Crack opening near reinforcement bars in concrete structures

摘要

Current concrete codes impose limitations of crack widths at the concrete surface. To investigate how the crack width at the surface affects risk for reinforcement corrosion, the related crack width close to the bar should be determined. An experimental study to investigate how concrete cover affects the crack width at the reinforcement level is presented. Axially loaded concrete prisms with a central 16 mm reinforcement bar were tested. Three different concrete covers, 30, 50 and 70 mm, were used. By continuous monitoring of strains and load, it was also possible to see how the crack width near the bar is affected by crack spacing. The test results showed that the crack width at the concrete surface is more than twice the crack width at the level of reinforcement. The influence of concrete cover seems to be rather small for the crack width at reinforcement level. It was also found that the crack width close to the bar is not affected by short term cyclic variations of five cycles or less with steel stresses in the range 200-400 MPa.