Microstructure Change and Phases Evolution of Alkali-Activated Slag upon Exposing to the Heating-Cooling Process

This article reports a study on the performance of the alkali activated slag (AAS) mortars upon exposing to the elevated temperatures. Two cooling methods (i.e., cooling in air and water-spring) were adopted following the heating treatment. The mechanical properties, durability, microstructure and phase evolution of AAS and OPC after heating-cooling process were researched. For AAS specimens, the compressive strength loss was smaller, but the flexural strength loss was greater compared to that of OPC specimens after undergoing the heating-cooling process. AAS specimens exhibited higher carbonation depth, and lower penetrated chloride ion. AAS-W specimens shows a higher resistance to cracks formation than OPC-W. With the heating temperature increased, the capillary pore proportion of AAS specimens gradually increased above 80% at 800°0;C. However, high content of transition pores and capillary pores were found at 800°0;C in OPC specimens. The new substances were generated when the temperature was 800°0;C for AAS specimens.