Role of early-age carbonation coupled with further hydration in high-temperature performance of cement blocks

This study investigated the effect of early-age carbonation coupled with subsequent standard curing (CS) on the properties of cement blocks before and after being subjected to different elevated temperatures. Mass loss, compressive strength, microhardness, backscattered electron microscopy, thermogravimetric analysis, and X-ray diffraction were employed to examine the mechanical properties development and microstructure variation of the blocks. The results showed that cement blocks with early carbonation and further hydration had a strength gain at 200 and 400 °C, but exhibited higher thermal stability at 600 °C compared to those only subjected to carbonation or standard curing. The micro-hardness and microstructure results revealed that the CaCO3 skeleton restricted the cracking by controlling the range of volume shrinkage of C-S-H gel. Meanwhile, the subsequently formed C-S-H can reinforce the CaCO3 skeleton. However, a 70% drop in strength occurred in the CS group after exposure to 800 °C because the carbonated layer was converted to a weakened layer as CaCO3 was decomposed into lime.