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Short Paper Proc. of Int. Conf. on Advances in Civil Engineering 2012

Mechanical Properties of High Strength High Performance Concrete Sarita Singla Assistant Professor,Civil Engineering Department, PEC University of Technology, Chandigarh, India. emailid: ssaritasingla@yahoo.com Abstract-High Performance Concrete is a concrete made with conventional concrete materials and admixtures such as fly ash, silica fumes blast furnace slag and superplasticizers, in varying proportions so as to give excellent performance in the various properties of concrete. In the present study, high performance concrete having characteristic compressive strength of 80 MPa had been proportioned by replacing cement partly with varying percentages of fly ash and silica fumes. It was seen that the properties of concrete were enhanced significantly by use of admixtures in concrete. Index Terms - High Performance Concrete, flyash, silica fumes, admixtures, cube compressive strength, cylinder compressive strength.

I. INTRODUCTION High Performance Concrete (HPC)is defined as a concrete made with appropriate materials (superplasticizers, retarders, fly ash, blast furnace slag and silica fumes) combined according to the selected mix design and properly mixed, transported, placed, consolidated and cured to give excellent performance in some properties of concrete such as high compressive strength, high density, low permeability and good resistance to certain forms of attack [1].Use of mineral and chemical admixtures reduces cement and water content in concrete, thereby reducing the porosity and making the micro structure of hardened cement matrix denser and stronger. The concrete so obtained is highly durable and strong.Two types of admixtures commonly used in High Performance Concrete are (i) mineral admixtures, which are products of natural rock deposits or by-products of combustion processes with various degrees of cementing capability; and (ii) chemical admixtures in many variations, which are produced by chemical processes and have a variety of functions, depending on the type of chemical admixture to be used with cement.

flyash and 5 percent silica fumes. The total binder content and coarse aggregates were kept same for all mixes. The quantity of sand was suitably adjusted.The structural characteristics of HPC to be investigated were cube and cylinder compressive strength, flexural and split tensile strength after 7, 28, 90 and 365 days of casting. III. EXPERIMENTAL PROGRAMME A. Materials used and the Mix Proportions The constituent materials used for making HPC were tested as per IS codal provisions [6, 7, 8] and were found to be complying with the codal requirements. The cement used was Ordinary Portland Cement of grade 53. Fine aggregates used were complying with Zone II. The specific gravity of fine aggregates was 2.55 and fineness modulus as 2.9. The coarse aggregates used were crushed 20 mm graded aggregates with specific gravity of 2.76. Fly ash was obtained from Ropar Thermal Power Plant, Ropar. Fly ash used was low calcium flyash (Class F). Silica fume used was microsilica. Superplasticiser used was in liquid form of the category of modified lignosulfates with trade name of CONPLAST. Ordinary potable tap water was used for mixing concrete.The concrete mix was designed as per the recommendations of ACI 211.4R-93[9]. Additional trials were carried out to optimize the ingredients.Final mix proportionsadopted are given in Table I. TABLE I. CONCRETE MIX PROPORTIONS

II. SCOPE OF PRESENT STUDY The objectives and scope of the present study were to design mix proportions for HPC using admixtures-fly ash, A. Preparation of Test Specimens silica fumes and superplasticiser in varying The ingredients of the mixes were weighed and casting proportions,having compressive strength of 80 MPaat 28 was carried out using a tilted drum type concrete mixer. days. A control mix was developed without using any Precautions were taken to ensure uniform mixing of admixtures (Mix M80), adopting guidelines of ACI 211.4R-93. ingredients.The specimens were cast in steel moulds and A w/b ratio of 0.3 was used. In M80A mix, 5 %of cement by compacted on a table vibrator. Cube specimens of size weight was replaced by flyash. In M80B mix, 10 % of cement 150x150x150 mm were cast for cube compressive strength. was replaced by 5 percent flyash and 5 percent silica fumes. Cylinder specimens of 150 mm diameterand 300 mm length In M80C mix 15 % of cement was replaced by 10 percent 169 ÂŠ 2012 ACEE DOI: 02.AETACE.2012.3.8

Short Paper Proc. of Int. Conf. on Advances in Civil Engineering 2012 were cast for cylinder compressive strength. Cylinder specimens of 100 mm diameter and 200 mm length were cast for split tensile strength. They were subjected to diametric compression so as to induce uniform lateral tension in the perpendicular plane.Beam specimens of size 100x100x500 mm were cast for flexural strength. They were subjected to standard two point loading. Curing was done for 28 days by keeping the specimens completely immersed in water. All the test results reported in this paper represent the average value obtained from a minimum of three specimens.

the 7 days compressive strength was about same as that of the control mix strength. This was due to the fact that these mixes contained silica fumes as admixture, in addition to the flyash. Silica fumes had faster rate of pozzolanic activity in early ages. Hence the slower rate of gain of strength, due to presence of flyash had been compensated by faster action of silica fumes. M80C at 28 days mix gave maximum strength of 86.22 MPa, followed by M80B mix. At 90 days, the strength of HPC mixes M80B and M80C mixes was about 4%-5% more than that of control mix M80. After a period of one year the strength of these mixes was 5%-6% higher than that of control mix. The strength of M80C mix was highest as compared to other mixes. This was due to the combined pozzolanic action of flyash and silicafumes.

