What are Asphalt Millings (RAP)?
Asphalt millings (also referred to as Reclaimed Asphalt Pavement or RAP) are the crushed byproduct of highway resurfacing projects. Large cold-milling machines grind off the top 2 to 3 inches of old roadway asphalt, pulverizing it into gravel-sized aggregate stones still coated in petroleum bitumen binder.
How to Harden "Bond" an Asphalt Millings Driveway
Unlike gravel which kicks out onto your lawn, asphalt millings contain residual asphalt cement. Under hot summer sun and vehicle tire compaction, the bitumen softens and fuses the particles together into a semi-solid pavement:
- Grading: Spread millings evenly with a skid steer or box blade at a uniform 3 to 4 inch depth. Crown the center with a 2% slope for water drainage.
- Vibratory Compaction: Roll thoroughly with a 3-ton to 5-ton vibratory steel-wheel roller while moist. Hand-tamping or driving a pickup truck will not generate adequate PSI to lock the aggregates.
- Solar Curing: The hot sun melts the oils. In mid-summer temperatures above 85°F, millings bond rapidly into an impermeable surface.