Role of Zn in aluminosilicate glasses used as supplementary cementitious materials

The cement industry relies on the use of supplementary cementitious materials (SCM) to lower the related CO2 emission. SCM are often amorphous materials containing minor elements, which is why it is important to study the impact of these materials on cement reactivity. Two calcium aluminosilicate glass series as model substances of SCM were synthesized and investigated. In both series Ca was partially replaced by Zn, Sr and Mg in different ratios. Moreover, four cement blends made with CEM I 52.5 R and aqueous solutions of Mg(NO3)2·6H2O, Zn(NO3)2·6H2O and Sr(NO3)2 were investigated. Zn retards the reactivity of both glasses and cements system. This retardation effect is suggested to be related both to the formation of the calcium hydroxozincate hydrate, which affects the portlandite formation and, thus, the pH of the system, and to the formation of surface complexes which retards the dissolution and so the reactivity of the glasses.