IV. ANALYSIS OF TEST RESULTS The concrete specimens were tested after 7, 28, 90 and 365 days of casting. The results of various test performed on various concrete mixes are discussed in the succeeding sections.

B.Cylinder Compressive Strength The cylinder compressive strength of mixes at various ages is given in Table III.

A. Cube Compressive Strength Cube compressive strength of mixes at various ages is given in Table II.The 7 days cube compressive strength of mix M80 was found to be 0.85 times its 28 days strength of 82 MPa. There was no significant increase in the strength after 90 days. After a period of one year the strength was increased by about 3.7%.The 7 days cube compressive strength of mix M80A was found to be 0.775 times its 28 daysstrength of 80 MPa. There was an increase of 3.7% in the strength after 90 days. After a period of one year the strength was found to further increase by about 6.4%.

Table III. Cylinder Compressive Strength At Various Ages

T ABLE II. C UBE C OMPRESSIVE STRENGTH AT VARIOUS AGES

The cylinder compressive strength of all mixes was found to be 0.97-0.98 times the cube compressive strength. This was due to the fact that core strength of high strength concrete is large, so difference between cube compressive strength and cylinder compressive strength is marginal. Gain in Cylinder Compressive strength with age: The 7 dayscylinder compressive strength of the control mix M80 was found to be 0.85 times its 28 days strength of 80.36 MPa. There was no 4% increase in the strength after 90 days. After a period of one year the strength was increased by about 5%. The 7 days cylinder compressive strength of the mix M80A was found to be 0.75 times its 28 days strength of 80.0 MPa. There was an increase of 3% in the strength after 90 days. After a period ofone year the strength was found to increase by about 5%.The cylinder compressive strength of the mix M80B was found to be 0.80 times its 28 days strength of 81.25 MPa. There was marginal increase of 1% in the strength after 90 days. After a period of one year the strength was found to increase by about 5%.The cylinder compressive strength of the mix M80C was found to be 0.8 times its 28 days strength of 83.93 MPa. There was increase of 5% in the strength after 90 days. After a period of one year the strength was found to further increase by about 6%. Themaximum gain in cylinder compressive strength of HPC mixes, with age was found to be 6%.

The 7 days cube compressive strength of mix M80B was found to be 0.843 times its 28 days strength of 83 MPa. There was increase of 1.5% in the strength after 90 days. After a period of one year the strength was found to further increase by about 6%. The 7 days cube compressive strength of mix M80C was found to be 0.8 times its 28 days strength of 86.22 MPa. There was no increase in the strength after 90 days. After a period of one year the strength was found to increase by about 4.3%.As compared to the control mix, the maximum gain in strength of HPC mixes with age was found to be 6%. Effect of percentage of Cement Replacement Material (CRM) on cube compressive strength of concrete:The cube compressive strength was significantly affected by the amount of CRM in the mix. At 7 days the reduction of 10% in the compressive strength for mix M80A was seen. This was attributed to the fact that flyash had slower pozzolanic action at early age. However, for M80B and M80C mixes ÂŠ 2012 ACEE DOI: 02.AETACE.2012.3.8

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Short Paper Proc. of Int. Conf. on Advances in Civil Engineering 2012 Effect of percentage of CRM on cylinder compressive strength of concrete: The cylinder compressive strength was significantly affected by the amount of CRM in the mix.M80A mix gave the lowest 7 days strength of 60 MPa. This was due to the slow pozzolanic action of flyash. M80B and the control mix M80 gave almost same strength of 65 MPa and 68 MPa respectively. This was because M80B mix though contained 5% flyash, which retards the pozzolanic activity but it also contained 5% silica fumes which had the property of early gain in strength. Due to the same cause, M80C mix had 7 days strength of 77.2 MPa. It was about 13% more than the 7days strength of control mix. The cylinder compressive strength of HPC mixes at 90 days was about 4%-5% more than that of control mix. After a period of one year the strength of HPC mixes was about 5% higher than that of control mix. The cylinder compressive strength of M80C mix was highest as compared to other mixes.

