Which constituent in cement is to be kept minimum to avoid a sulfate attack?
Tricalcium aluminate (C3A): Tricalcium aluminate is the compound of cement in which hydration reaction takes place first, thus its contribution in the development of strength is highest in the first week of concrete, cement, and mortar. It emits large quality of heat and attributes to rapid gain in strength.
C3A is fragile to the sulfate attack. Cement should contain less than 5% C3A. A high concentration of Tricalcium aluminate is accountable for low resistance to sulfate and escalation in shrinkage in drying mass. Therefore less percentage of Tricalcium aluminate in cement will result in low heat of hydration, good sulfate resistance, and good strength gain. Tricalcium aluminate liberates heat during the early stages of hydration and reacts with the gypsum when mixed with water to produce ettringite and heat.
Tricalcium aluminate + gypsum + water — ettringite + heat