Valorisation of palm oil decanter cake through thermal activation for enhanced performance of one-part alkali-activated fly ash

초록

This study examines the thermal activation of palm oil decanter cake (PODC) and its suitability as a supplementary precursor in fly ash (FA) based one-part alkali-activated materials (AAMs). PODC was calcined at 400, 600, and 800 degrees C to evaluate changes in physicochemical characteristics and their influence on the fresh, mechanical, and microstructural performance of FA-PODC AAMs. Thermal activation significantly modified PODC by removing organic matter, reducing particle size, increasing density, and generating reactive phases such as metakaolin, CaO, and Kfeldspar. These changes improved flowability and reduced setting times compared to raw PODC, which caused severe loss of workability due to high organic content and water demand. Compressive strength development showed notable long-term improvements for all calcined PODC mixtures, with the 800 degrees C sample achieving the highest gains. The enhancement was attributed to the release of reactive Ca2+ and K+ species and the increased availability of aluminosilicate phases, which may promote the development of calcium-rich and aluminosilicatebased reaction products. UPV and water absorption results further indicated improved matrix compactness. Microstructural analyses, i.e., XRD, TG-DTG, and SEM-EDX, supported the active contribution of calcined PODC to the reaction process, while raw PODC remained largely unreactive and contributed minimally to matrix development. Overall, PODC calcined at 800 degrees C demonstrates strong potential as a sustainable, reactive additive for FA-based one-part AAMs. Its incorporation not only enhances mechanical performance and microstructural compactness but also provides an effective valorisation pathway for palm oil industry waste, supporting the development of lower-carbon and more resource-efficient construction materials.

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