Early-age behaviour and cracking potential of fly ash concrete under restrained condition

Abstract

High performance concrete (HPC) has been extensively applied for its good workability, lasting durability, and high strength. However, the low water-to-cement (w/c) ratio generally induces a rather high autogenous shrinkage, therefore resulting in high early-age cracking potential in HPC. Fly ash (FA) is an effective mineral admixture to strengthen the early-age performance of concrete structures and lower the cracking potential. Although the mechanical properties of early-age fly ash concrete (FAC) have been studied, limit literatures on the cracking potential of FA HPC under adiabatic condition at uniaxial constant restraint degree are available. In the present study, the influence of FA as partial replacement of cement on the temperature, autogenous shrinkage, restrained stress, tensile creep, and cracking potential of HPC was simultaneously investigated. Three groups of large prismatic specimens with different FA replacement ratio (0%, 20%, and 50%) were tested by Temperature Stress Test Machine under adiabatic condition at full restraint degree. Test results and corresponding analysis indicated that (1) the autogenous shrinkage, cracking stress, and restrained tensile stress rate of HPC decreased with the increase in FA replacement ratio; (2) the use of FA as partial replacement of cement increased the ratio of cracking stress to axial tensile strength and cracking age of HPC; (3) the specific tensile creep for mixtures FA20, and FA50 was 0.96, and 1.16 times that of mixture FA00; (4) the integrated criterion which was utilized to evaluate the cracking potential decreased with the increase in FA replacement ratio.