772. Alumina, silica, lime and iron oxide are the basic raw material for the manufacture of portland cement. The component of Portland cement which first hardens is September 6, 2025 by Admin A. 5CaO . 3 Al2O₃ B. 3CaO . Al2O₃ C. 3CaO . SiO₂ D. 2CaO . SiO₂ ✅ The correct answer is option A.