Use of Fly Ash in Heat-cured Concrete and the Effect of Post-curing Storage Regimes on Strength, Modulus of Elasticity, and Freezing-thawing Durability

Abstract

Abstract This study examines the use of ASTM Type C fly ash from two western Canadian sources with a Type III cement and aslump-extending superplasticizer. The heat-cured concrete had a low water-to-cementitious ratio. The fly ash was used to replace cement at 10 and 20% by weight. Effects on strength development, modulus of elasticity, and durability of subsequent storage regimes are presented. A nonsuperplasticized mixture designed for use in precast pre-stressed concrete providing 31 MPa (4500 psi) release strength after heat curing and 41 MPa (6000 psi) at the age of 28 days of standard moist storage was used as the control mix. The total cement content of the control mix was kept constant while the remaining mixture proportions were adjusted in response to the reduced water requirement as a result of the incorporation of the slump-extending superplasticizer. The properties of the fly ash mixtures are compared with those of the control mix. The study showed that fly ash when used with a slump-extending superplasticizer can be incorporated at a low-to-moderate level of cement replacement in heat-cured precast prestressed concrete. The fly ash concretes were shown to meet adequate release and 28-day strengths and to possess very high scaling resistance and should provide excellent durability in a freezing and thawing environment. The compressive strength, modulus of elasticity, and durability of fly ash heat-cured concrete are no more seriously affected by post-heat-curing storage regimes than accepted and proven concrete containing no fly ash.