pavement maintenance.pdf

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Pavement Maintenance

Cornell Local Roads Program

NEW YORK LTAP CENTER


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byDavid P. Orr, PESenior Engineer


Cornell Local Roads Program416 Riley-Robb Hall

Ithaca, New York 14853-5701

Tel: 607-255-8033Fax: 607-255-4080

Email: [email protected]

Web site: www.clrp.cornell.edu

March 2006

CLRP No. 06-5


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i

PREFACE

Millions of dollars are spent each year maintaining and repairing pavements all over New YorkState. Since inadequate drainage is the source of many of the problems, the Cornell Local Roads

Program offers a one-day course devoted exclusively to drainage. I was fortunate to develop thatcourse,Roadway and Roadside Drainage, in 1997.

Another issue I have seen in my travels around the state is that of selecting the correct pavementrepair, particularly with regard to pavement surviving winter weather and heavy traffic. In manytextbooks and training manuals, there is a concentration either on the management of thepavement or on the specific repair. While these items are important, I feel it is essential to focuson the selection of the repair. Management of highway systems can only be accomplished with athorough knowledge of why pavements fail and what it takes to fix them.

To this end, this class onPavement Maintenancewas developed. We considered other titles suchas Pavement Preservation and Pavement Fixes.

This manual discusses choosing the proper repair techniques for paved and unpaved roads. Italso goes into more detail on some of the most common asphalt pavement maintenancetechniques such as patching and chip seals. It is not intended to provide all of the training neededto properly select and perform pavement maintenance. It is intended to answer the most commonquestions and to help you get what you expect when it comes to pavement repair.

David P. Orr, P.E.Senior EngineerCornell Local Roads ProgramIthaca, New York

March 2006


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ii Cornell Local Roads Program

ACKNOWLEDGEMENT

I would like to thank several people for helping out with this manual. Some of them may noteven realize that they played a role. In 1996, just after I joined the Cornell Local Roads Program,

J im Dean, the Town of Orangetown Highway Superintendent, asked me to teach a class onpavement maintenance. That class was repeated and upgraded several times, and has evolvedinto this manual and workshop. Ken Osborne and the members of the Liquid AsphaltDistributors Association (LADA) have provided insight and help with getting materials andexamples. Chris Blades and Ed Kearney teach our class onAsphalt Paving Principles. Thatworkshop and this one work well as a pair. Finally, I need to thank Lynne Irwin, Director of theCornell Local Roads Program. His lecture in a class on Pavement Engineering gave me the ideaof developing a class that focusses on understanding the solutions to repairing pavements.


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Cornell Local Roads Program iii

TABLE OF CONTENTS

Chapter

1. Introduction............................................................................................................................ 1

2. Why Roads Fail Prematurely................................................................................................. 53. Repair Techniques............................................................................................................... 13

4. Pavement Distresses............................................................................................................. 17

5. Choosing the Right Repair................................................................................................... 29

6. Crack Repairs....................................................................................................................... 33

7. Patching................................................................................................................................ 41

8. Thin Wearing Courses......................................................................................................... 47

Appendix A Crack Treatment Materials..............................................................................63

Appendix B Publications......................................................................................................64

Appendix C Videos..............................................................................................................65Appendix D Resources.........................................................................................................66

Appendix E NYSDOT Regional Offices.............................................................................68

Appendix F Glossary...........................................................................................................69


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iv Cornell Local Roads Program

List of FiguresFigure 1 Map of NY State towns & cities by population - 2000......................................1

Figure 2 Spread of wheel load pressure through the pavement.......................................5

Figure 3 Pavement deflection...........................................................................................6

Figure 4 High severity alligator cracking.......................................................................18

Figure 5 Sealed longitudinal cracks...............................................................................19Figure 6 Low severity transverse crack..........................................................................19

Figure 7 Medium to high severity block cracking.........................................................20

Figure 8 High severity edge cracking.............................................................................21

Figure 9 Medium severity rutting...................................................................................22

Figure 10 Shoving of asphalt surface...............................................................................23

Figure 11 Potholes caused by poor drainage....................................................................24

Figure 12 High severity ravelling of asphalt surface.......................................................25

Figure 13 Bleeding during hot weather............................................................................26

Figure 14 Polishing of asphalt surface.............................................................................26

Figure 15 Overlay delamination.......................................................................................27

Figure 16 Pavement deterioration curve..........................................................................30

Figure 17 Pavement repair alternatives............................................................................31

Figure 18 Crack with high level of edge deterioration.....................................................33

Figure 19 Basic crack repair configurations.....................................................................35

Figure 20 Crack sealing creating a safety hazard.............................................................36

Figure 21 Crack routing...................................................................................................38

Figure 22 Heat lance.........................................................................................................39

Figure 23 Basic wand application of crack sealer............................................................39

Figure 24 Finishing a crack with a squeegee...................................................................40Figure 25 Cut boundaries.................................................................................................42

Figure 26 Finished patch..................................................................................................43

Figure 27 Self contained spray patch truck......................................................................44

Figure 28 'Rolling' a cold mix patch.................................................................................46

Figure 29 Spreading stone for chip seal ...........................................................................47

Figure 30 Proper spacing of emulsion and chip spreader ...............................................48

Figure 31 Slurry seal equipment schematic .....................................................................49

Figure 32 Micropaving equipment schematic..................................................................50

Figure 33 Chip seal placement.........................................................................................55

Figure 34 Residual asphalt...............................................................................................56Figure 35 Average Least Dimension of chip seal after curing.........................................57

Figure 36 Self propelled aggregate spreader....................................................................59

Figure 37 Spray bar alignment.........................................................................................59

Figure 38 Spray lap coverage...........................................................................................59

Figure 39 Improper spacing of emulsion and chip spreader............................................60


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Cornell Local Roads Program v

List of Tables

Table 1 Average distribution of government expenditures on highways in NY ............2

Table 2 Pavement repair techniques...............................................................................2

Table 3 Maintenance activities.....................................................................................29

Table 4 Pavement repair matrix....................................................................................32

Table 5 Determining the type of maintenance for cracks.............................................34

Table 6 Guidelines for crack repairs.............................................................................35

Table 7 Properties of crack filling materials.................................................................37

Table 8 Proprietary cold patches on NYS OGS bids, 2005..........................................45

Table 9 Cost effectiveness of various demand patching methods................................46

Table 10 Distresses repaired by selected thin wearing courses......................................48

Table 11 Aggregate gradations used for slurry seals (ISSA 1998).................................49

Table 12 Sieve sizes for common chip seal aggregates (NYSDOT spec.).....................52

Table 13 Asphalt emulsions and residual asphalt content..............................................53

Table 14 Emulsion application rate adjustments............................................................58


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Cornell Local Roads Program 1

1 - Introduction_____________________________________________________________

Pavement MANAGEMENT:

Doing the right repair in the right place, at the right time.Pavement MAINTENANCE:Doing inexpensive repairs on good roads to keep them good.- Foundation for Pavement Preservation

The proper maintenance of roads, considering the State at large, isunquestionably of more importance than any of the problems that are solved andto be solved either in construction or maintenance of more expensive roads.- State of New York Department of Highways, 1910

The pressure on highway and street departments to do more with less is always a concern.

Whether in the largest city (New York) or the smallest town (Montague in Lewis County), thecost of construction and maintenance of highways can be a sore subject. As shown in Table 1,the average distribution of government moneys spent on highways in 1997 varies from 2.8percent for counties to almost 20 percent for towns. Not too many years ago, the highwaydepartment was the largest department in many towns and counties and a substantial portion ofthe budget in villages and cities.

Figure 1 - Map of New York State towns and cities by population, 2000,source:New York State Department of Transportation

Under 2,500

2,500 to 9,999

10,000 to 19,999

20,000 to 49,999

50,000 and over

Number of Persons


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2 Cornell Local Roads Program

Table 1 - Average distribution of government expenditures on highways in New York State,1997, source:Local Government Handbook

Function Counties Cities Towns Villages

Highways 2.8% 5.5% 19.8% 10.2%

While the portion of the budget spent on highways and streets has decreased, traffic levels haveincreased and the public continues to demand better roads. It is critical that we get the most outof every dollar we spend.

