Pavement Preservation with Micromilling in Georgia

Abstract

The micromilling technique to mill asphalt surface mix continues to be studied in the state of Georgia as part of a pavement preservation treatment in conjunction with thin asphalt overlays. Earlier research showed the results of micromilling on a deteriorated open-graded surface, which was overlaid with a new open-graded surface on I-75, south of Macon, Georgia. The micromilling produced a much finer surface texture than did conventional milling, with a ridge-to-valley depth (RVD) of less than 3 mm, and the technique could more accurately mill the deteriorated open-graded layer. A new open-graded surface was placed on top of that layer with no need for a new dense- or gap-graded layer. The result was a large cost savings compared with conventional milling and overlay. This paper summarizes research performed on a micromilling and open-graded inlay project on I-95 near Savannah, Georgia, and compares the results with those from the previous research. The new research affirms that significant cost savings can be achieved through the replacement of conventional milling with micromilling. Results obtained from the I-75 project indicated that, on the basis of 3 years of satisfactory performance of the open-graded overlay on the micromilled surface, the use of the 95th percentile RVD parameter as the threshold value for compliance with the 3.2-mm RVD acceptance requirement could be too conservative. Results from the I-95 project indicated that the mean RVD of the micromilled surface could meet the 3.2-mm RVD requirement. However, the appropriateness of this parameter's use should be determined on the basis of the long-term performance of the open-graded mix placed on the micromilled surface.