Performance based durability design of coastal reinforced concrete structures

Durability of a structure is defined as its ability to preserve functionality, stability and aesthetic properties under expected environmental influences without larger maintenance and repair costs during designed service life. Design service life of major concrete civil engineering structures, like bridges is usually 70, 100 or even 200 years. Numerous examples of early deterioration of reinforced concrete structures in marine environment have shown that this task is very difficult to achieve. That is why durability of civil engineering structures is today one of the key problems of structures worldwide. Premature loss in durability of structures is mainly caused by: poor quality of construction, wrong selection of building materials, poor design and non regular or absence of maintenance. All these are consequences of inadequate approach towards durability design. Procedures for bearing capacity design are well defined, mathematically precise, based on the principles of mechanics, standardized and commonly used in practice. On the other hand, durability design procedures of reinforced concrete structures in aggressive environment are for a large extent still empirical. It is based on deem-to-satisfy rules (e.g. minimum cover, maximum water/cement ratio) and the assumption that if these rules are met, then the structure will achieve an acceptably long but unspecified life. In this paper a performance based approach to durability design of reinforced concrete structures in aggressive marine environment is presented. Performance-based approach to the durability design of reinforced concrete structures means that it is based on durability indicators like materials parameters measured on laboratory and on site specimens and geometrical characteristic of cross section of reinforced concrete element. These durability parameters (chloride diffusion coefficient, gas permeability, water permeability, capillary absorption coefficient) are the input parameters for calculation models. In this paper mathematical modelling of materials degradation (corrosion of steel in concrete exposed to chlorides) based on materials performance parameters is presented. The result of such mathematical calculations is more realistic and reliable durability design of reinforced concrete structures.