Development of Bond Strength of Reinforcement Steel in New Generation Concretes

The paper presents an experimental investigation of the steel-to-concrete bond using a pull-out test. Namely, the development of bond strength of reinforcement steel in new generation concretes was investigated. In the tests high-performance self-compacting (HPSCC) and vibrationally consolidated concretes (HPC), with the same water-to-binder ratio and made of components with the same properties, were used. For comparison purposes, the normal concrete was also used. For each concrete used in the experiment, a compressive strength development test was performed. To assess the development of bond strength in the tests, cubic specimens with the dimensions 160x160x160 mm were used. In each test element, ribbed reinforcing bar with a diameter of 16 mm was embedded in. Two variants of orientation of reinforcing bars with respect to the direction of concreting were considered - perpendicular and parallel. Test results showed that the development of bond strength between steel rebars and concrete increases with the increasing age. Additionally, the bond strength between steel rebars and concrete escalated with the increasing concrete strength. However, the development of bond stress with age was faster than the development of compressive strength, especially at early test ages. No significant difference was noticed between HPC and HPSCC mixes in terms of bond or compressive strength development with age. The conducted studies showed that in new generation concretes as well as in normal concretes the rebars placed parallel to the direction of concreting obtained higher values of the bond strength in comparison to rebars placed perpendicularly. This behaviour was observed in all stages of bond development. (paper)