The effect of the pores physical microstructure on water transport and compressive strength in self-compacting concretes containing silica fume and metakaolin

Understanding the physical microstructure, including pores size distribution and water absorption of concrete, because of its effect on long-term durability is important. The aim of the present study is to investigate the effect of physical microstructure of pozzolanic self-compacting concretes on compressive strength and water permeability. Self-compacting concrete mixes were designed with total cementitious material content of 450 kg/m3 with water to cementitious material ratio of 0.35, 0.45 and 0.55. The binary and ternary blends of cement, silica fume and metakaolin were used for the purpose of present study. In order to investigate the difference between the effect of metakaolin and silica fume on the physical microstructure, mixtures containing binary and ternary blends of cement, silica fume and metakaolin with water to cement ratio of 0.45 were considered. Pore physical microstructure characteristics including median pore size, volume of large and small capillary pore in self-compacting concretes were investigated. Pore size distribution of self-compacting concrete samples were measured by mercury porosity test. The compressive strength, water absorption and capillary water sorptivity were performed on samples. The results showed that an important effective factor on compressive strength and water permeability is the medium size of the pores and the volume of large capillary pores. The concrete containing 20% metakaolin and 8% silica fume did not have the lowest porosity despite having the highest compressive strength. The lowest porosity with 8.6% belongs to self-compacting concrete containing silica fume with water to cement ratio of 0.35.