The hydration process of alkali activated calcium aluminosilicate glasses

Alkali activation of slags provides a route to the production of special low energy, high strength and durable binders. The best way to examine the influence of chemical composition of slags on the properties of hardened pastes is to focus on specially prepared synthetic glasses that have defined compositions. Four different calcium aluminosilicate glasses with Al₂O₃/SiO₂ ratios in the range 0·25 to 1·2 were studied. The alkali activation process of the glasses was observed by using the following methods: compressive strength tests, x-ray diffraction (XRD), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). It was confirmed that the Al₂O₃/SiO₂ ratio of the glass has a significant influence on the rate of hydration. The type of calcium aluminosilicate glass used and Al₂O₃/SiO₂ ratio in the binder has fundamental influence on the phase composition and microstructure of the hydrated pastes. In case of high Al₂O₃/SiO₂ ratio glasses there is a possibility of a very high compressive strength being obtained in very short times. Use of alkali activation allowed binders to be made with compressive strengths above 100 MPa after one day of hydration.