EVALUATION OF VOLUMETRIC PROPERTIES AND GYRATORY COMPACTION SLOPE FOR THE QUALITY CONTROL OF HOT-MIX ASPHALT PRODUCTION (WITH DISCUSSION)

Currently, many highway agencies control production of Superpave mixes volumetrically. Voids in total mix (V sub a) and voids in mineral aggregate (VMA) are used as quality control parameters. This report analyzes the relationship of volumetric data to asphalt binder content and aggregate gradation. The data, collected as part of the Federal Highway Administration's Demonstration Project No. 90, "Superpave Asphalt Mix Design and Field Management," derive from actual hot-mix asphalt (HMA) production projects. The projects, located throughout the United States, were constructed in 1995 through 1999. Analysis of the data indicates both V sub a and VMA are related directly to changes in asphalt binder content and aggregate gradation during production. Based upon this and other prior research which has shown links between volumetrics and performance, V sub a and VMA are effective and appropriate quality control parameters for Superpave mixes. One of the performance measures being considered under NCHRP Project 9-16, "Relationship Between Superpave Gyratory Compactor Properties and Permanent Deformation of Pavements in Service," is the slope of the compaction curve generated by the Superpave gyratory compactor. This report also analyzes the relationship of the slope of the compaction curve to asphalt binder content and aggregate gradation. Analysis of the data shows an excellent relationship between the compaction slope and changes in the aggregate gradation during production for six of the ten projects analyzed. One of the projects showed a good relationship, two of the projects showed a fair relationship, and one of the projects showed a poor relationship. Based on this, the slope of the compaction curve may not be appropriate for measuring the performance of Superpave mixes. Contractors may not be able to ascertain what actions are required during production to achieve acceptable results. In addition, research has not demonstrated a tie between the slope of the compaction curve and the performance of asphalt pavements.