ABSTRACT
As described previously, there are four key minerals in Portland cement, namely, C3S, βC2S, C3A, and C4AF, as well as gypsum CaSO4·2H2O. The C3A, C4AF, and C3S hydrate rapidly, but βC2S only slowly. C3A hydrates rapidly to form C3AH6 but in the presence of Ca(OH)2 forms 4CaO·Al2O3 ·19H2O, and if there is SiO2 available, then a substituted hydrogarnet 3CaO·Al2O3·xSiO2(6-2x)H2O can be formed slowly in the nal stage. C3A in presence of CaSO4·2H2O rapidly forms tricalcium sulphoaluminate hydrate (ettringite, 3CaO·Al2O3·3CaSO4·32H2O), which coats the surface of the cement grains, retarding the setting of the cement. When the gypsum is exhausted, the tricalcium aluminate may react with ettringite to form calcium sulphoaluminate hydrate of monosulphur type (3CaO·Al2O3·CaSO4·12H2O).
