Utilization of Algerian calcined clay in sustainable mortars considering thermal treatment and granulometry effects on mechanical properties.

This study investigates the potential of calcined Algerian clay as a supplementary cementitious material (SCM) for enhancing the sustainability of cement production by reducing the consumption of clinker and emissions of carbon dioxide (CO₂). The research novelty lies in the comprehensive evaluation of fineness effects, the statistical modelling of mechanical performance, and the assessment of the environmental impact. A case study of practical significance is also provided. Clay was thermally activated at 700 °C to achieve near-complete dihydroxylation, ground to fineness levels of 45 µm and 80 µm, and then incorporated into the cement at replacement ratios of 10-30% by weight of the cement. Compressive and flexural strengths were assessed at 2, 7, and 28 days, while thermal and structural modifications were analysed using thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR). The results demonstrated that at lower substitution levels (10-15%), the 80 µm fraction of clay enhanced early-age compressive strength (13.6 MPa at 2 days), whereas at higher replacements (20-30%), the 45 µm fraction exhibited superior long-term strength (36.85 MPa at 28 days), which was attributed to improved pozzolanic reactivity and matrix densification. Flexural strength increased by 7-20% for substitution rates up to 20%, in turn confirming the structural benefits of calcined clay. Life-cycle analysis indicated significant reductions in energy consumption, CO₂ emissions, and production costs, with the M30-45 and M30-80 mixtures achieving reductions of approximately 10.6%. The statistical modeling of compressive strength at 2 and 28 days demonstrated high predictive accuracy, with coefficients of determination (R