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15 2.1 Introduction This study was performed in three phases including nine tasks. Phase I (literature review), consisting of Tasks 1 through 4, included a search and review of existing information, synthe- sis of national and international practices, the identification and prioritization of knowledge gaps, and preparation of a draft protocol for sampling, testing, and evaluating steel corrosivity of earthen materials. Phase II (evaluation), consisting of Tasks 5 and 6, included a systematic study of alternative test methods for measuring electrochemical properties in the laboratory, algorithms for assessment of the corrosion potential of earthen materials, and further develop- ment of the protocol. During Phase III (validation), Tasks 7 through 9 were accomplished: the practicality of the proposed protocol and alternative laboratory test methods (from Phase II) was validated, the proposed protocol was modified as necessary, and the suggested labora- tory test methods were implemented in the field. Brief descriptions of all tasks are given in the following sections. 2.2 Phase I 2.2.1 Task 1. Information Search Task 1 consisted of three subtasks: 1. Compilation of relevant literature; 2. Documentation of differences between alternative test procedures; and 3. Identification of the best practice for applying each test procedure, depending upon material type and the environment and/or site conditions associated with particular applications. On the basis of that information, two items were developed: a preliminary draft protocol with guidance for selecting test methods and assessing the corrosion potential of earthen materials and a work plan to address the knowledge gaps that were identified. 2.2.2 Task 2. Identify Limitations of Approaches for Characterizing Materials The research team reviewed different practices to characterize the corrosion potential of earthen materials adopted by transportation agencies and identified the limitations associated with different practices. 2.2.3 Task 3. Develop Detailed Work Plan Detailed plans were prepared for sampling and a program of laboratory tests to address the limitations of different practices identified in Task 2. C H A P T E R 2 Research Approach
16 Electrochemical Test Methods to Evaluate the Corrosion Potential of Earthen Materials 2.2.4 Task 4. Submit Interim Report The research team submitted an interim report summarizing the results, conclusions, pre- liminary draft protocol, and the recommended work plans developed on the basis of Tasks 1 through 3. The interim report was submitted to NCHRP in January 2017. 2.3 Phase II 2.3.1 Task 5. Conduct Work Plan Approved in Task 4 Following the NCHRP review of the interim report, the research team implemented the approved work plan developed in Task 3. This task included analyses of results from alternative laboratory tests for measuring the electrochemical properties of earthen materials. Use of new or improved methods for sampling and testing was recommended on the basis of interpretation of these data, and this information was incorporated into the draft protocol. 2.3.2 Task 6. Prepare Work Plan for Field Trials Plans to implement the proposed protocol as a shadow specification were made in coopera- tion with owners and contractors on active construction projects. This step was necessary to refine the test methods and analysis procedures on the basis of working conditions and to assess the practical limitations of the proposed specifications. 2.4 Phase III 2.4.1 Task 7. Implement Work Plan for Field Trials The research team implemented the work plan that was developed and approved in Task 6. During Task 7, the team evaluated the practicality and ease of use of the new procedures through interaction with laboratories engaged in testing electrochemical properties of earthen materials, suppliers of MSE wall systems, and owners. The outcomes from Task 7 were used to determine whether the main technical goal of the research project (better characterization of corrosion potential as compared with traditional methods) was met. 2.4.2 Task 8. Propose Protocol The draft protocol was updated on the basis of the findings and experiences of Task 7. 2.4.3 Task 9. Prepare Final Report This final report summarizes the findings of NCHRP Project 21-11, including ⢠Review of the most important parameters affecting the corrosion potential of earthen materials; ⢠Review of current laboratory and field practices to characterize the corrosion potential of earthen materials as well as identify the limitations associated with each practice; ⢠Development of a protocol for improved sampling and testing of earthen materials; ⢠Recommendation of alternatives to the current AASHTO test procedures (AASHTO T 288-12) in accordance with the recommended test protocol; and ⢠Discussion of deficiencies in present knowledge and recommendations for future work.