We must spend these limited funds wisely. In many books and manuals, this is defined aspavement management. While it is important to do the right repair at the right place at the righttime, it is cheaper to maintain roads in good shape than it is to fix roads that are broken.

Pavement maintenance is doing repairs on good roads to keep them good. A good pavementmaintenance program is usually part of an overall management plan. It can also be used as thestarting point to develop such a plan.

One of the most important keys to successful pavement maintenance is to know what the properrepair is. This can range from doing nothing to reconstructing the entire road. It may be better todo nothing rather than to make a repair that fails prematurely.

We have all had to make a repair, even when it was not our first choice. In such a case, it isimportant to know what may go wrong and how to reduce the chances of it happening again.Understanding the reasons is important to making the correct choice.

There are many different pavement maintenance techniques. There are even different ways to listthem. Table 2 shows possible repair techniques for asphalt and gravel surface roads, listed inorder of increasing cost and durability. Concrete and brick streets are not addressed.

Table 2 - Pavement repair techniques

Asphalt concrete surfacedpavements

Gravel surfaced pavements

Do nothingDrainage maintenanceCrack treatmentPatchingArea repairsWearing courses

OverlaysRecyclingReclamationTotal reconstruction

Do nothingDrainage maintenanceBlading or gradingReshapingPatchingWearing courses

RecyclingReclamationTotal reconstruction


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1 - Introduction


This manual focusses mainly on asphalt surface-treated roadways. Almost forty percent of theroads in the United States are gravel, but much of the discussion on why roads fail prematurely isapplicable for all types of road surfaces. For more details on gravel road maintenance, theGravel Roads Maintenance and Design Manual from the South Dakota LTAP Center is a goodresource. See Appendix B for the the complete publication information, and Appendix D for the

SD LTAP contact information.


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2 - Why Roads Fail Prematurely_____________________________________________________________

In a perfect world, pavement would last forever. Unfortunately, this is not the case. Before

deciding on the proper repair, we need to understand why there may be premature distresses.Before discussing why roads fail prematurely, we need to start with, What is a road?

What is a road?

A road allows transportation from point A to B in all weather and traffic conditions. While abasic definition, this does not answer the question of why we build roads. Essentially, we buildroads to reduce the stress on the native material (i.e., subgrade) under the pavement. To do this,we have to place good materials on the subgrade to spread out the load.

Figure 2 shows how the load is spread out by the pavement. A thicker pavement will result inless stress on the subgrade. Figure 3 shows how pavement deflects under a wheel load. As thepavement flexes, there will be a combination of compression (pushing) and tension (pulling)

stress in the pavement. This can eventually lead to cracking due to fatigue.

Figure 2 - Spread of wheel load pressure through the pavement

The amount of deflection and stress in the pavement is also related to the amount of moisture in thesubgrade soils. If the subgrade soils are wet, there will be a great deal of deflection under the wheelloads. The deflection will be much less for the same soil when it is well drained. The excess

moisture in spring thaw will result in higher stresses in the pavement.Larger loads and thinner pavements result in more stress on the pavement. Pavements will failsooner than expected if:

There are heavier loads than expected

There are more loads than expected

The pavement is too thin for the traffic loads

The materials used in the pavement are weaker than expected


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Figure 3 - Pavement deflection

Understanding fatigue

Fatigue is the failure of a material due to repetition of many loads. The larger the load, the fewerthe number of cycles needed to cause failure. In a pavement, the result is typically cracking orrutting. Roads with heavier trucks or weakened pavement during spring thaw are more susceptibleto fatigue failure.

To understand this, take a paper clip and bend it back and forth until it fails. To simulate thesummer, bend it to 45 each time. Count how many cycles it takes to fatigue the paper clip. Tosimulate spring thaw, bend to 90. A very weak pavement with heavy loads might be like bendingthe paper clip to 180.

45 90 180

We need to build pavements to handle the loads. If the loads are heavy and frequent, we need tobuild a thick, well-drained pavement that does not bend as much.

Premature failure

Pavements fail prematurely because of many factors. When boiled down to the basics, there arefour primary reasons pavements fail prematurely:

Failure in design

Failure in construction

Failure in materials

Failure in maintenance


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2 - Why Roads Fail Prematurely


Generally when a road or street fails before we expect it to, one of these four factors is theprimary cause. Multiple factors can occur, but usually one of the four is the most critical.

Thethink system

Think of a section of highway in your municipality that never seems to last as long as youexpect. Pick one of the four factors above that you think is most likely to be the prime factor topremature failure. As you read the section below, see if your choice stays the same.

Design

Most roads are not specifically designed. They have evolved from paths and trails to thepavements we have today. This does not mean we need to go out and have a full-blownengineering design done for every road repair. In fact, most roads work just fine.

However, there are still many issues that need to be examined. Do we understand the conditionson the road? What is the traffic level? Has anything changed since the last major improvement?

Is anything likely to change?For low-volume roads, the most important design challenge is accounting for weather anddrainage conditions. If the drainage is done correctly, and the road is built to certain minimumsof thickness and quality, it should hold up just fine.

However, there are still many failures due to design.

Under-designed

A road that cannot handle the loads is under-designed. This could be due to a failure toaccount for conditions such as an increase in truck traffic. For instance, new roads toindustrial and commercial areas should be designed. Before the municipality takes over a

road, it must feel confident the road will last as long as possible. Get an engineer to helpdesign the road if you are not sure. Ask for a professional engineering certification thatthe road will last the desired number of years.

Failure to account for conditions

Even if the road is built to a quality standard, there may be premature failure if anyconditions remain unaccounted for in the design. The condition assessment problem thatleads to the most premature failures is a lack of good drainage. This is not a constructionor materials problem in many cases. When inspecting the road before work is done, thequality of the drainage MUST be assessed. Failure to do so will almost always result inpremature failure.

Changes after construction

If you build it, they will come. As soon as you build a smooth section of pavement,vehicles that had detoured in the past may suddenly decide to use the new roadway. Ifyou failed to anticipate this increased traffic, your road may fail too soon. This can beespecially bad if there is extra truck traffic in the spring during the thaw.


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Examples of failure in design

Overlay too thin for traffic load (Too thick is also not desirable. It wastes money.)

Failure to account for a spring in the middle of the roadway

Use of a chip seal over a badly cracked road

Selecting crack seals to fix badly deteriorated cracks

Using asphalt cement stabilizer when the fines content is too high(above about 12 percent)

Construction

Just as design can lead to premature failure, poor quality construction can cause a roadway to failearly. Many construction failures do not appear as defects for several years, so it can be difficultto determine the reason for the failure. Whether the work is done in-house or by contract, it isimportant to get the job done right.

If you are doing the work yourself, are you ready? Has the crew been trained? What training dothey need and where can you get the training? Municipalities have some of the best snowplowcrews anywhere. Part of that expertise is experience. You do something enough and you getpretty good at it. Part of the expertise is training. Riding with that old-timer can be some of thebest training you can get.

If you are contracting the work, are you ready? Do you need an inspector for the work? Is theinspector trained and ready to make sure the municipality gets what they pay for? What kind ofcontract are you using?

Construction may be the most difficult step because there are so many questions to be asked and

answered. The problem with not asking the questions is that we usually do not get a secondchance to do the work again.

Fortunately, experience is a great teacher, and for most operations some basic training andpractice is enough to make sure the work is done right. Complicated and specialized work canstill be problematic and failures due to construction can occur.

Poor workmanship

The best laid plans often go astray. If the work is not done properly then it may not last.A very common problem in culvert installation is the failure to compact the backfill inthin even lifts. It may be faster to put in thick lifts, but coming back to fix the problemafter settlement occurs is not a good alternative. Training and pride in your work go a

long way towards overcoming workmanship issues.

