Effect of curing time on the fracture toughness of fly ash concrete composites

This paper presents the results of an experimental investigation carried out to evaluate the compressive strength and fracture toughness of concrete mixtures in which main binder (Ordinary Portland Cement - OPC) was partially replaced with Class F fly ash (FA). OPC was replaced with two percentages (20% and 30%) of FA by weight. Compressive strength and fracture toughness under mode III - KIIIc (torsional loading), were determined at: 3, 7, 28, 90, 180 and 365 days. Test results indicate significant improvement in the strength properties and fracture toughness of mature concrete, by the inclusion of 20% FA as partial replacement of OPC. On the other hand, the additive of FA in the amount of 30% weight of OPC has a beneficial effect on the mechanical parameters of concrete only after half a year of curing. The obtained results are significant in the analysis of concrete structures subjected to complex loading, or structures where torsional moment is the basic load.