Crack widths near reinforcement bars for beams in bending

K. Tammo, Division of Structural Engineering, Lund Institute of Technology, Sweden
S. Thelandersson, Division of Structural Engineering, Lund Institute of Technology, Sweden 

Earlier research performed on axially loaded concrete prisms shows that crack widths close to reinforcement are smaller and less dependent on concrete cover than crack widths at the concrete surface. To check practical applicability of these results a similar experimental investigation of cracking behaviour has been undertaken for beams loaded in bending. The influence of steel stress and concrete cover on crack widths close to the reinforcement and at the concrete surface has been investigated. The results show that the main features of cracking behaviour for axially loaded prisms and beams are similar. Beams resemble axially loaded prisms in that cone-shaped concrete failure occurs in the bond zone where the bar meets a crack. At higher steel stresses this concrete cone follows the displacement. For this reason crack widths close to the bar are significantly smaller and much less affected by the thickness of concrete cover than at the concrete surface. Surface crack widths consequently are poor indicators of the potential for exposure to corrosive attacks on reinforcement and current design methods can be counter-productive for service life of concrete structures.