Using incorrect equipment

Everyone knows you should hit a nail with a hammer, yet how many of us have used awrench instead? Using the wrong tool in pavement maintenance can lead to prematurefailure. A rubber-tired roller should be used on a chip seal. A steel drum roller can crushand break the aggregate. NOT using a piece of equipment can also cause problems.Leaving gravel unrolled because no roller is available is a bad solution.


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Using equipment improperly

Even if you have the right piece of equipment, it is important to use it correctly. Adistributor with misaligned fans will lead to streaking. Using a compressor to blow outcracks can put water into the cracks. Know what a piece of equipment is for and how touse it properly.

Failure to follow plans

Do you have plans? Engineering drawings are not required for pavement maintenance,but writing down the steps and having a plan is a valuable tool. Examples of items in agood plan include stakeout, detours, materials, construction steps, and plans in case ofpoor weather. Without a plan, how do you know whether anything was done incorrectly?

Lack of training

Lynne Irwin likes to say: How do you know what you dont know, if you dont knowthat you don't know it? A crew cannot be expected to do something if they do not know

how. Provide training for everyone. It can be on-the-job, tailgate talks over breaks, hour-long training at an association meeting, or all-day training from the Cornell Local RoadsProgram or a vendor.

Wrong time of year or poor weather

We cannot control the weather, but we can account for it. A surface treatment placed inOctober is not likely to work as well as one placed in July. On the other hand, if it rainedduring construction in July, it is not likely to do very well either. Know the limitations forthe repair. You may have to do the work anyway, but you will be better prepared toovercome the problems that may arise.

Examples of failure in construction

Failure to compact cold patch with the truck tire

Failure to place the aggregate in a chip seal before the asphalt emulsion breaks

Using an air compressor without an oil/water separator to clean cracks (can introducewater and cause a loss of bond)

Paving over a base that is not properly prepared

Doing any work with asphalt emulsions after late October (or on any cold day)


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Materials

Using the wrong material in the right place or the right material in the wrong place can lead topremature failure. Sometimes the problems are obvious. Sometimes the problem does not appearto be related to the material choice. Backfilling an underdrain trench with large stone is actually

a materials problem. The stones will retain silt particles brought in by the drained water and willlead to premature plugging of the pipe. Be sure to select the correct material for the job.

Wrong material

The wrong material will lead to premature failure. Using a dirty gravel base is a classicexample. The use of the less expensive material can lead to much larger expenses in thefuture. Understand what the limitations of a particular product are before you use it. Askthe vendor, other highway departments, or the New York State Department ofTransportation. Get a clear picture of the best material for the job.

Material does not meet specifications

Once you select the material, make sure it meets specifications. By some estimates, 1/4 ofthe wire in the main cables of the Brooklyn Bridge did not meet the specifications. Whenthe contractor was caught, the extra expense of more cable was paid out of their contract.Some failures are due to a material not meeting specifications. One recommendation is toalways sample the materials on site. It is not always possible to go back and get a sampleafter the construction is complete.

Material installed incorrectly

If material is put in incorrectly, there can be premature failure. Is this a construction issueor a material issue? It could be both. It should be neither. Sometimes the problem isfailure to install the item using a newer technique. For instance, Superpave asphalt

concrete needs to be rolled differently than older Marshall Mix design asphalt concretes.

Incompatibility with other materials

Aggregate charge incompatibility is cited almost every time a chip seal fails. In reality, italmost never occurs. Much more common is using a dusty stone that does not adhere tothe asphalt emulsion. When this problem occurs, the consequences can be dramatic.

Examples of failures in materials

Chip sealing over a good quality surface gravel (a good surface gravel has toomany fines to be a base gravel)

Using an asphalt emulsion toseal cracks

Using a cheaper cold patch that may last only a few hours

Using a dusty or wet aggregate in surface treatment operations


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Maintenance

The most common maintenance problem is that not enough maintenance is done. This is abudgetary, planning, and communication issue that is sometimes very difficult to overcome.Once we decide to perform maintenance we need to remember that ALL maintenance techniquescan be designed to fit the conditions and need to be constructed properly using the correct

materials. Premature failure of pavement maintenance is usually a failure of design, construction,or material.

Design

The most common design issue is a lack of design. The first step in design is selecting thecorrect repair to fix the problem. In too many cases, the choice of repair is made for non-technical reasons. In addition, many maintenance repairs are made without any design.Even a chip seal can be designed to obtain the best result for the municipality. Knowingwhat needs to be done to get the right repair is one of the most critical steps in the design

of pavement maintenance.

Construction

Once a technique has been chosen, it needs to be done correctly. The failure to constructthe maintenance repair properly is a major cause of premature failure. A classic exampleis the lack of truck tire rolling of cold mix patch in the winter. Instead of lasting severalmonths, it lasts less than a day.

Material

Using the correct material is critical. It may be less expensive to buy cheaper gravel,patch, or emulsion, but can you afford the cost of replacement if it fails prematurely?


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3 - Repair Techniques_____________________________________________________________

There are many different pavement maintenance techniques. Before deciding which technique to

use, make sure you know all of the possible choices. Some problems can only be solved withcertain techniques. The list below describes the basic repairs that need to be in your pavementrepair toolbox.

All Pavements

Do nothing

This is the most common repair choice, because of cost. It is used whenever economics dictatethat no better choice exists. It is used on good and bad roads. A brand new road needs no repairs.On a poor, badly cracked surface, the best technique may be to do nothing. It may be better to

leave a road in rough shape than to cover over the problem and have it recur almost immediately.

Drainage maintenance

This is absolutely critical to allow roads to last as long as possible. Drainage is the single mostcommon problem that leads to premature failures. For more details on drainage, refer to theCornell Local Roads Program manual, Roadway and Roadside Drainage(see Appendix B).

Asphalt Surfaced Pavement

Crack repairs

When cracks are narrow (1/4 inch to 1 inch) and not deteriorated on the edge, crack repairs are agood alternative. Crack repairs generally fall into two categories of work: sealingandfilling.Sealing prevents the intrusion of water and debris into aworkingcrack. A working crack is onethat moves noticeably (more than an eighth of an inch) due to weather or traffic loads. Fillingreduces the infiltration of water into anon-workingcrack.

Patching

Patching is a year-round activity that is done to keep road surfaces drivable. Most patching isdone to fill potholes. Ruts, slippage and other pavement defects may also be fixed best bypatching. Patching does not fix base problems. Types of patches include: cold asphalt throw androll, hot asphalt semi-permanent, and spray patching. Patching is very economical if doneproperly.

Area repairs

Unlike patching, area repairs involve a more extensive repair. An area repair involves a cut outand replacement of a bad section of a road or street. It is relatively expensive for the arearepaired, but since it fixes any base problems and is not wasteful, it can be the best alternative forroads with small areas of distress.


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Thin wearing courses

Sometimes called surface treatments or seals, there is a large family of alternatives that fall intothe field of a thin wearing course. They are generally less than one inch thick. This large varietyof repairs is used to waterproof the pavement, restore skid resistance, and restore oxidizedsurfaces. Some surface treatments can fill minor ruts. Cracks and other defects will reflect

through. Thin wearing courses do not add any structural strength.

Overlays

Generally greater than one-inch thick, an asphalt concrete overlay adds strength and can correctminor ride defects. Good timing is critical, due in part to the relatively high expense versus othermaintenance activities. In an urban area, loss of curb reveal can be a problem. A tack coat is animportant step to help make sure the technique has as much chance of success as possible,Details of overlay construction can be found in the Cornell Local Roads Program manual,Asphalt Paving Principles (see Appendix B).

Recycling

Recycling is the reuse of the asphalt surface, but it does not usually reuse the base. Thisenvironmentally-friendly technique fixes cracks and restores the surface, but itdoes not fix anybase quality or drainage problems. Any isolated base or drainage problems should be repairedprior to recycling.

Reclamation

Reclamation or stabilization improves the base, as opposed to recycling, which does not. This isdone via the addition of aggregates or chemicals to improve the quality of the base. Whencompleted properly, it provides an almost new road. Reclamation can be very cost-effective, butthe choice of stabilizing agent is very critical.

