Early hydration properties and microstructure evolutions of MgO-activated slag materials at different curing temperatures

This study reports on the early hydration properties and microstructure evolutions of MgO-activated slag at five curing temperatures (20 degrees C, 40 degrees C, 50 degrees C, 60 degrees C, and 80 degrees C) and three MgO types (S-MgO, M - MgO, and RMgO). The results indicated that high-temperature curing substantially increased the compressive strength of the specimens. Particularly, the highest strength was obtained at 40 degrees C and 60 degrees C for the S-MgO and M-MgO-activated slag specimens, respectively, and the high curing temperature for the R-MgO-activated slag specimen was 40 degrees C. We focused on the relationship between the mechanical properties, pore structure characteristics, and hydration products. The combination of calcium-silicate-hydrate (C-S-H) gel and Al increased under hightemperature curing conditions. XRD, FT-IR, TG-DTG, and 27Al MAS-NMR results showed a high Al content in the formation of calcium silicate hydrate with Al in its structure (C-A-S-H gel) for the R-MgO-activated slag pastes under high-temperature curing; however, the microstructure was loose owing to the formation of excessive brucite. For the S-MgO-activated slag specimen, the Ca/Si ratio was high, with more Mg2+ penetrating the C-S-H gel interlayer, forming more hydrotalcite-like phases and increasing the chain length of the C-S-H gel. The microstructure showed good compatibility of the hydration products interweaving to form dense microstructures.