Deicer Salt-Scaling Resistance of Concrete Using Recycled Concrete Aggregates Pretreated by Silica Fume Slurry

Concrete wastes such as recycled concrete aggregates (RCA) make up a significant part of construction and demolition waste (C&DW) which can be used to minimize usage of natural aggregates and reduce carbon footprint. This paper studies the salt-scaling resistance of recycled aggregate concrete produced with pretreated RCAs. The test method for evaluating salt-scaling resistance in concrete according to DIN EN 1340: 2003 was performed. Four series of concrete mixes using natural aggregates, RCAs, manually pretreated RCA, and modified RCA in a desiccator were subjected to the different tests in terms of bulk electrical resistance in two directions (X and Y) before and after freeze-thaw cycles, ultrasonic pulse velocity, and weight loss of the surface layer of concrete specimens. Moreover, Scanning Electron Microscopy (SEM) of mixes was conducted and the microstructure of mixes considering the interface transition zone was studied. Results show that after exposure to cycles of freezing and thawing, the quality of concrete regarding ultrasonic pulse velocity did not change. The electrical resistance of specimens decreased significantly in X-direction and slightly in Y-direction after applying freeze-thaw cycles in all mixes. Nevertheless, surface modification of RCAs can increase electrical resistance and improve durability of concrete. SEM images show that the interface transition zone before and after freeze-thaw cycles remained unchanged which means strong bond between aggregate, new mortar, and old mortar. An estimation of the total charge passed indicated that all recycled aggregate concretes can be classified in a safe area and with very low chloride ion penetrability according to ASTM C1202.