The reactivity of aluminosilicate glasses in cements – effects of Ca content on dissolution characteristics and surface precipitation

The partial replacement of Portland cement (PC) by glassy aluminosilicates in cementitious binders has been common practice for decades, offering concretes with increased durability and long-term strength compared with PC concretes. However, these concretes typically display a much lower rate of strength development and this limits practical levels of cement replacement. The factors contributing to strength development in concrete are complex but among them is the reactivity of the supplementary cementitious material, which has been associated with glass content, and composition with respect to the ratio of network modifiers to network formers, etc. This paper revisits the assessment of reactivity using a fundamental dissolution approach and highlights a rapid migration of soluble constituents, specifically Ca, to the surface on contact with an activating solution. The conditions which affect the composition of Ca-bearing precipitates and their role in on-going hydration are discussed.