Electrochemical properties of earthen materials—resistivity (conductivity), pH, organic content, and salt content (e.g., chlorides, sulfates, and phosphates)—are used to characterize the potential for corrosion of buried or embedded steel elements. These elements are often incorporated into transportation-related construction projects within retaining walls, earth embankments, bridge foundations, abutments, and approaches. Electrochemical properties are typically evaluated using the current AASHTO standard methods T 288 through T 291. These methods are based upon procedures originally developed and applied to agronomy. They neither consider the different characteristics of materials used in transportation-related construction nor distinguish issues inherent to particular applications. For example, the moisture contents of mechanically stabilized earth (MSE) fills during service cannot exceed 100 percent saturation, which is not adequately addressed in AASHTO T 288. Moreover, current test standards do not accommodate the coarse sand, gravel, and aggregate fill types commonly used in construction. Construction practices and knowledge of in-ground corrosion have evolved since the 1990s, such that the limitations of the current AASHTO test methods must be recognized. Suitable alternatives must be developed and implemented. There are many transportation projects for which these limitations create issues such as project delays, the necessity of using more expensive sources of backfill, lower quality of the finished product, etc. Research is needed to address the limitations of the current AASHTO test methods used to measure the electrochemical properties of earthen materials surrounding buried or embedded steel elements. The research should identify alternative test methods that are more appropriate for particular applications (e.g., MSE walls). The alternative test methods developed should be used for assessing corrosion potential for different applications and should result in recommendations for updating the current AASHTO standards for the design and construction of highway structures.
The objective of this research was to develop new or improved laboratory and field test methods to measure the electrochemical properties of earthen materials surrounding buried or embedded steel elements. The methods shall be representative of field conditions, and provide acceptable calibration, repeatability, and reproducibility.