Low-carbon cement, LC3, as a sustainable binder

Abstract

This article investigates the hydration behavior, mechanical performance, and microstructural development of Limestone Calcined Clay Cement (LC³) compared to ordinary Portland cement (CEM I). Contrary to reports suggesting accelerated setting, the LC³ mixtures exhibited prolonged setting times, likely influenced by the high fineness and sorption capacity of the calcined clay, as well as the increased water demand required for normal consistency. Mechanical testing revealed that CEM I achieved higher early strength at 7 days; however, by 28 days, LC³ 650 surpassed the reference cement in both compressive and flexural strength. This trend reflects the delayed yet progressive pozzolanic activity characteristic of metakaolin-based systems. X-ray diffraction (XRD) analyses identified the formation of hemicarbonate and monocarbonate phases in LC³, absent in the Portland cement reference, resulting from the interaction of calcium and alumina species in the presence of carbonates. Scanning electron microscopy (SEM) confirmed a finer, less compact microstructure in LC³, indicative of active pozzolanic reactions. Overall, LC³ demonstrates comparable or superior long-term mechanical performance to OPC, while offering significant environmental advantages through reduced clinker content and the formation of stable hydration products that enhance durability.