Bond Performance Of Steel Bar And Recycled Concrete After High-temperature Water Spray Cooling

The utilization of recycled concrete technology holds immense significance in driving technological progress,enhancing the recycling rate of construction waste,and facilitating the sustainable development of construction resources.In recent times,the rapid development of infrastructure and urbanization has resulted in frequent building fire incidents,causing significant loss of life and property.Typically,firefighting measures like water spray cooling are employed to extinguish the flames.However,the substantial temperature difference during this process creates an uneven temperature field within structural elements,thereby impacting the harmonious interaction between steel bar and concrete.Consequently,investigating the bond performance between steel bar and recycled concrete after high-temperature water spray cooling can serve as a valuable reference for the fire-resistant design and post-disaster repair of reinforced recycled concrete structures.This research also lays the foundation for the practical implementation of reinforced recycled concrete structures in engineering projects.This paper conducted compressive strength tests on 12 specimens of normal concrete and 36 specimens of recycled concrete cubes.Additionally,central pullout tests were performed on 24 specimens of normal concrete and 72 specimens of recycled concrete pullout.The experiments were conducted under various variables,including temperature(20℃,200℃,400℃,and 600℃),replacement rates of recycled coarse aggregate(0%,30%,50%,and 100%),and rebar diameters(12mm,14 mm,and 16mm).The objective was to investigate the bond performance between steel bar and recycled concrete after high-temperature water spray cooling.The main work and conclusion of this paper are as follows:(1)The physical properties and residual compressive strength of recycled concrete after high-temperature water spray cooling were investigated.To achieve this,compressive strength tests were conducted on cube specimens.The effects of temperature and recycled coarse aggregate replacement rate on the changes in loss on ignition and residual compressive strength of the recycled concrete after high-temperature water spray cooling were analyzed.In addition,empirical equations for loss on ignition and a prediction model for the cubic compressive strength of recycled concrete after high-temperature water spray cooling were developed.The findings revealed that the loss on ignition of recycled concrete increased as the temperature and recycled coarse aggregate replacement rate increased.Similarly,the residual compressive strength of the recycled concrete decreased with higher temperatures and increased replacement rates of recycled coarse aggregate.(2)The bond performance between steel bar and recycled concrete was examined by conducting central pullout tests.The aim was to investigate the impact of temperature,recycled coarse aggregate replacement rate,and rebar diameter on bond performance.Bond–slip curves were plotted to analyze the changes in bond performance.The results indicated the occurrence of three failure modes in the pullout specimens: pullout failure,splitting failure,and splitting-pullout failure.The ultimate bond strength decreased as the temperature and rebar diameter increased.Interestingly,the ultimate bond strength of recycled concrete specimens with 100% recycled coarse aggregate replacement rate after undergoing various high-temperature water spray cooling scenarios exceeded that of normal concrete specimens.Furthermore,the relative ultimate bond strength of recycled concrete specimens after room temperature and high-temperature water spray cooling demonstrated an increasing trend with higher recycled coarse aggregate replacement rates.(3)By utilizing the prediction model for the cube compressive strength of recycled concrete after high-temperature water spray cooling and the data obtained from the central pullout test conducted on steel bar and recycled concrete,an empirical formula for the bond strength between steel bar and recycled concrete after high-temperature water spray cooling was developed.This formula was derived by modifying the existing empirical formula for the bond strength between steel bar and normal concrete at room temperature,taking into account the influence of temperature and recycled coarse aggregate replacement rate.(4)A suitable model for the bond–slip relationship between steel bar and recycled concrete at room temperature was chosen.Then,the bond–slip relationship model between steel bar and recycled concrete after high-temperature water spray cooling was developed by adjusting the parameters in the model to incorporate the effects of temperature and recycled coarse aggregate replacement rate.(5)The bond–slip relationship model developed was implemented in ABAQUS using the Spring-2 nonlinear spring element to simulate the bond–slip behavior between steel bar and recycled concrete.Through this simulation,bond–slip curves and stress distribution clouds were obtained,providing insights into the stress distribution and changes in bond stress during different loading stages and failure processes of the specimens.A comparative analysis of the experimental and simulation results demonstrated that the Spring-2 nonlinear spring element was capable of accurately simulating the bond–slip relationship between steel bar and recycled concrete.