Abstract
Using recycled aggregate concrete (RAC) in steel-reinforced concrete structure is an effective way to eliminate the adverse effects of recycled aggregate, which has an excellent application prospect. Fire has a great destructiveness to steel-reinforced recycled aggregate concrete (SRRAC) structure; hence, the bond performance of SRRAC after high temperature, as the prerequisite for the composite between steel and RAC, is the key problem for structural safety and the corresponding safety assessment after fire. In this article, the residual bond behaviors of steel-recycled aggregate concrete interface after different high temperatures and spraying water cooling were studied through the push-out test. The failure modes and load–slip curves were examined. The ultimate bond strength, residual bond strength, and elastic bond shear stiffness of specimens after high temperature and cooling for the regime of spraying water were evaluated and compared to that of natural air. A parametric analysis of temperature, replacement percentage, and studs was conducted. A calculation approach for the ultimate bond strength and residual bond strength of SRRAC after high temperature was developed based on the sensitive analysis of gray system theory and regression analysis. Results showed that the bond properties of SRRAC specimens after high temperature were decreased as exposure temperature increased. The cooling regime of spraying water has a more significant influence on the ultimate strength and residual strength than that of natural air. The specimens with studs on both flange and web have the highest bond properties after high temperature. In all the factors, the number of studs showed the largest gray relational degree to the bond strength of SRRAC. The developed approach provided a reliable prediction of bond strength for SRRAC after high temperature.
Highlights
Construction and demolition waste is one of the major city solid wastes, the treatment of which has become a big issue on environmental protection all over the world
All the study results indicated that the encased steel in steel-reinforced recycled aggregate concrete (SRRAC) elements can significantly reduce the negative effect of recycled aggregate concrete (RAC) on the structural performance, and SRRAC elements exhibited excellent ductility and load carry capacity under static and dynamic loading
The results demonstrated that the bond characteristic at the interface of SRRAC was affected by the factors such as the strength of RAC, the concrete cover thickness of protective layer, and ratio of stirrups, which was similar to that of steel and conventional concrete
Summary
Construction and demolition waste is one of the major city solid wastes, the treatment of which has become a big issue on environmental protection all over the world. Ma and Xue (2015) and Ma and Dong (2019) performed some cyclic loading tests on steel-reinforced recycled aggregate concrete (SRRAC) columns and joints. The bond behavior of SRRAC after high temperature and cooling by different regimes, especially water spraying, needs further study. This study was aimed at investigating the bond behavior of steel and RAC after high temperature and cooling by spraying water. To study the bond behavior between the steel section and RAC after high temperature, 18 SRRAC specimens with and without studs were designed and produced for push-out test after exposure to high temperature. The standard cube specimens of concrete were cast to obtain the strength of RAC after exposure to different high temperature according to the Chinese code GB/T 50081 (GB/T 50081-2002, 2003).
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