The carbonation of concrete or the chlorides penetrated in the concrete may lead to corrosion of the rebar and in a later phase to a reduced bond between rebar and concrete, cracks and to spalling of small to larger pieces of concrete. This can have a negative effect on the durability, serviceability and safety of concrete structures. The reason for cracking and spalling of concrete is the volume of the corrosion products which is larger than that of the originally un-corroded metal.
In course of condition evaluations of concrete structures (underside of bridges, walls etc.) the question of whether or not there is a risk of spalling (for third parties like car drivers, trains) is raised quite frequently. There are very similar questions related to insufficient durability of rehabilitated structures (patch repair). There are only a few investigations and no recommendation on these topics.
A State of the Art report on the damage of concrete caused by rebar corrosion should be elaborated. The main questions to be treated are:
• How can the risk for spalling (delamination) of concrete to be estimated for reinforced concrete structures?
• Which aspects of corrosion are important?
• Which specific aspects of repaired areas (patch repair) are to be considered?
• Which possibilities for a forecast are available?
• How can the actual and future propagation rate to be estimated?
• Which classes of risk (structure, goods and persons) can be distinguished?
• Which measures are to be taken for a given risk?
Following steps were done during the project:
- Review and analysis of existing literature.
- Contact acquisition with worldwide experts.
- Analysis of individual cases of damage.
During the work for this project it was recognized that important basics for the modelling are still missing. The actually available models lead to diverging and partly contradictory results. The insufficient knowledge leads to a cautious assessment of the risk and, finally, to eventually unnecessary and uneconomic rehabilitations.
To make a step forward to answer the questions treated within this project further research work is inevitable. This concerns the following topics: amount of data about spalling, techniques for the determination of the corrosion rate on-site, realistic models for the description of the development of damages due to corrosion and for purpose of prognosis, criteria for the serviceability and ultimate limit states.