Georgia's Pavement Preservation with Micromilling and Thin Asphalt Overlay

Friction courses in Georgia such as the open-graded friction course (OGFC) or Porous European Mix (PEM), have rarely been placed directly on top of a conventionally milled surface. Such placement could cause delamination of the surface layer, due to poor bonding between the friction course and the milled surface and to the likelihood of surface water being trapped in the valleys of the rough milled surface. Thus, a new layer of dense-graded surface mix would have to be placed on the milled surface before a new friction course could be placed on top of it. Use of the micromilling technique could address this problem. This paper presents the scope and findings of research that evaluated a micromilling operation in conjunction with 15.6 miles of PEM overlay on Interstate 75 south of Macon. The Georgia DOT (GDOT) Special Provision for the micromilling and PEM overlay stipulated that the micromilling operation must produce a milled surface with a ridge-to-valley depth (RVD) in the surface texture of 1.6 mm and would require corrective action when RVD exceeded 3.2 mm. The Circular Track Meter and the Ultra Light Inertia Profiler were used for measuring the macrotexture of the milled surface. Results obtained from the eight test sections indicated that the requirements were achievable and cost effective with the micromilling technology currently available. Bond strengths were also evaluated, and the results are presented herein. The estimated cost savings for the project evaluated was $58,000 per lane mile.