page_title: Reinforced concrete structures durability
section_title: Service life of a reinforced concrete structure
hierarchical_section_title: Reinforced concrete structures durability / Service life of a reinforced concrete structure
caption_attribution_description: English: Graphical representation of initiation and propagation periods, the two phases characterizing the service life of a reinforced concrete structure in relation to the corrosion of steel reinforcement.
context_page_description: The durability design of reinforced concrete structures has been recently introduced in national and international regulations. It is required that structures are designed to preserve their characteristics during the service life, avoiding premature failure and the need of extraordinary maintenance and restoration works. Considerable efforts have therefore made in the last decades in order to define useful models describing the degradation processes affecting reinforced concrete structures, to be used during the design stage in order to assess the material characteristics and the structural layout of the structure.
context_section_description: Initially, the chemical reactions that normally occur in the cement paste, generate an alkaline environment, bringing the solution in the cement paste pores to pH values around 13. In these conditions, passivation of steel rebar occurs, due to a spontaneous generation of a thin film of oxides able to protect the steel from corrosion. Over time, the thin film can be damaged, and corrosion of steel rebar starts. The corrosion of steel rebar is one of the main causes of premature failure of reinforced concrete structures worldwide, mainly as a consequence of two degradation processes, carbonation and penetration of chlorides. With regard to the corrosion degradation process, a simple and accredited model for the assessment of the service life is the one proposed by Tuutti, in 1982. According to this model, the service life of a reinforced concrete structure can be divided into two distinct phases.
  ,  initiation time: from the moment the structure is built, to the moment corrosion initiates on steel rebar. More in particular, it is the time required for aggressive agents (carbon dioxide and chlorides) to penetrate the concrete cover thickness, reach the embedded steel rebar, alter the initial passivation condition on steel surface and cause corrosion initiation.
  ,  propagation time: which is defined as the time from the onset of active corrosion until an ultimate limit state is reached, i.e. corrosion propagation reaches a limit value corresponding to unacceptable structural damage, such as cracking and detachment of the concrete cover thickness.
  The identification of initiation time and propagation time is useful to further identify the main variables and processes influencing the service life of the structure which are specific of each service life phase and of the degradation process considered.
caption: Initiation and propagation periods of steel rebar corrosion in a reinforced concrete structure
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