Review on Micro Structural Characterization of Recycled Concrete by Using Scanning Electron Microscopy

Abstract

This is a review paper focusing on the microstructure of recycled concrete and the application of scanning electron microscopy (SEM). The paper commences by outlining the environmental and economic merits of recycled concrete, while pinpointing that the inferior performance of its recycled aggregates constitutes a primary constraint on its widespread utilization. It is further noted that such drawbacks can be mitigated via technical measures including aggregate pretreatment and nanomaterial incorporation. Subsequently, the paper presents a comprehensive overview of the definition, classification, mechanical properties and durability of recycled concrete. Next, the paper elaborates on the application of SEM in the microstructural characterization of recycled concrete. Specifically, SEM is capable of capturing high-resolution imaging, thereby enabling the observation of the microtopography of recycled aggregates, pore structure, and interfacial bonding characteristics between aggregates and cement matrix. In terms of microtopography, SEM elucidates the distribution patterns of recycled aggregates and mortar, along with the presence of interfacial cracks; post modification, hydration products are found to fill the internal pores and enhance interfacial adhesion effectively. For pore structure analysis, SEM facilitates the accurate assessment of pore size and distribution, laying a solid theoretical foundation for the performance optimization of recycled concrete. With respect to interfacial bonding, SEM identifies the interfacial transition zone (ITZ) as the inherent weak link in recycled concrete, and verifies that the compactness of ITZ can be significantly improved through the incorporation of mineral admixtures. Finally, the paper concludes that SEM serves as a powerful analytical tool for the microstructural investigation of recycled concrete. It allows for the intuitive visualization of microtopography, quantitative analysis of pore structure, and in-depth exploration of interfacial characteristics, thus providing robust technical support for the performance optimization and quality control of recycled concrete. Looking ahead, the application of SEM technology in recycled concrete research is poised to become more extensive and in-depth.