[5 ] Benjamin A.Graybeal & Joseph L.Hartmann âStrength and durability of ultra high ... [11 ] Ping-Kun Chang,âStress curves And mechanical properties of.
International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013)
Experimental Study on Durability Characteristics of High Performance Concrete Er. Magudeaswaran. P1, Dr. Eswaramoorthi. P2 1
Assistant Professor, Dept.of Civil Engineering& Sri Ramakrishna Institute of Technology, Coimbatore-10 2 Professor, Dept.of Civil Engineering& Kumaraguru college of Technology, Coimbatore-06 To achieve the high performance concrete the super plasticizers and supplementary cementitious materials are to be used. The fly ash and silica fume are used in this study.
Abstract— The conventional concrete has lost its usage in modern days as it does not serve the present needs. Hence to improve the workability, durability and the ultimate strength of the concrete, high performance concrete (HPC) with super plasticizers and pozzolans are used. Another major problem which demands the use of HPC is the reduction in the CO 2 level for a green environment. There are various studies and research that are emerging related to the HPC. This study is mainly concentrated on the durability characteristics of HPC with partial replacement of cement by fly ash (F) and silica fume (SF). The cement was replaced with 25% F & 12.5% SF, 30% F & 15% SF, 35% F & 17.5% SF. Water cement ratio is kept constant for all mixtures. The main properties that are observed are water absorption capacity, the alkalinity to test and the durability. It was observed that for the increase in the percentage of fly ash and silica fume there was steady increase in the water absorption and alkalinity which significantly indicates the markable change in strength and durability characteristics of concrete.
II. EXPERIMENTAL STUDY 2.1 Materials The materials used for coarse aggregate, natural sand, fly ash, silica fume and 53 grades ordinary Portland cement. The sand and coarse aggregate used for locally available in the market and usual materials used. The fly ash and silica fume was replaced with 25%&12.5%, 30%&15%, 35%&17.5% for cement and plain concrete in cubes and cylinders. Fly ash is finely divided residue resulting from the combustion of powdered coal and transported by flue gases and collected by electrostatic precipitation. Silica fume is a byproduct of producing silicon metal or ferrosilicon alloys. One of the most beneficial uses for silica fume is in concrete. The silica fume is collected from ELKEM INDIA (P) LTD, Mumbai. Super plasticizers, also known as high range water reducers, are chemicals used as admixtures where welldispersed particle suspensions are required. ASTM C 494 type F as a high range water reducing admixture (CONPLAST SP 430) was used.
Keywords- Durability, fly ash, High Performance Concrete, silica fume, strength, workability
I. INTRODUCTION In the present day, world is witnessing the construction of very challenging and difficult civil engineering structures. Quite often, concrete being the most important and widely used material is called upon to possess very high strength and sufficient workability properties. Efforts are being made in the field of concrete technology to develop such concretes with special characteristics. Researches all over the world are attempting to develop high performance concrete by using silica fume and other admixtures in concrete up to certain proportions. ACI defined high-performance concrete as a concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practice.
2.2 Methods The materials are collected and the mix proportions are to be obtained. For acquiring the mix proportions basics tests are to be carried to find the specific gravity of cement, fine aggregate, coarse aggregate along with bulk density of fine and coarse aggregate are obtained.
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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) III. RESULTS AND DISCUSSION
TABLE 1 Values for the mix design
Specific gravity of cement
3.15
Specific gravity of FA
2.68
Specific gravity of CA
2.83
Bulk density of FA
1773.2 Kg/m3
Bulk density of CA
1647.2 Kg/m3
Based on the laboratory test it has been observed that strength of concrete is increasing with addition of admixtures. The various tests that are conducted to test the strength and durability characteristics and their results correlate with the study and derive positive result and improvement. 3.1 Compressive strength of concrete The compressive strength is tested for the nominal concrete for 3 cubes on different curing periods. Then it is tested for three different proportions of fly ash and silica fume. With the increase in the proportion, there is a gradual increase in strength. This is probably because the fly ash provides adequate lime needed to react with the pozzolans in the hydration process. More lime seems to inhibit the hydration process, but yet is still adequate to provide the needed design strength. The pozzolans added being finer than the cement fills the pores and voids in the concrete thereby increasing the compressive strength. The graph shows the improvement in the strength on 7,14 and 28 days of curing for different percentage of pozzolans.
With all the above values mix design is done and the following proportions are used. TABLE 2 Mix proportion used for the concrete
FLY ASH
SILICA FUME
FLY ASH
SILICA FUME
CEMEN T
(%)
(%)
(Kg/
(Kg/m3)
(Kg/m3)
FA
80 60 40 20 0
(Kg/ m3)
m3)
7 DAYS
14 DAYS 28 DAYS
25
12.5
149.8
74.6
374.8
764
30
15
176.76
89.88
329.62
764
35
17.5
209.72
104.86
284.62
764
Figure 1: Compressive strength of concrete performance comparison (cubes)
Analysis was carried out in concrete mixtures with the levels of fly ash and silica fume replacement ranging from 25% & 12.5, 30% &15%, 35% &17.5% and plain concrete. The specimens were casted tested to study the possibility of using fly ash and silica fume as the substitute materials for cement in concrete. The control mix using silica fume and fly ash replaced as the cement was designed for cubes, beams and cylinders. The specimens were investigated to determine the compressive, split tensile and flexural strength in cubes and cylinders respectively.
