Asphalt Mill and Overlay is a form of asphalt (flexible) pavement rehabilitation whereby the upper portion of a roadway surface is removed by scraping (milling) and replaced with a new layer of asphalt.
Why mill and overlay a roadway or parking lot?
The quick answer is to restore structural integrity and ride quality, and prevent future degradation. Asphalt degrades as a result of heavy traffic loads, weathering and age. Asphalt pavement defects can exist in the lowest layer (the subgrade), the rock base or the structural asphalt layer. Mill and overlay is suitable for rehabilitating asphalt pavements that have lost structural integrity or surface quality in the upper-most layer only (the asphalt layer), whereas seal coating acts more like a preventative. The upper layer of asphalt can lose structural integrity due to weathering of the asphalt binder that exists between the sand and rock particles. When the binder degrades, the upper portions of the asphalt begin to loosen up and you will see signs of pitting and loss of rock pieces from the surface (called raveling). Loss of structural integrity above accelerates the destruction of the layers below. A mill and overlay can restore the upper surface before the damage migrates below.
Mill and overlay also provides a new riding surface and restores the proper level of friction between a vehicles tires and the road surface.
Since asphalt repair becomes progressively more expensive the deeper the failure occurs, milling and overlaying an asphalt road or parking lot can provided the biggest return on investment for restoring longevity to an asphalt construction.
How often should one mill and overlay?
This answer depends on many factors, but in our experience the timeframe is around 25 years, plus or minus 10 years.
Can seal coating restore a pavement structure?
Seal coating can restore the very upper surface of an asphalt structure and does have a longevity-producing result. It also has cosmetic benefits. Seal coating lessens the degree of degradation by sun and heat and also the degree of water intrusion into a pavement structure. Seal coating does not address the degradation of the asphalt binder more than fractions of an inch below the surface, which will happen over time regardless. This is why after years of seal coating, one may see cracks in the seal coating extending into layers below.
Does mill and overlay fix all pavement issues?
While asphalt mill and overlay can rejuvenate an asphalt structure very successfully in most cases, it cannot address issues that emanate from below. For example, deep cracking (called reflective cracking,) if they extend all the way into the rock base, will ultimately work their way back to the surface. This is why a good eye should evaluate existing conditions prior to implementing such a project.
What are some asphalt pavement issues that cannot** be fixed by a mill and overlay?
Reflective cracking (short term yes - about a year, long term no)
"Shoving" - where pavement slides forward and exposes the rock base
**However, a mill and overlay project can be implemented along with additional, deeper repairs in limited spots to address the above.
What are some asphalt issues that can be fixed by a mill and overlay?
Degraded riding surface
Ravelling or loose and missing surface rocks
Minor misalignments in pavement surface
What about ADA (American with Disabilities Act)?
Although older parking lots may not meet current ADA criteria, many municipalities will expect the property owner to resolve ADA issues, such as slope and surface quality, whenever a mill and overlay project is done. More issues than one would thing can be resolved with this process.
How are mill and overlay projects executed?
Mill and overlay projects can be bid as lump sum or unit price. Unit price contracts allow for flexibility in case other issues are found. The following steps are usually involved:
1. An onsite visual evaluation to determine if other issues are occurring, such as drainage issues, failing subsurface pipes, issues with the base or subgrade, etc.
2. Evaluate the repair options, including the need for base repairs, full-depth replacements, overlay thickness, etc.
3. Prepare plans, details and specifications.
4. Apply for permits.
5. Select contractor.
6. Observe construction.
We can assist with the initial inspection, evaluation, design, plans preparation, permitting, bidding and construction-phase services for your mill and overlay project.
Jupiter Civil Engineering Company, LLC
5500 Military Trail, Ste 22-215, Jupiter, Florida 33458, United States
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