Interfacial transition zone in rubberized concrete: A panacea for the extreme environmental conditions

Abstract

The utilization of waste rubber in concrete, known as rubberized concrete (RubCrete), offers significant environmental advantages, primarily through enhanced waste management and circular economy benefits. However, a comprehensive understanding of the role of the interfacial transition zone (ITZ) that exists between the rubber aggregates and the cement becomes crucial for utilizing RubCrete to negotiate with extreme environmental conditions, such as marine environments, cold regions, and barrier systems. Keeping this in view, this study investigates the ITZ between rubber aggregates and the cement matrix in RubCrete. ITZ's mechanical and chemical features were analyzed through various physical, chemical, thermal, and mineralogical tests. XRD analysis identified Ca-rich hydration products such as calcium hydroxide (C-H) and calcium silicate hydrate (C-S-H), with Anorthite concentration ranging from 11.7 % to 37 %. FTIR analysis revealed bond characteristics within the ITZ, while TGA-DTG provided insights into thermal stability and decomposition behavior, representing weight loss ranging from ≈ 5–15 %, and possible hydration products. Based on these analyses, it has been demonstrated that the formation of ITZ (ranging from 35 µm to 120 µm) is due to the wall- and dilution- effect (WDE) that prevails on the surface of the rubber aggregates, a feature not significant in conventional cement concrete. This WDE results in the development of disconnected pores, as confirmed by SEM-EDS and X-ray micro-CT analyses, that in turn is responsible for a reduced micro-mechanical performance but retards the migration of mass flux (read contaminants) through it.