Effect of pulverized burnt clay waste as a partial replacement of cement on the fresh and mechanical properties of concrete

Abstract Cement production is a major contributor to global CO 2 emissions, with an estimated 4.4 billion metric tons produced worldwide in 2024. In pursuit of sustainable construction practices, this study explores the use of pulverized burnt clay waste (PBCW), a locally available material from Malete, Ilorin (Nigeria), as a supplementary cementitious material (SCM). The objective was to assess the viability of PBCW as a partial cement replacement in concrete, focusing on its mechanical performance and pozzolanic potential. PBCW was used to replace cement at 5%, 10%, 15%, and 20% by weight. The material was characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray fluorescence (XRF), revealing a high amorphous content and kaolinite-rich composition favorable for pozzolanic activity. Concrete mixes were prepared at a 1:2:4 ratio with a water-to-binder ratio of 0.5, and a total of 120 specimens were tested for compressive strength and split tensile strength at 7, 28, 56, and 90 days. Results showed that while strength slightly declined with increased PBCW content, the 5% replacement achieved a 90-day compressive strength of 28.7 N/mm 2 compared to 30.2 N/mm 2 for the control. SEM analysis also revealed irregular PBCW particles enhancing packing density and interfacial bonding. The study demonstrates the potential of regionally sourced PBCW as a sustainable SCM for non-structural concrete, offering a low-cost strategy to reduce cement usage and carbon emissions, while promoting local waste valorization in line with circular economy principles.