Dual-phase Optimization of Local Kaolinite Clay via Thermal Activation for Enhanced Metakaolinite Development

Variety in sustainable construction material resources is a requirement, alongside the environmental need to reduce CO2 emissions. The main objective of this paper is to determine the optimal calcination parameters of kaolin clay collected from two cities in Oman. The calcination temperatures and durations were assessed in two rounds using two strategies: the compressive strength assessment of mortar incorporating a 10 wt.% replacement of Portland limestone cement and X-Ray Diffraction (XRD) analysis. The calcination temperatures for HMR-4 clay (Hamara city) were 480°C, 520°C, 600°C, and 680°C, while for IZK-1 clay (Izki city), they were 520°C, 600°C, 720°C, and 760°C, all for a constant duration of 3 hours. Both methods demonstrated consistency in results. The optimal calcination temperatures for HMR-4 and IZK-1 were found to be 600°C and 760°C, respectively. In the second round, the calcination durations were 1 hour, 1.5 hours, 2 hours, and 3 hours. The optimal calcination duration was found to be 2 hours; however, the XRD results for IZK-1 show identical results, indicating that 1 hour is sufficient for the dehydroxylation of the kaolinite mineral, unlike the compression test assessment. Therefore, the calcination parameters depend on the mineralogical and chemical composition of the material.