Effect of specimen shape, silica fume, and curing age on durability properties of self-compacting concrete incorporating coarse recycled concrete aggregates

The usage of recycled concrete aggregates (RCAs) can be effected as a replacement of natural aggregates in the assurance of the environment. Utilizing these products of construction and demolition wastes in self-compacting concrete (SCC) has positive advantages such as reducing the extravagant consumption of natural supplies and decreasing carbon dioxide emissions. However, using RCAs may be affected on the properties of concrete such as reduction in compressive strength, electrical resistivity (ER), increasing in water absorption (WA) and porosity. In this study, the durability performance of SCCs containing coarse RCAs as a partial or total replacement of natural aggregates, and silica fume (SF) as a partial replacement of cement is investigated. The replacement level of SF was considered 8% by weight of cement. Replacement level of RCAs with natural aggregates is selected at 0, 25%, 50%, 75% and 100%. Fresh properties of SCC were evaluated by measuring slump flow and J-ring tests. Durability performance of hardened concrete was investigated using WA, ER and rapid chloride penetration tests. Cube and cylindrical specimens were used to recognize the effect of shape and size specimen on ER and ultrasonic pulse velocity (UPV). Results showed that replacing RCAs decreased durability performance, but using SF in mixes significantly enhanced the ER and chloride ion penetration resistance of SCC. Results illustrated that cylindrical specimens have more consistent results than cube ones. Likewise, assessing durability performance at 91 days concluded reliable results than that in 28 days.