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PARTIAL DEPTH MILL PATCHING
Partial depth asphalt mill patching is a relatively new process that uses milling machine technology to save our customers a lot of money on repairs of certain types of deteriorated asphalt.
 
If a site visit determines that pavement deterioration is not linked to failure originating from the sub base, then mill patching is a viable option. In many instances, pavement deterioration occurs in only the top 1 inch or 2 inches of the asphalt.
The following list provides examples of surface deterioration that can be corrected using partial depth mill patching.
- An old asphalt overlay was not put down properly and is peeling away in sections causing 1" - 2" potholes around the parking lot (overlay has delaminated from existing base pavement).
- The top layer of asphalt is shoving in an area where traffic slows down abruptly (bus lane traffic).
- Surface cracking (possibly due to drying out of the asphalt cement over a long period of time) has allowed water to penetrate into the pavement and cause deterioration from the top down.
- Pavement has started to “ravel” from the top down. (Usually occurs due to poor compaction on asphalt overlay in cooler working conditions.)
- The asphalt pavement is in a critical drainage area and drainage swales need to be cut into the pavement so the surface can be reshaped allowing water to drain properly.
- Pavement shows signs of low and moderate severity alligator failures. Since pavement hasn´t fully failed to subgrade, use of milling machine to cut off surface course overlay into binder course pavement can reduce cost of repair by 50% without impacting performance of completed repair over time.
The Process:
- Lay out and mark each area to be mill patched. Make all patches square or rectangular and extend 2' beyond visual edges of distress area.
- Grind the top 1" - 3" of asphalt with a milling machine and scrape it away leaving the bottom layers or “base course” of asphalt intact.
- Conveyor milled material is into waiting dump trucks and haul off site.
- Sweep the base pavement to a broom-clean condition.
- Apply a tack coat to the exposed asphalt base course and sides of each patch.
- Install bituminous surface course asphalt mix to the proper line and grade using an asphalt paver (material can be placed by hand for smaller patches).
- Compact the asphalt thoroughly using a steel drum vibratory roller.
- Apply a bead of sealant around the edge of each patch to help minimize water penetration.
- Keep the patch free of traffic for 1 - 8 hours depending on ambient temperature (longer curing times are necessary when the temperature is especially high because the asphalt remains soft).
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