A test method to establish realistic bond stresses

The bond strength of reinforcement in concrete can be measured by means of various test methods. There is a considerable difference of opinion amongst engineers regarding the most appropriate test method relating to practical design. This Paper describes a practical test method to determine the bond strength. It is shown that the bond strength using this test arrangement can be directly compared with bond strengths given in design codes. The test specimen used consists of a rectangular concrete prism in which parallel bars are cast close to the four corners. It enables the bond strength to be determined for both a top cast and bottom cast condition. The specimen is set up so that an axial force is applied to the bar being tested. The restraints are sufficently rigid, to ensure minimum rotation or twisting of the specimen during loading. Each bar is loaded incrementally to failure. The development of cracking is noted at each load stage and failure is defined as the maximum load achieved. It is found that this type of specimen gives results that relate more closely to practice than do the conventional pullout specimens. It can also be used for comparing the bond strength of different types of bar, by casting the bars in alternate positions in the prism.