Bond behavior of plain bar in highly ductile fiber-reinforced concrete (HDC) subjected to monotonic and repeated loading

The combination of highly ductile fiber-reinforced concrete (HDC) with plain bar mesh has found extensive application in the strengthening field. The bond properties between steel bar and HDC significantly influence the combined action of these two materials. Seven groups of specimens were tested to investigate the bond behaviors of plain bars in HDC via monotonic and repeated loading. The design variables comprised the bar diameter, HDC compressive strength, and matrix type. The experimental results indicated that HDC specimens demonstrated a more ductile failure mode and higher bond strength in comparison to both concrete specimens and specimens without fibers. The increase in bar diameter negatively influenced the bond strength, but the increase in compressive strength contributed to the improvement of bond strength. Moreover, after under-going repeated loading, the HDC specimens that experienced premature bond failure displayed a decline in both residual bond strength and bond strength, with the former declining more significantly than the latter. Finally, according to the experimental data, in this study, a formula is proposed to calculate the bond strength, along with constitutive models for predicting the bond stress-slip response of plain bar in HDC subjected to monotonic and post-repeated monotonic loading.