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    2001 DESIGN GUIDE

    122 State Street, Suite 507 Madison, WI 53703Tel: (608) 255-3114 Fax: (608) 255-3371

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    WISCONSIN ASPHALT

    PAVEMENT ASSOCIATION

    DESIGN GUIDEMAY, 2001

    This version of the 2001 WAPA Design Guide is provided as a web-baseddocument which can be viewed, downloaded, and/or printed as desired. TheWAPA web site allows you to complete an on-line registration which will ensure that

    your name appears on our list of registered users and that you will be notified ofupdates to this Guide as they are published. If you have not yet registered, pleasedo so by visiting the WAPA website or by faxing or emailing the followinginformation directly to WAPA:

    Name

    Title

    Employer

    Address

    City/State/ZipPhone

    Fax

    Email

    If you have any questions regarding the information in this Guide or if you needassistance in the design, construction, or rehabilitation of Hot-Mixed Asphaltpavements, members of the Wisconsin Asphalt Pavement Association are ready tohelp. Please contact:

    Wisconsin Asphalt Pavement Association122 State Street, Suite 507Madison, WI 53703PH: (608) 255-3114FAX: (608) 255-3371Email: [email protected] Site: www.wispave.org

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    2001 WAPA Design Guide - i

    FOREWORD

    This Asphalt Paving Design Guide has been prepared to assist you inunderstanding Hot Mix Asphalt (HMA) pavement design, construction andrehabilitation.

    Quality HMA pavement may be constructed in a wide range of soil, weather and

    loading conditions. The examples contained in this Design Guide are designs,procedures, and applications that have been proved successful in the State ofWisconsin. All HMA mixtures given in this Design Guide are proven mixes whichare readily available throughout the State of Wisconsin from companiesexperienced in producing and constructing quality HMA pavements.

    This Design Guide was developed based on information contained in the State ofWisconsin Standard Specifications for Road and Bridge Construction and isintended for use by architects, engineers, developers, owners and governmentalofficials. References to authorities and agencies do not constitute theirendorsement of this Design Guide. If further clarification of the material presented

    is desired, you are encouraged to contact the appropriate authority, review thereferences cited, or contact the Wisconsin Asphalt Pavement Association or aWAPA member in your area.

    This Design Guide has been developed to provide you with basic information onHMA pavements so that you can develop an understanding of those topics whichare critical in the design and construction of quality HMA pavements. This DesignGuide is not intended to preclude the design of HMA pavements based on soundpavement engineering principles and valid data on soils and traffic. The reader iscautioned that the information contained in this Design Guide may be insufficientwhen used alone. Other resource materials and authorities should be consultedwhen field conditions differ from those given in this Design Guide.

    This Design Guide presents background information on HMA pavements andpavement design considerations (Sections 1 -5). Included thickness design tables(Section 6) are applicable for a variety of roadway and other uses. Sections onpavement management (Section 7), pavement rehabilitation (Section 8), and specialuse HMA (Section 9) are also provided.

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    2001 WAPA Design Guide - ii

    OBJECTIVES AND PURPOSE

    The Wisconsin Asphalt Pavement Association, and its members whose namesappear in the Membership Directory in Section 12, are dedicated to fulfilling theseobjectives:

    !Cultivation of sound relationships and cooperative effort betweenmembers and governmental agencies, and other similar organizationsand associations

    ! Stimulation of public interest in the durability, economies, safetyfeatures and other benefits accruing through the use of asphalt pavingmaterials.

    ! Advocation of sound planning in highway construction andmaintenance to insure maximum benefit from the expenditure ofpublic funds.

    ! Dissemination of information gathered from all available sources,resulting from extensive research, relating to the manufacture anduses of asphalt paving materials.

    The ultimate quality of your asphalt paving project is directly related to theexperience, skill and equipment of the contractor doing the job. That is whythe Wisconsin Asphalt Pavement Association urges you to be sure that

    bidders for your asphalt paving project are properly qualified HMA pavers.

