DETERMINATION OF THE POZZOLANIC PROPERTIES OF PEANUT SHELL ASH AS CEMENT REPLACEMENT IN CONCRETE IN NIGERIA

Abstract

The global imperative for sustainable construction materials, combined with Nigeria's acute agricultural waste management challenges, has driven interest in supplementary cementitious materials (SCMs) derived from agro-industrial by-products. This study systematically investigates the pozzolanic properties of peanut shell ash (PSA) and evaluates its performance as a partial cement replacement in concrete. Peanut shells sourced from Kano State, Nigeria, were calcined at 650°C for 2 hours, and the resulting ash was subjected to comprehensive physicochemical characterization, including X-ray fluorescence (XRF) analysis, Blaine fineness testing, specific gravity determination, and scanning electron microscopy (SEM). Concrete mixes were designed at water-to-binder ratios of 0.5, incorporating PSA at replacement levels of 0%, 5%, 10%, 15%, 20%, and 25% by weight of ordinary Portland cement (OPC). Specimens were evaluated for workability (slump test), compressive strength at 7, 14, 28, and 56 curing days, water absorption, porosity, and setting time in accordance with ASTM C618, BS EN 197-1, and ASTM C109 standards. XRF results revealed that the combined SiO₂ + Al₂O₃ + Fe₂O₃ content of PSA was 69.88%, marginally below the ASTM C618 Class N minimum threshold of 70%, indicating near-pozzolanic classification. The pozzolanic activity index (PAI) at 28 days exceeded 100% at the 10% replacement level (101.1%), confirming significant pozzolanic reactivity. Compressive strength at 28 days was maximized at the 10% replacement level (27.9 MPa), marginally exceeding the control mix (27.6 MPa). Durability indicators — water absorption and porosity — were optimized at the 15% replacement level. Workability declined progressively with increasing PSA content due to the high surface area of ash particles. A two-way ANOVA confirmed that PSA replacement level and curing age are both statistically significant determinants of compressive strength (p < 0.001). The study concludes that PSA at 10–15% replacement levels is a viable, sustainable, and cost-effective partial cement substitute for concrete production in Nigeria, contributing to circular economy objectives and reduced carbon emissions from the construction sector.