Acceleration of cement blended with calcined clays

Abstract

Supplementary cementitious materials are needed to reduce the carbon impact of cementitious materials. In particular, calcined clay mixtures are a sustainable alternative which are abundantly available worldwide. Although binders containing calcined clays may exceed the reference cement in strength after 28 days, early strength development is too slow for many applications. In order to overcome this obstacle, microlimestone and C-S-H seeds were tested in different dosages as hydration accelerators and the most promising dosage was determined by calorimetry and mortar tests. The accelerators increased the amplitude of the maximum heat flow and shortened the time when Qmax occurred compared to the blended binder made with calcined clay. They also acted as a strength accelerator. The reactivity index slightly increased with the microlimestone and with C-S-H seeds it was on the level of the blended binder. These accelerators are promising for the precast concrete industry.