ABSTRACT

An ongoing research project seeks to provide recommendations for time of inspection of reinforced concrete structural elements susceptible to carbonation-induced concrete and its repair with ultra-high performance concrete. The risk of steel corrosion can vary depending on several inter-related factors that include the structural design, its materials, and its environmental exposure. The risk of corrosion furthermore can be separated into two phases; 1) corrosion initiation where atmospheric carbon dioxide diffuses into the concrete cover and lowering the beneficial high pore water pH and 2) corrosion propagation where the active corrosion continues at an adequate rate to cause structural damage. It is evident that both corrosion initiation and propagation should be considered when establishing recommendations for structural health monitoring and inspection. Even though corrosion initiation may occur, the rate of carbonation-induced corrosion can greatly vary. The drop in concrete pore water pH can change the anodic behavior of the steel and the cathodic behavior will vary by the oxygen availability. Furthermore, there is a contradicting effect of moisture presence. Greater internal moisture content would extend the initiation time but may decrease the propagation time. The use of UHPC as a repair material can restore structural capacity and was thought to provide some level of corrosion mitigation due to its very low permeability and high electrical resistivity. Concepts involving the increase in material resistivity and reducing internal moisture availability to minimize corrosion activity were reviewed.

INTRODUCTION

Recent occurrences of high visibility structural failures have spurred interest to revisit inspection and repair of aging reinforced concrete structures. Chloride-induced corrosion can cause premature damage of structures in coastal regions. Corrosion induced by carbonation of the concrete and the concrete pore water, on the other hand can occur in many other environments including structures in both wet and dry exposures. This type of corrosion can become increasingly relevant in residential buildings as housing structures age to where sufficient carbonation occurs at reinforcing steel depths. A current research project seeks to provide recommendations for time of inspection of reinforced concrete structural elements susceptible to carbonation-induced concrete and retrofit with ultra-high performance concrete, UHPC. The risk of corrosion for the embedded reinforcing steel in residential buildings can vary depending on several inter-related factors that include the structural design, its materials, and its environmental exposure. The risk of corrosion furthermore can be separated into two phases; 1) corrosion initiation where atmospheric carbon dioxide diffuses into the concrete cover and lowering the beneficial high pore water pH by consuming OH to allow steel passivation and 2) corrosion propagation where the active corrosion continues at an adequate rate to cause structural damage. It is evident that both corrosion initiation and propagation should be considered when establishing recommendations for structural health monitoring and inspection. Repair of corrosion damaged reinforced concrete structures with UHPC has been suggested due to the growing interest in the material and its beneficial mechanical and material characteristics such as high compressive strengths and low permeability.

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