Bond behavior between steel bars and carbon nanotube modified concrete

Abstract The effect of different carbon nanotube (CNT) dosage, concrete cover thickness, steel bar diameter on bond behavior between steel bars and CNT modified concrete was experimentally studied. Beam specimens were prepared and tested for better simulation of the stress state of concrete in the vicinity of steel bars in real structures. The test results indicated that the initial bond strength, defined at a slippage of 0.01 mm, and the peak bond stress can be increased by approximately 37.2% and 49.7% at a CNT dosage of 0.1 wt% and 0.15 wt%, respectively. It was also found that the peak bond stress increased nearly linearly with the ratio, c/d, of the concrete cover thickness to the reinforcing bar diameter, and for a given c/d ratio, varied with the CNT dosage synchronously with the uniaxial tensile strength of concrete. The bond slip corresponding to the peak bond stress and the two shape parameters of the ascending and descending branches of the bond slip curve remained nearly constant over different CNT dosages and c/d ratios. Based on the synchronousness between the peak bond stress and the tensile strength, a time dependent bond slip model for CNT modified early-age concrete was proposed. The generated knowledge can be used for cracking control of young concrete members.