Total reconstruction

This is a very expensive technique, but it may be the only option for a badly deteriorated road.Total reconstruction can be cost-effective if done in conjunction with utility replacement. Thischoice is usually a last resort.

Gravel Surfaced Pavements

Dust control

Dust palliatives (emulsions, wood lignins, and salts) are used to keep the dust on the surface ofthe pavement and to improve safety for the traveling public. As opposed to stabilization, dustcontrol is the primary reason for application and generally no working of the surface is needed.In many cases, dust control operations are scheduled to coincide with blading or grading.

Blading or dragging

A grader routinely needs to be used to resmooth a gravel surface. This is done with the blade ofthe grader set to vertical with a slight down pressure. Going slow is the key to success.


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3 - Repair Techniques


Sometimes this is called dragging, after the historical practice of using a horse-drawn woodendrag to perform the same function.

Reshaping

Reshaping and grading are done when blading is not enough. This generally requires pulling the

gravel material into a windrow and respreading with the grader. Rolling the surface will improvethe durability of this repair.

Patching and area repairs

For gravel roads, most patching is done in conjunction with other work. Scarify the material inthe area needing patch to a depth of an inch more than the deepest pothole. Filling in potholes ongravel roads is usually not successful.

Stabilization

Usually one of the highest levels of repair on a gravel road, stabilization involves usingchemicals or aggregate to help improve the quality of the material in the pavement. Asphaltemulsion, portland cement, calcium chloride, and salt have all been used as chemical additives.The choice of additive is critical to the success of the repair.

Overlays and surface treatments

Placing an asphalt overlay or surface treating the gravel is sometimes necessary to deal withincreased traffic. When performing this repair, be sure the gravel surface does not have too manyfines. If the fines content is above eight percent, the new surface will probably trap moisture andfail prematurely.

Total reconstruction

As with asphalt surfaced roadways, total reconstruction is a very expensive technique, but it maybe the only option. For most gravel roads, this is usually done only when the road will be pavedwith asphalt.


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4 - Pavement Distresses_____________________________________________________________

To understand which repair to choose, it is important to understand the distresses that occur in a

pavement. Some repairs do not fix certain distresses. Since this manual concentrates on asphaltmaintenance techniques, only asphalt surface distresses are listed below. For gravel roads, seethe Federal Highway Administration (FHWA) publication, Problems Associated with GravelRoads.More detailed information on asphalt pavement distress is available in theDistressIdentification Guide from the Long-Term Pavement Performance Program. See Appendix B.

The severity and extent of a distress determine the proper repair. If a distress covers more thanone-third of the pavement surface, the entire roadway may need to be repaired. If the distress isisolated to a couple of small areas, then spot repairs may fix the problem. Low severity distressesusually require less extensive repairs. For example, a thin wearing course may seal fine cracks oflow severity. Once the distress is very severe, crack repairs may not be enough to properly fix it.

The four major categories of common asphalt pavement surface distresses are:

1. Cracking

2. Surface deformation

3. Disintegration (potholes, etc.)

4. Surface defects (bleeding, etc.)

Cracking

Cracks in asphalt pavements can take many forms. The most common types of cracking are:

1. Fatigue cracking

2. Longitudinal cracking

3. Transverse cracking

4. Block cracking

5. Slippage cracking

6. Reflective cracking

7. Edge cracking

Fatigue cracking (Alligator cracking)

Fatigue cracking is commonly called alligator cracking. This is a series of interconnected crackscreating small, irregular shaped pieces of pavement. The cracking pattern gives the appearanceof alligator skin or chicken wire.


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It is caused by failure of the surface layer or base due to repeated traffic loading (fatigue).Eventually the cracks lead to disintegration of the surface, as shown in Figure 4. The final resultis potholes. Alligator cracking is usually associated with base or drainage problems.

Small areas may be fixed with a patch or area repair. Larger areas require reclamation orreconstruction. Drainage must be carefully examined in all cases.

Figure 4 - High severity alligator cracking

Longitudinal cracking

Longitudinal cracks are long cracks that run parallel to the center line of the roadway. These maybe caused by frost heaving or joint failures, or they may be load induced. Understanding thecause is critical to selecting the proper repair.

Multiple parallel cracks may eventually form from the initial crack. This phenomenon, known asdeterioration, is usually a sign that crack repairs are not the proper solution.

Filling or sealing longitudinal cracks can work if the cracks are narrow and not deteriorated toomuch. Figure 5 shows sealed longitudinal cracks. Multiple cracks may require patching or arearepairs to fix the problem.


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4 - Pavement Distresses


Figure 5 - Sealed longitudinal cracks

Transverse cracks

Transverse cracks form at approximately right angles to the centerline of the roadway. They areregularly spaced and have some of the same causes as longitudinal cracks. Transverse cracks willinitially be widely spaced (over 20 feet apart). They usually begin as hairline or very narrowcracks and widen with age. If not properly sealed and maintained, secondary or multiple cracksdevelop, parallel to the initial crack.

The reasons for transverse cracking, and the repairs, are similar to those for longitudinalcracking. In addition, thermal issues can lead to low-temperature cracking if the asphalt cementis too hard. Figure 6 shows a low-severity transverse crack.

Figure 6 - Low severity transverse crack


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Block cracking

Block cracking is an interconnected series of cracks that divides the pavement into irregularpieces. This is sometimes the result of transverse and longitudinal cracks intersecting. They can

also be due to lack of compaction during construction.Low severity block cracking may be repaired by a thin wearing course. As the cracking getsmore severe, overlays and recycling may be needed. If base problems are found, reclamation orreconstruction may be needed. Figure 7 shows medium to high severity block cracking.

Figure 7 - Medium to high severity block cracking

Slippage crackingSlippage cracks are half-moon shaped cracks with both ends pointed towards the oncomingvehicles. They are created by the horizontal forces from traffic.

They are usually a result of poor bonding between the asphalt surface layer and the layer below.The lack of a tack coat is a prime factor in many cases. Repair requires removal of the slippedarea and repaving. Be sure to use a tack coat in the new pavement.

Reflective cracking

Reflective cracking occurs when a pavement is overlaid with hot mix asphalt concrete and cracks

reflect up through the new surface. It is called reflective cracking because it reflects the crackpattern of the pavement structure below.

As expected from the name, reflective cracks are actually covered over cracks reappearing in thesurface. They can be repaired in similar techniques to the other cracking noted above. Beforeplacing any overlays or wearing courses, cracks should be properly repaired.


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Edge cracking

Edge cracks typically start as crescent shapes at the edge of the pavement. They will expandfrom the edge until they begin to resemble alligator cracking. This type of cracking results fromlack of support of the shoulder due to weak material or excess moisture. They may occur in acurbed section when subsurface water causes a weakness in the pavement.

At low severity the cracks may be filled. As the severity increases, patches and replacement ofdistressed areas may be needed. In all cases, excess moisture should be eliminated, and theshoulders rebuilt with good materials. Figure 8 shows high severity edge cracking.

Figure 8 - High severity edge cracking

Surface deformation

Pavement deformation is the result of weakness in one or more layers of the pavement that hasexperienced movement after construction. The deformation may be accompanied by cracking.Surface distortions can be a traffic hazard.

The basic types of surface deformation are:

1. Rutting

2. Corrugations

3. Shoving

4. Depressions

5. Swell


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Rutting

Rutting is the displacement of pavement material that creates channels in the wheel path. Verysevere rutting will actually hold water in the rut. Rutting is usually a failure in one or more layersin the pavement. The width of the rut is a sign of which layer has failed. A very narrow rut is

usually a surface failure, while a wide one is indicative of a subgrade failure. Inadequatecompaction can lead to rutting. Figure 9 shows an example of rutting due to subgrade failure.

Figure 9 - Medium Severity Rutting

Minor surface rutting can be filled with micropaving or paver-placed surface treatments. Deeperruts may be shimmed with a truing and leveling course, with an overlay placed over the shim. Ifthe surface asphalt is unstable, recycling of the surface may be the best option. If the problem isin the subgrade layer, reclamation or reconstruction may be needed.

