PERFORMANCE OF REPAIRED REINFORCED CONCRETE SLABS

Abstract

Reinstatement of concrete cover in reinforced concrete slabs is not uncommon. The work is of a specialized nature involving many operations using specialized materials and frequently in unfavourable circumstances. Problems that are generally encountered in such repair have been identified and possible solutions are presented in various specifications and guidelines. As a result of the proliferation of many commercially available materials, there has been fairly extensive use of such materials in the reinstatement of spalled cover of reinforced concrete slabs and beams. The apparent success with which such work has been carried out has demonstrated effectiveness under short term conditions. Performance in the long run particularly under cyclic loading remains a point of contention due mainly to a lack of adequate experimental evidence. Therefore the main objective of the present study was to generate information on the performance and durability of repaired reinforced concrete slabs subjected to static and cyclic loadings. Since the thickness of concrete cover reinstatement may vary, it is important to study the effect of the position of the interface between concrete substrate and repair material with respect to the position of reinforcement as this may significantly affect the performance and durability of the repaired structure under service loads which is cyclical in nature. A total of 50 unrepaired and repaired reinforced concrete slab specimens was tested under static and cyclic loading conditions in this study. Four types of specimens were tested, these include control specimens which are unrepaired and three other types of repaired specimens with cover reinstatement up to the level of the reinforcing steel, to mid depth of the reinforcing steel and up to the full depth of the reinforcing steel. The performance of specimens statically loaded to failure were monitored while the deterioration of flexural rigidity of specimens subjected to cyclic loading were evaluated after being subjected to a predetermined number of cycles at various stress ranges. A probabilistic approach to strength and service life predictions of both unrepaired and repaired specimens was discussed and mathematical formulations for analyzing the reliability of these slabs with respect to static and cyclic loadings were presented. Uncertainties inherent in the strength predictions were also identified. Unlike conventional fatigue strength studies where the specimens were cyclically loaded to failure, the approach employed in the present study involves obtaining the normalized residual flexural rigidity of the specimen after it has been subjected to predetermined number of cycles of loading. Within the range of applied stresses considered, the residual flexural rigidity of both unrepaired and repaired specimens were found to deteriorate with the number of loading cycles. However, the results of the reliability analysis obtained indicate that the repaired reinforced concrete slab specimens possess good flexural resistance against cyclic loadings.