Drying shrinkage of alkali-activated slag and fly ash concrete; A comparative study with ordinary Portland cement concrete

This study investigates the drying shrinkage and the shrinkage-induced stress of alkali-activated blast furnace slag and fly ash concrete (AC) in comparison with ordinary Portland cement concrete (OC). For samples that were dried from 1 day after casting, the drying shrinkage of AC was much higher than that of OC. For samples that were stored in a sealed condition for 28 days before drying, the subsequent drying shrinkage amplitudes of AC and OC were comparable. In both conditions, the stresses generated in AC were higher than in OC at the beginning, but experienced great reductions after certain ages, reaching less than one-fourth of the stresses in OC in the end. The stresses decrease, i.e. relaxation in AC was attributed to the pronounced non-elastic deformability of CASH gels. The non-elastic deformability of AC reduced the risk of thorough cracking, but maybe at the expense of the development of local microcracks. It is recommended to protect AC from drying at an early age to avoid micro and macrocracking.