An asphalt patch is any area of pavement that has been removed and replaced with new material. Patches are generally used to fill in potholes, which are caused when thin asphalt cannot withstand the pressure of heavy loads resulting in base failure. Poor drainage can also contribute to the problem by weakening the subgrade and base.
1. What types of patch repairs exist?
There are two key types of patch repairs that provide a quality solution to many asphalt issues.
Full-depth patching (peel and pave) is when an entire layer of pavement surface is removed all the way down to, or including the subbase. This is based upon the condition of the stone base. A new subbase is put to work, followed by a new tack coat. New asphalt pavement is backfilled into the patched region.
Surface patching is a more temporary form of patching that involves asphalt that remains in overall good condition. This process does not include removal of the existing surface or subbase; hence why asphalt needs to be in overall better condition to benefit from this method. Instead, asphalt is layered over existing surfaces and feathered so that it matches the in-place grade. In some cases, feathering is skipped in exchange for a rebate milled into the surface.
2. How do you determine patching severity?
There are three main classifications of patching severity: low, medium and high.
Low severity patching includes BST patching or chip seal patching used to cover low severity cracking or raveling of asphalt. This is the result of applying hot asphalt directly on the roadway using a truck with a spray bar. The hot asphalt is spread evenly and crushed stone is rolled onto the top surface. You can identify this level of patching by its straight edges, coarse texture and surface contours that tend to mimic the surface below.
Medium severity patching is fulfilled with the use of blade patching and is used to cover or replace medium to severe alligator cracking, rutting, potholes and other forms of larger defects in pavement. The edges of this type of patch are meant to contour with surrounding surfaces and have feathered edges. Medium patching can be of varying thickness.
High severity patching is fulfilled through dig-out or full depth patching used to correct severe alligator cracking. This type of repair includes cleanly removing an entire section of asphalt along with any damaged materials. The freshly made hole is then refilled with an appropriately matched pavement that is at least as strong as the original materials and in some cases stronger.
3. Are all patches considered a defect?
Yes. No matter how well an area is patched, and patches can be made to look really good, it is still considered a defect in the pavement. This is because a patched surface and any adjacent surfaces are not going to perform as highly as unpatched pavement. There is some roughness associated with any patch, which can be dedicated by the trained (and sometimes even untrained) eye.
A patch provides a benefit to the overall stability and longevity of pavement, so in itself it is a positive thing. Yet, when a patch is needed it signifies a weakness in the original pavement, hence why it is always considered a marker of defect.
4. Are patches used for large asphalt issues?
In most instances, a patch is used for smaller issues and not large sections of asphalt. A patch tends to be less than a typical rehabilitation in terms of overall scope and size; patches are never the entire width or length of the full roadway.
5. What is original WSDOT patching?
WSDOT is a lane that includes “new surfacing” in patchwork form but measures less than half a mile lengthwise. Agency policy differs between companies to define exact minimum rehabilitation vs. maximum patch length.
6. Can patches be temporary?
Yes. There are temporary patches as well as localized permanent patches, both of which are included in the same distress category. Utility cut patches are also categorized as patching values.
7. When is the best time to perform patchwork repairs?
The spring and summer months offer the best times to make patchwork repairs. This gives the asphalt plenty of time to cure over the winter and be ready for sealant the following year.
8. How does one go about measuring the extent of patching?
The length of wheel paths will determine the extent of patchwork needed. Each half of the road is equivalent to one wheel path. The guidelines for estimating patch size and extent include:
1% – 9% of both wheel paths
10% – 24% of both wheel paths
25% + of both wheel paths
Another way to identify extent of patching is to focus on the entire survey area. In this case, patching is measured in square feet in regards to the entire inspection area. In order to determine the total level of severity, other distresses within the patch area are taken into consideration.