Discussion of 'Design Process of Asphalt Mixture Incorporating Compaction-Effort Variable'

摘要

The authors have presented a study incorporating compaction effort variables into the asphalt mix design process by analyzing the influence of two cases (N_(des) and asphalt content, and N_(des) and aggregate gradation) on asphalt mix performance. The conclusions from the work were that the original Superpave compaction effort (N_(des)) might not always provide the mixture with required performance, and N_(des) has a significant role in the high- and low-temperature performance. The discussers highly appreciate the work presented by the authors. The discussers would like to share some comments regarding the experiment design, the results, and data analysis. The attempt to optimize the Superpave mix design compaction effort has a long history in the United States since its implementation in 1993. Currently, almost all states utilize the Superpave mix design method. Since the introduction of Superpave, material specifications and the test procedure have been continuously refined along with the increased field experiences. There have been voices from different contractors and agencies that Superpave mix design resulted in mixtures containing lower than optimal asphalt cement content (Brown et al. 1999). After that, the National Cooperative Highway Research Program (NCHRP) evaluated the issue in NCHRP Report 573 (NCHRP 2007) and suggested a new, lower gyratory compaction level (Table 1).