Hydration Reactions and Mechanical Strength Developments of Iron-Rich Sulfobelite Eco-cements

Belite calcium sulfoaluminate (BCSA) cements are low-CO<sub>2</sub> building materials. However, their hydration behavior and its effect on mechanical properties have still to be clarified. Here, we report a full multitechnique study of the hydration behavior up to 120 days of nonactivated and activated BCSA laboratory-prepared clinkers, with β- or α<sub>H</sub>-belite as main phase, respectively. The effects of the amount of gypsum added were also studied. The hydration and crystallization processes are reported and discussed in detail. Finally, shrinkage/expansion data are also given. The optimum amount of gypsum was close to 10 wt %. Our study has demonstrated that β-belite reacts at a higher pace than α′<sub>H</sub>-belite, irrespective of the gypsum content. The hydration mechanism of belite determines the development of the mechanical strengths. These are much higher for activated BCSA cement, ∼65 MPa at 120 days, against ∼20 MPa for nonactivated BCSA cement, with the latter having larger amounts of stratlingite.