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Road Management & Engineeing Journal
Copyright © 1997 by TranSafety, Inc.
February 1, 1997
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402
transafety@live.com

FHWA Field Tests Anti-Icing in 15 States: New Winter Maintenance Methods Look Promising
Prewetting with Salt Brine for More Effective Roadway Deicing
Iowa's Old-fashioned, Corny Snow Fences


















Army Corps of Engineers "Pothole Primer" Is a Good Source Booklet

The U.S. Army Corps of Engineers' Cold Regions Research & Engineering Laboratory originally published "Pothole Primer: A Public Administrator's Guide to Understanding and Managing the Pothole Problem" (Special Report 81-21) in September 1981. A revised edition came out in December 1989. Highlighting major causes of pothole problems and their general solutions, authors Robert A. Eaton, Robert H. Joubert, and Edmund A. Wright wrote a highly readable booklet to assist "elected officials and non-engineering administrators of cities, towns, and military facilities . . . in understanding and managing their pothole problems in asphalt pavements."

At the time they wrote the booklet, Eaton and Wright worked with the U.S. Army Cold Regions Research & Engineering Laboratory (CRREL) in Hanover, New Hampshire. Joubert was a District Engineer with The Asphalt Institute in Lawrence, Massachusetts. This article summarizes the 28-page booklet.

Authors' Introduction
In an introduction from the authors, Eaton pointed to traffic fatalities, vehicle damage, and wasted gasoline as reasons to address pothole prevention and maintenance issues. Joubert discussed the prevalent attitude that "there's simply nothing that can be done about [potholes]." He disagreed and wrote, "[T]here's a great deal that can be done about eliminating them if we only focus on where and why they have been increasing in recent years."

Financing and Traffic Growth
Automobiles are becoming more fuel-efficient. The downside for local highway departments is that decreasing fuel sales result in decreasing gas tax revenues and less money in highway maintenance coffers. Moreover, inflation increased highway maintenance costs by two to three times during the 1980s.

While money decreased, traffic increased. From 1960 to 1980, as the U.S. population grew by 30 million, motor vehicle registrations increased by 75 million. Use of railroad transportation is down, and increasing numbers of increasingly heavy trucks travel local roads--roads that were not designed to support such traffic. One result is potholes, especially in the spring when water saturates the roadway's ground support and weakens its ability to stand up to heavy traffic.

Safety--Legal and Public Relations Aspects
Several factors have lead to increased safety concerns related to pothole problems. Small cars, motorcycles, mopeds, and bicycles are becoming more common on today's roads, and all are easily damaged by potholing. Beyond vehicle damage, personal injuries and fatalities may result from pothole-related incidents. Moreover, highway maintenance, especially emergency work done under adverse conditions, exposes highway department employees to injury and death. As injuries and claims have become more frequent, governmental immunity has diminished; and juries are awarding large settlements to plaintiffs.

Public relations concerns demand attention to potholes and other road maintenance problems. The authors called roads and streets "the most visible public facility that affects every citizen's safety, comfort and economy each day of the year."

Weather and Budgets
Asphalt is brittle in cold temperatures. When spring thaws saturate the soil that supports the asphalt, the pavement becomes vulnerable to cracking and breaking as heavy traffic passes over. The more severe the winter weather, the more likely it is there will be a pothole problem. However, the more severe the winter weather, the more likely it is that the road maintenance budget will go for snow removal and nothing will remain for pavement maintenance. To avoid this problem, the authors recommended separate budgets for these two areas of highway maintenance.

Identifying and Cataloging Causes
The authors offered this practical, as opposed to technical, definition of a pothole:

    any pavement defect involving the surface, or the surface and base, to the extent that it will cause significant noticeable impact on vehicle tires and vehicle handling.

They listed four causes of potholes:

    1. Roads that have insufficient thickness to support traffic during winter/spring thaw cycles without localized failures.
    2. Poor drainage, which will usually cause failure in combination with thin pavements, but can also affect thick pavements and new overlays.
    3. Failures at utility trenches and castings.
    4. Miscellaneous paving defects and cracks left unmaintained or unsealed from water intrusion.

When water and traffic are present at the same time, potholes form in two ways: fatigue failure and raveling failure.

Fatigue failures produce classic, bowl-shaped potholes when water weakens the soil under the pavement and traffic flexes the asphalt up and down until it breaks apart. This process is rare in thicker pavements (three to four inches) and common in thinner pavements of under three inches.

Raveling failures occur when water and traffic wear away adhesive asphalt films and stone aggregate from the surface of the road. Raveling is also common at the edge of the paved roadway or at cracks and joints where pavement has not been properly sealed. Potholes that maintenance crews have filled with cold mixes (liquid asphalt with solvents) on an emergency basis in cold weather often generate raveling failures.

Drainage
Poor drainage is a major contributor to pothole problems. Standing water and subsurface water weaken pavement support and contribute to heaves and cracking from frost penetration and freeze-thaw cycles. The authors felt, "maintenance of drainage features offers the greatest return for most rural counties, towns, and townships in the spending of annual funds for maintenance of roads."

The booklet described several options for improving drainage. Preventive maintenance includes clearing debris and foliage from roadside ditches, storm drains, and culverts. Sometimes paved and lined ditches may be necessary for a permanent drainage solution. Curbs, paved shoulders, and sealed shoulders can help efficient movement of water away from the road, and installing underdrains along shoulders may alleviate drainage problems. Finally, roadway designs that provide for sloped pavements, shoulders, and ditches reduce the number of low spots and improve drainage.

