Effect of silica fume on durability of self-compacting concrete made with waste recycled concrete aggregates

Abstract

Due to adhered mortar in recycled concrete aggregates, some of the properties of concrete made with these types of aggregates, such as water absorption, porosity, electrical resistivity, and chloride ion penetration, may be affected. In this study, silica fume was used as a part of cementitious materials to improve the properties of self-compacting concrete (SCC), which were made with fine and coarse recycled aggregates. Three series of mixtures were made in the laboratory. In the first and second series, coarse recycled aggregates with replacement of 25%, 50%, 75% and 100% were used with and without silica fume. In the third series, 25% of fine recycled aggregates were replaced with fine natural aggregates. Slump flow and J-ring tests were considered for fresh state of SCC. The compressive strength, water absorption, ultrasonic pulse velocity, electrical resistivity, and chloride ion penetration tests were performed for hardened concrete. The use of silica fume improved the properties of fresh SCC. The results showed that silica fume can reduce water absorption and porosity. The silica fume showed that can resulted in a significant increase in electrical resistivity. On the other hand, the replacement of 25% of recycled aggregates did not have a significant effect on electrical resistivity, the electrical resistivity decreased by increasing the amount of replacement. Silica fume was very effective in controlling chloride ion penetration and reducing total charge passed. Silica fume also controlled the temperature of the solutions used during the test which indicates the control of the movement of ions in the penetration into concrete.