Theoretical bond model between rebar and ultra-high performance concrete considering the effect of coarse aggregate

This paper considered the effects of coarse aggregates and proposed a continuous bond-slip theoretical model between Ultra-high performance concrete with coarse aggregates (UHPC-CA) and rebar. Due to the impact of coarse aggregate on crack development and fiber distribution, an improved fiber-matrix discrete model was proposed, combining the thick-walled cylinder solution and the fictitious crack model to analyze the bond-slip behavior across the uncracked, partial cracking, and complete cracking stages. This paper investigated the effects of rebar diameter, coarse aggregate particle size, coarse aggregate content, bond length, and cover thickness on the ultimate bond strength. The results showed that rebar diameter had minimal impact on ultimate bond strength, while bond stress loss increased by 35.0 % as the coarse aggregate content increased from 10 % to 40 %. A total of 76 sets of pull-out test data were collected and compared, indicating that the predicted ultimate bond stress and peak slip of the proposed model had average ratios of 1.000 and 1.022 to the experimental values, with coefficients of variation of 0.124 and 0.284, respectively, and the error was generally within 20 %. Furthermore, the relative error between the predicted and test results remained within 15 %, while the bond-slip relationships based on different softening curves exhibited a relative error not exceeding 5.0 %. The proposed model accurately predicted the bond-slip relationship between UHPC-CA and rebar.