Soundness of mortars containing ground palm oil fuel ash from different sources and finenesses

In this study, palm oil fuel ash (POFA) from three distinct locations in Thailand was investigated to determine its suitability as a cement replacement in mortar. POFA was ground to varying fineness levels retained on a sieve no. 325 at 5 ± 1%, 15 ± 1%, 25 ± 1%, and 35 ± 1% by weight. Mortars were prepared by replacing 20% of Portland cement with each type of ground POFA. Compressive strength, drying shrinkage and expansion were evaluated, the latter by autoclave test. After 28 days, most POFA mortars achieved compressive strength above 75% of the control mortar, with normalised strengths ranging from 73.0% to 90.9%, and at 91 days the JS05 mixture (20% cement replaced by ground POFA from the JS source with 5 ± 1% retained on a sieve no. 325) developed slightly higher strength than the control mortar. The difference in drying shrinkage from the control mortar at 28 days remained below 0.03%, while autoclave expansion did not exceed 0.10%, well below the 0.8% limit for pozzolanic admixtures. These results indicate that ground POFA, particularly at optimised fineness levels, can enhance strength while reducing shrinkage, confirming its practical potential as a sustainable supplementary cementitious material for durable and long-lasting mortar applications, contributing to UN SDGs 9, 12 and 13.