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

Abstract

High-performance concrete (HPC) has been used extensively due to its good workability, lasting durability and high strength. However, the low water/cement ratio in HPC generally induces rather high autogenous shrinkage, resulting in high early-age cracking potential. Fly ash (FA) is an effective mineral admixture used to strengthen early-age concrete performance and lower the cracking potential. Although the early mechanical properties of concrete containing FA have been studied, literature on the cracking potential of FA HPC under adiabatic conditions and constant uniaxial restraint is limited. The influence of FA as a partial replacement of cement on the temperature, autogenous shrinkage, restrained stress, tensile creep and cracking potential of HPC was simultaneously investigated in this study. Three groups of large prismatic specimens with different FA replacement ratios (0, 20 and 50%) were tested using a temperature–stress test machine under adiabatic conditions at full restraint. The test results indicated that: autogenous shrinkage, cracking stress and restrained tensile stress rate of the HPC decreased with an increase in FA content; the use of FA as partial replacement of cement increased the ratio of cracking stress to axial tensile strength and the cracking age of the HPC; the specific tensile creep of mixtures with 20% (FA20) and 50% (FA50) replacement with FA was 0·96 and 1·16 times that of the mixture with 0% replacement (FA00), respectively; the integrated criterion used to evaluate the cracking potential decreased with an increase in FA content.