Chapter 4: Patching and Edge Repair

2.0 Project Selection

2.1 Potholes

Potholes are a form of disintegration of the pavement that may be associated with poorly compacted material, raveling, cracking, base failure, or aging of the pavement.  Potholes often appear after rain or during thaws when pavements are weaker.  Generally accepted mechanisms for pothole formation are as follows:

• Raveling, stripping, or cracking in the pavement surface.
• Water penetrates the surface layers of the pavement, softening the underlying pavement layers, which increases deflections.  Figure 1 illustrates how water can penetrate a pavement.
• Ice formation and heaving in the pavement occurs in some climatic areas.  Figure 1 illustrates heaving due to a freeze-thaw cycle in a cold climate.
• Fines from the underlying pavement layers are lost, reducing overall structural strength and support for the pavement surface.  Figure 1 illustrates the resulting cavity when the fines are lost due to migration or pumping.
• Once a hole is formed, it will continue to grow until it is repaired.  Figure 1 illustrates the role traffic plays in enlarging a pothole.

2.2 Edge Failure

Edge failures occur when the edge of a pavement breaks up.  This failure is caused by traffic loading at the edge of the pavement (usually due to a horizontal geometry problem) and/or the infiltration of water at the edges of the pavement or shoulder.  Although edge failures are usually out of the primary wheel paths, their presence can accelerate the normal deterioration of the pavement in the traveled way.

2.3 Costs and Performance

The main costs associated with patching include:

• Labor
• Materials
• Equipment
• Traffic delays

Cost effectiveness is determined by the patch survival rate.  To determine the patch survival rate, repairs should be monitored for at least one year.  Monitoring consists of checking for the presence of repairs and noting the survival or failure of each pavement section.  Figure 2 shows typical survival rate curves, where A, B and C represent three separate patch locations.  The area under the curve represents the patch survival rate.

Dig outs are generally carried out using larger equipment and are the most expensive method of patching.  The effectiveness of dig outs is determined in the same manner as described for patching above.

2.4 Design and Specification

Patching design and specification are based on application procedures and the use of appropriate materials.  Materials should be tested in accordance with the appropriate specifications.  The mix type used may vary with traffic conditions.

Patching cold-mixes are generally proprietary products and should be handled according to the manufacturer’s specifications.