Strength Development Characteristics of High Strength Concrete Incorporating an Indian Fly Ash

Abstract

In the present investigation a humble effort has been made to finding the possibilities of an Indian fly ash in the production high strength high performance concrete and to evaluate the contributions of some significant mix composition parameters and age upon the strength development characteristics of concrete. A siliceous fly ash having a glass content of 34% and a fineness of 70% passing a 45 micron sieve was used. Experimentation has been performed over water-cementitious material ratios (w/cm) ranging from 0.27 to 0.42, cementitious material contents (cm) varying from 430 to 550 kg/m³ and fly ash replacements ranging from 0 to 40% by weight of cementitious material. Compressive strengths of concrete have been evaluated at 7, 28 and 90 days age. Slump values of fresh concretes are in the range of 150-200 mm.

Results of the present investigation indicate that compressive strength decreases as the w/cm and the fly ash replacement percentage increase at all the ages. 28 day strength of concrete has varied between 33 to 68 MPa while that of 90 day strength has ranged from 42 to 71 MPa. It is also revealed that a judicious use of fly ash has a tremendous potential in producing HSC. Based on statistical analysis of the database of the work, optimum fly ash replacements leading to strength similar to control (0% fly ash) have been determined as 10% and 17% for 28 and 90 days respectively. The results also suggest that HSC incorporating fly ash as a partial replacement of cement may be developed with a w/cm less than 0.34. Contribution of fly ash in improving strength of concrete increases with increasing replacement levels beyond 28 days. The average ratio of fly ash concrete strength between 7 and 28 days has been observed as 0.61 whereas gain in strengths from 28 to 90 days is about 20%.