The PW and FW methods convert cash flows resulting from a proposed solution into their equivalent worth at some points in time, i.e. at the beginning of the study period for the former or at the end of the latter, by using an interest rate. While the economic profitability of an alternative is evaluated by using the PW or FW value, the PW method makes it easy to determine the economic advantage of one alternative over another, and the FW method is often used to estimate the alternative's worth at the time of sale or disposal. The both methods were applied to the same example to compare their features. Economic and functional obsolescence is often reached before physical life expectancy. If a structure becomes redundant due to economic and functional obsolescence then the investments made for future maintenance requirements can be reduced. The chance of a structure becoming redundant within each 10 year period of its life was assumed and the maintenance cost was compared by using the PW method.
Steel bridges often have plural girders. Though the form of girders is the same, the difference of the position of girder in a bridge potentially causes different feature of corrosion environment around each girder. The purpose of this study is to clear the influence of solar radiation on corrosion of steel girders of bridge. In this study, these authors surveyed the eastern and the middle girders of the weathering steel bridge, which run north to south and has three girders. The eastern girder is exposed to solar radiation in the morning, while the middle one is not directly exposed to solar radiation. In this study, these authors analyzed, solar radiation, precipitation rate of airborn salt, temperature and relative humidity of area between girders, and temperature of girders. Both girders get wet due to dew during night to before morning, and get dry during daytime. In the case of clear weather in morning, solar radiation remarkably increased temperature of the eastern girder relative to middle one. In such case, the speed of the desiccation of the eastern girder was faster than that of the middle one. As a result, the time that the middle girder gets wet was three times as long as that of the eastern one. Therefore there is a possibility that corrosion of the middle girder will progress relative to that of the eastern one.
Corrosion mass loss and polarization curve of aluminum in 1 mol dm－3 aluminum chloride solution were measured. The polarization resistance-current density plotting, which is differentiated from the experimented polarization curve, was simulated and considered as a parallel electric circuit of both anodic and cathodic polarization resistances. Current density（0.013～0.017 mA･cm－2）obtained by differential polarization method has roughly agreed with value of 0.012 mA･cm－2 of corrosion current density calculated from corrosion mass loss of the aluminum specimen in the aluminum chloride solution.
When various types of rust powder coexist on the process of rust occurrence, the feature of the formed rust was investigated. As a result, the rust of the same crystalline morphology as the coexisted rust was formed preferentially. Moreover, the protective rust was formed by coexistence of rust homogeneous as the protective rust formed on weathering steel. Furthermore, by surface treatment of resin mixing the rust which promotes protective rust formation on weathering steel, the protective rust layer was formed under the surface treatment film from the corrosion early stage, and the suppression of corrosion dissolution reaction or the noble of corrosion potential was checked.
In order to estimate the effects of anions on passive film breakdown, the values of the time required for breakdown, tbd were determined for a passivated iron electrode in aqueous solutions of 0.1 M various anions. Relationships between log tbd and the hardness of anion base, H were discussed on the basis of the hard and soft acids and bases principle. According to the principle, anions were classified into four groups, hard base, oxidative hard base, soft and hard base, and soft base. For the former three groups, log tbd increased with H but in reverse, decreased with an increase in H for the latter. The former relationships could be interpreted by suppression of anion incorporation into the film due to stable hard acid-hard base interaction. However, the relationship could not be explained by this interaction for the group of soft base anions.