Asphalt millings are recycled in almost every new asphalt mix that is produced. Not all of the milled asphalt is reused in new asphalt. Most projects limit millings to no more than 30 per cent of the volume of the new mix. There are other uses for millings such as on driveways or on less travelled roads. Loose asphalt millings generally are not good for groundwater runoff or the environment. Ideally, the asphalt millings should be compacted with a binder and placed under either a new asphalt surface coarse or a chip-seal mix.
Evaluate the existing subgrade by driving a vehicle over the drivewy. Select the largest vehicle that will use the driveway for the test. Look for tire ruts or lateral movement of the subgrade under the wheel loads. If weak subgrade material is found remove the weak material and replace with stone.
Look at the asphalt millings. Determine if it has a lot of fine material or if the material is coarse. For coarse material, use an added emulsion per cent of 2.5 to 3 per cent. For fine material, use an added emulsion per cent of 3 to 3.5 per cent. Emulsion is an additive that contains suspended droplets of asphalt in water helping to bind the mix. Choose an emulsion that is designed for a cold mixture of asphalt.
Screen the millings to make sure that no pieces are larger than two inches. Crush the millings larger than two inches in size to make the material pass through the two-inch screen opening, if needed.
Add the emulsion to the screened millings in the pug mill. Mix the combined emulsion and millings in the pug mill until a homogeneous material is created.
Transport the mixture to the driveway location using a dump truck.
Dump the mixture into a spreader or asphalt paver. Spread the millings using the spreader or the asphalt paver. Place at least 3.5 inches of the recycled mix over a soil subgrade. If rock is already under the recycled material it may be possible to use less material, depending on the size of the vehicles using the driveway.
Compact the millings first using a 25-ton pneumatic-tired roller then a 12-ton or larger double drum vibratory steel-wheeled roller. Provide water on the steel drums to avoid material sticking to the roller.
Place a chip seal mix over the recycled milled pavement mat or a 1.25 inch layer of new asphalt surface course. Placement of one of these materials seals the surface of the recycled pavement.
Nonconstruction equipment could be used to place asphalt millings on lesser-travelled driveways, however, a quality emulsion should be considered to help bind together the asphalt. Laboratory testing will help determine the optimum per cent of emulsion for a mix design. Add different amounts of emulsion and compact the specimens and test the unconfined compressive strength and stability.
For heavily-travelled roads or public roadways a licensed professional engineer should perform the pavement design before building the driveway.