This article introduces the methodology for durability design of concrete repairs for infrastructures affected by deterioration in mid-life. A change of design approach is recommended, from the conventional “prescriptive approach” practiced by current design standards to performance-based approach” which considers the actual ageing process through probabilistic treatment. Corrosion of steel reinforcement is considered as the most critical process and subject to performance-based design. The target design-life and durability limit states are attributed to concrete elements according to their desired maintenance free life. This article is based on experience of the author in dealing with durability assessment of infrastructures.
1.Motivation
Signicant amount of national funds are invested worldwide in the construction of infrastructure required to support society’s needs. In India it was forecasted that an investment of about Rs. 65 lakh crores in infrastructure was required for the 12th five year plan [Planning Commission]. Such high initial cost of infrastructure justies the importance of durability for such facilities. However existing infrastructure is undergoing deterioration faster than predicted, because the mechanism of degradation was not understood well at the time of construction and was not taken into account in the planning [Faroz and Ghosh, 2017]. As a result infrastructures such as bridges have degraded well before their expected service life is reached. As a result extensive repairs are needed for such infrastructures. In U.S., the annual cost for repair, maintenance and strengthening is estimated between $18 and $21 billion [Emmons and Sordyl, 2006]. Similar estimates can be expected for our country. Additionally, hindrance to the usability of facilities because of repair works cause signifcant revenue loss.
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