Titanium in GGBS-like calcium-magnesium-aluminosilicate glasses: Its role in the glass network, dissolution at alkaline pH and surface layer formation

Small TiO2 contents in the slag-glass significantly reduce their cementitious reactivity. We investigated the role of Ti in the glass network and its influence on slag-glass dissolution. XANES and EPR analysis showed that 67% of Ti was present as Ti(IV) with about 70% in Ti-[5] and 30% in Ti-[4] coordination, and 33% as Ti(III). The presence of Ti had only a minor impact on initial dissolution rates at pH 11 (R asymptotic to 10(-6) molglass.s(-1).m(-2)). During dissolution, Ti accumulated in an amorphous layer at the glass-surface. Ti-coordination in this layer was 50% Ti-[5] and 50% Ti-[6]. At pH 11, the layer was mainly composed of TiO2 (66 wt%), but intermixed with a hydrotalcite-like phase at pH 13. The loss of cementitious reactivity in the presence of Ti appears to be not only due to stabilization of the glass structure but also to the formation of a Ti-rich surface-layer, that may become passivating.