New insights into restrained stress and deformation mechanisms of concretes blended with calcium sulfoaluminate and MgO expansive additives using multi-scale techniques

The early-age cracking performance of expansive concrete relies heavily on the temperature, restraint and curing conditions. Empirical methods to use expansive additives are not always reliable in diverse engineering conditions. By using a novel approach with the self-developed temperature stress testing machine (TSTM), this study evaluates the early-age cracking sensitivity of concretes blended with Calcium Sulfoaluminate and MgO expansive additives under different engineering conditions. Their performances under wetting–drying cycles are also compared. To interpret the deformation mechanism in a microscopic scale, pore structures are characterized by mercury intrusion porosimetry and nitrogen adsorption/desorption tests. It is found that MgO concrete with proper reaction activity can offer more effective shrinkage-compensation effect than CSA concretes under high temperature or drying condition, due to its less demand for hydration water, delayed expansion and finer pore structure. The findings in this study offer us new insights in modelling and application of expansive concretes on site.