Question: what is the average composition of portland cement?
Answer: Its typical compound composition is: 38% (C3S), 43% (C2S), 4% (C3A), 9% (C4AF), 1.9% MgO, 1.8% (SO3), 0.9% ignition loss, and 0.8% free CaO. This cement has a very low (C3A) composition which accounts for its high sulfate resistance. The maximum content of (C3A) allowed is 5% for type V Portland cement.