• Tuesday, May 21st, 2013

What:  Potholes are filled with some mixture of aggregate, asphaltic binder and additives.  There are many commercially available materials and techniques.  They include: “throw-and-roll”, the conventional application where cold mix is shoveled into the pothole then compacted (usually by truck tires); edge seal of throw-and-roll patch, using asphalt tack to bond the mix to the hole and sand to prevent tracking of the mix; semi-permanent, in which debris and water are removed and the edges squared before cold mix is placed and compacted using equipment; and spray injection, in which water and debris are blown out of hole, virgin asphalt and aggregate sprayed into the pothole, and an aggregate layer placed on top of the patch.  There are several equipment manufacturers who supply machines designed for the spray injection method.

Where:  As a pavement preservation technique, pothole patching is appropriate for pavements that are in generally good condition, but have some weak spots that have developed potholes or when pavements are cut for utility repair or other reasons.  If the pavement is in poor condition with many potholes, more aggressive corrective maintenance or rehabilitation should be considered.  Whenever a pothole is patched, repairing the cause of the pothole will result in a more permanent fix.

Why (advantages):  Obviously, a filled pothole gives a smoother ride, prevents vehicle damage and prevents accidents.  It also prevents entry of surface moisture into the base as well as further deterioration, thereby prolonging pavement life.  Patching is very economical if done properly.  If not effectively patched, utility cuts can result in severe damage to good pavements.  Sunken or raised patches affect the smoothness, rideability and therefore pavement life, as well as safety and vehicle damage.  Unsealed interfaces between the cuts/patches/pavement can ravel and allow moisture to damage the pavement structure.

Why not (disadvantages):  Monies spent on excessive patching might be better spent on maintaining good roads, base and drainage repair, and/or rehabilitation.  In the ideal scenario, with a sound pavement preservation program, potholes would not occur.  FHWA’s Strategic Highway Research Program (SHRP) found that the use of quality materials is the most important variable in effective pothole patching, and that the throw-and-roll technique proved as effective as the semi-permanent procedure in most situations.  The material should have a strong aggregate structure, the binder should have cohesive strength to hold the patch material together, and the patch should bond firmly to the sides of the pothole and resist moisture damage.

When:  Potholes usually first appear in the early spring when the ground is saturated and weakened by moisture and multiple freeze-thaw cycles.  It is most cost-effective to repair and patch potholes as soon as they appear on pavements with sound structures and good drainage.  Materials should be selected that are appropriate for the weather at the time of patching.

Estimated life extension: 2-12 years on pavements in good to fair condition, 1-4 years on pavements in poor condition.

For more information on successful pothole patching, consult the SHRP report.

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