Bond behavior between cement-based grouting material and steel bar under repetitive loading after being exposed to high temperature at early age

Abstract

Cement-based grouting material (CBGM) had many characteristics such as high-early-strength, high strength and high fluidity. It has been widely used in building structural reinforcement projects. This paper presents an experimental study to investigate the bond behavior between CBGM and steel bar under repetitive loading in early age after fire. The hysteretic behavior of pull-out specimen cast with CBGM and steel bar was investigated. The research focused on the influence of different temperatures, curing ages, stirrups and loading methods on the bond behavior between CBGM and steel bar. The microscopic morphology of the specimen was analyzed by scanning electron microscopy (SEM). The results showed that under repetitive loading, the ultimate bond stress decreased gradually with the increase of temperature, and the ultimate bond displacement increased first and then decreased with the increase of temperature. According to the hysteretic curve, the influences of curing age, heating temperature and the stirrups on hysteretic behavior were analyzed. The bonding behavior, ductility and energy dissipation capacity of specimens with 7 days curing age before heating were the best. When the early age specimens subjected to fire continued to be cured for 28 days, the bond behavior of the CBGM was slightly restored. Under the same conditions, the bond behavior, ductility and energy dissipation capacity of the specimens with stirrups were better than those without stirrups. Compared with different loading methods, the repetitive loading aggravated the destruction of the bond specimens and reduced the ultimate bond stress and displacement of specimens.