Articles

This study investigates the effects of palm oil fuel ash (POFA) incorporation and water-to-binder ratio on the chemical shrinkage (CS) and autogenous shrinkage (AS) of cement pastes. Cement is partially replaced with ground POFA at levels of 0, 10, 20 and 30%, while the water-to-binder ratio (w/b) varies between 0.3, 0.4 and 0.5. Both shrinkage mechanisms were measured during the first 24 h using hydrostatic weighing based on Archimedes' principle. CS was determined on paste specimens immersed in water in open crystallisation dishes, whereas AS was measured volumetrically on specimens sealed in latex membranes. The results show that the w/b ratio has only a minor influence on 24-h CS, which decreases by approximately 8% on average as the ratio increases from 0.3 to 0.5. In contrast, AS is strongly influenced by the w/b ratio, with the 24-h value for the control paste decreasing by approximately 23%, from 35.8 × 10⁻³ to 27.5 × 10⁻³ cm³/g, over the same range. A 10% POFA replacement produces the lowest CS at all three w/b ratios, with reductions of 8.1–10.7% relative to the corresponding control pastes. However, replacement levels of 20 and 30% result in CS values comparable to or up to 7.5% higher than those of the control, together with a faster increase during the 15–24 h interval. The influence of POFA on AS remains comparatively small, with variations ranging from −8.6% to +3.4%. The 24-h AS/CS ratio exceeds unity in several mixtures, particularly at lower w/b ratios, pointing to limitations in the comparability of the two measurement procedures. Overall, the findings indicate that 10% POFA reduces chemical shrinkage without substantially increasing autogenous shrinkage during the first 24 h.