Lattice defects and the effect of Melment on the hydration of alite

Abstract

The hydration of alite has been studied in the presence of different concentrations of the superplasticizer Melment by using various experimental techniques. Heat of hydration and non-evaporable water content determinations show that Melment retards the hydration; pH measurements indicate that in presence of Melment, Ca²⁺ ion dissolution is reduced. Zeta potential measurements give definite proof that Melment molecules are adsorbed at alite surfaces and the retardation of hydration may be due to adsorption. Thermoelectric power measurements prove that the material is an n-type semiconductor, whereas electrical conductivity measurements of solid pellets of C₃S (C = CaO, S = SiO₂) show that the material is an intrinsic semiconductor above 746 K and an extrinsic semiconductor below 746 K. Extrinsic semiconductivity may be due to the presence of defects or impurities in the crystal lattice. The results also show that oxide ion vacancies are created in the crystal lattice and the reactivity of C₃S is related to the defects. Probably Melment molecules are adsorbed at the sites of defects and oxide ion vacancies and hence retard the hydration.