Research on sulfate resistance of PC, SRPC and CSAC mortars incorporating coral waste filler

Coral waste filler partial replacing Portland cement facilitates the utilization of coral debris waste, the reduction of the economic cost of oceanic construction as well as the CO₂ emission. Thaumasite-related sulfate attack needs to be concerned because of rich calcium carbonate in form of aragonite in coral waste filler and the sulfate resources in the oceanic environment. The sulfate resistance of Portland cement (PC), sulfate resistant Portland cement (SRPC), and calcium sulfoaluminate cement (CSAC) incorporating coral sand powder (CSP) were studied under corrosion in 5 wt% NaSO₄ solution at 5 and 20 °C up to 540 days. The results show that CSAC-CSP specimens possess greater sulfate resistance than PC and SRPC specimens incorporating with CSP filler. Cracking was the main way for PC and SRPC specimens’ failure under sulfate attack at 20 °C. Exceeding 20 % of CSP filler replacing PC leads to server thaumasite-related sulfate attack exposure at 5 °C for 540 days. The formations of sulfate products including gypsum, ettringite, and thaumasite in PC-CSP and SRPC-CSP specimens were confirmed by XRD and FTIR tests. The ettringite-thaumasite cluster and deteriorated products were detected in PC and SRPC blended specimens. CSP filler in contrast with limestone powder (LSP) filler results in less sulfate resistance of blended specimens.