Long-term thaumasite sulfate attack on mortar containing coral sand filler and SCMs exposed to sodium sulfate solution

The use of coral sand filler and supplementary cementitious materials partially replacing Portland cement facilitates the utilization of coral debris waste in oceanic construction as well as CO2 emission. The effect on thaumasite sulfate attack by coral sand powder is compared with lime-stone powder since thaumasite sulfate attack has been studied extensively in limestone Portland cement. This work was conducted on the evaluation of resistance to sodium sulfate solution by measuring changes in visual appearance, compressive strength and length, as well as XRD, FTIR, SEM and MIP analyses. The results show that thaumasite sulfate attack would occur in mortars with coral sand powder and SCMs probably without noticeable expansion and a reduction in compressive strength of the specimens' core. The mortar incorporating coral sand powder and silica fume leads to greater sulfate resistance than coral sand powder-Fly ash and Coral sand powder-Slag mortars, and the coral sand powder performs severer deterioration compared with the limestone powder by simultaneously used with fly ash or slag. More deteriorated crystal morphologies of portlandite and C-S-H were exhibited in Coral sand powder-SCMs mortars under sulfate attack at low temperatures. No obvious deterioration occurred in blended mortars under corrosion at 20 degrees C for up to 18 months in this work.