Abstract: The effects of six slag dosages of 0%, 10%, 20%, 30%, 40% and 50% (mass fraction, the same below) on the shrinkage of fly ash-based geopolymer (FAGP) concrete during thermal curing process were studied with digital image correlation (DIC) method. The compressive strength of concrete and paste after thermal curing were tested, and the microscopic mechanism was analyzed by combining simultaneous thermal analysis (TG-DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that with the increase of slag content, the total shrinkage and shrinkage rate of FAGP first decrease and then increase, the compressive strength increases first and then decreases, the hydration degree increases, and the number of microcracks increases. When the slag content is 40%, FAGP concrete has the smallest shrinkage and the highest compressive strength. When the slag content is low, the hydration degree of the geopolymer is small, and there are fewer microcracks. At this time, the main reason for the shrinkage of the geopolymer is the lower elastic modulus at the beginning of thermal curing. When the slag content is high, the hydration degree of the geopolymer is high, and there are many microcracks. At this time, the shrinkage deformation of the geopolymer is mainly caused by a large degree of chemical reaction.

Key words: digital image correlation method, slag, fly ash-based geopolymer, thermal curing, deformation, compressive strength