The influence of high-strength concrete – rebars bond conditions on the mechanism of its failure

The failure of reinforcing bars in high-strength concrete may cause the bar to be pulled out of the concrete, or split the concrete cover. However, owing to the modified microstructure and mechanical properties of new-generation modern concretes, the mechanisms of reinforcing bar–concrete bond failure are completely different. This paper presents the results of experiments the authors performed on samples of different heights with thick concrete cover, made of high-strength concrete. The experiments showed that, in samples of considerable height (600 mm), various mechanisms of bond failure take place. It was proved that the mode of bond failure mechanism depends on the zone of quality bond conditions. Analysis of the loss of reinforcing bar–concrete bond in samples of thick concrete cover confirms that the same failure mechanisms occur in close vicinity to the ribs as in samples with thin cover. The final effects of bond failure are, however, different. On the basis of literature data and experiments performed, it was also shown that the influence of high-strength concrete through modification with silica fume and superplasticiser on the bond failure mechanism depends on concrete cover thickness and bond conditions.