The effect of type of fly ash on mechanical properties of geopolymer concrete

The development of alkali activated binders with equivalent or better engineering properties has emerged as an alternative to Portland cement concrete. It is possible to use alkali activated fly ash to prepare environmentally friendly geopolymer concrete, which contribute to sustainable development. This paper presents a summary of an experimental program that has been conducted to determine mechanical properties of geopolymer concrete prepared with five different fly ashes obtained from different power plants in Australia. The variation in optimum 28-day compressive strength for the five fly ash based geopolymers was observed to be between 21.3 and 40.6MPa. The applicability of current relationships between compressive strength and tensile and elastic properties of concrete in AS 3600 for the range of fly ash geopolymers was then examined. The analysis showed that the flexural strengths of all geopolymer concretes are higher than the prediction of AS 3600, however, splitting tensile results appeared to depend on the fly ash source. When compressive strengths of fly ash based geopolymer concrete are below 40 MPa the model employed by AS 3600 for Portland cement concrete overestimates the modulus of elasticity. The Poisson's ratio's lie in the range reported for Portland cement concrete and show a general increase with increasing of compressive strength.