Industrial-Scale Production of Low-Clinker LC3 Cements Using Low-Grade Clays

Clays and limestone are widely available materials used as supplementary cementitious material (SCM’s) and filler, respectively, to reduce the clinker content in cement. The pozzolanic reactivity of clays is known to correlate directly with their kaolinite content; however, sourcing kaolinite-rich clays can be challenging in certain regions, despite the general abundance of clays deposits. This study investigates the feasibility of utilising low-kaolinite clays, in combination with limestone, for the production of low-clinker cements. The clays were calcined at 850 °C and 950 °C and subsequent characterisation was carried out via X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray fluorescence (XRF) to determine their mineralogical and chemical composition. Clay reactivity was assessed through the R³ test using isothermal calorimetry; in addition, the reactive silica content of selected clays was quantified. Finally, low-clinker cements incorporating calcined clay and limestone were produced at industrial scale. Their mechanical strength, setting times, and workability were evaluated. The results indicate that clays containing only 45% kaolinite can significantly contribute to the development of low-clinker cements, providing a viable alternative in regions where high-kaolinite clays are not readily available. Moreover, this study presents a practical approach to clay characterisation for industrial cement applications, which may serve as a useful reference for cement manufacturers interested in incorporating calcined clays into new products.