Chapter 4: Patching and Edge Repair

3.0 Construction Procedures

Construction procedures for pothole patching vary according to the method and materials selected.  The three primary patching techniques along with edge sealing technique are described below.  Appendix A, “Suggested Field Considerations,” at the end of this chapter, provides a series of tables to guide project personnel through the important aspects of performing a patching or edge repair project.

3.1 Throw and Roll

The “throw and roll” method is often used for temporary patches.  This is appropriate only when weather conditions are too poor for a semi-permanent patch to be placed or the road is due to be rehabilitated soon.  It is the most inexpensive and least labor-intensive method for patching a pothole and includes the following steps.  Figure 3 illustrates a typical throw and roll application. 

• Patching material is placed into the hole, with or without cleaning and/or drying of the hole.
• The material is compacted using the maintenance truck tires.
• The finished patch should have 3 to 6 mm (1/8 to ¼ in) of crown to help avoid water ponding.
• Clean up is generally not required.

3.1.2 Semi-Permanent Patches

Semi-permanent patching is considered an effective patching method, second only to complete removal and replacement of the failed area.  The following steps describe how this form of patching is carried out:

• Mark the boundaries of the distressed area, taking care to encompass a slightly larger area than that reflected by the distress.  The repair boundaries should be as rectangular as possible and take into consideration the dimensions of the equipment that will be used for removal of the old material and compaction of the new material.
  
• Cut the boundaries of the patch square using either a diamond saw or pneumatic hammer with a spade bit.  In the case of the latter, care should be taken not to damage the HMA surface layer in the sound pavement.
  
• Remove water and debris from the hole.  Figure 4 illustrates a hole that has been dewatered and cleaned of debris.  Depending on the size of the pothole, this may be accomplished manually with a pick and shovel or with various combinations of power equipment, i.e., a pneumatic hammer and shovel, backhoe, or front-end loader.  Cold milling equipment can also be very effective for this operation.
  
• Square up the sides of the hole until the edges of the hole are sound pavement.  This step is usually very simple if the boundaries of the repair area were cut with a diamond saw or established with cold milling equipment.  It is usually only required when manual techniques of material removal are employed.  Figure 4 illustrates a hole that has been extended to sound pavement and firm supporting material.  It is suggested that the depth of the patch be 50% thicker than the thickness of the failed layer.
  
• Apply a tack coat of asphalt emulsion to the sides and bottom of the hole at a rate of approximately 1 liter/m² (0.2 gal/yd²) of slow or rapid setting emulsion.  The tack coat should either be sprayed or brushed on the edges of the repair, never poured.  Figure 4 illustrates the tack coat application.
  
• Place the patch material in the hole.  If the patch is placed manually, use a shovel (not a rake) to place the HMA material taking care to avoid segregation.  The hole should be overfilled by 20 to 25 percent of its depth to provide adequate material for compaction.  An asphalt rake should be used to feather or blend the patch edges.
  
• Compact the patch material with a hand device or a small vibratory roller.  It is preferable to use compaction equipment whose surface is smaller than the size of the patch.  It is very difficult to achieve satisfactory compaction with equipment that bridges the repair area.  Figure 4 illustrates the compaction of the patch material.
  
• The finished patch should have a 3 to 6 mm (0.1 to 0.2 in) crown.  This allows for further compaction by traffic and helps prevent standing water in the patch area.  Figure 4 illustrates the finished patch.
• The patched area should be seamed with crack sealant and fog sealed.

3.1.3 Injection Patching

Injection patching is a rapid and effective method of patching that requires specialized equipment.  This method is used for lower trafficked roads and is an alternative to the throw and roll method.  These patches are temporary, but generally have a longer life than throw and roll patches (4).  The steps for injection patching are described below:

• Prepare the site for patching by blowing debris and water from the hole with the application nozzle.  Figure 5 illustrates site preparation.
• Spray a tack coat of emulsion on the sides and bottom of the hole at a rate of approximately 1 liter/m² (0.2 gal/yd²s).  Figure 6 illustrates the application of a tack coat.
• Blow asphalt/aggregate mixture into the hole, filling the hole to the top.  Figure 7 illustrates filling the prepared hole.
• Finish with a layer of dry aggregate.  Figure 8 illustrates the application of a finish coat to minimize pick up.  Note:  An advantage to the injection method is that it is not necessary to roll a pothole patched this way.

