Reducing Clinker-Related Carbon Emissions with Calcite and Calcined Clay: The Chemistry, Performance, and Practical Potential of LC3 Cement

Abstract

Clinker production is responsible for the majority of greenhouse gas emissions associated with ordinary Portland cement, driven by both high-temperature kiln energy consumption and the chemical decarbonization of limestone. Limestone calcined clay cement (LC3) presents a highly effective and scalable near-term solution to mitigate these environmental impacts by substantially reducing clinker content. This review examines the fundamental thermochemical, hydration, and microstructural mechanisms that govern LC3 systems, emphasizing that their exceptional performance extends far beyond simple physical dilution. The synergistic interaction between reactive silica and alumina from calcined clay, particle packing and nucleation from fine calcite, and sulfate regulation creates a dense, refined binder matrix. These components react to form secondary calcium-silicate-hydrate (C-(A)-S-H) gels, stable carboaluminate phases (hemicarboaluminate and monocarboaluminate), and ettringite, which compensate for the reduced clinker fraction. Furthermore, this paper analyzes key practical considerations, including optimal mixture design, sulfate balance, mechanical strength development, chloride and carbonation durability, and life-cycle carbon emissions. Evidence from recent literature indicates that optimized LC3 formulations can decrease clinker content to approximately 50% and lower cement-related carbon dioxide emissions by 30% to 40%. However, realizing these benefits requires rigorous local characterization of raw materials, precise calcination control, and performance-based standard validation under specific exposure conditions.