Using the Results of Contractor-Performed Tests in Quality Assurance: Contractor's Final Report (2007)

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1 CHAPTER 1: INTRODUCTION PROBLEM STATEMENT AND RESEARCH OBJECTIVES The results of extensive sampling and testing at the AASHO Road Test in the late 1950’s and early 1960’s revealed unexpectedly large variabilities in measured properties of highway construction materials and products. This has led to considerable changes in the way highway construction projects are managed. The overall construction quality assurance process that has evolved includes three basic elements depicted in Figure 1. Process (quality) control, acceptance and independent assurance procedures are integral parts of the quality assurance process. In the traditional separation of responsibilities, contractors are responsible for their quality control and state DOTs are responsible for acceptance and independent assurance. However, with the enactment of the federal regulation 23 CFR 637B in 1995 (2), the roles of state DOTs and contractors have become less clear and distinct. Under certain conditions 23 CFR 637B permits the use of contractor tests for acceptance which results in a mixing and mingling of traditional responsibilities.

2 Figure 1. Elements of Quality Assurance (Ref. 1)

3 There seems to be general agreement, or at least no serious controversy, as to the value of contractor quality (process) control. Issues arise when contractor- performed tests are used in the acceptance process. This shift in responsibilities and associated risks has caused concern within some state DOTs. A particular concern is the viability of contractor-performed tests when used in the acceptance process. The results of surveys reported by Hancher, et al (3) indicated this was the primary concern of state DOTs. This concern is consistent with results of a survey reported by Burati et al (4) that ranked “procedures for verifying or validating contractor’s and agency’s test results” as the topic that most needs additional study and analysis for developing effective and efficient quality assurance specifications. The objective of this research, as stated in the Research Project Statement, “…is to develop procedures to assist state DOTs in effectively using contractor-performed tests in the quality-assurance process.” To satisfy this objective requires a focus on the acceptance element of the overall quality-assurance process. More specifically, study and analysis of procedures for verifying contractor-performed tests are needed to address concerns as to the viability of these tests for determining acceptance of construction materials and products. SCOPE The study conducted to accomplish the research objectives included the following components: ● An investigation of the state-of-practice for using contractor-performed tests in the quality-assurance process for highway construction. This included a limited review of state specifications and practices. ● Collection and comparisons of state DOT and contractor-performed tests for hot mix asphalt concrete (HMAC), portland cement concrete (PCC), and granular base course. Data were selected to allow evaluation of as many as possible of the quality-assurance variables that might affect comparisons.

4 ● Analysis of the effects of differences in state DOT and contractor-performed tests on acceptance outcomes. ● Surveys of technicians to investigate potential reasons for observed differences in state DOT and contractor-performed tests. ● Conclusions and recommendations for using contractor-performed tests in the quality- assurance process for highway construction materials and products. RESEARCH APPROACH The basic premise for this research was that contractor-performed tests can be effectively used in the quality-assurance process if they provide the same results as state DOT-performed tests. Consistency between contractor-performed and state DOT- performed tests is important even if the tests are used for different purposes, i.e., contractor-performed tests for process (quality) control and state DOT-performed tests for acceptance. However, consistency becomes critical when contractor-performed tests are also used for acceptance. Legal issues are then added to technical and material or product quality issues. Considerable effort was devoted to comparing state DOT and contractor- performed tests to determine if statistically significant (α = 0.01) differences in variability and proximity to target or limiting values exists. In addition to statistical comparisons, the effects of differences in test results on acceptance outcomes were investigated. Measures of variability and proximity to target or limiting values were used in acceptance procedures to compute the probability of certain acceptance outcomes. Comparisons of these probabilities of acceptance outcomes provide a more practical assessment of differences than the statistical comparisons. Data provided by one state permitted comparison of contract payment levels that were computed with state DOT and contractor-performed tests. The effects of quality assurance procedure variables on the above described comparisons were evaluated. Among the variables considered were contractor to state DOT sampling and testing ratios, LOT/subLOT size, verification method, utilization of

5 contractor-performed tests (control or control and acceptance) and acceptance methodology. In addition, surveys of contractor, consultant and state DOT asphalt technicians were conducted to assess potential causes for differences in test results between these three types of organization.