An overview of assessment and retrofit of corroded reinforced concrete structures

摘要

The corrosion of steel in reinforced concrete structures surely represents the main form of degradation. Carbonation and chloride attacks lead to a loss of performance during the service life of the structure. The reduction of the cross section of the steel bars and the formation of corrosion products lead to reduction of bond between steel and concrete, to concrete cover cracking and spalling, to reduction of concrete cross section resulting in a reduction of structural capacity. The structural engineer needs to face corrosion starting from the design phase, however in presence of real existing structures the first step is the evaluation of corrosion level and the evaluation of actual global structural capacity. The most critical corrosion involves the stirrups, being the most exposed steel elements, yielding to brittle failures in the most stressed elements, generating unexpected structural collapses. In particular in seismic conditions, the structure is not able to exploit its ductility, since limited ductile failures (i.e. combined shear/flexure) could occur. The last phase of the study is on the structural retrofit by using High Performance Concretes. Such materials allow recovering some of the bending capacity of the structural elements and can increase their ductility, reducing dramatically the vulnerability of the structures. This is particular true for seismic vulnerability, since the strength recover is partial if the structural retrofit intervention is designed to have a negligible impact on the structure. In fact the considered intervention is aimed to recover the original geometry of the elements with a reduced cost and impact on the fruition.