    The Wisconsin Asphalt Pavement Association takes pride in presenting this 2001

    Design Guide, and will be happy to provide you with additional information.

    CREDITS

    The 2001 Design Guide has been written and developed under the direction of Dr.James Crovetti, Marquette University, Department of Civil and EnvironmentalEngineering. Special thanks are also extended to Melissa Janda for her cover art.

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    2001 WAPA Design Guide - iii

    TABLE OF CONTENTS

    1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

    2.0 QUALITY HMA PAVEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    QUALITY MANAGEMENT PROGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    ASSURANCE TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3HMA PAVEMENT STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

    HMA with Aggregate Bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Full-Depth HMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

    3.0 MATERIALS FOR HMA PAVEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

    ASPHALT CEMENT BINDER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5EMULSIFIED ASPHALTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5CUTBACK ASPHALTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6ASPHALT BINDER GRADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

    Performance Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6AGGREGATES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

    Natural Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Recycled Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Synthetic Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

    AGGREGATES FOR BASE COURSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Desirable Properties of Aggregates for Base Courses . . . . . . . . . . . . . 8

    AGGREGATES FOR HMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Desirable Properties of Aggregates for HMA . . . . . . . . . . . . . . . . . . . 11

    4.0 HMA MIX DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

    WHAT IS AN HMA MIX DESIGN ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13PROPERTIES CONSIDERED IN MIX DESIGN . . . . . . . . . . . . . . . . . . . . . . . 13WISDOT HMA PAVEMENT TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15AGGREGATES FOR HMA LAYERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16HMA LAYER THICKNESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17JOB MIX FORMULA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17WISDOT HMA DESIGN SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    5.0 PAVEMENT DESIGN CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    TRAFFIC LOADINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19TRAFFIC CLASSIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19ESAL FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20DESIGN DAILY ESALs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20ESAL CALCULATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21SUBGRADE SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

    Subgrade Soil Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

    DRAINAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Surface Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Subsurface Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

    GEOTEXTILE FABRICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

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    2001 WAPA Design Guide - iv

    TABLE OF CONTENTS

    6.0 THICKNESS GUIDES FOR HMA PAVEMENTS . . . . . . . . . . . . . . . . . . . . . . 27

    7.0 PAVEMENT MANAGEMENT SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

    ESTABLISHING A PAVEMENT MANAGEMENT SYSTEM . . . . . . . . . . . . . . 33DEFINITION AND USE OF PASER MANUAL . . . . . . . . . . . . . . . . . . . . . . . . 35

    8.0 PAVEMENT REHABILITATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

    HMA OVERLAYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Thin HMA Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Structural HMA Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Open-Graded Friction Courses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

    SURFACE PREPARATION METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Localized Surface Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38HMA Cold Milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39In-Place Recycling (Pulverizing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Concrete Pavement Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

    9.0 HMA FOR RECREATIONAL AND OTHER USES . . . . . . . . . . . . . . . . . . . . . 41

    SIDEWALKS AND WALKWAYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41BICYCLE AND GOLF CART PATHS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41PLAY AREAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41CURBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42TENNIS COURTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42ASPHALT-RUBBER RUNNING TRACKS . . . . . . . . . . . . . . . . . . . . . . . . . . . 42HMA FOR HYDRAULIC STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42RAILROAD TRACK BEDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

    10.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

    11.0 CONVERSION TABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

    12.0 MEMBER AND ASSOCIATE MEMBER FIRMS . . . . . . . . . . . . . . . . . . . . . . . 47

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    2001 WAPA Design Guide - 1

    1.0 INTRODUCTION

    Hot Mix Asphalt pavements have many advantages over pavement surfacesconstructed using other materials. A quality mix is more easily maintained becausethe asphalt mixture is produced in a central plant to strict specifications and the mixis not altered in transit.

