Using recycle concrete aggregate coating agent for improving concrete microstructure and hardened characteristics

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Recycled concrete aggregates (RCA) have been widely used as concrete aggregates in construction. This is due to economic and environmental benefits of using RCA in concrete. Unlike natural aggregate (NA), the use of RCA in concrete seems not promising to the users implementing it, especially in structural purposes. The RCA concrete is reported to have lower quality than NA concrete, especially when a high RCA content is used. The product improvement to ensure the quality of RCA-based concrete is needed. This work aims to examine the microstructures of different RCA concretes. A new surface coating agent has been developed to improve paste-aggregate bonding. After casting coated-RCA (C-RCA) concrete specimens with the replacement level of 30%, interfacial transition zone (ITZ) between C-RCA particle and cement paste was characterized using a Scanning Electron Microscope with Energy-Dispersive X-ray methods. Results indicated a reduction of ITZ region when using the C-RCA concrete and, consequently resulting in improved hardened performance characteristics. The compressive and flexural strengths of the C-RCA concrete were similar to the NA concrete and were higher than the RCA. The use of surface coating agent for RCA is one of the promising alternatives such that the use of RCA can be broadened in the construction industry.