The effect of fineness, gypsum content and water – cement (w/c) ratio on the hydration of C3A systems have been quantitatively investigated using a combination of experimental techniques (isothermal calorimetry, TGA, XRD, 27Al MAS NMR) and numerical modelling. It is proposed that the retardation of C3A in the presence of calcium sulphates could be (or partially) due to the surface coverage of C3A from ettringite precipitation. After the depletion of gypsum, the main calorimetric hydration peak is analyzed using a dissolution mechanism. The numerical model captures the main hydration peak, including peak broadening effects, which increase with the gypsum content and decrease with the fineness. It is found that the increase in w/c ratio (from 0.5 to 1.0) enhances the overall degree of hydration of C3A by 7 days of hydration in systems with and without gypsum, which is attributed to the increase in free water with increasing w/c ratio.
