Study on local bond behaviors between steel bars and high-strength concrete exposed to early disturbances

This paper investigates the effects of early vibration exposure on the local bond behaviors between deformed steel bars and high-strength concrete (HSC). The effects of steel fiber and vibration intensity (ranging from static to peak particle velocity (PPV) of 10 cm/s) on the deterioration laws of bond performances and mechanisms were revealed. Finally, an empirical prediction model was developed to uniformly describe the bond stress-slip relations of specimens subjected to different vibration levels. Results indicated that early vibration could produce separation gaps and the surrounding viscous layers around steel bars, leading to the reduction/ elimination of initial debonding resistances. Besides, the failure mode of pull-out specimens may alter due to the degradation of concrete. The bond stiffness of HSC is more vulnerable to environmental vibration (up to 62.6%), followed by bond strength (39.4%) and compressive strength (33.7%). The bond toughness of specimens, especially with the addition of steel fibers, is less sensitive to vibration (29.8%/6.8% for HSC/HSFRC). The increases in concrete strength grades and additions of fibers significantly enhance the threshold resistance to early vibration, making it a recommended solution for vibration scenarios. Using a consistent expression, the proposed empirical model reasonably reproduces bond stress-slip curves of specimens with/without vibration exposure.