Fire-insulation properties of recycled aggregate concrete, its application in composite concrete structures, and concrete-concrete interface effects: a review

Cement-based materials inherently face a conflict between load-bearing capacity and fire resistance. To address this issue, combined using several types of concrete has the potential to improve both mechanical and fire performance. Therefore, this paper focuses on the composite concrete structures, particularly the fire performance of those incorporating recycled aggregate concrete (RAC), and explores their future development. This study considers three main aspects: the properties of RAC, composite concrete structures, and the concrete-concrete interface. The findings indicate that RAC exhibits excellent fire-insulation properties due to its lower thermal conductivity. The use of RAC in composite concrete structures can effectively enhance fire resistance while having a limited impact on mechanics. The bonding properties of discontinuous concrete-concrete interface in composite concrete structures significantly decreases when exposed to elevated temperatures, which may adversely affect structural integrity and requires attention. In summary, this paper provides a comprehensive understanding of the thermal insulation properties of RAC, thereby promoting its application in composite concrete structures and offering a viable approach to enhancing the fire resistance of concrete structures.