Properties of Belite-Rich Cement with Supplementary Cementitious Materials

Abstract

The article deals with the role of supplementary cementitious materials (SCMs) on the properties of laboratory belite-rich cements prepared from low-energy clinker doped with SO₃. The low lime saturation factor (LSF) clinker with belite as the main phase was synthesized at 1350 °C using industrial raw materials. Alite/belite ratio is opposite to that of ordinary Portland cement (OPC). ß-C₂S and M₁ alite are the main modifications in doped clinkers. Cements were prepared by grinding clinkers to 400 m²/kg fineness in a laboratory ball mill. Replacement of 10, 20 and 30 wt.% of calcined clay, ground limestone, blast-furnace slag, ground glass and 5, 10 and 15 wt.% of silica fume were tested. Along with clinker properties, early properties of cement pastes and mortars were studied by isothermal calorimetry. Strength development of mortars were monitored after 2, 7, 28 and 90 days. Heat flow development during early hydration is strongly affected by SCMs, as seen in the position and intensities of aluminate, silicate, second aluminate and ettringite to monosulfate (AFt-AFm) conversion peaks. Despite low alite content, the cements have decent early and good long-term strengths, even at higher replacement levels. Binary combinations of OPC with calcined clay, blast-furnace slag or ground grass gave the best results. The introduction of such cements would significantly decrease the CO₂ emissions and energy demand and partly save the primary sources of limestone.