Chemical reactions of glass cullet used as a cement component

The recovery of container glass (cullet) for recycling can often lead to the generation of surplus quantities of the material. The pozzolanicity of finely ground glass cullet (GGC) can be exploited by using it as a cement component in concrete. This paper examines two of the chemical reactions most significant to this mode of use, namely, the pozzolanic reaction and the potentially deleterious alkali-silica reaction. Although the presence of GGC has little effect on the reactions of portland cement, larger quantities of calcium silicate hydrate gel are formed, which are thought to contain quantities of sodium. Blends containing the largest quantities of calcium silicate hydrate gel also displayed the highest strengths. Expansion due to alkali-silica reaction of mortars containing GGC is reduced relative to controls. This can be understood when it is considered that the pozzolanic and alkali-silica reactions are chemically identical. The fine cullet particles have a high surface area and, hence, favor the rapid pozzolanic rate of reaction over the slower alkali-silica reaction rate.