in resisting the adverse effect of temperature on the compressive strength, Based on the study, conclusion were made that fly ash and Micro silica can be used as an additional cementing material to obtain enhanced proper-ties of Ternary Blended Concrete especially for structural elements subjected to elevated temperature.

EXPERMENTAL INVESTIGATION

Introduction

The present investigations are aimed at to study residual compressive strength of Ternary Blended Concrete, hav-ing 5% Silica fume and 15% Fly Ash by weight of cement with different W/B ratios 0.55, 0.45and 0.35 in the labo-ratory after the age of 28 Days.

MATERIALS

Cement

Locally available 53 grade of Ordinary Portland Cement (Ultra Tech Brand.) confirming to IS: 12269 was used in the investigations. Table 4.1 gives the physical properties of OPC used in the present investigation and they con-form to IS specifications.

Photomicrograph of Portland cement (Curtsy Micro Silica Man-ual)

Fly Ash

The fly ash obtained from Hyderabad Industries, Andhra Pradesh is used in the present experimental work.The chemical composition of fly ash is rich in silica content which react with calcium hydroxide to form C-S-H gel. This gel is responsible for the strength mortar or concrete. The fly ash used to the specification of grade 1 fly ash.

SEM micrograph showing: Fly Ash (Courtesy ACI Journal)

Micro Silica

The Micro Silica obtained from Oriental Trexim Pvt Ltd . Micro Silica conforming to a standard approved by the deciding authority may be used as part replacement of cement provided uniform blending with the cement is en-sured. The Micro Silica (very fine non-crystalline silicon

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dioxide) is a by-product of the manufacture of silicon, fer-rosilicon or the like, from quartz and carbon in electric arc furnace.

Micrograph showing: Micro Silica (Courtesy by Micro Silica Man-ual)

Mix Proportion in the Laboratory

The proportion used in preparation of mix is calculated as per BIS Method.

The ratio between F.A and C.A is p: (1-p)

Illustrative Example for Mix Design

Mix Design for W/C ratio = 0.55

i.Text data for materials Specific gravity of cement =2.95Specific gravity of Coarse Aggregate =2.70Specific gravity of Fine Aggregate =2.53

ii. Selecting W/B ratio =0.55iii. Determination of cement content Water =178 Ltr. Cement =323.6 Kg.

iv.Determination of F.A and C.A

Fine Aggregate

0.98= [178+ (323.6/2.95) + (1/0.42)*(F.A/2.53)]*1/100

=736 Kg

Coarse Aggregate

0.98=[178+(323.6/2.95)+(1/1-0.42)*(C.A/1-2.2.7)]*1/100

= 1084 Kg.

v.Mix Proportion = 1.00:2.27:3.34:0.55

Similarly Mix proportions for other W/B are obtained and are as follows:

For W/B ratio 0.55 Ternary Concrete mix proportion is 1.00:2.27:3.34:0.55

For W/C ratio 0.45 Ordinary Concrete mix proportion is 1.00:1.78:2.73:0.45


For W/C ratio 0.35 Ordinary Concrete mix proportion is 1.00:1.26:2.11:3.55


PREPARATION OF TEST SPECIMENS

Mixing

Mixing of ingredients is done in a rotating drum. Thor-ough mixing by hand, using trowels is adopted.

The cementitious materials are thoroughly blended with hand and then the aggregate is added and mixed followed by gradual addition of water and mixing. Wet mixing is done until a mixture of uniform color and consistency are achieved which is then ready for casting. Before cast-ing the specimens, workability of the mixes was found by compaction factor test.

The concrete mix design using the data obtained from the test on its ingredients. The mix proportions with different W/B ratios are shown in the table 4.6.1, 4.6.2 and 4.6.3 for Ordinary Concrete and Ternary Blended Concrete. The adopted method is BIS method.

Testing of Specimen

A time schedule for testing of specimens is maintained to ensure their proper testing on the due date and time. The cast specimens are tested as per standard procedures, immediately after they are removed from curing pond and wiped off the surface water. The test results are tabulated carefully

TESTS CONDUCTED

Compressive Strength of Concrete Specimen

The compressive strength of Ordinary Concrete (ordinary concrete) and Ternary concrete contain 5% Micro Silica and 15% Fly ash concrete specimens having W/B 0.55, W/B 0.45 and W/B 0.35 were tested.

In the preparation of standard cement mortar cubes to assess the cement strength a fixed w/c ratio is followed as per the codal procedure. However, when cement is re-placed with Micro Silica by 5% and Fly ash by 15 % this procedure may yield adverse results because of the water content in the mix may not be sufficient to combine with all particles of Micro silica and Fly ash which are very fine. Hence to know the influence of Micro Silica and Fly ash replacement on cement strength various W/B ratios have been adopted and strengths at various ages have been found.

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EXPERIMENTAL RESULTS

Sieve analysis: Sample 1000 gm

S.No. I.S Sieve Size

Wt. Re-tained (gm.)

Cumu-lative Wt. Re-tained (gm.)