    It's Durable. Asphalt pavements have long life. All asphalt pavements have abridging action and because they're flexible can withstand occasional overloadswithout serious damage. They are not harmed by ice and snow removal chemicals.

    It's Economical. Asphalt pavements can be designed for the intended use.There's no need to use a predetermined pavement thickness when conditionspermit otherwise. Asphalt also permits the use of local materials with correspondingsavings.

    It's Safe. Asphalt pavements offer high skid resistance and provide high contrast

    and improved visibility for traffic markings. The dark color also reduces glare andmelts ice and snow more rapidly than other pavement types. Asphalt pavementmaterials also eliminate potentially dangerous and expensive pavement blow-ups.

    It's Convenient. Asphalt pavements require no curing or extensive sitepreparation. Traffic can use the pavement immediately following final rolling.

    It's Adaptable. Asphalt pavements can be designed to suit any conditions of traffic,soils and materials.

    It's Smooth. Asphalt pavements provide a more uniform surface and a quiet ride

    unmatched by other pavements.

    It's Attractive. Asphalt pavements have no built-in, unsightly cracks. They blendwith and enhances the natural surroundings.

    It's Recyclable. Asphalt pavements are completely recyclable. Not only can theaggregate be reused, the asphalt cement binder retains its cementing properties.Cold milling, to remove a predetermined depth of asphalt material, will also furnisha ready supply of reclaimed mix for use in hot-mix recycling - a process which canbe repeated over and over again as the need arises in the years ahead.

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    2.0 QUALITY HMA PAVEMENTS

    Quality Hot Mix Asphalt (HMA) pavements are constructed using a designed pavingmixture. The required amount of each mixture ingredient is typically establishedthrough a recognized mix design procedure as described in Section 4. To ensurequality HMA pavements, a documented mix design report should be provided for

    each paving project.

    Quality HMA is produced in a mixing plant under controlled conditions. The mixtureis transported, placed and compacted while still hot. Specially designed pavingmachines place the mixture to the required thicknesses and grade specifications.After the mixture has been rolled to desired compaction, it's ready for immediatetraffic use.

    QUALITY MANAGEMENT PROGRAM

    A Quality Management Program (QMP) represents a cooperative effort between thecontractor and owner aimed at assuring the construction of quality HMA pavements.The contractor provides and maintains Quality Control (QC) during the project toensure continual production of quality HMA which meets or exceeds projectspecifications. The owner provides Quality Assurance (QA) by conducting tests onHMA samples taken at the mixing plant. Samples are obtained by the contractorunder the observation of, or in a manner approved by the owner. All QMP testingmust be conducted by a WISDOT Certified Asphaltic Technician.

    ASSURANCE TESTING

    Assurance testing may be requested by the owner to compare with the contractorsquality control test data. Assurance tests may include any or all of the followingtests: aggregate gradation, asphalt binder content, bulk specific gravity ofcompacted mixtures, maximum specific gravity, air voids content, and voids in themineral aggregate. Assurance tests are conducted by the owner on split samplesobtained by the contractor at the point of production. Differences between theowners split sample test results and the contractors quality control test results areconsidered acceptable if they fall within limits established by WISDOT. In the eventcomparison test results variations are outside established limits, the currentWISDOT procedures governing assurance testing should be followed.

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    HMA PAVEMENT STRUCTURES

    HMA with Aggregate Bases

    HMA pavements with aggregate bases are appropriate for use where localaggregates and subsurface drainage conditions are suitable. These pavements areconstructed by first placing and compacting an aggregate base on a prepared

    subgrade. The HMA materials are then placed and compacted in layers tocomplete the pavement structure. The thickness of each compacted layer is basedon considerations of layer position and nominal maximum aggregate size. Figure2.1 illustrates the cross section of an HMA pavement with an aggregate base.

