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Canadian Civil Engineer, 21, May 2, pp. 4-5, 19, 2004-05-01
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Durability of concrete structures: prevention, evaluation, inspection,
repair and prediction
Cusson, D.; Isgor, B.
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Durability of concrete structures: prevention, evaluation,
inspection, repair and prediction
Cusson, D.; Isgor, B.
NRCC-46624
A version of this document is published in / Une version de ce document se trouve dans :
Canadian Civil Engineer, v. 21, no. 2, May 2004, pp. 4-5, 19
Durability of Concrete Structures:
Prevention, Evaluation, Inspection, Repair and Prediction Dr. Daniel Cusson, P.Eng.
Research Officer
National Research Council Canada Ottawa, Canada, K1A 0R6
Dr. Burkan Isgor Assistant Professor Carleton University Ottawa, Canada, K1S 5B6
Concrete is the primary construction and repair material of many structural systems in Canada, such as highway bridges, high-rise buildings, parking structures, and dams. Today, many of the concrete structures, which have been exposed to aggressive environments, suffer from durability problems and fail to fulfill their design service life requirements. The problem is particularly serious in reinforced concrete structures where corrosion of reinforcing steel can impair their safety. Carbonation and chloride-induced corrosion are two major causes of deterioration of concrete structures in Canada and several other countries. The cost of the repair and rehabilitation of corrosion-damaged structures in the United States, Canada, and most European countries constitutes a large portion of their infrastructure expenditures. The limited knowledge of the field performance of corrosion-damaged structures and the lack of systematic approaches for their inspection, maintenance and repair contribute to the increase of their life-cycle costs, and result in the loss of functionality and safety.
It is estimated that over 40% of all bridges in Canada are older than 40 years and are in need of rehabilitation or replacement. The backlog of maintenance, rehabilitation and replacement of highway bridges is estimated at $10 billion. The prohibitive costs needed to upgrade highway bridges require the development of innovative decision support tools for bridge owners. Such tools will enable owners to assess the condition of their structures, predict their future performance and allocate limited funds in order to better manage their maintenance and achieve adequate reliability and minimum life cycle costs. The rehabilitation of concrete structures is a complex problem due to various factors. Their performance is difficult to predict, owing to the complexities associated with assessing material characteristics, environmental effects, damage initiation and accumulation, structural strength, failure mechanisms, and their impact on serviceability and safety. Most of the damage mechanisms are not well understood, such as the processes of corrosion initiation and damage accumulation. Other difficulties arise in detecting damage early in the life of the structure, and assessing the field performance of repaired concrete structures. Furthermore, there is a need for the implementation of a systematic approach for inspection and rehabilitation of concrete structures in order to ensure their safety and durability and minimize their life cycle costs.
The featured articles selected for this special issue will provide an excellent overview of the state of practice on important aspects related to durability of concrete structures, namely: prevention of deterioration, evaluation and inspection of structures, repair technologies, and prediction of deterioration and performance.
In their article, Mr. Lessard and Dr. Bédard from Euclid Admixtures Canada discuss the roles of design engineers, ready-mix suppliers, contractors and structure owners in preventing deterioration and ensuring long-term durability of concrete structures. They emphasize that each player intervening in the construction of a structure should be concerned with the primary causes of deterioration. A systematic approach to minimizing the causes of deterioration and failures, and to maintaining the design function of the structure over its effective life is presented.
In his article, Dr. Michael Thomas, reviews the primary causes of steel corrosion in concrete structures. As Dr. Thomas states, carbonation-induced steel corrosion is an important phenomenon in North America, which is largely overlooked. When an extended service life (e.g. > 75 years) is required from a structure, additional considerations need to be taken into account. This article provides an excellent review of these considerations.
Since the economic impact of extensive structural repairs can be prohibitive, the early detection of corrosion-induced damage in reinforced concrete structures is significantly important for taking the necessary steps for early intervention. In their article, Mr. Mancio, Dr. Zhang, and Professor Monteiro present a brief review on the main non-destructive methods currently available to evaluate corrosion activity of rebars in concrete structures, and introduce a new surface measurement method, which can determine the position and corrosion state of the reinforcing bars from the concrete surface, with no need for a connection to the reinforcement.
Mr. Bouchard of the Ministère des Transports du Québec summarises their approach to inspecting the condition and assessing the reliability of the 4800 concrete bridges they own, and the 4400 municipal bridges for which they provide technical assistance. It is stressed in the article that systematic bridge inspections must be carried out frequently in order to find defects before they become serious and pose a risk to safety of the users. The development of a new non-destructive technique for the assessment of reinforcement corrosion in concrete bridge decks is also discussed.
Mr. Vaysburd and Mr. Emmons provide an excellent summary of the concrete repair technologies that are available to us today, and discuss the advantages and disadvantages of these methods. They demonstrate how misconceptions can become “received wisdom” and lead us to place too much emphasis on the wrong issues.
Professor Chidiac offers a review of the models and approaches that have been proposed for predicting the durability of concrete structures and their remaining service lives. The features and shortcomings of each type of approach are discussed and exemplified. It is stressed that quantitative prediction of
durability can be achieved either by applying stochastic / reliability concepts or using analytical modelling based on the deterioration processes. As Professor Chidiac notes, the use of reliable predictive durability models coupled with inspection and maintenance programs are the evolving trends for developing economically sustainable infrastructure.
Finally, we would like to thank our contributors who kindly accepted to prepare articles for this special issue on durability of concrete structures. We believe that these articles will pave the road to a common understanding on the problems associated with durability problems in concrete structures.
