CaCl2-driven phase instability in low-carbon calcium sulfoaluminate binders

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This work studies the effect of CaCl 2 , at 5 wt.% and 20 wt.%, on the hydration of a commercial calcium sulfoaluminate clinker (KCSA) and cement (CSA). For this purpose, CSA and KCSA pastes were prepared with CaCl 2 substitution and hydrated for 1, 3, 28 and 90 days. The mechanical strength of the pastes and the hydration kinetics were assessed by compressive strength testing and isothermal conduction calorimetry, respectively. The results show that CaCl 2 content modifies hydration and strength development in different ways depending on the binder composition. With 5 wt.% CaCl 2 , hydration was delayed, early mechanical strength decreased, and the main phases formed were ettringite, Friedel’s salt, monosulfoaluminate and AH 3 . In contrast, 20 wt.% CaCl 2 accelerated hydration, but its effect strongly depended on the system. In KCSA, mechanical strength was maintained up to 90 days, whereas in CSA, severe degradation occurred from 28 days onwards and was associated with thaumasite formation.

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