Steel, Structural--Corrosion

Critical chloride threshold, CT values for initiation of reinforced steel corrosion m
mortar typical of Florida coastal bridge substructures were determined in laboratory tests.
Previous research has reported CT values that vary by more than an order-of-magnitude,
making design life estimation for structures difficult. On this basis, experiments on
piling type specimens focused on [Cl-] contamination in the splash zone and coupling of
this steel to a large surface area submerged anode. The lower portion of simulated piling
was immersed and the region above the waterline periodically sprayed with NaCI
solution. Corrosion potential with respect to height above the waterline was monitored.
A temporary depolarization method for determining as to whether or not corrosion had
initiated is proposed. Chloride distribution at the reinforcement-concrete interface was
determined in piling using energy dispersive x-ray analysis and related to height with
respect to the waterline. Chloride threshold was related to corrosion potential.

This research tests the corrosion resistance of weathering steel against carbon
steel exposed to dry and humid cycles during laboratory experiments. Various
environments are tested and include the following parameters: chloride
concentration, pH and wetting time. Corrosion values from weight loss analysis are
given and studied for the same environments. X-ray diffraction characterized the
formation of different oxides as a function of the environment and gave a better
understanding on the formation of the protective patina on the weathering steel, and
validated that chamber experiments reproduce field conditions. The study is
supported by the design, test and validation of an easily deployable galvanic
atmospheric corrosion sensor that allowed the monitoring of the corrosion rate on
an hourly basis.

In order to identify the influence of chlorides and surface finish on pitting potential of high performance reinforcing steel, cyclic polarization scans were performed on types 304, 2201 and 3Cr12 stainless steels and MMFX-II in simulated pore solution to which chloride was incrementally added. Furthermore, the surface condition was investigated with regard to the pitting potential. Pitting potential distributions versus the chloride content and surface finish were obtained. Pitting resistance was lowered as chloride was added and as the surface became rougher. Furthermore, a critical chloride to hydroxide ratio as a function of potential was determined for each material. Finally, according to the results of this study, the MMFX reinforcing steel was considered to have a corrosion performance close to that of Type 2201 stainless steel for bridge use. MMFX-II specimens with a polished surface exhibited more positive pitting potentials than did ones with an as-received finish.