Evaluation of Binary and Ternary Blends of Pozzolanic Materials Using the Rapid Chloride Permeability Test

Abstract

The effect of replacing cement by pozzolanic materials was investigated. This was done by a systematic increase in pozzolanic material inclusion, and was evaluated using the Rapid Chloride Permeability Test. The materials used were fly ash, blast furnace slag (BFS), and silica fume. The blending was at the increasing levels of 25, 50, and 70% of fly ash or BFS, with or without addition of silica fume at 10% cement replacement to form binary and ternary blends. A commonly practiced initial curing regime of seven days was administered. The experimental results obtained in this study were analyzed using statistical methodology. The results indicated that an increase in fly ash content increased the charge passed in the specimens but the reverse trend was observed with increase in the BFS content in the absence of silica fume. Silica fume alone as well as its ternary blend with 25% fly ash showed lower charge when compared with the control or with the binary blend of cement and fly ash. However, in ternary blends containing fly ash at more than 25%, the presence of silica fume did not cause a reduction in the charge. All ternary blends comprising BFS and silica fume passed lower charges than the respective binary blends. These ternary blends exhibited dense microstructure compared to the corresponding binary fly ash blends. The highest percentage replacement of cement with 70% BFS and silica fume was comparable with the addition of silica fume alone. The results showed that concretes with BFS blends exhibit lower charge passed and higher compressive strength than comparative blends using fly ash.