Taxonomy for protective ability of rust layer using its composition formed on weathering steel bridge

For a quantitative evaluation of the protectiveness of a rust layer formed on a weathering steel bridge, the relationship between the corrosion rate of the bridge and the composition of the rust layers formed on the girders was first investigated. These corrosion rates were clearly classified by the protective ability index (PAI) of alpha/gamma* and (beta + s)/gamma*, where alpha, gamma*, beta and s are the mass ratio of crystalline alpha-FeOOH, the total of gamma-FeOOH, beta-FeOOH and the spinel-type iron oxide (mainly Fe(3)O(4)), beta-FeOOH and spinel-type iron oxide, analyzed by XRD, respectively. The inequality of the former index alpha gamma* > 1 expressed the protectiveness criterion of the rust layer, while that of the latter index, (beta + s)/gamma < 0.5 or > 0.5, classified the corrosion rate of the non-protective rust layer. The PAI is useful for a quantitative evaluation of the protectiveness of a rust layer formed on a weathering steel bridge and is an important item for the corrosion assessment of the bridge. (c) 2006 Elsevier Ltd. All rights reserved.