Preventive Maintenance Programs and Pavement Inventories
The authors declared, "A policy of only repairing potholes and blocked drains is not a maintenance program." Detecting early signs of roadway failure and taking prompt preventive maintenance action before potholes form can result in less expensive, more effective road maintenance. Using well-trained crews and limited funds to best advantage requires an expert inspector or engineering aide. Such experts are expensive, but their skill in identifying areas in need of attention will more than pay for them. Comprehensive inventorying of all roads in a local system by pavement type, thickness, and condition of roadway allows highway departments to coordinate and prioritize maintenance efforts for maximum economy and effect.

Utility Cut Control
A study in New York City showed that utility locations accounted for more than 85 percent of pavement defects. This booklet recommended strictly enforced quality control requirements for pavement utility cuts and a first-class system for coordinating installation of underground utilities with roadway resurfacing programs. The latter will help prevent poor communication that can sometimes result in tearing up a road that one crew resurfaced in July for another crew to make utility improvements in August.

Pothole Patching Procedures
Proper pothole patching requires four steps: (1) removing the surface and base to the level of firm support, (2) applying a coat of tacking material, (3) placing a full-depth patch of asphalt mixture, and (4) compacting and finishing the patch so it is level with surrounding pavement. As shown in the table below, not following these procedures can result in unnecessarily expensive pothole repair.

Comparison of Costs for Different Methods of Pothole Repair
No. Description Equipment Tons in place
per shift
(7.5hr)
Cost per ton
of material
in place ($)
Life of patch
(months)
Annual
cost per
ton ($)
1 Fill hole in one lift with mixture, and compact by hitting the patch with the back of a shovel twice. No effort made to clean or shape the hole, and no tacking of the exposed surfaces of the hole. Dump truck
Shovels
18.0 25.64 1 307.68
2 Same as no. 1, except compaction is performed with the tire of the dump truck. Dump truck
Shovels
12.0 31.80 2 190.80
3 Shape the area to be patched with an axe and sledge, remove loose asphalt with mattock, sweep area clean, tack the exposed surfaces of patch area, shovel in material and level with lute. Compact with wacker (vibratory compactor) and seal edges with tack oil and #IB stone. Dump truck, Pickup
Heating kettle, Wacker,
Axe, Sledge, Brooms,
Mattocks
6.0 63.29 7* 63.29
4 Same as no. 3, except a pup roller is used for compaction. Dump truck, Pickup
Heating kettle, Pup
roller, Axe, Sledge,
Brooms, Mattocks.
7.0 61.41 7* 51.41
5 Same as method no. 4, except the area to be patched is shaped with a pavement breaker. 2 Pickups, Dump truck,
Heating kettle, Air
compressor and
Pavement breaker, Pup
roller, Brooms
7.0 65.22 7* 65.22

* For methods 3,4 and 5 it will be assumed that failure will occur after 12 months, though in all probability patch life will extend beyond one year. (Editor's Note: This table reproduced from page 16 of the 1989 Pothole Primer. There appears to be a $10 discrepancy between the cost per ton and the annual cost figures for item 4.)

To achieve the best results, maintenance crews need time and good conditions. Warm, dry weather is ideal. It is essential that crews receive training in timely identification of problems and appropriate use of machinery and materials. Finally, safety is a primary consideration. Crews should wear reflective clothing, work from the center of the road to the shoulder, and receive safety training both for equipment use and traffic control procedures.

The authors completed this section of the booklet by describing patching procedures for pavement that lacks density and for joints, bridge decks, railroad crossings, areas of delamination, and macadam pavements.

Intersections, Utility Castings, and Other Common Problem Areas
Intersections, manholes, and other utility castings are "major pothole generators." Numerous utility structures at intersections break up pavement continuity and weaken pavement strength. Starting, stopping, and turning traffic increases wear on intersection pavement. In addition, it is difficult to slope intersections for good drainage. The booklet suggested intersections could be improved by removing the top inch of pavement with a milling machine or heating the surface with infrared heaters. Crews can then rework (overlay) the surface to achieve a smooth finish that drains well.

Manholes and other utility castings require special attention to prevent severe breakout problems. The authors suggested some possible treatments. For thin pavements, a five-foot-diameter transition area around a manhole that thickens the pavement to at least four inches, and preferably to the full casting depth of eight inches, may help prevent deterioration. Some success has been achieved by placing Portland cement concrete collars around castings and filling the top one or two inches with hot asphalt mix.

Training and Education
The American Public Works Association (1313 East 60th Street, Chicago, Illinois, 6063) offers schools, seminars, and conferences to train pavement maintenance practitioners. State associations of highway officials provide valuable opportunities for information sharing. The Asphalt Institute (Lexington, Kentucky 40512-4052) conducts seminars, conferences, and special schools on asphalt pavement. In addition, they offer a complete manual and a slide/tape show on pavement maintenance. Help is also available from trade magazines and journals, such as Better Roads, Rural and Urban Roads, American City & County, and Public Works Journal.

TranSafety Reporter editor's note: Additional sources of current information on the latest materials, methods, and equipment used for patching potholes and other pavement maintenance activities are Local Technical Assistance Program (LTAP) Technology Transfer (T2) newsletters. All 50 states, Washington, D.C., Puerto Rico, and four American Indian transfer centers publish T2 newsletters at least four times a year.

References and Appendix
The booklet concluded with a list of twelve practical references. A four-page appendix called "Materials and Equipment for Patching" described in more technical detail materials and equipment recommended for patching, tacking, and sealing and gave further information on pavement management systems.

Copyright © 1997 by TranSafety, Inc.


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