Quantifying the Variability of Production of Asphalt Mixtures through newly implemented Performance Tests for the Wisconsin Department of Transportation

Abstract

This study aims to determine an appropriate standard deviation of Balanced Mix Design performance tests for Wisconsin specifications based on field-produced mixes. Identifying variability is an essential aspect of the pavement materials and construction industry. Federal Highway Administration (FHWA) and State Department of Transportation (DOTs) quantify the variability of material properties to manage quality. Typical asphalt mixture properties measured to assess variability have been binder content, aggregate gradation, and mix volumetrics. New performance tests are being used to assess the quality of an asphalt mix. These new performance tests included in the balanced mix design are rutting and cracking indicators on an asphalt mix. This study used mixtures from ten shadow projects from various locations across Wisconsin to obtain representative production variability data to determine the within-lot pooled standard deviation. For this study, two performance tests, Hamburg Wheel Tracking Test (HWTT) and Indirect Tensile Asphalt Cracking Index (IDEAL-CT), were performed for the mixtures from the ten shadow projects and their representative lots/sublots. The analysis methods used to quantify the variability include the standard deviation, coefficient of variation, normality, outlier test, and cumulative distribution function of production standard deviations. The final conclusions of this study indicated that asphalt content was the least variable quality characteristic measured with a COV of 2.8%. The most variable quality characteristic measured was HWTT passes to 12.5 mm with a COV of 16.6%. IDEAL-CT had a mean COV of 13.1%. The mean COV for air voids was 10.4%. The mean COV for HWTT CRD20k was 10.9%.