Calcium sulfoaluminate and geopolymeric binders as alternatives to OPC

This work presents calcium sulfoaluminate (CSA) cement and geopolymeric binder (GEO) as environment-friendly alternatives to ordinary Portland cement (OPC). Mortars based on these binders were tested and compared at the same non-structural strength class (R2 = 15 MPa, according to EN 1504-3). Binder pastes were preliminarily prepared to study their hydration behaviour by means of differential thermal-thermogravimetric (DT-TG) and X-ray diffraction (XRD) analyses. Afterwards, the relative mortars were compared in terms of both fresh (workability) and hardened state properties (compressive strength, dynamic modulus of elasticity, adhesion to bricks, and water vapor permeability). Durability was also investigated in terms of capillary water absorption, drying and restrained shrinkage. Porosimetric analysis allowed to better correlate experimental results with microstructural features of the investigated mixtures. Results showed that GEO-based mortar exhibits the lowest modulus of elasticity, causing the lowest restrained shrinkage and the highest free drying shrinkage. Moreover, its highest porosity determines both the highest capillary water absorption and permeability to water vapor. On the contrary, the CSA-based mortar displays the lowest drying shrinkage, the greatest modulus of elasticity, and the lowest porosity which ensures the lowest capillary water absorption.