Found to be 21 when 30 of cement was replaced with

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found to be 21%, when 30% of cement was replaced with fly ash. The compressive strength of M20 grade of concrete for different proportions of fly ash after 7 and 28 days of curing are listed below in table 5 and 6 respectively. Table-5: Compressive Strength of M20 grade of concrete for different proportions of Fly Ash at the age of 7 days Mix 7 days curing Load (kN) Compressive Strength (N/mm 2 ) Average Compressive Strength (N/mm 2 ) 0% fly ash 296.10 316.80 322.65 13.16 14.08 14.34 13.86 10% fly ash 275.40 279.68 306.22 12.24 12.43 13.61 12.76 20% fly ash 246.15 262.58 268.88 10.94 11.67 11.95 11.52 30% fly ash 210.60 224.32 247.50 9.36 9.97 11.00 10.11
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International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 02 | Feb -2017 p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 318 Table-6: Compressive Strength of M20 grade of concrete for different proportions of Fly Ash at the age of 28 days Mix 28 days curing Load (kN) Compressive Strength (N/mm 2 ) Average Compressive Strength (N/mm 2 ) 0% fly ash 456.30 459.68 473.18 20.28 20.43 21.03 20.58 10% fly ash 437.63 441.45 446.85 19.45 19.62 19.86 19.64 20% fly ash 401.85 406.80 411.22 17.86 18.08 18.28 18.07 30% fly ash 358.88 365.85 379.12 15.95 16.26 16.85 16.35 Chart-1: Compressive Strength (MPa) for different proportions of fly ash after 7 and 28 days of curing 6. CONCLUSIONS From the experimental work carried out for M20 grade of concrete by partial replacement of cement with 10%, 20% and 30% of fly ash, the following conclusions were drawn. 1. The compressive strength of concrete decreases with increase in fly ash content. The reduction in compressive strength of concrete at the age of 28 days was found to be 4.57%, 12.20% and 20.55% for 10%, 20% and 30% replacement of cement with fly ash. 2. As the cement was replaced with fly ash, the reduction in compressive strength of concrete was higher at the age of 7 days as compared to 28 days. This occurs as the secondary hydration due to pozzolanic action is slower at initial stages for fly ash concrete. 3. The workability of concrete improves with the increase in fly ash content. 4. The consistency of cement increases with increase in fly ash content. This happens because the consistency of cement depends upon its fineness, and the fly ash molecules are finer than cement. 5. The increase in fly ash content also leads to retardation in the setting time of concrete. It was observed as the compressive strength for normal concrete with no fly ash at 7 days was 67% of characteristic compressive strength, whereas the compressive strength for concrete with 30% fly ash at 7 days was 60% of characteristic compressive strength. 6. Not more than 30% of cement should be replaced with fly ash; otherwise it may lead to significant reduction in the compressive strength of concrete. REFERENCES [1] C. Marthong, T. P. Agrawal, “Ef fect of Fly Ash Additive on Concrete Properties”, International Journal of Engineering Research and Applications, ISSN 2248- 9622, Volume 2, Issue 4, July-August 2012, pp 1986- 1991.
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