Influence of steam curing regimes on the properties of ultrafine POFA-based high-strength green concrete

Abstract This paper investigated the influence of steam curing regimes on the properties of high-strength green concrete (HSGC) containing varying quantities of ultra-fine palm oil fuel ash (U-POFA) from 0%, 20%, 40% and 60% from the mass of Portland cement. The HSGC specimens were steam cured at 50°C, 65°C, and 80°C for 16 hours in order to evaluate the effect of curing temperatures. Besides, the HSGC specimens were also cured at 80°C for 6, 11 and 16 hours in order to investigate the effect of curing period. The influence of different temperatures and periods of steam curing on the development of the compressive strength (CS) and microstructure of the HSGC was investigated at 1, 3, 7, 28, 90, 180 and 360 days. The results showed that replacing 20%, 40% and 60% of ordinary Portland cement (OPC) with U-POFA exhibited a decrease in the CS in early ages up to 7 days, whereas the long-term CS at 360 days improved by 5.4%, 10% and 9.2%, respectively in comparison to the control concrete mixture. It was also found that the application of steam curing regime at 80°C for 16 hours contributed towards increasing the strength of concrete by 193% at 1 day for HSGC containing 60% U-POFA when compared to normally cured specimen. The trends in CS development were complimented with microstructural analyses based on TGA, XRD and SEM/EDX. It was observed that steam curing has a significant influence on microstructures of matrix in early ages. However, it can be concluded that the partial replacement of U-POFA has positive impacts on the long-term properties of the HSGC at 360 days.