Roles of fly ash, granulated blast-furnace slag, and silica fume in long-term resistance to external sulfate attacks at atmospheric temperature

This paper presented the role of supplementary cementitious materials (SCMs), including fly ash (FA), granulated blast-furnace slag (GBFS), and silica fume (SF) in long-term resistance to external sulfate attack (ESA) of cement mortar at atmospheric temperature. The cement mortars were immersed in 5% sodium sulfate solution at a temperature of 20 °C for 36 months. The results showed that the amount of deterioration products and pore characteristics were the two critical factors affecting sulfate resistance. The pore characteristics played more integral roles in influencing the long-term sulfate resistance than the amount of deterioration products. FA maintained excellent sulfate resistance after exposure to ESA for 36 months. SF exhibited higher sulfate resistance than FA because it primarily supported total porosity and percentage of harmless pore, rather than the portlandite removal by the pozzolanic reaction. On the contrary, the addition of GBFS accelerated the deterioration process and exhibited the worst sulfate resistance because the total porosity and percentage of harmless pore occurred massive changes.