Corrugation

Corrugation is referred to as washboarding because the pavement surface has become distortedlike a washboard. The instability of the asphalt concrete surface course may be caused by toomuch asphalt cement, too much fine aggregate, or rounded or smooth textured coarse aggregate.Corrugations usually occur at places where vehicles accelerate or decelerate.

Minor corrugations can be repaired with an overlay or surface milling. Severe corrugationsrequire a deeper milling before resurfacing.

Shoving

Shoving is also a form of plastic movement in the asphalt concrete surface layer that creates alocalized bulging of the pavement. Locations and causes of shoving are similar to those forcorrugations. Figure 10 shows an example of shoving.

Repair minor shoving by removing and replacing. For large areas, milling the surface may berequired, followed by an overlay.


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Figure 10 - Shoving of asphalt surface

Depressions

Depressions are small, localized bowl-shaped areas that may include cracking. Depressionscause roughness, are a hazard to motorists, and allow water to collect. Depressions are typicallycaused by localized consolidation or movement of the supporting layers beneath the surfacecourse due to instability.

Repair by excavating and rebuilding the localized depressions. Reconstruction is required forextensive depressions.

Swell

A swell is a localized upward bulge on the pavement surface. Swells are caused by an expansionof the supporting layers beneath the surface course or the subgrade. The expansion is typicallycaused by frost heaving or by moisture. Subgrades with highly plastic clays can swell in amanner similar to frost heaves (but usually in warmer months).

Repair swells by excavating the inferior subgrade material and rebuilding the removed area.Reconstruction may be required for extensive swelling.

Disintegration

The progressive breaking up of the pavement into small, loose pieces is called disintegration. Ifthe disintegration is not repaired in its early stages, complete reconstruction of the pavement maybe needed. The two most common types of disintegration are:

1. Potholes

2. Patches


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Potholes

Potholes are bowl-shaped holes similar to depressions. They are a progressive failure. First,small fragments of the top layer are dislodged. Over time, the distress will progress downwardinto the lower layers of the pavement. Potholes are often located in areas of poor drainage, asseen in Figure 11.

Potholes are formed when the pavement disintegrates under traffic loading, due to inadequatestrength in one or more layers of the pavement, usually accompanied by the presence of water.Most potholes would not occur if the root cause was repaired before development of the pothole.

Repair by excavating and rebuilding. Area repairs or reconstruction may be required forextensive potholes.

Figure 11 - Potholes caused by poor drainage

Patches

A patch is defined as a portion of the pavement that has been removed and replaced. Patches areusually used to repair defects in a pavement or to cover a utility trench. Patch failure can lead toa more widespread failure of the surrounding pavement. Some people do not consider patches asa pavement defect. While this should be true for high quality patches as is done in a semi-permanent patch, the throw and roll patch is just a cover. The underlying cause is still under thepothole.

To repair a patch, a semi-permanent patch should be placed. Extensive potholes may lead to arearepairs or reclamation. Reconstruction is only needed if base problems are the root source of thepotholes.


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Surface defects

Whereas the previous types of distress are mostly related to the supporting layers beneath thesurface, surface defects are related to problems in the surface layer. The most common types ofsurface distress are:

1. Ravelling2. Bleeding

3. Polishing

4. Delamination

Ravelling

Ravelling (see Figure 12), is the loss of material from the pavement surface. It is a result ofinsufficient adhesion between the asphalt cement and the aggregate. Initially, fine aggregatebreaks loose and leaves small, rough patches in the surface of the pavement. As thedisintegration continues, larger aggregate breaks loose, leaving rougher surfaces. Ravelling can

be accelerated by traffic and freezing weather. Some ravelling in chip seals is due to improperconstruction technique. This can also lead to bleeding. Repair the problem with a wearing courseor an overlay.

Figure 12 - High severity ravelling of asphalt surface

Bleeding

Bleeding is defined as the presence of excess asphalt on the road surface which creates patches

of asphalt cement. Excessive asphalt cement reduces the skid-resistance of a pavement, and itcan become very slippery when wet, creating a safety hazard.

This is caused by an excessively high asphalt cement content in the mix, using an asphalt cementwith too low a viscosity (too flowable), too heavy a prime or tack coat, or an improperly appliedseal coat. Bleeding occurs more often in hot weather when the asphalt cement is less viscous(more flowable) and the traffic forces the asphalt to the surface. Figure 13 shows an example ofbleeding during hot weather.


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In some cases, a repair can be made by applying hot sand or slag to blot up the excess asphalt.This is a very difficult problem to solve. It sometimes requires removing the bleeding pavementand placing a new surface. A thin wearing course will only solve the problem temporarily. Thebleeding asphalt will eventually work its way upward.

Figure 13 - Bleeding during hot weather

Polishing

Polishing is the wearing of aggregate on the pavement surface due to traffic (see Figure 14). Itcan result in a dangerous low friction surface. A thin wearing course will repair the surface.

Figure 14 - Polishing of asphalt surface

Delamination

Delamination is a failure of an overlay due to a loss of bond between the overlay and the olderpavement (see Figure 15). Common causes of delamination include: wet or dirty surface duringpaving of the overlay, failure to use a tack coat, or poor compaction of the overlay. Properpaving techniques, including cleaning the surface and use of tack coat, will reduce the chances ofdelamination.


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Figure 15 - Overlay delamination


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5 - Choosing the Right Repair_____________________________________________________________

According to the Foundation for Pavement Preservation, pavement maintenance involves doing

the right treatment, at the right place, at the right time. To achieve this, good management and anunderstanding of the choices are required.

For a given set of conditions, at a given time, there is usually onebest repair. If a road needs anoverlay, a chip seal will not suffice. If crack repairs will do the job, there is no good reason toplace a more costly slurry seal. Sometimes the wrong choices are made due to politics, citizencomplaints, or lack of money. If such choices are made, it is important to understand why theywere made and what the consequences are.

Maintenance activities

There are four different categories of maintenance activities: demand, routine, corrective andreconstructive.

Table 3 explains how these different activities fit into a pavement management plan. Some canbe performed before significant deterioration occurs. An example is a chip seal done beforecracks develop. Preventive maintenance must be done before even moderate cracking occurs, orit will not last as long as it should.

Table 3 - Maintenance activities

Type ofmaintenance

Planned?Performed before

deterioration?Extends

pavement life?

Demand No No Not necessarily

Routine Yes Not necessarily Sometimes

Preventive Yes Yes Yes

Corrective Generally No Yes

Demand maintenance: Performing a technique to correct a hazard or meet a service request.Pothole patching in the spring is the most common form of demand maintenance.

Routine maintenance: Performed on a routine basis for operational reasons. Examples includemowing grass, cutting shoulders, and striping centerlines.


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Preventive maintenance: Application of a treatment before significant deterioration occurs. Ittypically extends the life of the pavement and is usually planned. Surface treatments are usuallyconsidered preventive maintenance.

Corrective maintenance: Fixes pavement failures after they have occurred. A semi-permanentarea patch is a form of corrective maintenance. A truing and leveling layer to fill minor ruts, with

a follow up overlay, is another example. Corrective maintenance generally costs more thanpreventive or routine maintenance.

Planned maintenance is generally preferred to unplanned (demand) maintenance, and preventivemaintenance is preferred to corrective maintenance. Figure 16 shows the relationship betweencondition and the life of the pavement. The pavement starts in very good shape and deterioratesslowly at first. Maintenance repairs done early in the life of the pavement are much lessexpensive.

Figure 17 shows the relationship between pavement condition and the various levels ofmaintenance. These two figures show that routine and preventive maintenance are the mosteconomical options. Reconstruction techniques are the most expensive, and are usually done

when there is no other choice. Although not shown in Figure 17, there are times in the life of apavement when the best alternative is to do nothing. This is usually when the pavement is not acandidate for maintenance, and rehabilitation or reconstruction are not yet justifiable.

