Adding pozzolanic materials with high Sio2 oxide that react with Ca(OH) 2 of hydration process to form C-S-H as additional gel and consuming Ca(OH) 2 prevent its harmful reactions with sulfate
Basically for increasing the sulfate resistance, we have to reduce the chances of forming sulfate salt, or in another way, in Type-1 cement, we have to reduce C3A. By adding fly ash generally, the amount of C3A in type-1 cement reduces hence sulfate resistance increases. In general reducing calcium, potassium, and magnesium content in concrete increases the sulfate resistance of concrete