Experimental study and modeling on bond-slippage behavior of steel bar in polyvinyl alcohol-steel hybrid fiber engineered cementitious composite

In order to understand and estimate the composite action of steel bar and fiber reinforced low drying shrinkage engineered cementitious composite (LSECC), bond strength-slip relation of steel bar embedded in LSECC was studied in this paper. Series pullout tests, smooth steel bar and deformed steel rebar, with four LSECC mixtures and two embedded lengths were performed. Failure on bond between steel bar and LSECC under pullout load can be divided into debonding and pullout stages. In debonding stage, constant bond strength that principally controlled by chemical and physical bond of steel bar and cement matrix can be used to describe the pullout behavior. In pullout stage, bond strength first increases with slippage (slip-hardening stage of bond). After the peak, bond strength decreases with slippage (slip-softening stage of bond). In the slip-hardening stage, much higher bond strength is observed in slip-hardening stage of rebar than that of the smooth bar, while much smaller slippage corresponding to the peak bond strength is observed of rebar than that of the smooth bar. An analytical three stage bond strength-slippage model was proposed based on pullout test results with small embedded length (30 mm). Meanwhile, pullout model of steel reinforcement from ECC with arbitrary embedded length was developed based on debonding and pullout theory, which can well simulate initial ascending, slip-hardening and slip-softening stages under pullout load. Good agreement between model and test results in terms of load-slippage relationship of longer reinforcement embedded in ECC was observed.