3.1.4 Edge Sealing

To improve the durability of a patch, the edge of the patch should be sealed to prevent the intrusion of water and other debris.  Edge sealing refers to the application of asphaltic material along the edges of a patch.  Once set, this ensures that water cannot penetrate the patch seam.  Sealing materials may be rubberized to allow for differential movement between the existing pavement material and the new patch material.  Figure 9 illustrates a finished edge seal application.

3.2 Dig Outs and Edge Repairs

When the edge of the pavement has broken away or the base has failed due to severe alligator cracking, the complete removal (dig out) of failed asphalt and base materials is typically required.  Dig out selection is important, as areas that fail due to alligator cracking will produce reflective cracks through new surface treatments if the distressed pavement is not replaced.  When in doubt, a dig out should be performed.

3.2.1 Dig Outs

The typical dig out construction process is as follows:

• Mark the boundaries of the distressed area to be replaced.  Strive for rectangular areas, taking into consideration the dimensions of the equipment that will be used for removal of the failed material and compaction of the new material.
  
• Cut out the perimeter of the area with a diamond saw or cold milling machine.
  
• Break up and remove the failed pavement to the subgrade material using appropriate combinations of pneumatic hammers, backhoes, front-end loaders, and cold milling equipment.
  
• Clean and dry the dig out area.
  
• Place and compact new (virgin) base course material using appropriate combinations of front-end loaders and roller compaction equipment.  The finished base course surface should typically be 25 mm (1 in) below the original base course surface.  This provides for a thicker and more stable patch.
  
• Apply a tack coat of emulsion at a rate of approximately 1 liter/m² (0.2 gal/yd²) to the sides of the repair area.  Tack may also be placed along the bottom of the repair area if local experience indicates good performance.  Place the patch material in the prepared dig out area.
  
• Generally, larger aggregates 12 to 19 mm (1/2 to ¾ in) are used for dig outs because of their thickness.  Place the patch material in the prepared dig out area.  Note: HMA is typically used as the patch material (AR-4000 with 9mm aggregate.  AR-8000 should be used if the area has a history of pushing or shoving.).
  
• The patch material is typically placed in lifts if the depth of the repair is greater than 100 mm (4 in).  The thickness of any lift should not exceed 100 mm (4 in).  The final lift should be made using enough material that 3 to 4 roller passes are required to roll the patch flush with the old pavement.
  
• Compact each lift using equipment similar to that typically used in hot-mix asphalt compaction operations.  The width of the compaction equipment should be narrow enough to fit within the repair area.  Equipment that bridges the repair area is less likely to achieve adequate compaction of the HMA material.
  
• The finished patched area should have a crown of 3 to 6 mm (1/8 to ¼ in).

Figure 10 illustrates a completed dig out project.  Before the new pavement is open to traffic, it is recommended that the edges are seamed with crack sealant and the entire patch is fog sealed.

3.2.2 Edge Repair

Basic construction steps associated with a repair along the edge of the pavement depend upon the severity and depth of the deterioration.  If the distress is confined mainly to the HMA surface, the steps associated with a regular patching operation should be employed.  If the deterioration extends well below the surface, the steps associated with a dig out are more appropriate.  In both cases, the intent is to improve the lateral support along the pavement’s edge.  Accordingly, extra precautions should be taken for achieving adequate compaction and maintaining good drainage at that interface with the shoulder.

3.3 Skin Patching (Surface Reinstatement)

Choosing the appropriate skin patching method depends largely on what materials are available.  Table 1 summarizes three typical approaches.