Crack widths close the reinforcement

Currently used design methods predict that the crack widths at the concrete surface increase significantly with concrete cover. Requirements concerning limitation of crack widths therefore makes it difficult to use large concrete covers, which otherwise is desirable to reduce the corrosion of reinforcement. For this reason it would be more relevant to limit the crack width in the vicinity of the reinforcement bars. In this paper experimental studies to investigate how concrete cover affects the crack width at the reinforcement level are presented. Axially loaded concrete prisms with central reinforcement bars and beams loaded with bending moment are tested with a method making it possible to measure crack widths near the reinforcement. Concrete cover, bar diameter and concrete quality are varied. The test results show that the crack width close to the bar is only to a limited extent affected by concrete cover, bar diameter and concrete quality. Three-dimensional, non-linear FE-calculations are also performed to understand the mechanisms determining the properties of a crack.