Corrosion Of Prestressed Concrete Bridge In Service Research

1. IntroductionFor the pre-stressed concrete bridges in offshore and cold area, due to the corrosion effect of the corrosive agents in the environment to the structures, the safety of the bridge structures will decline with the service time, and this will affect the normal use of the bridge structures in the residual service time. So methods on design, construction and protection should be used to protect the normal use of the bridge structures in the designed service time.The research on corrosion of pre-stressed concrete bridge is a very complex project, the research involve the theory of pre-stressed concrete engineering, electrochemical mechanism, structural durability analysis, theory of control and etc. Due to this reason, the research on this field is rare, and most relevant research is mainly on the development of pre-stressed concrete engineering, structural electrochemical mechanism, the method of monitoring, corrosion protection of service structure and structural durability analysis separately.In this paper, based on the previous research result, by using theory of electrochemical mechanism, probability math, reliability theory, basic theory of pre-stressed concrete structures, structure optimum design, theory of control, maintenance strategy decision theory of structures and etc., the research on steel corrosion monitoring method, structural corrosion damage model, reliability analysis, the maintenance and repair method that based on corrosion control, the optimum structural design method of new bridge structures that consider durability and the optimum maintenance strategy decision theory are carried out.2. Corrosion mechanism and monitoring techniqueIt is widely accepted that the corrosion of steel in concrete structure is a electrochemical process, include the formation of anode & cathode area on metal surface and potential difference between different'area.Because the residual service life of concrete structure may be predicted by sitemeasurement result, and the site measurement result can give a guide for further maintenance and repair, engineers begin pay more attention to the site non destructive test methods. Based on practical application conditions, half-cell potential method, concrete resistance measurement, linear polarization resistance method and etc.3. Corrosion durability and maintenance control of pre-stressed concrete bridgeCompared with that of normal reinforcement, the corrosion damage characters of pre-stressed steel have its own specialty. So, for pre-stressed concrete bridge structure member, it may be assume safely that the initial corrosion time be regarded as the limit state of corrosion damage of structure or members. The initial corrosion time may be decided by structural protection degree and penetration rate of corrosive agents.The damage of structure is normally begun from local area, so the reliability evaluation of structural member is pre-condition of reliability evaluation of whole structure. For structural member, the following assumption may be taken:Failure perfect correlation assumption of structural member: when structural member failure, the function restriction that correspondence to the most serious failure mode will failure first; or when structural member failure, the serious failure mode will be true first.For normal pre-stressed concrete bridge structure, the following assumption may be taken to simplify the calculation:Weak element assumption: when the service structure failure, the element that with the lowest reliability will failure first; that is, when the element that with the lowest reliability fulfill the service requirement, other elements will fulfill accordingly.Then the reliability of structural system will be:Because the corrosion of service pre-stressed concrete bridge structure is an electrochemical process, certain electrochemical method may be taken to control the corrosion initiatively.For large service pre-stressed concrete bridge, due to the structural character, external pre-stress...