Development of Rapid QC Procedures for Evaluation of HMA Properties During Production

DISCLAIMER The contents of this report reflect the views of the author who is responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the National Center for Asphalt Technology or Auburn University. This report does not constitute a standard, specification or regulation.-ii-ABSTRACT Current processes for quality control of Hot Mix Asphalt (HMA) are inefficient and place considerable risks on HMA producers and transportation agencies. This project was established to explore possible new ways of gathering real-time quality control information. The two primary goals of real-time testing are: to dramatically shrink the time lag for quality control information, and to improve the reliability of the data. To meet the objectives of this study, a panel of individuals familiar with current and or new QC technologies was assembled to discuss concepts, brainstorm possibilities, and map out a general strategy for evaluation of new methods and technologies. Based on this meeting, the most promising concept for real-time testing appears to be the utilization of automation technologies to check the consistency of the materials feeding into an HMA plant. Specific automation technologies that appear most promising include: • Continuous, in-line viscosity of the asphalt binder. The viscosity of the binder should provide an indication that the appropriate grade of binder is being used in the mix. • Automated belt sampling of the virgin aggregate from the conveyor before it enters the dryer. An automated sample dryer and gradation device integrated with belt sampler should provide rapid feedback of the consistency of the aggregate. • For continuous mix plants, asphalt contents of HMA mixtures can be monitored with the readings from the plant's asphalt meter and belt scales. Calibration of the components used to determine real-time asphalt content is a key to the reliability of this data. • The automated technologies should be integrated as a system with programmable controls, data acquisition, and report generation. At the present time, there do not appear to be any technologies that can be used to automatically determine the composition of RAP or to test important characteristics of the produced mixtures such as volumetric or other performance-related properties. It is strongly recommended that automated methods for characterizing these materials be researched. A national oversight group specific to exploring real-time testing of HMA is also recommended. .