Research Pays Off: Preserving Georgia Pavements with Micromilling

Georgia’s experience shows that pervious friction course (PFC) placed on pavement surfaces can improve tire friction and surface drainage and provide good pavement performance for 10 to 12 years. When a PFC approaches the end of its service life, the underlying layer of dense-graded hot-mix asphalt or stone matrix asphalt is generally still in good condition and could last for several more years. Despite the effectiveness of using the PFC procedure, the Georgia Department of Transportation (DOT) sought a more economical pavement maintenance procedure. Georgia DOT initiated a research project to investigate micromilling for the removal of deteriorated open-graded friction course to maintain asphalt pavements on interstate highways. It conducted research studies on Interstates-75 and -95 to explore the use of micromilling and retrofitting a laser road profiler (LRP) with software to estimate surface texture parameters. The research produced several findings that would benefit Georgia DOT and other highway agencies, including the following: micromilling in conjunction with thin asphalt overlays is an effective pavement preservation treatment; variable-depth micromilling provides the required surface texture without sacrificing milled surface texture and smoothness; and the LRP can measure both surface texture and smoothness on micromilled surfaces and can serve as a tool for quality acceptance and performance measurement. In addition, Georgia DOT has accrued cost savings from this preservation treatment. Replacing conventional milling with micromilling on the two interstate projects saved an estimated $11 million—nearly 50 times the expenditures for the research. After 4 to 7 years in service, both projects have shown good performance.