T ABLE V. FLEXURAL STRENGTH AT VARIOUS AGES

The increase after one year was in the range of 1530%. M80C gave the maximum split tensile strength at all ages.The increase in flexural strength due to presence of CRM in the mix was significant. The control mix M80 had flexural strength of 6.6 MPa at 28 days and 8.0 MPa at 365 days. The flexural strength of M80A and M80B mix at 28 days was found to be about 10% more than that of the control mix. The flexural strength of M80C mix at 28 days was found to be 15% more than that of the control mix and at 365 days was found to be 23% more than that of the flexural strength of control mix.

C.Split Tensile Strength The split tensile strength of mixes at various ages is given in Table IV.

E. Relationship between Strength Parameters The relationship between various strength parameters - cube compressive strength, cylinder compressive strength, split tensile strength and flexural strength at 28 days is given in Table VI.

T ABLE IV. SPLIT T ENSILE STRENGTH O F VARIOUS MIXES

T ABLE VI. R ELATIONSHIP B ETWEEN VARIOUS STRENGTH PARAMETERS

The split tensile strength was found to be about 5 MPa - 6 MPa. The gain in split tensile strength of mixes and with age was not found to be significant. The gain in strength with age was 4-5%. Effect of percentage of CRM on split tensile strength of concrete: The variation in split tensile strength of the control mix and HPC mixes with varying percentage of CRM was in the range of 5-7%. At 28 days and onwards the split tensile strength of HPC mixes was comparable to the control mix. M80C mix at all ages gave more split tensile strength than the control mix. The increase of strength was in the range of 5-6%.

The ratio between cylinder compressive strength to cube compressive strength for M80 mix was 0.98 and for other HPC mixes the ratio was about 0.97-1.0. The ratio was slightly higher for HPC mixes but it was not significantly affected by the amount of flyash in the mix. This was due to the fact that core strength of high strength concrete is large, so difference between cube compressive strength and cylinder compressive strength was marginal.Thesplit tensile strength for M80 mix was 6.4% of the cube compressive strength of the mix. For other HPC mixes the split tensile strength for the mix was about 6-7% of the cube compressive strength of the mix. The flexural strength for M80 mix was 8% of the cube compressive strength of the mix. For other HPC mixes the split tensile strength for the mix was about 9% of the cube compressive strength of the mix.

D.Flexural Strength The flexural strengthof mixes at various ages is given in Table V. The flexural strength of mixes at 28 days was found to be in the range of 6.5 MPa-8 MPa. The variation in flexural strength of the control mix and HPC mixes was significant. It was seen there was significant increase in flexural strength with age for all the mixes.

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Short Paper Proc. of Int. Conf. on Advances in Civil Engineering 2012 CONCLUSIONS

REFERENCES

It was seen that the properties of concrete were enhanced significantly by use of admixtures in concrete. Mix M80 C in which 15 percent of cement was replaced by admixtures- 10 percent flyash and 5 percent silica fumes performed the best. In this mix, the delayed hydration of flyash was compensated by the early gain of strength of silica fumes. It gave maximum strength at all ages.

[1] S.W. Foster, “High performance concrete-stretching the paradigm,”Concrete International, vol. 16, No. 10, pp. 33-35, October 1994. [2] ACI Committee 232. 1996. “Use of flyash in concrete”. ACI report 226.3R-96. American Concrete Institute, Farmington Hills, Mich. [3] Mehta, P.K, “Role of pozzolanic and cementitious material in sustainable development of the concrete industry”. ACI SP178, 1998, pp. 1-20. [4] ACI Committee Report 234 -06, “Guide for the use of silica fumes in concrete.” [5] Collepardi M “Flyash, silica fumes and natural pozzolonasState of the art and future needs”ACI SP-144 pp 399-416. [6] IS 516:1959"Method of test for strength of concrete” [7] IS 2386(Part 1):1963"Methods of test for aggregates for concrete.” [8] IS 12269:1987 “Specification for 53 grade ordinary portlandcement.” [9] ACI Committee 211, 1993, “Guide for selecting proportions for High Strength Concrete with Portland Cement and Flyash.”, ACI Report 211.4R-93.

ACKNOWLEDGMENT The author wishes to thank AICTE. This work was supported by a financial grant from AICTE under the Research Promotion Scheme.The author also wishes to express deep sense of gratitude to her elite guide & mentor Dr. N.P.Devgan, Professor, Civil Engineering Department, PEC University of Technology, Chandigarh, under whom this research work had been successfully completed. The author is thankful to him for his persistent interest, constant encouragement, and critical evaluation.

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