Recycling Agricultural Waste for Green Concrete: The Case of Palm Oil Ash

Abstract

Aim of the Study: This study explores the potential of palm oil ash  (POA), an agricultural by-product rich in amorphous silica and alumina, as a partial cement replacement in concrete. The aim is to assess POA’s effectiveness in reducing cement consumption and environmental impact while maintaining adequate mechanical performance and durability.

Methodology: Concrete mixes were prepared using a 1:2:4 ratio, with 30% of cement replaced by POA. The POA was sourced from a palm oil mill, air-dried, sieved, and finely ground before use. Mechanical and durability tests, including compressive strength at 7, 14, and 28 days, a slump test for workability, and water absorption assessment, were conducted to evaluate performance.

Findings: Results indicated that concrete containing POA developed lower early-age compressive strength compared to the control mix (5.4 MPa at 7 days, 10.2 MPa at 14 days). However, at 28 days, POA-based concrete (17.5 MPa) surpassed the conventional mix (15 MPa), confirming its pozzolanic contribution to long-term strength. Workability decreased slightly due to POA’s high water absorption, with slump values reducing from 38 mm (control) to 36 mm (POA mix). Water absorption increased progressively during curing, indicating higher porosity, but remained within acceptable limits for structural use.

Conclusion: The study demonstrates that POA can effectively substitute up to 30% of cement in concrete, contributing to sustainable construction practices. Although early-age strength and workability are reduced, extended curing enhances compressive strength and durability. POA utilisation offers a promising pathway for recycling agricultural waste into green building materials.