Investigation of influence factors and surface treatment on palm oil boiler ash (POBA) based geopolymer artificial aggregate: Impregnation vs. coating method

Producing man-made aggregates from industrial waste or biomass is feasible. Solid waste from the palm oil industry is a significant environmental problem requiring both immediate and long-term solutions. This study investigated the effect of influence factors of palm oil boiler ash (POBA)-based geopolymer aggregate based on its physico-mechanical, thermal, and characterization properties. The cold-bonding method was chosen due to its lower energy consumption. All POBA-based geopolymer aggregates had specific gravities below 2.0, classifying them as lightweight aggregates. Some ratios provide aggregate impact values (AIV) that are less than 30% and are characterised as strong aggregates. The overall thermal conductivity obtained from the POBA-based geopolymer is 0.161–0.243 W/m.K. The optimum ratio of POBA-based geopolymer aggregate microstructure had a denser and more complex structure. The high water absorption of the POBA-based geopolymer aggregate necessitated the development of additional surface treatment techniques, including vacuum impregnation and coating. The vacuum impregnation process with geopolymer enhanced aggregate characteristics. Microstructure analysis indicated that geopolymer had filled the voids and strengthen the matrix, as proven through Micro-XRF analysis. The properties of concrete made with treated POBA-based geopolymer aggregate can be used as a structural application.