Figure 16 - Pavement deterioration curve


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5 - Choosing the Right Repair


Figure 17 - Pavement repair alternatives

Selecting the repair

The first step is to evaluate the road. Divide the road network into segments, and do a conditionsurvey on each segment. A condition survey documents the extent and severity of each type ofpavement distress. Using the results of the condition survey, determine the possible pavementrepairs. During the evaluation, ask the following questions:

What kind of maintenance can fix the defects found?

What repair, if any, will extend the life of the pavement?

Which maintenance technique will be the most cost effective?

Table 4 shows a basic matrix to help select the proper repair. The table only shows which repairsmay be used to fix a given distress at a reasonable price. Generally, the less expensive solutionswill be in the lefthand columns. Within a treatment category, specific operations may not fix thedistress in question. One example is a fog seal, which will not restore skid resistance, due to lowfriction. In actual field evaluation, other factors will need to be taken into account.


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Table

4-Pavementrepairmatrix

RepairTreatmentCategory

Crack

treatments

Patching

Thinwearing

courses

Overlays

Recycling

Reclamation

Re

construction

Averageduration

3-5years

1-10years

3-10years

5-15years

10-20years

15-50years

25-50years

Averageunitcost

(2005prices)

$0.2

5-

1.7

5/l.f.

$1.0

0-

5.0

0/s.y.

$0.6

0-

2.0

0/s.y.

$2.7

5/in./s.y.

$1.0

0-

2.0

0/in./s.y

$3.0

0-7.5

0/s.y

$4

0.0

0-

50

.00/s.y.

Distresstoberepaired

Lowskidresistance

X

X

Raveling

X

X

X

Bleeding

X2

X

X

Rutting

X1

X4

X

X

X

Lowseveritycracks

X3

X

Moderateseveritycracks

X3

X5

Highseveritycracks

X

X

X

X

Potholes

X

X

Roughness

X4

X

X

1-MicropavingandNovachipwillfillsomeruts.

2-Bleedingmayre

appearafterafewyears.

3-SeeChapter6to

helpdeterminewhichcracksaregoodcandidatesforrepairs.

4-Overlayswitha

shimlayeraddedmaybeusedtofillrutsandimproveridequality.

5-Crackswillrefle

ctthroughunlesscrackrepairsarecompletedfirst.




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6 - Crack Repairs_____________________________________________________________

Crack repairs are the proper and timely maintenance of cracks using sealing or filling techniques

to extend pavement life. Crack repairs are very cost effective if done properly. A crack repairprogram begins by determining if crack repairs are suitable for the type of distress.

Determining Type of Maintenance

The first step is to inspect the roadway and examine the cracking. Two different factors need tobe examined: crack density and the level of edge deterioration. The width of the crack also needsto be determined.

Crack density is a subjective term describing the spacing of the cracks. If there are only a fewcracks along the length of roadway, then the density is low. If there are cracks over the fulllength of the pavement, the density is high. If you are not sure, the density is probably moderate.

Edge deterioration is a measure of the condition of the cracks. Spalling, secondary cracks,cupping, and faulting are all examples of edge deterioration. A single transverse crack may below in density. A badly deteriorated single crack is still low in density, however, it is not acandidate for crack repairs. If the edge is deteriorated too much, crack repairs will not besuccessful, and patching or area repairs are needed.

Crack width is important to determine, if the repair is to be successful. If the crack width is lessthan 1/4 inch (the width of a pencil eraser), then the crack is too narrow for sealing and filling. Acrack this size is not wide enough to allow the repair material to enter and function. Narrowcracks may be surface treated. Alternatively, they can be widened by routing or sawing.

Figure 18 shows an isolated crack with a large amount of edge deterioration. The initial crackhas spawned many secondary cracks. If all the cracks were combined together, the width wouldbe significantly more than one inch. This is a good candidate for patching.

Figure 18 - Crack with high level of edge deterioration


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Table 5 shows how crack density and edge deterioration can be used to select the proper type ofmaintenance. In the table, rehabilitation includes recycling and reclamation. Be sure anydrainage issues are resolved when choosing this option. In the case of low density, moderatelevel cracking, crack repairs may not be cost effective. Pavement should be evaluated on a caseby case basis.

Table 5 - Determining the type of maintenance for cracks

Average level of edge deterioration

CrackDensity

Low

(0-25%)

Moderate

(26-50%)

High

(51-100%)

Low Nothing Crack repair? Patching

Moderate Crack repair Crack repair Patching

High Surface treatment Surface treatment Rehabilitation

Sealing versus Filling

There are two distinct techniques used to repair cracks: sealing and filling.

Crack sealing

The placement of specialized materials either above or intoworkingcracks usingunique configurations to prevent the intrusion of water anddebris into the crack.Working cracks are defined as those that experience significant horizontalmovements, generally greater than about 1/8 inch over the course of the year.Working cracks are generally more widely open during winter months, and lessopen in summer months. Cold weather causes the pavement surface to contract,which opens the cracks.

Crack filling

The placement of materials intononworkingcracks to reduce infiltration of waterand to reinforce the adjacent pavement.

It is important to remember that sealing uses more flexible materials than filling. This allows theseal to move with the crack. Sealing material is more expensive, but is usually worth the extramoney. Substantial savings can result if the cracks are not moving.

Table 6 shows the basic guidelines for choosing between crack sealing and crack filling.


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6 - Crack Repairs


Table 6 - Guidelines for crack repairs

Crackcharacteristics

Sealing Filling

Crack width 1/4" to 3/4" (5 to 19 mm) 1/4" to 1" (5 to 25 mm)Edge deterioration(spalls, secondary cracks)

Minimal to none(equal to or less than 25%

of crack length)

Moderate to none(equal to or less than 50%

of crack length)Annual horizontalmovement

equal to or less than 1/8" (3 mm) less than 1/8" (3 mm)

Type of crack

Transverse thermalTransverse reflectiveDiagonalWorking longitudinal

Longitudinal reflectiveLongitudinal cold jointLongitudinal edgeDistantly spaced block

PreparationRouting/sawingCleaning/drying

Backer rod (if required)

Blowing out debris

Materials

Various materials can be used to repair cracks. There are many different desirable characteristics.All crack repair materials need to have good adhesion to the sides of the crack. Installation andperformance issues are also factors that need to be examined. Table 7 shows the desirableproperties of the various materials. Appendix A summarizes the most commonly used crack-treatment materials and provides recommendations for use, as well as basic cost information.

As a general rule, materials that are more flexible will perform better in sealing operations.Polymer and rubberized materials have shown the best performance.

Configuration

Crack repair material is placed in a specific configuration that is most suitable for theapplication. Three basic configurations are shown in Figure 19. There are many other specializedconfigurations, but they are all variants or combinations of the three shown.

Figure 19 - Basic crack repair configurations

Flush-Fill Overband Reservoir


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Flush-fill

The easiest and most common technique is the flush-fill. The material is placed into the crack.Excess material is then removed or blotted up. It is an easy repair, but edge deterioration canresult in premature failure. The crack must be clean and dry prior to the repair.

Overband

Overbanding places material into and over an uncut crack. This technique is better than a flush-fill at dealing with small deterioration, but the overband must be kept narrow. As a general rule,no overband should be wider than four inches. The material is slippery when wet and can resultin a safety hazard. Multiple cracks filled in this way can lead to a patched area of crack sealant asshown in Figure 20.

Reservoir

In the reservoir technique, a saw or router is used to prepare a place to insert the repair material.This is more commonly done with sealing repairs. It increases the costs, but it may be necessary

in order to provide sufficient working room for the sealant.

Figure 20 - Crack sealing creating a safety hazard

Limitations

Crack repairs do not restore the structural integrity of the pavement. They can improve the

strength of the pavement during wet periods, such as spring thaw, by eliminating or reducing theinflow of water under the pavement.

Cracks should be sealed when they are at the middle of their working range. This allows thecracks to expand and contract with less stress on the sealant. A sunny day in spring or fall is avery good time to seal cracks, if all of the other weather factors are favorable.


