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16 Chapter 2. Research Approach 2.1. Introduction We performed this study in three phases including nine tasks. Phase I, consisting of Tasks 1 through 4, included a search and review of existing information, synthesis 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 development of the protocol. During Phase III, (Validations) including Tasks 7 through 9, we evaluated the practicality of the proposed protocol and alternative laboratory test methods (from Phase II), validated and modified the proposed protocol as necessary, and facilitated implementation of the suggested laboratory test methods in the field. Brief descriptions of all tasks are presented in the following sections. 2.2. Phase I 2.2.1 Task 1 â 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. Based on that information, we developed a preliminary draft protocol with guidance for selection of test methods and assessing the corrosion potential of earthen materials, and a work plan to address the knowledge gaps that we identified. 2.2.2 Task 2 â Identify Limitations of Approaches for Characterizing Materials We reviewed different practices to characterize the corrosion potential of earthen materials adopted by transportation agencies, and we identified the limitations associated with different practices. 2.2.3 Task 3 â Developed Detailed Work Plan We prepared detailed plans for sampling and a program of laboratory tests to address the limitations of different practices that we identified in Task 2. 2.2.4 Task 4 â Submit Interim Report We submitted an Interim Report summarizing the results, conclusions, preliminary draft protocol, and recommended work plans developed from Tasks 1 through 3. The Interim Report was submitted to NCHRP in January 2017.
17 2.3. Phase II 2.3.1 Task 5 â Conduct Work Plan Approved in Task 4 Following the NCHRP review of our Interim Report, we 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. We recommended use of new or improved methods for sampling and testing based on the interpretations from these data and incorporated this information into the draft protocol. 2.3.2 Task 6 â Prepare Work Plan for Field Trials We made plans to implement the proposed protocol as a âshadow specificationâ in cooperation with owners/contractors on active construction projects. This step was necessary to refine the test methods and analysis procedures based on working conditions, and to assess the practical limitations of the proposed specifications. 2.4. Phase III 2.4.1 Task 7 â Implement Work Plan for Field Trials We implemented the workplan developed and approved in Task 6. During Task 7 we evaluated the practicality and ease-of-use of the new procedures through the interaction with laboratories engaged in testing electrochemical properties of earthen materials, suppliers of MSE wall systems and owners. We used the outcomes from Task 7 to determine whether the main technical goal of the research project for better characterization of corrosion potential as compared to the traditional methods was met. 2.4.2 Task 8 â Propose Protocol We updated the draft protocol based on the findings and experiences from Task 7. 2.4.3 Task 9 â Prepare Final Report This final report summarizes the findings of NCHRP 21-11 project including: â¢ Review of the most important parameters affecting the corrosion potential of earthen materials. â¢ Review of current laboratory and field practices to characterize the corrosion potential of earthen materials as well as identifying the limitations associated with each practice. â¢ Development of a protocol for improved sampling and testing of earthen materials. â¢ Recommended alternatives to the current AASHTO test procedures (AASHTO T 288-12 2016) in accordance with the recommended test protocol. â¢ Discussion of deficiencies in present knowledge and recommendations for future work.