Carbonation: A Probabilistic Approach to Derive Provisions for Prescriptive Requirements in Codes and Standards

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Title: Carbonation: A Probabilistic Approach to Derive Provisions for Prescriptive Requirements in Codes and Standards

Author(s): M. Maage

Publication: Special Publication

Volume: 212

Issue:

Appears on pages(s): 701-720

Keywords: carbonation; concrete; prescriptive requirements; probabilistic approach; reinforcement corrosion; standardization

Date: 6/1/2003

Abstract:
In most existing standards and guidelines, durability of reinforced concrete structures is covered by prescriptive requirements. For corrosion initiated by carbonation, this may include requirements on w/cm, type and content of cement, compressive strength, concrete cover etc. Future requirements will probably be performance based, defined according to a probabilistic approach. However, today we don’t have the appropriate information on the correlation between carbonation rate and factors like w/cm, type and content of cement and environmental situation, especially air humidity and CO2 concentration. Therefore, requirements in standards are still prescriptive. However, the pre- scriptive specifications within codes and standards may be based on testing of existing structures and using a probabilistic approach when analysing the results. A probabilistic approach to the process of defining prescriptive requirements for concrete exposed to carbonation, is presented. The approach is based on the philosophy given in the European standard EN 1990 (1) "Basic of Structural Design," which means that the "failure" reliability Z is calculated as the difference between a resistance against "failure" R (e.g., concrete cover) and an environmental load or action F (e.g., time dependent carbonation depth). Both resistance and load are expressed in a probabilistic way. The new European standard EN 206-1 (2) is used as example, but the presented principle may be used in other situations.