Effect of active MgO on the hydration kinetics characteristics and microstructures of alkali-activated fly ash-slag materials

The effects of active S-MgO contents, MgO types, Na2O concentrations, and alkali activator modulus on the hydration kinetics, compressive strength, hydration products, pore structure, and microstructure of alkaliactivated fly ash-slag (AAFS) were studied. The results showed that adding active S-MgO can reduce the total hydration heat of AAFS pastes, and the total hydration heat of samples incorporating 9% R-MgO increased significantly. Krstulovic-Dabic model was not completely suitable for the hydration reaction process of AAFS pastes. When the value of hydration degree alpha was small, the alpha value corresponding to the peak value of d alpha/dt can be used as the basis of evaluating the hydration kinetics of AAFS; When the value of hydration degree alpha was larger, the reaction process can be explained by the Krstulovic-Dabic model. The addition of active MgO reduced the amount of unreacted raw materials, and the volume of micropores, macropores, harmful pores and porosity increased. The addition of active MgO enriched the micromorphology of hydration products. The changes in hydration products, pore structure, and microstructure caused by the addition of MgO were the important reasons for the change in compressive strength.