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Freeze-thaw (F-T) damage is the major factor destroying the bond behavior of reinforced concrete in the cold areas of China. The bond behavior between recycled fiber recycled concrete (RFRC) and reinforcement after F-T cycles was investigated in this paper. The pull-out tests were undertaken with the replacement rate (0, 50%, and 100%) of recycled aggregates (RA) and volume content (0, 0.12%, and 0.24%) of recycled fibers (RFs) as test variables. The results demonstrate that the F-T cycles will reduce the bond strength between RFRC and reinforcement. Bond strength decreases by 69.41% after 150 cycles. Moreover, RF can improve the bond strength between RFRC and reinforcing steel. Bonding strength increases by 11.35% with the addition of 0.12% RF. A simplified two-phase bond-slip model between RFRC and reinforced steel after F-T cycles was eventually established, and it correlated well with the experimental results. This research presents a theoretical basis for the application of RFRC in building structures in cold areas.

In order to investigate the characteristics of boiling heat transfer for hydrocarbon mixture refrigerant in plate-fin heat exchanger which is used in the petrochemical industry field, a model was established on boiling heat transfer in vertical rectangular channel. The simulated results were compared with the experimental data from literature. The results show that the deviation between the simulated results and experimental data is within 6 15%. Meanwhile, the characteristic of boiling heat transfer was investigated in vertical rectangular minichannel of plate-fin heat exchanger. The results show that the boiling heat transfer coefficient increases with the increase in quality and mass flux and is slightly impacted by the heat flux. This is because that the main boiling mechanism is forced convective boiling while the contribution of nucleate boiling is slight. The correlation of Liu and Winterton is in good agreement with the simulation results. The deviation between correlation calculations and simulation results is mostly less than 6 15%. These results will provide some constructive instructions for the understanding of saturated boiling mechanism in a vertical rectangular minichannel and the prediction of heat transfer performance in plate-fin heat exchanger.

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The mechanical properties, failure forms, and deformation characteristics of 10 beam-to-column joints under monotonic loads were compared and analyzed. The design variables were waste fiber content (0.08%, 0.12%, and 0.16%), waste fiber length (12 mm, 19 mm, and 30 mm), and replacement rate of recycled aggregates (0%, 50%, and 100%). The results indicated that, under an axial compression ratio of 0.4, all specimens underwent plastic hinge failure at the beam end under monotonic loading and experienced four stages of the initial cracking, full-cracking, limit, and failure stages. There was no shear oblique crack in the core area of the joint, and no shear failure occurred. When the replacement of recycled aggregates is 50%, the tensile strength of concrete mixed with a specific amount of fibers can be effectively improved. The ultimate bearing capacity of the beam end is improved when the length and volume of the waste fibers are 19 mm and 0.12%, respectively. The ratios between the calculated and tested ultimate bearing capacity of beam-column joints are in the 0.99–1.10 range, and the calculated and tested values are in good agreement.

Concrete made using recycled aggregates is a practical way to reduce construction waste. The purpose of this study is to improve the mechanical qualities of recycled aggregate concrete by incorporating waste fibers. The replacement rate of recycled coarse aggregate and volume content of waste fibers were planned as the study variables. The cubic compressive strength, splitting tensile strength, axial compressive strength, and elastic modulus were used to explore the mechanical characteristics of specimens. Additionally, the test results were optimized utilizing the response surface method, focusing on the influence of study variables on performance. The axial compressive constructive equation of waste fiber-reinforced recycled aggregate concrete was created based on the stress–strain curves of the specimens, and it serves as a foundation for further in-depth theoretical investigations.

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