This paper presents the results of the laboratory investigations on the corrosion of paint-coated steel plates with defects under laboratory conditions of simulated marine environment and in the field. First, experimental qualitative evidence showing significant similarity of the polarization behavior between divided, which were used for measurement of each potential and macrocell current, and undivided steel plates was established. Macrocell and microcell corrosion were then monitored in paint-coated steel plates with defects under different exposure situations and temperatures. Lastly, corrosion rates in an existing paint coated steel structure in the field were estimated. Results show that values of electro-chemical measurements in divided steel plates are almost the same and showed the same trend as the undivided steel plate. Macrocell corrosion occurred between the painted part and the defect part of the steel plates. The exposure condition where high oxygen supply and high temperature exist, provided the most severe environment for corrosion of paint coated steel with defect. Moreover, corrosion rates in an existing steel structure in the field were successfully estimated.
Using seawater in concrete can be considered as one of the sustainable approaches in construction industry not only to save the freshwater resource but also to promote the use of abandoned seawater resource, especially in the construction at the uninhabited area close to the sea where the procurement of fresh water is difficult. In this study, durability against chloride attack of seawater mixed concrete with different replacement ratio of BFS (blast furnace slag) and FA (fly ash) is discussed and the life time until the occurrence of corrosion crack is evaluated. The results show that: (1) Chloride penetration rate of seawater mixed specimens with BFS and FA is lower than that of freshwater mixed OPC (ordinary Portland cement) specimens; (2) Oxygen permeability of seawater mixed specimens with BFS and FA is almost the same or lower than that of freshwater mixed OPC specimens; (3) Total life time (corrosion incubation period and propagation period) of seawater mixed specimens with BFS and FA is almost the same or only slightly shorter than that of freshwater mixed OPC specimens. From the results, it was confirmed that the usage of seawater in concrete mixing is feasible in concrete with the appropriate BFS and FA replacement ratio.
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