Self consolidating high performance palm oil fuel ash and pulverised burnt clay blended concrete

Abstract

Self-consolidating high performance concrete (SCHPC) is an advanced class of concrete that can flow through congested reinforcement or intricate geometric configurations under its own weight without any compaction activity and it does not segregate. Research and development in the use of supplementary cementing materials (SCM) to produce SCHPC have continued to gain attention worldwide. This is as a result of the global quest to reduce carbon dioxide emission to the threshold that will be tolerated by the earth. Despite the successes achieved by replacing cement with supplementary cementing materials (SCM), a number of drawbacks were unavoidable. The inclusion of palm oil fuel ash (POFA) into the SCHPC mixes increases the water demand due to high surface area and also induces segregation at replacement levels above 20%. In contrast, the inclusion of pulverised burnt clay PBC in the mix reduces the water demand due to lower surface area and improves the rheological properties of SCHPC at a replacement level of up 37.5%. Although PBC improves the rheological properties of SCHPC, its contribution to strength development is less effective in comparison to POFA. This research, therefore, focuses on the impact of blended POFA and PBC on the fresh and hardened properties of SCHPC. Assessment of the microstructure, physical and chemical characteristics of the binders was carried out. Furthermore, a simple mix design approach and the evaluation of the fresh and hardened properties of the SCHPC systems were executed. Various techniques, including the use of X-ray diffraction, scanning electronic microscope, Particle size analysis, BET surface area analysis and thermogravimetric analysis were used to study the microstructure of the SCM and the hardened SCHPC systems. Series of paste, mortar and concrete were prepared with blended POFA and PBC at a replacement level of 10%, 15%, 20% and 30%, using water to binder ratio (W/B) of 0.30, 0.35 and 0.40 respectively. Fresh properties of the paste, mortar and concrete were studied with respect to their filling ability, passing ability, segregation resistance, unit weight, air content and heat of hydration. The hardened properties examined are; mechanical strengths, deformation characteristics and durability properties. A 4-phased investigation revealed that both POFA and PBC are good pozzolanic materials having excellent physical and chemical properties. At 30% replacement, the filling ability was improved by 7%, the passing ability was improved by 7% and the segregation index was reduced from 7 to 2.4%, with a visual stability index of 0. The unit weight and air content decreased by 2.5% and 5.6%, respectively, while the heat of hydration was reduced by 19%. Also, the mechanical strengths were increased between 5 to 6% and the increase in the drying shrinkage values was less than 0.01%, while the modulus of elasticity was increased by 4%. The durability and microstructural characteristics of the respective SCHPC were significantly improved. Consequently, a blend of POFA and PBC of up to 30% (15% POFA and 15% PBC) with a high range water reducer dosage of ≤ 2.5% was considered suitable for the production of SCHPC with W/B ≤ 0.3 and up 0.40.