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Author: Travis M. Gerber
Publisher:
Published: 2010
Total Pages: 74
ISBN-13:
DOWNLOAD EBOOKThe primary objective of this study was to extract reinforcement coupons from select MSE walls and document the extent of corrosion. A secondary objective of this project was to develop and assess techniques for removal of coupons on two-stage MSE walls.
Author: Christopher L. Raeburn
Publisher:
Published: 2008
Total Pages: 42
ISBN-13:
DOWNLOAD EBOOKMechanically Stabilized Earth (MSE) retaining walls have become the dominant retained wall system on ODOT projects. The permanent MSE walls constructed on ODOT projects, in recent years, use metallic reinforcements and facing connections buried directly in the backfill soil. Accelerated deterioration of these structural elements would have serious financial and safety impacts for the Department. Classical MSE wall design incorporates an estimate of deterioration of reinforcement by corrosion. Monitoring of actual corrosion performance, however, is an important element of managing the current inventory of MSE walls. Monitoring could answer key questions that can provide for the best management of the existing walls, and provide feedback to the design process for future installations. This report details a literature review of methods for estimating and measuring deterioration of structural reinforcing elements in both concrete and MSE walls. It also presents a selected history of metallic reinforcement design specification and utilization. A listing of the MSE walls that can be identified in the ODOT Bridge Data System is included.
Author: Robert A. Thompson
Publisher:
Published: 2020
Total Pages: 0
ISBN-13:
DOWNLOAD EBOOKBased on the results of laboratory testing, the initial galvanization coating was likely greater than the specified thickness of 2.0 oz/ft2 (86 μm). The zinc galvanization is corroding at a slower rate than the AASHTO design rate. The AASHTO design rate for depletion of zinc coating and subsequent corrosion of the steel reinforcement is conservative for the corrosion conditions present in the MSE wall reinforcement coupons tested. The integrity of the steel reinforcement that is currently in place is not likely to be compromised by corrosion.
Author: Travis M. Gerber
Publisher: Transportation Research Board
Published: 2012
Total Pages: 211
ISBN-13: 0309223741
DOWNLOAD EBOOK"Mechanically stabilized earth (MSE) walls are an important class of infrastructure assets whose long-term performance depends on various factors. As with most all other classes of assets, MSE walls need periodic inspection and assessment of performance. To date, some agencies have established MSE wall monitoring programs, whereas others are looking for guidance, tools, and funding to establish their own monitoring programs. The objective of this synthesis project is to determine how transportation agencies monitor, assess, and predict the long-term performance of MSE walls. The information used to develop this synthesis came from a literature review together with a survey and interviews. Of the 52 U.S. and 12 Canadian targeted survey recipients, 39 and five, respectively, responded. This synthesis reveals that unlike bridges and pavements, MSE walls and retaining walls in general are often overlooked as assets. Fewer than one-quarter of state-level transportation agencies in the United States have developed some type of MSE wall inventory beyond that which may be captured as part of their bridge inventories. Fewer still have the methods and means to populate their inventories with data from ongoing inspections from which assessments of wall performance can be made. In the United States, there is no widely used, consistently applied system for managing MSE walls. Wall inventory and monitoring practices vary between agencies. This synthesis examines existing practices concerning the nature, scope, and extent of existing MSE wall inventories. It also examines the collection of MSE wall data, including the types of performance data collected, how they are maintained in wall inventories and databases, the frequency of inventory activities, and assessment practices relevant to reinforcement corrosion and degradation. Later parts of this synthesis discuss how MSE wall performance data are assessed, interpreted, and used in asset management decisions. This synthesis finds that the most well-implemented wall inventory and assessment system in the United States is the Wall Inventory Program developed by FHWA for the National Park Service. However, this system, like some others, uses 'condition narratives' in a process that can be somewhat cumbersome and subjective. Other systems use more direct numeric scales to describe wall conditions, and an advantage of such systems is that they are often compatible with those used in assessments of bridges. As experience with MSE walls accumulates, agencies will likely continue to develop, refine, and better calibrate procedures affecting design, construction, condition assessment, and asset management decisions. One portion of this synthesis is dedicated to summarizing the actions taken thus far by survey respondents to improve the long-term performance of their MSE walls. Many agencies prescribe the use of a pre-approved wall design and/or wall supplier. Other actions or policies frequently focus on drainage-related issues."--Summary.
