Cracking potential of alkali-activated slag and fly ash concrete subjected to restrained autogenous shrinkage

This study aims to investigate the cracking potential of alkali-activated slag (AAS) and alkali-activated slag-fly ash (AASF) concrete subjected to restrained autogenous shrinkage. Temperature Stress Testing Machine (TSTM) is utilized, for the first time, to monitor the stress evolution and to measure the cracking time of alkali-activated concrete (AAC) under restraint condition. The stresses in AAS and AASF concrete are calculated based on the experimental results while taking into consideration the influence brought by creep and relaxation. It is found that AAS and AASF concrete showed lower autogenous shrinkage-induced stress and later cracking compared to ordinary Portland cement (OPC) based concrete with similar compressive strength, despite the higher autogenous shrinkage of AAS and AASF concrete. The low autogenous shrinkage-induced stress in the AAC is mainly attributed to the pronounced stress relaxation. A good prediction of the stress evolution in AAC is obtained by taking into account the elastic part of the autogenous shrinkage and the stress relaxation. In contrast, calculations ignoring the creep and relaxation would lead to a significant overestimation of the stress in AAC.