Evaluating the mechanical performance of Kukui seed shells as coarse aggregates in light weight aggregate concrete

Abstract

Uganda’s population growth, currently at 3.2%, has increased the demand for residential, commercial, and industrial buildings. Concrete constitutes nearly 60% of construction materials on building sites, and aggregates contribute 70–85% of its total weight. This places pressure on existing natural aggregate sources, creating the need for sustainable alternatives. Lightweight aggregates offer a potential solution, yet kukui seed shells (an organic and waste-derived option) have never been studied in the Ugandan context, despite their possible contribution to sustainable construction. This study adopted a combined experimental and numerical methodological framework to evaluate the suitability of kukui seed shells as lightweight aggregates. Mechanical characterisation of the shells was followed by an experimental program in which normal aggregates were partially replaced with kukui seed shells at 25%, 50%, 75%, and 100% for both Half Seed Shells and Quarter Seed Shells. The resulting concrete mixes were assessed through mechanical and water absorption, Fire resistance, and Thermal conductivity performance tests, while serviceability behaviour was analysed using ANSYS finite element simulations. The shells demonstrated satisfactory Aggregate Impact Value (AIV), Aggregate Crushing Value (ACV), Los Angeles Abrasion (LAA), and soundness performance. Increasing the replacement percentage led to reductions in density, compressive strength, flexural strength, splitting tensile strength, and thermal conductivity. Quarter Seed Shell mixes generally outperformed Half Seed Shell mixes. Based on overall performance, a 50% replacement using Quarter Seed Shells is recommended, yielding a compressive strength of 25.1 MPa, thermal conductivity of 1.6 W/mK, and reduced density of 2,112 kg/m³, making it a viable lightweight concrete option for sustainable construction in Uganda.