Bond of high-strength concrete under monotonic pull-out loading

Abstract

An experimental investigation was conducted on high-strength concrete specimens to examine the bond strength characteristics under monotonic loading. The range of compressive strengths tested was between 70 and 95 MPa. The influences of load history, confining reinforcement, bar diameter, concrete strength, reinforcement spacing and rate of pull out were investigated experimentally. The internal concrete strains close to the contact surface and also the steel strain were measured. The test set-up, load application, instrumentation and measurement, and test procedure were designed to measure strains and deformations. Several specimens with reinforcement bar diameters of 20, 25 and 35 mm were tested. The test results revealed that the bond strength of high-strength concrete is higher than the corresponding normal strength concrete. However, the bond behaviour of high-strength concrete is more brittle in comparison with normal strength concrete. The concrete strains were measured around the steel reinforcement. Concrete strain measurements are useful to identify the internal crack pattern and to predict possible failure modes. The area under the curve of the bond stress–slip curve can define the bond energy. The bond energy is related to ductility and can be used along with the bond strength in evaluating the bond behaviour of high-strength concrete.