Engineering and transport properties of high-strength green concrete containing high volume of ultrafine palm oil fuel ash

The engineering and transport properties of high-strength green concrete (HSGC) containing up to 60% of ultrafine palm oil fuel ash (POFA) have been studied. POFA obtained from a palm-oil industry was treated via heat treatment to remove excess carbon and ground to a median particle size of about 2 μm. The ultrafine POFA obtained was then utilized in the production of HSGCs with POFA replacement levels of 0%, 20%, 40% and 60% by mass of ordinary Portland cement. The results show that the treatment processes undertaken results in a highly efficient pozzolan. For fresh concrete, the inclusion of the ultrafine POFA tends to increase the workability of the HSGCs, and retards the setting times in particular at higher POFA contents. In the case of compressive strength, the inclusion of the ultrafine POFA reduces early age strength of the HSGCs at 1, 3 and 7 days, but enhances the strength at 28 days for all HSGCs containing POFA, where strength exceeding 95 MPa was achieved for all the POFA–HSGCs. Whereas the transport properties as assessed via porosity, initial surface absorption, rapid chloride permeability, gas permeability and water permeability tests are significantly improved with the inclusion of the ultrafine POFA, with the HSGC containing 60% POFA exhibiting the greatest improvement at 28 days. Thus, the overall results show that the ultrafine POFA possesses significant potential as an efficient pozzolanic mineral admixture for the production of HSGC with promisingly superior engineering and transport properties.