Corrosion Effects of Cement Stabilized Backfill on Galvanized Steel Earth Reinforcements
Corrosion Effects of Cement Stabilized Backfill on Galvanized Steel Earth Reinforcements

Author: Derek V. Morris

Publisher:

Published: 1994

Total Pages: 156

ISBN-13:

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Cement stabilization of backfill has been used for some time in mechanically stabilized earth type retaining walls. However, there has been no data on the corrosion life of galvanized steel reinforcement in this environment, which is intermediate in pH between normal soil and pure cement. Field observations had indicated a potential corrosion problem at a particular site in District 12. As a result of the test program conducted during this project, the following conclusions were made. First, cement addition to backfill in the usual quantities (i.e. 7% or more) raised the pH environment to values close to that of normal concrete. At these levels corrosion rates of zinc coatings were not significantly accelerated -- if anything, corrosion rates were less than for unstabilized fill. Second, very small amounts of cement addition, of the order of 1% to 4% producing pH values significantly less than 12, could cause limited acceleration of corrosion. It is, therefore, advisable to control minimum cement levels and to encourage efficient mixing. Third, elevated corrosion rates were associated primarily with the presence of inorganic ions, both for stabilized and unstabilized fill. In the case of the problem site in District 12, this appeared to be the result primarily of unusually high sulfate content in the fill. Fourth, the use of crushed concrete as backfill did not accelerate corrosion. This material, therefore, appears to be acceptable for this application.

Long Term Corrosion of Reinforcing Strips in Mechanically Stabilized Earth Walls
Long Term Corrosion of Reinforcing Strips in Mechanically Stabilized Earth Walls

Author: Brandon Seth Berke

Publisher:

Published: 2009

Total Pages:

ISBN-13:

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ABSTRACT: Mechanically stabilized earth (MSE) walls are a more advanced form of a retaining wall, often larger and able to hold back more backfill. This is achieved by reinforcing strips or meshes (most often galvanized steel) placed into the soil, which are held in place by friction. The strips mechanically stabilize the earth while undergoing tension. The wall is covered with concrete medallions that connect to the reinforcements. The medallions have only a secondary structural role in holding up the wall but provide cover that protects the soil from washing away. MSE walls are structures expected to have very long service lives (e.g. 100 years). Confirmation is needed that such durability can be achieved, especially to show that the progression of corrosion of the reinforcement is slow enough. Ten MSE walls around Florida were instrumented (electrical connections were made through the concrete covers to the buried elements) between 1996- 1998 and used to survey corrosion rates of galvanized strip or mesh soil reinforcements. Initial estimates of corrosion-related durability were obtained at that time, indicating a good prognosis for long term durability. The objective of the research in this thesis was to obtain additional indications of the durability of reinforcements in MSE walls in Florida so as to perform a more reliable projection of future performance. Corrosion behavior was measured at the same locations as the initial survey by electrochemical nondestructive tests and by destructive tests. The nondestructive testing consisted of half-cell potentials, polarization resistance measurements, and electrochemical impedance spectroscopy. Corrosion rates reported in this thesis are based upon polarization resistance measurements. The destructive testing consisted of soil extraction and hardware extraction. Hardware extraction enabled independent verification of estimates of electrochemical corrosion rate. Analysis of extracted soil verified that soil composition was within construction specifications. The data from the current survey were also used to further improve prediction of corrosion. The present series of evaluations confirm that the structures are performing as desired based upon the updated model projection of future corrosion.

LRFD Metal Loss and Service-life Strength Reduction Factors for Metal-reinforced Systems
LRFD Metal Loss and Service-life Strength Reduction Factors for Metal-reinforced Systems

Author: Kenneth L. Fishman

Publisher: Transportation Research Board National Research

Published: 2011

Total Pages: 128

ISBN-13:

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TRB's National Cooperative Highway Research Program (NCHRP) Report 675: LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems explores the development of metal loss models for metal-reinforced systems that are compatible with the American Association of State Highway and Transportation Officials' Load and Resistance Factor Design Bridge Design Specifications.

Corrosion of Steel in MSE Walls Due to Deicers and Backfill Aggregates
Corrosion of Steel in MSE Walls Due to Deicers and Backfill Aggregates

Author: Dipesh Tajhya

Publisher:

Published: 2017

Total Pages: 570

ISBN-13:

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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.