Improving Processes for Characterizing Corrosion Potential of Soils and Fill Materials

Electrochemical properties of soils and aggregates such as resistivity (conductivity), pH, salt (chlorides, sulfates, phosphates), and organics contents are used to characterize the potential for corrosion of buried/embedded metal elements that may include piles, drains, culverts, or soil reinforcements. These elements are often incorporated into transportation-related construction projects within earth embankments, bridge foundations, abutments, and approaches. Electrochemical properties are evaluated using current American Association of State Highway and Transportation Officials (AASHTO) test standards, adopted in the early 1990s, that were based upon preexisting test procedures applied to agronomy. These methods do not consider the vastly different characteristics of materials used in transportation-related construction, nor do they distinguish issues inherent to particular applications. For example, moisture contents of mechanically stabilized earth (MSE) fills during service cannot exceed the saturation limit, and often coarse sand, gravel, and aggregate types of fills are used, which current test standards fail to consider. Construction practices and the knowledge of underground corrosion have evolved since the 1990s, such that the limitations of the current AAHSTO test standards must be recognized and suitable alternatives need to be evaluated and implemented. There are many projects for which this issue generates considerable conflict, and often results in use of more expensive sources of backfill. The needless use of more expensive sources of backfill from greater distances is not a wise use of available resources, does not contribute to proper asset management, and is inconsistent with sustainable design and construction practices. Research is needed to address limitations of current AASHTO-specified test methods. These limitations are related to (1) particle sizes that may be included in the test specimen (must pass a #10 sieve), (2) identifying the proper end-point for the test, and (3) the small size of the specimen included in the measurement. These attributes limit the appropriateness of the test results to finer soil types, and do not consider practical limits on water contents that may be experienced in the field. The research will evaluate alternative test methods that may be more appropriate for particular applications (e.g., MSE walls) and will consider a wider range of fill types. Protocols for assessing corrosion potential for different applications, and recommendations for updating the current AASHTO standards for the design and construction of bridges will be developed based on the evaluation of test alternatives. The research will address needed revisions and clarifications to existing standards, and the need to adopt new test methods. Results from this study will be a resource for highway and bridge engineers and contractors who need to evaluate the corrosiveness of soils and fill materials for construction, and will be of great interest to the AASHTO Subcommittees on Materials and on Bridges and Structures who review standards for material testing and design and construction of transportation facilities. The objective of this research is to review existing test procedures and evaluate alternatives that may enhance or extend the abilities to characterize the corrosiveness of earthen materials for a wider range of conditions and considering different applications compared to the current protocol. Specific tasks include to (1) identify alternative test methods for measuring the resistivity of soil/aggregate. Review and recommend existing procedures for testing coarse aggregate that apply to materials that do not have a significant amount of material passing a #10 sieve; (2) document differences in test procedures including sample preparation, methods of measurement, and potential interferences. Indicate the range of application for each test in terms of soil types and function (e.g., culverts, piles, MSE, etc.). Assess the occurrences of materials with minimum resistivity at the slurry state, and the relevance (or irrelevance) of this to in-service conditions; (3) recommend alternative test techniques that apply to coarse sands, gravels and aggregates and evaluate the test methods by comparing results obtained with different test methods including AASHTO T 288. Document relationships between measurements, expected correlations, trends, and other means that may be useful to crosscheck and verify the veracity of laboratory measurements. Verify results of the laboratory study with field measurements of corrosion from sites where the corrosion potentials of the fills have been assessed using laboratory test methods; (4) propose alternative tests that may be useful to replace, improve, modify, or enhance current AASHTO test standards; (5) recommend an updated protocol to assess corrosion potential of different materials and for various applications. The protocol may cite several test standards for measurement of resistivity, or other electrochemical properties, and provide guidance on when the different tests should be applied. For example, establish a boundary to describe coarse soil and aggregates and the different tests that apply to coarser and finer materials. Sample size will also vary with respect to the coarseness of the material (i.e., maximum size); and (6) recommend updates to the current AASHTO standards that may include new test standards and protocols for design and construction. Outcomes from this research include updated protocols for evaluating the corrosiveness of soils and fill materials, which will distinguish between specific applications, e.g., MSE wall systems as opposed to culverts and steel piles.


  • English


  • Status: Proposed
  • Contract Numbers:

    Project 21-11

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway & Transportation Officials

    444 North Capitol Street, NW, Suite 225
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Harrigan, Edward

  • Start Date: 20150915
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 40227

Subject/Index Terms

Filing Info

  • Accession Number: 01572342
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 21-11
  • Files: TRB, RiP
  • Created Date: Aug 6 2015 1:00AM