The Influence of Cracks on the Durability and Service Life of Reinforced Concrete Structures in relation to Chloride-Induced Corrosion: A Look from a Different Perspective

Abstract

The service life of concrete structures can be significantly shortened when corrosion of steel reinforcement occurs, especially in a marine environment and in structures exposed to de-icing salts. The influence of load- or deformation-induced cracks on corrosion progress is an important issue which was studied in this research in relation to the durability and service life of reinforced concrete structures. An experimental set-up was designed in order to generate knowledge and contribute to existing codes and practice. 32 reinforced concrete beams (1500×100×150 mm3) were exposed to alternately wetting and drying cycles in order to simulate an aggressive chloride environment. The interrelated influence of surface crack width, crack frequency (distance), concrete cover thickness and loading conditions on the corrosion development of steel reinforcement has been monitored during two years. After two years of exposure all concrete beams were split into two parts in order to visualize the achieved chloride penetration and the development of steel corrosion. In order to limit the influence of load- or deformation-induced cracks on the potential reduction of service life, this research showed that maximum steel stress in cracked reinforced concrete members/structures plays an important role in corrosion behaviour, rather than the maximum surface crack width, since the stress level determines directly the damage of the concrete at the steel reinforcement level. Two different types of corrosion processes can be distinguished in concrete structures, localized and uniform corrosion. The localized depassivation of steel reinforcement is not necessarily the theoretical end of service life of a concrete member where a negligible localized reduction of the steel cross-section should be allowed in the SLS. Uniform corrosion along a certain bar length occurs mainly by chloride transport through the uncracked part of the concrete surface, between the main cracks. The maximum steel stress affects both, localized and uniform corrosion along a certain bar length by the damage of the concrete around the main crack at the bar level and the reduction of the effective undamaged concrete cover in the uncracked part at the concrete surface (between the main cracks), respectively. In order to take a step forward towards direct incorporation of the influence of load- or deformation-induced cracks in a more reliable assessment of the structure’s service life, an explanatory model for cracked reinforced concrete members/structures in an aggressive environment is proposed. It is highlighted that the maximum service load level governs the development of the steel corrosion, rather than the frequent or the quasi-permanent service load level, as is prescribed at present by codes. Furthermore, the influence of load- and deformation-induced cracks in future codes and regulations, should be limited by defining the maximum allowable steel stress in conjunction with bar diameter and concrete cover at a certain concrete strength under the maximum service load, in order to assure the desired service life of a concrete structure exposed to an aggressive environment.