RESPONSE SURFACE MODELLING AND COST-EFFECTIVENESS EVALUATION OF RAW AND TREATED PALM KERNEL SHELL FOR UNBOUND PAVEMENT MATERIALS

Abstract

Palm kernel shell (PKS), an abundant agricultural by-product, offers potential as a lightweight granular pavement material for construction. However, untreated PKS may exhibit variable strength, compaction, durability, and bearing characteristics, while chemical treatment increases production cost. This study applies response surface modelling and cost-effectiveness evaluation to raw and treated PKS mixtures to identify combinations best suited for unbound pavement material applications. PKS was collected, washed, dried, sieved, and prepared as raw, lime-coated, cement-coated, and cement–lime-coated material, with granite as control. Twenty-five mixtures were evaluated using compaction, unconfined compressive strength (UCS), triaxial shear strength, abrasion, unsoaked and soaked California Bearing Ratio (CBR) tests, and the results were modelled using response surface methodology (RSM) to identify favourable combinations. Processing costs were computed and compared with engineering performance to establish cost-effectiveness. Compaction produced maximum dry densities of 437.20–1800.20 kg/m³ and optimum moisture contents of 15.40–45.50%. UCS ranged from 362.79 to 615.60 kN/m², while cohesion and friction angle reached 38.00 kN/m² and 33°, respectively. Abrasion resistance ranged from 89.59% to 98.71%. Unsoaked and soaked CBR ranged from 38.46–76.20% and 42.83–82.47%, respectively. Response surfaces identified M2–M4 as favourable combinations, with unsoaked CBR above 70% and soaked CBR above 74%. Production cost ranged from N34,000 to N1,298,000 per tonne, demonstrating substantial variation between raw and treated mixtures. The study confirms that optimized treated PKS mixtures can provide suitable unbound pavement performance, with M2–M4 recommended for practical application, subject to field validation, lifecycle costing, and long-term durability assessment.