Sustainable Production of Geopolymer Lightweight Concrete Incorporating Palm Oil Clinker and Fly Ash

Reducing CO₂ emissions from cement production is a critical challenge for sustainable construction. This study promotes waste valorization by converting industrial fly ash and agricultural palm oil clinker into high-performance lightweight geopolymer concrete. The proposed approach delivers structural efficiency while significantly lowering environmental impact. Mitigating and minimizing the environmental burden of concrete requires simultaneous substitution of virgin aggregates and Portland cement with low-impact alternatives. This study presents a two-stage experimental program to develop structural lightweight concrete that simultaneously replaces natural aggregates and Portland cement using palm oil clinker and fly ash. Trial 1 investigates cement-based POC lightweight concrete by replacing natural granite coarse aggregate with POC at 0–100% in 25% increments while controlling cement content and water–cement ratio; slump, density, water absorption, and compressive strength development are evaluated. Trial 2 advances to a cement-free system by combining 100% POC aggregate with a FA-based alkali-activated binder; the alkali-to-fly ash ratio is varied to identify optimum performance. Trial 1 shows that 100% POC replacement is required to meet structural LWC density criteria, while low replacement (≤25%) can improve strength and limit absorption. Trial 2 delivers an excellent green lightweight geopolymer concrete with peak 28-day strength at alkali/FA ≈ 0.50 and minimum absorption, highlighting strong potential for CO₂ reduction and circular construction. This research develops high-strength lightweight concrete, as defined by the American Concrete Institute, achieving an air-dry density below 1850 kg/m3 and a compressive strength exceeding 40 MPa.