A review of processing structure and property relationships in limestone calcined clay cement systems with implications for locally sourced clays

Abstract

The cement industry contributes seven to eight% of global CO2 emissions, with approximately 60% arising irreducibly from the decarbonation of limestone during clinker formation. Limestone Calcined Clay Cement (LC3) addresses this through synergistic reactions between calcined clay, fine limestone, and clinker hydration products, producing carboaluminate hydrates that refine pore structure and improve durability at substantially reduced clinker content. However, LC3 performance is not transferable between clay sources; it is controlled by the specific mineralogy of the clay used, its degree of calcination, and the balance between reactive alumina and carbonate availability. This review synthesises literature published primarily between 2015 and 2025, organising the evidence within a processing–structure–property framework that connects raw material selection and calcination conditions through hydration chemistry and microstructural evolution to mechanical and durability performance. Special attention is given to mineralogically variable and low-grade clays, with locally sourced Ghanaian clay resources, including tropical kaolinitic deposits and bauxite-associated lithomargic clays, examined as a case study in the challenges facing LC3 implementation in regions lacking industrial by-product supplementary cementitious materials. The review establishes that clay mineralogy governs calcination windows and alumina availability; that carboaluminate phase stability underpins both mechanical and durability performance; that pore refinement through pozzolanic reaction improves chloride and sulphate resistance substantially relative to ordinary Portland cement (OPC), with strength retention improvements of 2–10% points under accelerated exposure; but that reduced portlandite content creates measurable carbonation vulnerability that represents the principal durability trade-off in LC3 systems. Research gaps are identified in processing–structure maps for mixed and low-grade clays, phase-level durability modelling, and composition-informed mix design frameworks. The findings support the design of LC3 as an engineered composite rather than a prescriptive replacement, and provide a basis for region-specific LC3 formulation across clay-rich, SCM-poor regions.