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.

Automated summary

This study investigates the effects of different curing temperatures and MgO types on the early hydration properties and microstructure of MgO-activated slag. The results show that high-temperature curing significantly improves the compressive strength of the specimens, with different MgO types having different optimal curing temperatures. Furthermore, the study reveals a relationship between the mechanical properties, pore structure characteristics, and hydration products.