Synthesis, hydration properties and environmentally friendly features of calcium sulfoaluminate cements

Calcium sulfoaluminate (CSA) cements, due to low synthesis temperature and limestone requirement, reduced thermal input and CO2 generation, may contribute to a sustainable development which can be further enhanced using industrial wastes and byproducts in the manufacturing process. Clinkers with high conversion degrees towards 4CaOּ3Al2O3ּSO3 were obtained heating for two hours in a laboratory electric oven, at temperatures ranging from 1100° to 1350°C, raw mixes consisting of limestone (up to 40%), red mud (up to 16%), bauxite (up to 25%), fluidized bed combustion waste (up to 35%) and pulverized coal ash (up to 41%). Every CSA cement (clinker plus about 20% desulfogypsum) was paste hydrated and characterized by XRD, DTA-TGA and SEM. Moreover mercury porosimetry showed that pastes cured even at early ages have a bimodal pore size distribution with the region of smaller pores (threshold pore radius, 20-25 nanometers) largely prevailing on the other (threshold pore radius, 150-200 nanometers)