Early-Age Tensile Strength of Concrete Containing Lowcalcium Fly Ash as Partial Replacement of Cement

Abstract

The benefits of using fly ash include improvements of the durability and sustainability features of concrete. However, the slow strength development of low-calcium fly ash concrete at the early ages is viewed as a drawback in applications such as tilt-up, precast and prestressed concrete structures, where specified early-age strength is required. This study investigated the development of the early-age tensile strength of concrete containing locally available low-calcium fly ash. Fifteen concrete mixtures containing fly ash from 0 to 40% of the binder were designed. The 3-day compressive strength varied from 22 to 51 MPa (3 to7.4 ksi). The splitting tensile strengths at 3 and 28 days were calculated from the compressive strengths using the AS3600, ACI 318 and the EC2 Codes. The test-prediction ratios of splitting tensile strengths show that the early-age tensile strength correlated well with the compressive strengths. No effect of the early age or inclusion of fly ash was observed on the test-prediction ratios. This suggests that the Code equations based on the compressive strength can be used for designs related to early-age tensile strength of concrete containing up to 40% of low-calcium fly ash.