Research Pays Off | August 2024: Asphalt Milling Best Practices by Understanding Milling Operations

NRRA Research Pays Off: August 2024
Determining Asphalt Pavement Milling Best Practices through Enhanced Understanding of Milling Operations presented by Kaleigh Miech, Graduate Student, University of New Hampshire

Milling of asphalt pavements is a commonly used technique in many cases of maintaining and rehabilitating roadways. That said, implementing these milling operations has potential to cause harm to the layers below the mill line due to it being a relatively high-stress and energy activity. In this study, the impact of milling to the pavement layer directly below the mill line was evaluated for five parameters: the pavement temperature at the time of milling, the amount of time between milling and post-mill overlay construction, the depth of milling relative to the asphalt lift interfaces, the structure of the existing pavement, and operational parameters such as rotor speed. To compare the impact of these parameters on the milled pavement, pre- and post-milling cores were collected under each parameter variation and were then trimmed to represent the equivalent layer directly below the mill line. Laboratory testing was then performed on both the pre- and post-milling cores and a statistical analysis was conducted to determine if the milling operations inflicted a significant impact to the physical or mechanical properties of the pavement layer directly below the mill line. The results from this analysis determined that performing milling operations while the pavement is at a cooler temperature, or leaving milled pavement exposed to traffic and weather for extended periods, can cause the strength of the layer directly below the mill line to decrease significantly. Pavement life evaluations were also conducted using lab measured properties as well as field testing (pre- and post-milled falling weight deflectometer testing). The results of this analysis found that leaving a milled pavement exposed for 2 weeks before overlay placement and milling at cooler temperatures have the potential to decrease the pavement life.