What is cold planing (milling) of airfield pavement?

Cold planing is the removal of a layer of pavement to a set depth and grade with a power-operated milling machine. FAA advisory circulars call the same work cold milling or milling, and this page uses the terms alike.

What the machine must do

AC 150/5370-10H, paragraph 101-3.5, sets the base requirements. The machine must produce a uniform finished surface without tearing or gouging the layer below. It must have grade and slope controls and a means of dust control. The contractor removes the millings and disposes of them off the airport or in areas the plans designate. If the contractor cuts deeper or wider than the plans specify, the contractor replaces the material at its own expense.

For patching, the machine must cut a vertical edge without chipping or spalling the remaining pavement. It must also have positive depth control. The area milled covers only the failed area.

For profiling and grade correction, the machine needs electronic grade control. The tolerance is +0 inch and -1/4 inch (+0 mm and -6 mm) of the specified grade. After milling, the contractor sweeps the surface daily. Before paving, the contractor wets the surface and sweeps or blows it clean.

Why airfields mill

• Before an overlay. AC 150/5320-6G section 4.6 says to remove weathered, raveled or distressed asphalt by milling before the overlay. The designer then enters the final milled thickness in the FAARFIELD design program, not the original thickness.
• Profile correction. Profile milling plus a leveling course corrects shoving, rutting, settlement, birdbaths and bleeding (section 4.10.1.2).
• Surface cleaning. Paragraph 101-3.3 lists cold milling among the ways to remove rubber, fuel spills, oil and paint before an overlay. The paragraph defines major damage from such removal methods as removing pavement over 1/8 inch (3 mm) deep.
• Concrete. AC 150/5320-6G names cold milling, or shot peening, to prepare a surface for a bonded concrete overlay.

Limits

Milling removes structure as well as distress. AC 150/5320-6G section 4.8 warns that a surface course thinner than 2 inches (50 mm) often delaminates under construction traffic. The AC advises coring before milling to find the thickness and condition of the surface. A note in P-101 adds that delamination is possible when the milling depth is about equal to the thickness of the layer placed. It suggests removing the whole layer or considering full depth reclamation.

Reclaimed asphalt pavement (RAP) is the name for milled material that the engineer allows in a new mix. In the model P-401 specification, RAP is for intermediate courses and shoulder surface courses only, and a drafting note limits it to 30 percent.