Chapter 4: Patching and Edge Repair
1.0 Description
Patching is one of the most expensive of the maintenance procedures for hot-mix asphalt (HMA) pavements, (per unit of measure, i.e. cost/ton, cost/in2, cost/yd2). It is often done in preparation for other forms of corrective maintenance, pavement preservation, or pre-treatment prior to an overlay. Patching restores the pavement surface to a state at which other preservation treatments can be used with a good chance of success.
Primary methods of patching include the replacement of materials that have been lost due to localized pavement distress or disintegration, the complete removal (dig out) and replacement of continuous segments of failed pavement, and the application of a thin layer of HMA material over segments of pavement that exhibit more surface-related distress or distortion. Once patched, the distressed area is repaired or strengthened so that it can carry significant traffic volumes with improved performance and lower rates of deterioration.
Patching may be temporary, semi-permanent, or permanent. The appropriate method to be used depends on the traffic level, the season, the time until scheduled rehabilitation, and the availability of equipment and personnel.
Patching is best carried out during clear, moderate weather. However, emergency repairs may require patching to be performed during poor winter weather conditions. In these instances, the durability of the patch is likely to be poor and the patch should be considered temporary. It is advisable to plan for a more semi-permanent repair of these areas when moderate weather conditions prevail.
This chapter is divided into pothole patching, material dig out and replacement, edge repair, and surface reinstatement. The procedures and materials associated with each method are addressed in a similar fashion.
1.1 Patching
Patching is a process by which the material in a highly distressed area is either removed and replaced or additional material is added to cover the distressed area. Merely filling a hole will not prevent the development of distress adjacent to or within the patch. Maximum performance is achieved when the boundaries of the distressed area are appropriately marked and cut, the failed material is removed, the remaining underlying material is recompacted, the hole is properly prepared, and new material is added and compacted to a level similar to that for a new pavement.
The primary methods used to perform pothole patching are:
- Temporary
- Semi-Permanent
- Injection Patching
The primary materials used for pothole patching are:
- Hot-mix asphalt (HMA) – preferred
- Cold-mix asphalt – temporary fix only
- Aggregate / asphalt emulsion combinations (i.e., injection patching)
- Special patching mixtures
1.2 Dig Outs
Dig outs are used when the pavement has failed in localized areas to such an extent that even the underlying support materials have disintegrated, become infiltrated with fine-grained materials, or otherwise lost their load-carrying capacity. Unlike typical patching, dig outs require the removal and replacement of much, if not all of the underlying base/subbase materials. Due to the thorough nature of this method, it has sometimes been referred to as spot reconstruction.
The main steps associated with dig outs are:
- Marking and cutting of the boundaries
- Breakup and removal of the pavement surface and affected base/sub base layers
- Placement and compaction of new base/sub base layers
- Application of tack coat along the edges of the repair area
The main materials used for dig outs are:
- Hot-mix asphalt (HMA) – preferred
- Cold-mix asphalt – emergency fix only
- Granular base course – for remote areas or low-volume roads
1.3 Pavement Edge Repairs
Edge repairs are used when the pavement has failed along the edges due to the action of traffic and the loss of edge support that occurs due to the presence of water, aggressive-growth vegetation, and wind from either traffic or the atmosphere. The main materials and methods used in edge repairs are the same as those associated with patching and dig outs.
1.4 Surface Reinstatement
The main method used for surface reinstatement is skin patching. Skin patching does not require a dig out. Typically, either a thin layer of HMA or a cold mix blanket can be applied to the existing surface or a coat of spray binder (emulsion) is applied and covered with a layer of aggregate. Aggregate is either washed sand or fine aggregate [3 to 5 mm (0.1 to 0.2 in)] compatible with the emulsion being used. HMA skin patches are rolled with a light or hand roller, while spray-on patching is rolled by maintenance truck wheels.
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