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Road Management & Engineering Journal
Copyright © 1997 by TranSafety, Inc.
April 1, 1997
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402
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Sealing Cracks Extends Life of Asphalt Pavement
Pothole Was Repaired after Louisiana Parish Notified of Hazard; Parish Not Liable Without Knowledge of Recurrence
Automated Pothole Patching--Better Patches for Less Money


















Article Outlines Six Steps to Patching Potholes

The September 1995 Asphalt Contractor enumerated six steps to effective pothole patching. The authors developed these steps by combining information from Guidelines for Field Evaluations of Pothole Repairs published by the Highway Innovation Technology Evaluation Center (HITEC) of the Civil Engineering Research Foundation (CERF) in Washington, D.C. and from Hot Mix Asphalt Materials, Mixture Design and Construction published by the National Asphalt Pavement Association (NAPA) Education Foundation in Lanham, Maryland. The article entitled "Pothole Patcher's Primer: Six Easy Steps Lead to a Long Repair Life" described the six steps in some detail.

To create a pothole patch that "can be considered a permanent repair and should last for years," the article recommended a full-depth patch where crews have removed the pavement down to the subgrade or intermediate subbase layer. The article also advocated hot mix asphalt (HMA) rather than cold mix. Below is an outline of the steps listed in the article.

SIX STEPS TO LONG-LASTING POTHOLE REPAIR

  1. Set up traffic control measures.

    Depending on the class of highway, crews need the protection of correct signing, flaggers, or other traffic control.

  2. Mark the area to remove.

    Crews use paint or chalk to mark a straight-sided rectangle or polygon. Lines should delineate the inclusion of at least a foot of sound pavement surrounding the pothole.

  3. Prepare the pothole.

    Remove damaged material to reach a firm base and make certain the remaining material is sound and free of cracks. This step usually involves three operations: (1) cutting to remove deteriorated pavement material, (2) cleaning the hole of dirt and debris and backfilling if subgrade is removed, and (3) drying with air or heat to eliminate moisture that would negatively affect adhesion.

  4. Apply tack to sides and bottom.

    Immediately before filling, the crew hot mops, pours, or sprays a tack coat onto the sides and bottom of the pothole. The tack improves adhesion between the old pavement and the patching mixture.

    Tack materials described later in the article included: asphalt cement (poured or sprayed while hot), cut-back asphalt (may be poured cold, but is usually slightly heated), and emulsified asphalt (add water to spray, pour, or mop into the hole).


  5. Place layers of HMA, compacting each layer, and extend final uncompacted lift above the surrounding pavement.

    Crews should layer filler four inches at a time and compact each layer. Compacting "reduces the ability of water to penetrate, ties the stones together, and increases resistance to rutting and shoving." Among filler mixes described later in the article were: HMA, cold stockpiled patching materials, sprayed-in-place materials, and loose stone.

    According to the article, the most effective compacting technique is a vibratory roller followed, in order of decreasing effectiveness, by steel-wheeled or rubber-tired roller, vibrating plate, hand tamper, delivery truck tires, and the back of a shovel.

    The article recommended extending the final lift above the surrounding pavement "about 0.25 inch (6.25 mm) per inch (25 mm) of the compacted height of the last lift to ensure the compacted patch will have adequate density and be at the same height as, or slightly higher than, the original pavement."


  6. Seal the edges of the patch.

    To reduce water penetration, crews should seal patch edges with a sand or chip seal. Sealing involves applying a light, six-to-eight-inch-wide coat of hot asphalt cement or cold-applied liquid asphalt and blotting the liquid with sand or aggregate chips.

POTHOLE REPAIR FAILURES

The article classified repair failures into four categories:

  1. Lack of adhesion to the sides or bottom of the repair--Lack of adhesion can lead to cracking. When water gets into cracks, freezing action may dislodge the repair.

  2. Dishing--Dishing is surface settling that results when the repair mix is inadequately compacted.

  3. Pushing or shoving of the patching mix--Pushing or shoving has several possible causes: "inadequate shearing resistance in the mix or a poorly compacted mix, the bleeding of tack or liquid asphalt to the upper portion of the repair, or a poorly designed mix."

  4. Loss of material through raveling, delamination of the patching mix, and drainage failures--Raveling is losing material from the surface of the repair and may result from a variety of causes, such as inadequate cohesion within the repair mix or poor compacting.

Other causes of premature pothole repair failure are: reflective cracking, delamination, and poor drainage: Reflective cracking is cracking that originates in old, underlying pavement and continues into the patch. Delamination is the peeling away of thin overlays of asphalt concrete from the surface of the roadway due to poor adhesion. And poor drainage becomes a factor when the pothole repair is in a low-lying area, where it remains constantly wet and water damage results.

Copyright © 1997 by TranSafety, Inc.


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