Microstructure and Mechanical Properties of Slag Activated with Sodium Silicate

The study focuses on developing a detailed understanding of microstructure and mechanical behaviour of alkali-activated slag with sodium silicate. The slag used in this study was provided by Ecocem (Netherlands) and consists of 38.8 % CaO, 36.3 % SiO$_2$, 12.8 % Al$_2$O$_3$ and 8.0 % MgO. It was activated with two sodium silicate solutions. The two mixes were studied on a paste level. They have the same water/slag ratio w/s = 0.4 kg/kg and the same sodium content n = 5.0 g Na$_2$O / 100 g slag. Two silicate ratios were investigated: Ms = 0.5 and Ms = 2.2 moles of SiO$_2$ / moles of Na$_2$O. Early-age mechanisms and reaction products of the activation of the slag were analysed with isothermal calorimetry, SEM images and chemical characterization. In addition, compressive and flexural strength were determined. Despite different reaction steps in comparison to ordinary Portland cement, the obtained mechanical properties seem to be sufficient for structural application.