Supersulfated cements based on pumice with quicklime, anhydrite and hemihydrate: Characterization and environmental impact

Abstract

This investigation reports on the mechanisms of reaction, microstructure, hydration products, compressive strength and environmental impact of supersulfated cements based on pumice (SSC-PM), using 10–20%wt of quicklime (CaO) as the alkaline activator and 5–15%wt of sulfatic activators of anhydrite or hemihydrate; three different initial curing temperature (ICT) regimes were used for 24 h, of 20, 40 and 60 °C. The main hydration products were C–S–H and ettringite; minor phases included monosulfate, gypsum, portlandite and calcite. The ICT of 60 °C accelerated the reactions of formation of ettringite and C–S–H, improving the early strength, whereas; the higher contents CaO (20%) and An or HH (15%) slowed the hydration reactions and consequently the early strength development. The activation with CaO-Anhydrite densified the microstructure leading to 360-day strengths of up to 34 MPa. These SSC-PM represent a good sustainable alternative as these showed emissions of 159–281 kgCO2-eq/t, which are at least 67% lower than the manufacture of clinker of Portland cement.