Variability, Sensitivity, and Econometric Analyses of Field Density in Pay for Performance Data for Hot-Mix Asphalt in Illinois

Pay for Performance (PFP) is a statistical-based quality assurance specification used to evaluate asphalt concrete construction for projects having mix quantities greater than 7,260 t (8,000 US tons). The contractor pay is adjusted based on mix field density, air voids, and voids in mineral aggregate. In this study, data were analyzed from the 2015 to 2017 highway construction seasons in Illinois to determine variability trends. Density was the major factor driving contractor pay disincentives in PFP, followed by air voids. To identify the impact of construction field density consistency on the final pay factor, a sensitivity analysis was performed to determine the changes in the contractor pay with respect to variability, which is measured by standard deviation. In addition, an econometric analysis based on sensitivity analysis using linear regression was conducted. The results showed that a 1% reduction in density standard deviation led to a 0.066 increase in density pay factor. Based on the 79 projects analyzed, if the density standard deviation had been reduced from 1.67 to 1.0, the average increase in pay per project would be $38,000.