Cumu-lative % of wt. Re-tained

% Pass-ing

1 4.75 mm

0.61 0.61 0.061 99.939

2 2.36 mm

2.6 3.21 0.321 99.679

3 1.18 mm

40 43.21 4.32 95.68

4 600 463 506.21 50.62 49.38

5 300 432 938.21 93.82 6.18

6 150 59.8 998.01 99.8 0.2

7

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DISCUSSION OF TEST RESULTS

Compressive Strength of Ternary Blended and Ordinary Concrete exposure at 200oC

Graphs 1-3 shows the compressive strength of Ternary Blended and Ordinary Concrete for 0.55, 0.45, 0.35 w/b ratios after exposure to 4,8 and 12 hours duration for 2000C. The compressive strength of Ternary Blended and Ordinary Concrete for 12 hours exposure are 28.7, 38.1 and 59.9 MPa and 2 4.8, 30.5 and 46.2 MPa respectively.5.7 Compressive Strength of Ternary Blended and Ordi-nary Concrete exposure at 400oC

Graphs 1-3 shows the compressive strength of Ternary Blended and Ordinary Concrete for 0.55, 0.45, 0.35 w/b ratios after exposure to 4,8 and 12 hours duration for 4000C. The compressive strength of Ternary Blended and Ordinary Concrete for 12 hours exposure are 22.5, 31.5 and 52.1 MPa and 19.4, 25.0 and 38.2MPa respectively.

Compressive Strength of Ternary Blended and Ordinary Concrete exposure at 600oC

Graphs 1-3 shows the compressive strength of Ternary Blended and Ordinary Concrete for 0.55, 0.45, 0.35 w/b ratios after exposure to 4,8 and 12 hours duration for 6000C. The compressive strength of Ternary Blended and Ordinary Concrete for 12 hours exposure are 17.8, 26.5 and 42.8 MPa and 15.0, 19.6and 30.6 MPa respectively.

Percentage decrease of Compressive Strength of Ter-nary Blended and Ordinary Concrete exposure at 200oC

graphs 4-6 shows the compressive strength of Ternary Blended and Ordinary Concrete for 0.55, 0.45, 0.35 w/b ratios after exposure to 4,8 and 12 hours duration for 2000C. The compressive strength of Ternary Blended and Ordinary Concrete for 12 hours exposure are 27.3, 24.4 and 20.1 MPa and 30.2, 27.9and 23.7 MPa respectively.

Pulse velocity (m/sec) of Ternary Blended and Ordi-nary Concrete exposure at 600oC

Graphs 10 -12 shows the compressive strength of Ter-nary Blended and Ordinary Concrete for 0.55, 0.45, 0.35 w/b ratios after exposure to 4,8 and 12 hours duration for 6000C. The compressive strength of Ternary Blended and Ordinary Concrete for 12 hours exposure are 1970, 2360 and 2620 (m/sec) and 1890, 2265 and 2490 (m/sec) respectively.

EXPERIMENTAL PHOTOGRAPHS

CURED AND NUMBERED SPECIMEN

WEIGHING OF SPECIMEN

OVEN

HEATED AND COOLED SPECIMEN

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TESTING OF SPECIMEN

CONCLUSION

1. The percentage decrease of compressive strength is higher for higher exposure time for ordinary concrete at all temperature.

2. The rate of percentage decrease of compressive strength is less for ternary blended concrete at all temperature for all exposure of time.

3. A gradual reduction in strength was found in ternary blended concrete and ordinary concrete with increase in temperature and increase in exposure time.

4. The ternary blended concrete has shown improved re-sistance for higher temperatures for all w/b ratios com-pared to ordinary concrete.

5. The percentage decrease of weight loss is higher for higher time for ternary blended concrete compared to or-dinary concrete.

6. The percentage decrease of weight loss is lower for ter-nary blended concrete for lower w/b ratio compared to ordinary concrete.

7. The pulse velocity of ternary blended concrete is lower for higher exposure time compared to ordinary concrete.

8. Ternary blended concrete exhibited maximum decrease of compressive strength of nearly 40 to 45% at 600oC for 12 hours duration, whereas ordinary concrete exhibited maximum decrease of nearly 55% at 600oC for 12 hours duration.

9. Ternary blended concrete exhibited maximum per-centage weight loss of 5 at 600 oC for 12 hours duration, whereas ordinary concrete exhibited maximum percent-age weight loss of 7 at 600oC for 12 hours duration.

REFERENCES

1. Mohamedbhal, g.T.G., The residual strength of con-crete subjected to elevated temperature, concrete, vol.17, No.12, 1983, Pp 22-27.

2. S.C. Chakrabarti, k.N.Sharma and abha mittal., Resid-ual strength in concrete after exposure to elevated tem-perature. December 1994*. The indian concrete journal. Pp 713-717.

3. K.Sreenivasa rao, m.Potha raju and p.S.N.Raju, effect of age of hsc on residual compressive strength under el-evated temperatures. Proceedings of icacc 2004, 16-18 december 2004, hyderabad, india.

4. Crushing strength of concrete at various temperatures by mr.H.L.Malhotra.

5. Phan, long t (2002) effects of test conditions and mix-ture proportions on behaviors of high strength concrete exposed to high temperatures, aci materials journal, and january- february 1996.

6. Sarshar r, khaury g a (1993), material and environ-mental factors influencing the compressive strength of unsealed cement paste and concrete at high tempera-tures, magazine of concrete research, vol 45, no.162, 1993, 51-61.

7. Janotka, nurnbergurora t (199(), thermo-mechanical properties of penly reactor envelop at temperatures up to 200oc, materials and structures vol.32, December 1999,pp 719-726.

8. Prof.P.Srinivasa rao and p.K.Aravindan behavior of concrete under extreme temperature, iit madras.

Author

N.Somanath ReddyResearch Scholar,Department of Civil Engineering,Aurora Scientific Technological and Research Academy, Hyderabad India.

Venkata Ratnam Associate professorDepartment of Civil Engineering, Aurora Scientific Technological and Research Academy, Hyderabad India.

Abstract

ijri-cce-02-007

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concrete structures

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behavior of concrete

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