A quantitative study of the C3A hydration

The effect of fineness, gypsum content and water - cement (w/c) ratio on the hydration of C(3)A systems have been quantitatively investigated using a combination of experimental techniques (isothermal calorimetry, TGA, XRD, Al-27 MAS NMR) and numerical modelling. It is proposed that the retardation of C(3)A in the presence of calcium sulphates could be (or partially) due to the surface coverage of C(3)A 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 C(3)A 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.