The influence of Al2O3, CaO, MgO and TiO2 content on the early-age reactivity of GGBS in blended cements, alkali-activated materials and supersulfated cements

GGBS composition and the choice of the activation systems have a large impact on the reactivity of GGBS-based binders. Here, the reactivity of 16 artificially -modified GGBSs was investigated in blended cements, alkaliactivated binders and supersulfated cements, using isothermal calorimetry for hydration times between 24 h and 120 h. Lower glass network polymerization by addition of CaO or MgO increased the reactivity at all ages and in all activation systems. Increased Al2O3 content mainly resulted in higher early reactivity. This effect was more pronounced in blended and supersulfated cements. TiO2 addition decreased GGBS reactivity in all activation systems but the negative effect was reduced at high Al2O3 contents, especially at later ages in supersulfated cements. In alkali -activation, the hydration was delayed by several hours for some compositions. In summary, the results suggest that it is possible to increase the reactivity of GGBS by choosing an activation system optimized for a given GGBS composition.