Alternative prime materials for developing new cements: Alkaline activation of alkali aluminosilicate glasses

This study explored the use of alkali aluminosilicate glass obtained by melting and quenching common clay, feldspar and fluxing oxides as a possible starting material for alkaline activation. The glass was synthesized at two different temperatures (1250 and 1400 °C), using Na2O (8 wt%) as a fluxing oxide. The effect of including small amounts of calcium in the starting mix (5.6 wt% of CaO) was likewise studied. The alkaline activation of such glasses yielded cements with high compressive strength (65 MPa after 20 h at 85 °C). The presence of calcium in the vitreous network favored the formation of a very compact cementitious matrix. TEM-EDX analyses showed that the gel forming in these systems was compositionally (and presumably structurally) non-uniform, with some local high-calcium, high Si/Al ratio (CASH-type gel) areas co-existing with low calcium and low Si/Al ratio clusters (NASH-type gel).