Author: Nelson Pearson
Publisher:
Published: 2015
Total Pages: 572
ISBN-13:
DOWNLOAD EBOOKThe inability of soil to provide sufficient tensile strength presents challenges for soils being used as a structural building material. However, it is possible to improve the structural performance with the inclusion of a reinforcing system. The development of these systems has been a major advancement of the civil engineering practice. Mechanically stabilized earth (MSE) wall systems typically consist of a: concrete facing panel, specified backfill, reinforcing elements, and the retained fill. The interaction of the backfill with the reinforcements, and the reinforcements with the facing panels, produces a system that when properly designed, can be a cost effective engineering solution. In Nevada there are over 150 MSE walls that have been constructed using metallic reinforcements (Thornley 2009). Corrosion of metallic elements a naturally occurring electrochemical process is irreversible an inevitable. The rate of metal loss (corrosion) is a function of the environmental conditions and metal type. For MSE walls key parameters include the backfill's: salt content, organic content, saturation level, as well as the metal type of the reinforcements. Nevada has two previous corrosion investigations, an extensive site investigation at I-515/ Flamingo Rd. and a statistical analysis of as-built soil records along with a preliminary investigation for I-15/ Cheyenne Blvd. These studies form the foundation for this investigation of in-situ corrosion conditions. Seven MSE wall sites were investigated using electrochemical backfill characterization and linear polarization resistance (LPR) corrosion rate monitoring. Evaluation of electrochemical backfill characteristics has resulted in the discovery of six sites that fail current NDOT/ AASHTO MSE wall backfill requirements. The in-situ soil samples collected and analyzed more than doubled the available data used to describe the corrosiveness of the backfill. Linear polarization resistance corrosion rates were obtained for more than 200 different elements. These data suggest that despite the aggressive nature of the backfill, most elements are preforming well and are below the anticipated rates. However, several elements were discovered with corrosion rates in excess of five times the design model. The use of the LPR corrosion monitoring has concluded that the conditions at I-15/ and Cheyenne Blvd. are equivalent to or worse than the conditions evaluated in 2004 at the I-515/ Flamingo Rd. complex. The discoveries at Flamingo Rd. led to remediation of the largest wall at the complex. Through the use of electrochemical backfill characteristics and LPR corrosion rates, the seven sites investigated have been ranked. The rankings are dependent on several factors such as backfill electrochemical conditions and comparison of corrosion rates data with design models. This study has confirmed that observations of conditions along the exterior of the wall are not sufficient when determining the condition of the soil reinforcements. Routine corrosion monitoring is required to monitor the depletion of the soil reinforcements and should be incorporated into a Long-term Corrosion Monitoring and Asset Management Plan (LCMAMP). It is anticipated that a program will be integrated into Nevada's current asset management systems. The development and implementation of LCMAMP, directly reflects the federal initiative for systematic detailed evaluation of critical assets, MAP-21.
Author: Brandon Seth Berke
Publisher:
Published: 2009
Total Pages:
ISBN-13:
DOWNLOAD EBOOKABSTRACT: 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.
Author: Enrique A. Paz
Publisher:
Published: 2015
Total Pages: 54
ISBN-13:
DOWNLOAD EBOOKThis project provided information and recommendations for material selection for best corrosion control of reinforcement in mechanically stabilized earth (MSE) walls with void repairs. The investigation consisted of small- and large-scale experiments and modeling to examine corrosion aggravation effects and conduct durability projections.
Author: Michael Watts Esfeller (Jr)
Publisher:
Published: 2010
Total Pages:
ISBN-13:
DOWNLOAD EBOOKA Mechanically Stabilized Earth (MSE) wall is a vertical grade separation that uses earth reinforcement extending laterally from the wall to take advantage of earth pressure to reduce the required design strength of the wall. MSE wall systems are often prefabricated to reduce construction time, thus improving constructability when compared with conventionally cast-in-place reinforced wall systems. However, there is a lack of knowledge for predicting the service-life of MSE retaining wall systems when recycled backfill materials such as Recycled Asphalt Pavement (RAP) and Crushed Concrete (CC) are used instead of Conventional Fill Material (CFM). The specific knowledge missing is how these recycled materials, when used as backfill in MSE wall systems, affects the corrosion rate of the reinforcing strips. This work addresses this knowledge gap by providing recommendations for MSE wall systems backfilled with CC or RAP, and provides a guide to predict the service-life based on corrosion rate test data obtained from embedding steel and galvanized-steel earth reinforcing strips embedded in MSE wall systems backfilled with CC, RAP, and CFM. Experimental data from samples emulating MSE wall systems with steel and galvanized-steel reinforcing strips embedded in CC and RAP were compared to samples with strips embedded in CFM. The results of the testing provide data and methodologies that may, depending on the environmental exposure conditions, justify the use of RAP and CC for the construction of MSE walls. If these backfill materials are obtained from the construction site, this could provide a significant cost savings during construction.
Author: Highway Innovative Technology Evaluation Center (U.S.)
Publisher: ASCE Publications
Published: 2005-01-01
Total Pages: 232
ISBN-13: 9780784475591
DOWNLOAD EBOOKAuthor: Dipesh Tajhya
Publisher:
Published: 2017
Total Pages: 570
ISBN-13:
DOWNLOAD EBOOKMechanically 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.
