United States Department of Transportation
i
Data Trends and Variability in Quality Control for Performance and Pay for Performance Specifications: Statistical Analysis
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2020-06-01
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[PDF-12.41 MB]
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Alternative Title:ICT PROJECT R27-189: Evaluation of Data Trends and Variability in the Quality for Performance (QCP) and Pay for Performance (PFP) Programs
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Edition:Volume I Report 1/1/18–6/30/20
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Abstract:Quality assurance programs for hot-mix asphalt (HMA) have evolved from method specifications to quality assurance specifications that distribute responsibilities and risks between contractors and owners. The Illinois Department of Transportation (IDOT) developed two acceptance specifications, quality control for performance (QCP) and pay for performance (PFP), integrating contractor pay incentives and/or disincentives associated with air voids (AV), voids in mineral aggregate (VMA), and in-place density limits. A major factor that could compromise contractors’ pay in both specifications is the variability of test results due to mix production, construction, sampling, and/or inherent testing variability. Therefore, the objective of this project was to understand the distribution and variability of the test results observed under QCP and PFP specifications, as well as the potential causes of variability. The assessment approach included statistical analysis of the test results obtained for the 2015– 2017 construction seasons and on-site field observations of 11 projects visited during the 2018 construction season. The pay factors of the 2015–2017 construction seasons showed contractors earned pay incentives under the PFP specification but received disincentives under QCP and PFP specifications. Contractors appeared to have more experience working with QCP projects than PFP projects. The statistical analysis identified that more than 80% of the test results between the contractor and the district were not significantly different. In those cases, it is likely that issues with mix production or construction were the reasons that led to a disincentive. However, there are possible testing issues that need to be addressed by the district and contractor such as reheating consistency and test weight control. Density was a major factor driving contractor disincentives in both specifications, followed by AV. Finally, the site visit identified mix production and construction issues that can lead to possible causes of pay disincentives, including mix switching, dust control, and aggregate contamination.
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Content Notes:Conducted in cooperation with the U.S. Department of Transportation, Federal Highway Administration. A complementary report to this project is available: Case Studies Using Quality Control for Performance and Pay for Performance Specifications: Field Observations.
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