Bond behavior of epoxy-coated rebar in ultra-high performance concrete

The bond behavior of epoxy-coated rebar embedded in two different ultra-high performance concrete (UHPC) mixtures is experimentally investigated by a uniaxial pullout test, and the effect of embedment length, side cover, and mixture type on the bond stress-slip relationship is predicted using a double-phase analytical model. The bond mechanism and failure modes of rebar in UHPC are similar to those observed in normal concrete. The embedment length and side cover have significant influence on the bond behavior of epoxy-coated rebar in UHPC, and more drastic bond stress hardening and softening are observed for the case of larger embedment length and side cover. Two UHPC mixtures exhibit comparable bond strength and critical development length because they have close mechanical properties gained at test age. The adopted analytical model matches well with the experimental bond-slip response of epoxy-coated rebar in UHPC, and both the characteristic parameters in the model show an increasing trend when more dramatic hardening and softening of bond stress exhibit.