Variability Analysis of Hot-Mix Asphalt Concrete Containing High Percentage of Reclaimed Asphalt Pavement

Abstract

A research project was undertaken to evaluate the production and construction variability of hot-mix asphalt concrete (HMAC) containing large quantities of recycled asphalt pavement (RAP) material. Four construction projects were selected. Two of the projects used 35 percent RAP material, while the other two used 40 and 50 percent RAP, respectively. The projects differed in size with total hot-mix ranging from 12,000 to 30,000 tons. In all cases, dedicated RAP stockpiles were used. A series of tests were performed at both the hot-mix plant laboratory and the University of Texas (UT) asphalt laboratory. The tests at the plant included extraction, gradation, and asphalt content using nuclear gauge. A number of specimens were also compacted and shipped to the Texas Department of Transportation Materials and Tests Division for Hveem stability testing. Asphalt recovery, penetration, and viscosity tests for both HMAC and RAP were conducted at the UT laboratory. Each day, four sublots were sampled. The results obtained from the tests were analyzed. The gradation and asphalt content deviations, air voids, penetrations and viscosities, and stabilities were included in the analysis. Pay adjustment factors were determined for gradation and asphalt content deviation, as well as for air voids. In general, these high-percentage RAP projects indicated higher variability than a typical HMAC project without RAP. The gradations of plant-produced mixtures were finer than the job mix formula target gradations, possibly because of aggregate crushing during the milling operation.