CORROSION OF STEEL IN MSE WALLS DUE TO DEICERS AND BACKFILL AGGREGATES

Author

Dipesh Tajhya, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2017

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Kolay, Prabir

Abstract

Mechanically Stabilized Earth (MSE) wall is a civil structure that has been used for various purposes e.g., supporting bridges, residential or commercial buildings, roadways, railroads etc. In general, MSE wall uses either metal strip, bar or geosynthetics materials as reinforcement. Roger et al. (2010) mentioned that an approximately 57% of the MSE wall constructed in U.S. utilize steel strips as the resources of reinforcement. The usage of metal steel strips is followed by usage of steel bar mats (24%) and geosynthetics grids (18%). Even though MSE walls are designed for a service life of 75 to 100 years, early complication has often been reported. Corrosion of the reinforced steel has been the major cause that afflicts the long-term performance of these walls. The deicing salts used on pavements to melt down snow is one of the major cause of corrosion of these reinforced steels. The aggressiveness of deicers in terms of corrosion of these reinforced steel is studied through the potentiodynamic polarization technique at various concentrations. This study aims to determine the corrosion behavior on galvanized steel and bare steel in presence of individual deicing salt or deicers e.g., sodium chloride, calcium chloride, magnesium chloride and potassium acetate at various (i.e., 0.25, 0.50 and 1.0 M) concentration. Subsequently, the surface morphology was analyzed by using Scanning Electron Microscopy (SEM) and the mineralogical composition was observed through X-Ray Diffraction (XRD). In addition, the corrosivity of two backfill aggregates, natural aggregate and recycled concrete aggregate, was compared. The result shows that the corrosion effect of deicers on reinforced steel depends on its chemical composition and concentration. The SEM imaging showed the presence of micro cracks on the surface of galvanized steel, resulting in pitting corrosion rather than general surficial corrosion. Comparing the corrosion rate of these deicers, the aggressiveness of these deicers on galvanized steel can be arranged in the following order: sodium chloride > calcium chloride > magnesium chloride > potassium acetate. Although sodium chloride was most aggressive for both the steel, the aggressiveness of these deicers on bare steel was different from that of galvanized steel and can be arranged in following order: sodium chloride > magnesium chloride > calcium chloride > potassium acetate. The pH and electrical resistivity of the natural and recycled aggregates were compared with standard provided by American Association of State Highway and Transportation Officials (AASHTO) and found to be non-corrosive. The corrosion rate of both the aggregates on galvanized and bare steel were inappreciable. While analyzing the corrosiveness of these two aggregates, recycled concrete aggregate was observed to be more aggressive than the natural aggregate.