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6 - Crack Repairs


Self-

leveling

silicone

99

9

9

9

99

99

99

99

Sealing

Low-

modulus

rubberized

asphalt

99

99

9

99

99

99

9

9

9

Sealing

Rubberized

asphalt

99

99

9

9

9

9

9

9

99

Sealing

Asphalt

rubbe

r 99

99

9

9

9

9

9

9

Sealing

(filling)

Fiberized

asphalt

99

99

9

Filling

Asphalt

cement

99

99

99

Filling

Polymer-

modified

emulsion

9

9

9

9

9

9

Filling

(sealing)

Materialtyp

e

Asphalt

emulsion

9

9

99

Filling

Property

Shortprep

Easytoplace

Shortcuretime

Adhesion

Cohesiveness

Resistancetosofteningand

flowincuredstate

Flexibility

Elasticity

Resistancetoaging

and

weathering

Resistancetotrack

ingand

abrasion

Recommended

application

Table7P

ropertiesofcrackfillingmate

rials

9=

Applicable

9

9=

Veryapplicable


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Cracks should be repaired as soon as possible. Waiting a year can lead to additionaldeterioration, which may render crack repairs ineffective. A crack repair program can reduce, butnot eliminate, the chances of cracks deteriorating too much before the work can be performed.

Cracks are a sign of a failure somewhere in the pavement. Crack repairs do not generally fix theassociated problems. When performing crack repairs, thought should be given to what future

treatments may be needed.

Performance

There are many factors that can influence the expected life of a crack repair. Proper selection ofgood repair candidates is critical. When repairs are done on the correct candidates, the repair canlast several years.

Crack filling is expected to last two to four years when using emulsions or asphalt fillermaterials. Use of sealing products in non-working cracks has been shown to last six to eightyears. Crack sealing without any routing or sawing typically lasts from three to five years.Routing out the cracks increases the life by two years, for a total of five to seven years.

Costs

Sealant materials costs are provided in Appendix A. As expected, sealing materials costsignificantly more than filling materials. The cost of the application varies significantlydepending on the construction operation and the productivity. Prices per lineal foot of crack canrange from $0.02/foot for simple filling with asphalt emulsion, to over a $1/foot for a routedcrack sealed with rubberized sealant.

Crack repairs can be bid out by the municipality. The New York State Office of General Servicesbids out crack repairs with an award available to all municipalities. The award can be found attheir web site (www.ogs.state.ny.us) under Highway Bituminous Materials.

Construction Operations

Crack treatment operations consist of five steps.This does not include traffic control, which needsto be set up properly beforehand. Crack repairoperations are generally slow-moving, but specialconsiderations may be needed on high-speedroadways. All five steps may not always beneeded, depending upon the specific materialconfiguration and placement options. Each stepis described below.

Crack cutting (optional)

If there is a need to produce a reservoir for thecrack material, then sawing or routing is required.Routing has a higher production rate, but sawingproduces more vertical faces and a more uniformreservoir. Figure 21 shows crack routing.

Figure 21 Crack routing


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6 - Crack Repairs


Cleaning & drying

Because dust and water will adversely affect theadhesion of crack repair materials, this is one ofthe most important steps.

Airblasting with a backpack unit or air compressorwill remove dust, debris, and some loose asphaltconcrete pieces, but is not effective at removingsurface moisture. If a moisture and oil filter is notproperly installed, airblasting can actuallyintroduce contaminants to the face of the crack.This is especially problematic when sealing.

An alternative is to use a heat lance (Figure 22).This device removes dust and surface moisture.The heat from the lance can also help improve thebond of the crack repair, if the material installation

follows closely behind the lance.Other cleaning methods include sandblasting andwire brushing. Depending upon the surfaceconditions, these methods may improve thequality of the crack repair.

Crack repairs should never be done in rainyweather. Even the best heat lance cannot deal withthe excess moisture.

Material installation

The method of installation depends on the materialto be placed. Emulsions can be applied with handheld pour pots. Distributor wands with hoses areoften used to place material in the crack. Figure 23shows basic wand application of crack sealer.

In most cases, the materials need to be heated.The temperatures can be as high as 425F. Safetyaround, and with, the crack material is a primaryconcern. Crews must be trained to properly heatand place the material.

Figure 22 Heat lance

Figure 23 Basic wand application ofcrack sealer


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Material finishing (optional)

Squeegees or special attachments on the end of thedistributor wand can be used to strike off theexcess material. Squeegees are typically molded

into a "U" shape which helps control the width ofthe material. Figure 24 shows a squeegee in use.

Even when the work is supposed to be a flush-fillconfiguration, some material may not get into thecrack. To control this excess material, finishingneeds to be done with a squeegee or by blotting.Finishing can also reduce waste by pushing excessmaterial into unfilled portions of the crack.

Blotting (optional)

Blotting reduces tracking and soaks up excess material.

Sand is typically used, but if necessary it can be done with absorbent paper on a stick.

Crack treatment weather

As long as the crack is dry, crack repairs can be done almost any time of year. Spring and fallare very good times to repair cracks. The following conditions are recommended:

Temperature above 40F (for sealing working cracks, the temperature should be below 80F)

Humidity less than 80 percent

No chance of rain

Figure 24 Finishing a crack with asqueegee


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7 - Patching_____________________________________________________________

Patching is the single most common pavement maintenance technique. As the repair area gets

larger, some agencies refer to it as a box-out or an area repair. The goals and concerns for an arearepair are the same as for patching. The difference is scale and economics.

Reasons for Patching

Patching fixes localized distress and may improve safety by reducing roughness. It is used torepair structurally deteriorated pavement. Patching can also reduce the rate of deterioration ofnearby pavement and fix distressed areas prior to pavement overlays. There are three generaltypes of patching: semi-permanent, spray, and demand.

Semi-permanent patching is done in the summer to fix potholes, repair poor patches, and replacedemand patches placed earlier in the year. It is also performed with utility cuts and culvertinstallations. These types of patches should have nearly the same strength as the surrounding

area. Drainage repairs are generally performed at the same time. The base is replaced ifnecessary. If drainage and base repairs are not made, the original problem may reappear.

Spray patching is done with specialized equipment. It can either be planned or demand driven. Aspray patch vehicle can be used in almost any weather, but summer spray patching is generallymore successful.

Demand patching is an unplanned repair to fix potholes. It is performed in the winter or spring,in all kinds of weather. It is usually done with patch material taken out by dump truck. Thechoice of material greatly influences the success of the patch.

Semi-permanent Patching

Semi-permanent patching is essentially a small-scale hot-mix asphalt paving operation. Some ofthe same concerns about patching (weather, materials and construction) also apply to semi-permanent patching. For more details on asphalt paving, see the Cornell Local Roads Programmanual entitledAsphalt Paving Principles(see Appendix B).

A recent Pennsylvania study found semi-permanent patching to be three times more costeffective than other patching techniques, when full life cycle costs were considered. The initialcapital cost is high, but the overall success rate may justify it. The study found that the less-permanent patches usually had to be repeated multiple times, which made them more costly inthe long run.


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Construction of semi-permanent patches

Mark the patch boundaries

When determining the area to be patched, straightboundaries are better (see Fig. 25). These are easier tocut and compact. Cut at least 12 inches beyond anysevere cracking. The width of the patch area shouldaccommodate the compaction equipment. Be sure tocut into sound material adjacent to the patch.

Cut the boundaries

The boundaries should provide a vertical face. A sawis preferred, but a jackhammer can be used. If using ajackhammer, be sure to keep the blade vertical.

Remove the old material

Remove the old broken asphalt. Try not to damage the good material outside the cutboundary. For larger area repairs, a small milling machine may speed up the process. Thematerial removed can be used in other pavement repairs. The depth of removal willdepend upon the site. In some cases, all of the asphalt is removed. If a lower layer ofmaterial is intact, try to leave it in place.

Clean and repair the foundation

After the old asphalt layer is removed, inspect the base and its drainage. In many cases,replacing the base and drainage is already planned. There will never be an easier time toreplace the base than while the surface is open. When replacing the base, do not dig all

the way to the edge of the cut boundary. Settlement may result in a premature failurealong the edge of the patch.