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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) 3.2 Flexural strength of beams The flexural strength is found to increase by the addition of the fine grained particle due to increase in bond strength as they form a rigid structure comparatively. The theory behind this is that when these pozzolans are added to the cement, they react with them and forms a uniform paste of concrete and increase the binding capacity of concrete. This phenomenon increases the flexural strength of concrete.
3.4 Durability characteristics 3.4.1 Alkalinity test The changes and the decrease in the pH values is resulted which enhances the alkalinity resistance. The chemical reaction undergone is that CH crystals in Portland cement pastes are a source of weakness because cracks can easily propagate through or within these crystals without any significant resistance affecting the strength, durability and other properties of concrete. Silica fume which is siliceous and aluminious material reacts with CH resulting reduction in CH content in addition to forming strength contributing cementitious products which in other words can be termed as „„Pozzolanic Reaction‟‟.
3.3 Split tensile test on cylinders The result implore that the fly ash and silica fume have pronounced effect on the tensile strength of concrete. In addition, the splitting tensile strength of pozzolan concretes seemed to be higher than that of control concrete, since the grain and pore refinement of concretes resulted from the very high fineness of particles and pozzolanic reaction of the ashes.
3.4.2 Water absorption test The graphs indicate that there is a decrease in the water absorption by the concrete. The pozzolanic reaction combined with filler effect increases the water tightness and reduces water absorption. The water absorption is proportional to particle size and voids. Hence both are taken care by the pozzolans.
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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) REFERENCES [1 ] AZI Mohammed Faouzi and Belachia, (2007). “Supplementary cementitious materials”. High performance concrete in Algeria for a more economical and more durable concrete(state of art report) [2 ] Sarath Chandra Kumar and P.Saha, (2011,Oct). “Contribution of Fly ash to the properties of Mortar and Concrete”. International Journal of Earth Sciences and Engineering . ISSN 0974-5904, Volume 04, No 06 SPL, October 2011, pp 1017-1023 [3 ] R.Ilangovan, N.Mahendrana & K.Nagamanib “Strength and durability properties of concrete containing quarry rock dust as fine aggregate”, aprn Journal of Engineering and Applied Sciences, Vol 3, No.5, Oct 2008 [4 ] Karthik H.Obla & Colin L.Lobo “Acceptance criteria for durability test”, Concrete International, May 2007 [5 ] Benjamin A.Graybeal & Joseph L.Hartmann “Strength and durability of ultra high performance concrete”, Concrete Bridge Conference,2003 [6 ] Pazhani.K, Jeyaraj.R, “Study on durability of high performance concrete with industrial waste”, Applied Technology and Innovation, Vol 2, Issue 2, Aug 2010, pp 19-28. [7 ] Muthupriya, “Experimental study on high performance reinforced concrete column with silica fume and fly ash as admixtures”, Journal of Structural Engineering, Vol 38, No.1, April–May 2011, pp- 4659. [8 ] ACI 211.4R Code Book.. [9 ] Mukesh Limbachiya, “Performance of Portland / silica fume cement concrete produced with Recycled concrete aggregate” ACI material Journal, Vol109,Issue 1,Jan1 2012,pp91-100. [10 ] Thilagavathi.S,”Durability of Fly Ash Concrete to chloride Ingress”, The IUP Journal of structural Engineering, Vol. III, No. 3, July 2010, pp. 47-65. [11 ] Ping-Kun Chang,”Stress curves And mechanical properties of HPC” Journal of the Chinese Institute of Engineers, Vol.27, Issue 7, 6Jun2002-5Feb2004, pp. 1081-1085. [12 ] Amudhavalli.N.K, “Effect of silicafume on strength and durability parameters of concrete”, International Journal of Engineering science and Engineering Technologies, Vol.3, Issue 1, Aug 2012, pp.28-35. [13 ] Mostafa Jalal , “Chloride penetration , water absorption and electrical resistivity of high performance concrete containing nano silica and silica fume”, Journal of American Science, 2012;8(4).
IV. CONCLUSION According to the test results, it can be conclude that structural grade concrete can be produced by partial replacement (25%&12.5%, 30%& 15%, 35%&17.5%) of cement by fly ash and silica fume. The strength of the concrete and durability characteristics of the concrete is increased by using admixtures. Compression strength is increased by 31.6% for 35% & 17.5% replacement of fly ash and silica fume. Flexural strength of concrete is increased by 24.46% for 35% & 17.5% replacement of fly ash and silica fume. Spilt tensile strength of the concrete is increased. The pH value of the concrete decreases by 5.47%. The rate of absorption of the concrete is reduced by 0.24%. However, an acceptable strength and durability characteristics can be achieved by using a fly ash and silica fume. The use of fly ash and silica fume which are to cause environmental pollution when dumped as waste can be reused for strengthening the concrete gives a double fold advantage.
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