Combined effect of fine fly ash and packing density on the properties of high performance concrete: An experimental approach

• HPC with superior properties has been optimized using 312 kg/m3 binder.
• Fine FA is more effective than normal FA on improving concrete properties.
• Total porosity is reduced to 3% by combination of fine FA and SF.
• The optimized HPC has a chloride diffusion coefficient of 1.4 × 10−13 m2/s.

High performance concrete often contains large amount of cement which makes ecological, economical and technical problems. This study provides a new approach to optimize high performance concrete with low cementitious materials content. The ideal grading curve according to Fuller has been used in concrete mix design to ensure high packing density of concrete mixtures and to reduce the required binder content. Several systems comprising various pozzolanic materials (silica fume, fly ash and fine fly ash) have been prepared and tested. The role of fine fly ash on concrete performance has been estimated by measuring the concrete mechanical properties, porosity and durability. The mechanical properties were assessed from compressive strength and modulus of elasticity, whilst the durability characteristics were investigated in terms of water permeability, water absorption and chloride diffusion. The results showed that fine fly ash performed better than normal fly ash for the strength development and durability aspects. The ternary system containing slag cement, fine fly ash and silica fume with low w/b ratio performed the best amongst all the systems regarding concrete mechanical properties and durability. Combination of fine fly ash and silica fume with OPC or with slag cement resulted in a significant reduction in concrete porosity. All mixes containing fine fly ash exhibited high performance concrete with excellent durability properties.