Since a pothole is evidence of distress, it is usually a good idea to remove at least the topcouple of inches of the base material. The new patch will then be slightly thicker than thesurrounding asphalt concrete layer. This will provide a bit of insurance if the underlyingproblem is not resolved during the repair.

Apply a tack coat

A tack coat should be applied to the vertical faces of the old asphalt. The tack coat shouldbe sprayed or brushed into place. It should never be poured, which will lead to puddling

and possible bleeding. RS-2 asphalt emulsion can be used as the tack.In some cases, the bottom of the hole may need to have a tack coat applied. This isespecially true when patching over asphalt or concrete base materials. If patching overgravel, a tack coat may be able to replace the prime coat that is normally used. It can behard to justify using two different materials to help bond the various layers together.

Cut Boundary

Poor

Cut Boundary

Good

Figure 25 Cut boundaries


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7 - Patching


Fill the hole with patching material

Place enough material in the hole to allow for compaction. As a general rule, one quarterinch of compaction will occur for every inch of material placed. If the patch is fourinches thick, the material should be placed to one inch above the surrounding area.

The material chosen will depend on the availability of hot-mix, and the number ofpatches being done. Doing several patches at once can be more efficient and allow for thepurchase of full truck loads. For more information on the types of asphalt mixesavailable, refer toAsphalt Paving Principles(see Appendix B).

Do not back the truck into the hole. This will damage the edge of the cut area. If the patchis very large, plywood can be layed down, to spread the load out and allow the truck tocarefully back into the excavated area. Move the material around with a shovel. Draggingthe asphalt with a rake can lead to segregation.

Compact the patch

Compaction can be done a variety of ways.A roller is best. Put down no more than sixinches at one time. If the patch is deeperthan six inches, use multiple lifts.

A plate tamper may be used, but thecompactive effort is much smaller and therequired density may not be achieved. Thiscan result in premature failure. When usinga plate tamper, keep the lifts no more thanthree inches thick.

A compacted patch should be flush with the surrounding surface. If properly compacted,the patch will not settle significantly and create a traffic hazard. Figure 26 shows aproperly finished and compacted patch.

Cleanup

Clean up the site. Pick up any loose material, and police the area around the patch. Thisis primarily for safety. Loose material hit by passing vehicles could also expose amunicipality to liability. This is good for public relations as well.

Spray Patching

Spray patching potholes is a very effective technique. It requires a specialized truck or trailer-mounted equipment. These units can be purchased or rented as needed. The quality of spraypatch is very good. One advantage is that the equipment can be used in almost any weather.

The equipment is self-contained. In some cases it can be done by the driver alone. The trailer-mounted patchers require a driver and an operator, but can sometimes reach patches more easilythan the truck-mounted devices. In all cases, traffic control is critical to ensure safety. Figure 27shows an example of a self-contained spray patch truck.

Figure 26 Finished patch


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Spray patching involves the following steps.

Blow debris from the hole

Spray a tack coat of binder on thesides and bottom of the hole

Blow a mixture of aggregate andbinder into the hole

Top off with a layer of uncoatedaggregate, to blot the surface andprevent tracking

Demand Patching (Cold patch)

Demand patching is one of the most common pavement maintenance techniques. There isusually pressure to make repairs as quickly as possible. Some municipalities have a 24-hourstandard for patching potholes. If the patch fails, the municipality still has a liability problem,and has to go back and refill the pothole. Demand patching restores safety, but does not repairthe underlying distress.

Materials

Demand patching materials generally come in three different forms:

Standard cold patch or plant mix

Fiber reinforced patch material

Modified cold patch (proprietary)

Materials can be prepared ahead of time and placed into stockpiles or even packed in buckets orbags. Bags of patching mix can be kept in the back of a pickup for emergency repairs. The extraweight can also help improve the vehicles traction in the winter.

The optimum material is made with high quality aggregate. The binder needs to contain anti-stripping agents. These agents deal with the water found in many potholes which are filled in thewinter and spring. The material needs to be workable at low temperatures, but still have stabilityunder traffic.

This unique combination of properties makes cold patch material difficult to manufacture. Lessexpensive mixes tend to either strip or have no stability under traffic. They cannot handle thetraffic load placed upon them, and they fail very quickly.

The first major improvement to cold patch was the addition of fibers. This improved the stability,but also increased the price. More recently, proprietary mixes with specially formulated bindershave been produced. These materials can be twice as expensive as standard mixes, but may bemore cost effective, due to a higher success rate.

Proprietary mixes are bid out by the New York State Office of General Services (OGS). Newproducts are being developed all the time, so a comprehensive list of materials cannot be easilyproduced. Table 8 lists the proprietary cold patch products bid out in 2005 via OGS.

Figure 27 Self-contained spray patch truck


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7 - Patching


Table 8 - Proprietary cold patches on NYS OGS bids, 2005

Patch name Producer or manufacturerBOND X Seaboard Asphalt Products, Inc.DURO PATCH Gorman Bros.HYPERPATCH Vestal Asphalt, Inc.I.A.R. I.M.U.S., Inc.MAC-V Midland Asphalt Corp.MC-400P Koch Materials Co.NORJOHN SPC Norjohn Ltd.OPTIMIX Optimix, Inc.PARCO PATCH Peckham Materials Corp.PERFORMIX Seaboard Asphalt ProductsQPR QPR, A Division Of Lafarge N.A.S-K MOD Suit-Kote Corp.SYLCRETE EV Sylcrete Corp.

TOP MIX Tech MixUPM Unique Paving Materials

There are differences between the various proprietary cold patch materials. Some work better incold weather, some are easier to finish, some are more forgiving under traffic. When choosingwhich material to use, price is not usually a significant factor. All of the proprietary materials aresimilar in price. The one you should use is the one which will work properly in your conditions.

Repair technique

Cold patch should be compacted with a roller or a plate tamper, but in practice it is rarely done.

Speed of repair is the primary reason for this, which has earned the technique the name Throwand Go. The problem with Throw and Go is that the lack of compaction causes the material tofail very quickly. Patches placed one day are often gone the next.

A more effective technique is Throw and Roll. Theonlydifference is that the truck is used tocompact the mix. Truck tires do a fairly good job of compacting the mix. With compaction, morepatches will survive the season. The steps of Throw and Roll are listed on the next page.

The production speed of Throw and Roll is not much less than Throw and Go. Rolling over thepatch typically increases the survival rate (the number of patches that will survive the season)from 10 to 25 percent . Using a proprietary mix, as opposed to a standard cold patch, can doublethe survival rate to 50 percent.


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Throw and Roll steps

1. Place the material into a pothole(remove as much water and/or debrisas possible from the hole beforehand).

2. Compact the patch using truck tires,as shown in figure 28.

3. Verify that the compacted patch hassome crown (1/4 inch above thesurrounding pavement).

4. Move on to the next pothole.

Cost effectiveness

Table 9 illustrates the effect of rolling the patch, and using modified mixes. Typically reportedsurvival rates are given for each technique. The price is the average from the NYS OGS. Thecalculations are for 20 tons of cold patch. The productivity is 20 tons per day for Throw and Goand 15 tons per day for Throw and Roll.

The total cost assumes that the failed potholes have to be refilled up to three times. Even with thehigher initial cost and slower production rate, Throw and Roll is more cost effective. The highersurvival rate of a proprietary mix can justify the extra initial expense.

Table 9 - Cost effectiveness of various demand patching methods

Method

Throw & Go(standardcold patch)

Throw and Roll(standard cold

patch)

Throw & Roll(proprietarycold patch)

Price ($/ton) $45/ton $45/ton $72/ton

Materials $900 $900 $1,440

Labor $676 $901 $901

Equipment $200 $267 $267

Initial cost $1,776 $2,068 $2,608

Survival rate 10% 25% 50%

Total cost $4,813 $4,782 $4,564

Figure 28 'Rolling' a cold mix patch


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8 - Thin Wearing Courses_

pavement maintenance.pdf

Documents

Transcript of pavement maintenance.pdf