A refined analytical model for bond strength and stress–slip behaviour in reinforced concrete

The influences of concrete compressive strength (fc), bar diameter (db), concrete cover (c) and water/cement ratio (w/c) on the bond behaviour between thermo-mechanically treated rebars and concrete were investigated through pull-out tests. Both pull-out and splitting failure modes were observed, primarily governed by the combined effects of db and c. The reference specimens mostly exhibited ductile pull-out behaviour with gradual slip and a sustained post-peak response, whereas specimens with reduced cover or larger bars failed abruptly in splitting. Increasing fc from 21 MPa to 28 MPa enhanced the bond strength (τmax) by nearly 35% for 12 mm dia. rebars owing to improved interfacial adhesion and confinement, although the gain was less pronounced for larger bars. Increasing c from 20 mm to 75 mm improved both bond capacity and ductility, delaying splitting onset. Conversely, varying w/c in the range 0.41–0.48 had negligible influence when fc was constant. Despite the differences in τmax, all specimens exhibited similar τ–s curve shapes, indicating that fc, db and c affect the magnitude rather than the fundamental bond mechanism. The proposed analytical method for estimating τmax correlated well with the test results, predicting bond stress–slip response within ±10% of measured values.