Bond behavior of steel bar embedded in Engineered Cementitious Composites under pullout load

Composite action of steel bar and Engineered Cementitious Composites (ECC) plays an important role in reinforced ECC structures, which depends on the bond performance of two materials. To evaluate the bond behavior of steel bar embedded in ECC, direct pullout tests were conducted on 10 groups of ECC specimens and 2 groups of control specimens in this paper. The parameters investigated were bar shape, bar diameter, cover thickness, ECC strength and fiber volume content. Experimental results indicated that the ultimate bond strength of the plain bar embedded in ECC increased 1.71 times than that in concrete. For the deformed bar, the bond failure mode of ECC specimens exhibited an obvious ductility due to fiber bridging effect preventing the opening and propagation of internal cracks, whereas the brittle splitting failure occurred for concrete specimens. Furthermore, the ultimate bond strength increased 2.14 times as ECC strength increased from 27.7 to 57.2 MPa. Besides, a critical relative cover thickness was confirmed as 3.41. Finally, based on the distribution of bond stress along the embedded length, the anchorage position function was ascertained and then an accurate bond slip relationship was built, which was significant in structural design and numerical simulation.