What is Milling?
Milling (also referred to as Cold Planing) is the controlled milling of a pavement to restore its surface to a specified grade and cross slope. This milled surface provides an excellent base for a smooth-riding asphalt overlay. It can be used to remove all or part of the existing pavement layers, depending upon the depth of the pavement defects. The process yields a crushed, somewhat gap-graded RAP (reclaimed asphalt pavement) material (95% passing a 2-inch sieve is typical) that can be reused as base or in hot or cold asphalt mixes. It makes sense for a range of applications, the most common being the removal and replacement of aged and cracked courses, restoring curb-reveal for oft-overlaid roadways, and restoring surface friction on structurally sound pavements using micro-milling or carbide grinding equipment. It doesn’t make sense when an in-place recycling process or a simple overlay can meet an agency’s performance requirements for a lower cost.
Mill-and-Fill, the removal of the top 2 to 5 inches of pavement and replacing it with new hot-mix asphalt, is the classic milling application in North America. It provides a relatively fast restoration of a road without loss of curb reveal or bridge clearances and the process can cure previously existing problems such as drainage flow and surface friction.
Tricks of the Trade
Modern milling machines use a high degree of automation to achieve precise depth, grade and cross slope. The sophistication, condition and size of a contractor’s equipment can have a great deal of bearing on how well the company’s crews perform on the job. For this reason, some milling contracts require pre-approval of the contractor’s equipment. Equally vital is the experience and professionalism of the crew. Even with today’s high degree of automation, success depends on managing the machines’ performance and its high-maintenance features, especially the cutting tools.
What it Costs
Milling costs vary widely according to the hardness of the material, depth of cut, job complications, and general location.