التصرف الإنشائي للكمرات الخرسانية المعالجة من الصدأ

Abstract

The undertaken research work included in the paper presents the results of a laboratory investigation of the structural behavior of corroded and repaired beams in comparison with undamaged identical beams. The investigated structural behavior included shear and flexural strengths, ductility expressed by the middle span deflection, crack development and mechanical properties of the corroded reinforcing steel bars. The test program included fourteen beams; ten out of them were tested as simply supported beams subjected to two concentrated point loads. Two out of these ten beams acted as control beams, other two as corroded beams without repair and the remaining six beams were repaired after been corroded using different repair techniques. The other four were used to investigate the corrosion rate and the mechanical properties of the corroded steel bars. Special laboratory setup was assembled to allow fast corrosion of beam reinforcement. An electrochemical system was used to achieve the specified corrosion level. Repairing of beams was achieved by casting underlay inside which using additional longitudinal steel reinforcement bars to compensate the loss of steel reinforcement cross section due to corrosion. The deteriorated concrete bottom layer was replaced by a new underlay. To ensure monolithic behavior of the repaired beam the new reinforcement bars were fixed to the beam with shear connectors. Three repair techniques were investigated. Repair type 1 consisted of casting normal concrete overlay without bonding. In repair type 2 bonding agent was applied at the interface between the old and new concretes. Type 3 consisted of casting repair material as underlay bonded to the old concrete with bonding agent similar to repair type 2. The test results showed that the flexural capacity of the corroded beams have been reduced by 28% compared to the control beams. The ductility of the corroded beams was also adversely affected. On the other hand, the repair techniques succeeded in not only regaining the original strength, but have also resulted in a strength increase by up 47 % compared with the control beams. In general, the requirements of the serviceability limit state in terms of crack width and deflection were satisfied. Using different techniques in bonding new to old concrete did not affect the results significantly since all techniques have succeeded in preventing premature shear or laminar shear failure and thus allowed the beams to reach their full capacities which were enhanced using additional reinforcement and increased effective depth.