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1 In the development of a quality assurance (QA) program, a state highway agency (SHA) incorporates policies and procedures for assessing how well the materials and construc- tion used by a contractor on a construction project satisfy the SHAâs specifications. Such procedures, commonly referred to as acceptance procedures, include detailed requirements for sampling and testing methods, selection of acceptance quality characteristics (AQCs), limits for those AQCs, and often procedures for calculating pay factors. One of the key considerations in the QA program is whether the SHA (or SHAâs designee) will conduct the acceptance sampling and testing or use contractor data for acceptance. According to a December 2015 FHWA Quality Assurance Assessment Report, 31 SHAs were using contractor test results in one or more of their acceptance decision processes. Title 23 Code of Federal Regulations Part 637 Subpart B (23 CFR 637B) permits the use of results from contractor testing in determining the degree of compliance of materials and construction with project specifications, provided that the SHAâs QA program meets certain requirements. One of those requirements is that the SHA must use an appropriate process to validate the contractorâs results. This project addresses the need to identify procedures currently available for validating contractor test data for construction materials and to develop statistically sound and practi- cal procedures for validating contractor construction materials test data. The project was then to recommend procedures for validating contractor test data for construction mate- rials and to prepare guidelines for their application. This report documents the research performed and presents a proposed practice for validating contractor test data. When a SHA conducts all sampling and testing used in acceptance decisions, validation testing is not required. However, agencies may find value in the procedures and guidelines provided for identifying outlier data and dispute resolution. A literature review revealed a handful of statistical methods with F- and t-tests appear- ing significantly more often than any other method. The literature review was summa- rized into seven categories: (a) Validation Techniques and Diversity in Procurement Methods; (b) Modification of Existing or New Statistical Tests; (c) Concern with Bias; (d) Nonparametric Tests; (e) Potential Risks Associated with F- and t-tests; (f) State of the Practice; and (g) Policy, Standards, and Guidelines. A web-based survey of SHAs was conducted to obtain information in addition to that obtained from the search and review of literature. Twenty-nine SHAs completed the survey, with 22 SHAs responding that they do use contractor test results as part of the acceptance procedure. A breakdown of the SHA responses based on material type was presented. The survey also identified challenges that SHAs face with QA programs that needed to be considered in developing recommendations and conclusions. S U M M A R Y Procedures and Guidelines for Validating Contractor Test Data
2 Procedures and Guidelines for Validating Contractor Test Data The research approach builds upon the findings from the literature review and the survey of SHAs, with three major stages: gathering information, numerical analysis, and analysis of SHA data. A proposed AASHTO practice was prepared to describe appropriate processes for vali- dating contractor test results and recommending subsequent actions when the results are validated or not validated. The proposed practice identifies the purpose, the target audi- ence, background resources, and applicability of the recommended procedures. It also cites applicable standards and other relevant documents, and defines key concepts, such as acceptance plan, dispute resolution, and validation. The main part of the proposed practice incorporates the procedures and guidelines for validating contractor test data and includes an overview of the validation process and description of validation steps. Two recom- mended sampling and testing plans are presented as an appendix of the proposed practice.