    Full-Depth HMA

    Full-Depth HMA pavements have wide applications ranging from residentialdriveways and parking areas to heavy duty pavements where high volumes of heavytraffic are anticipated, such as interstate highways and airport runways. A Full-Depth HMA pavement uses HMA materials for all layers above the subgrade. The

    thickness of each compacted layer is based on considerations of layer position andnominal maximum aggregate size. Figure 2.1 illustrates the cross section of a Full-Depth HMA pavement.

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    2001 WAPA Design Guide - 5

    3.0 MATERIALS FOR HMA PAVEMENTS

    ASPHALT CEMENT BINDER

    Asphalt cement binder is obtained by distillation of a crude petroleum using differentrefining techniques. At ambient air temperatures, asphalt binder is a black, sticky,

    highly viscous material. It is a strong and durable binder with excellent adhesiveand waterproofing characteristics. The largest use of asphalt binder is for Hot MixAsphalt (HMA). Ninety-six percent of the hard surfaced roads in the United Statesare paved using HMA.

    Asphalt binders can be readily liquefied by applying heat, which facilitates mixingwith mineral aggregates to produce HMA. Asphalt binders are very sticky andreadily adhere to the surface of dry aggregate particles, binding them to form HMA.After compacting and cooling to air temperature, HMA is a very strong pavingmaterial which can sustain heavy traffic loads.

    EMULSIFIED ASPHALTS

    Emulsified asphalts (also called emulsions) are low viscosity mixtures of tiny asphaltbinder droplets, water and emulsifying agents, as shown in Figure 3.1. Theemulsifying agent coats the surfaces of the asphalt binder droplets and keeps themsuspended in the water prior to application. After application, the asphalt bindercoalesces (breaks) and the water evaporates. Emulsions are brownish in colorduring application, but after breaking the coalesced asphalt binder returns to itsoriginal black color.

    Emulsified asphalts are used for surface treatments, penetration macadams, open-graded cold asphalt-aggregate mixtures, tack coats, fog seals, dense-graded coldasphalt-aggregate mixtures, and slurry seals.

    Figure 3.1 - Emulsified Asphalt

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    CUTBACK ASPHALTS

    Cutback asphalts are low viscosity mixtures manufactured by diluting (cutting back)asphalt binders with petroleum solvents (cutter stock or diluent). After application,the petroleum solvent evaporates, leaving the asphalt binder residue.

    ASPHALT BINDER GRADING

    Asphalt cement binders appropriate for pavement construction were previouslygraded based on resistance to penetration and/or by viscosity measures. Currently,asphalt binders are graded based on the temperature range over which the binderretains certain desirable characteristics. These desirable characteristics includeadequate flexibility to resist cold temperature cracking and sufficient rigidity to resistwarm temperature rutting. The current binder grading system is known as thePerformance Grading (PG) system.

    Performance Grading

    Performance grading specifications were developed as part of the StrategicHighway Research Program (SHRP). Binders are specified on the basis of theclimate and attendant pavement temperatures in which the binder is expected toserve. Performance graded (PG) binders appropriate for use in Wisconsin includethe PG 64-22 and PG 58-28 binders. The first number (64 or 58) represents theaverage 7-day maximum pavement design temperature, in degrees Celsius. Thismaximum temperature establishes the upper temperature limit for the binder toretain adequate rigidity to resist rutting. The second number (-22 or -28) representsthe minimum pavement design temperature. This minimum temperature

    established the lower limit for the binder to retain sufficient flexibility to resist thermalcracking.

    Physical properties of the binders are measured at various temperatures bothbefore and after laboratory aging. The laboratory aging is conducted to simulatefield conditions imposed during the HMA production process as well as from long-term environmental exposure. Binder physical properties are measured using fourdevices:

    ! Dynamic Shear Rheometer! Rotational Viscometer

    ! Bending Beam Rheometer! Direct Tension Tester

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    Dynamic Shear Rheometer (DSR): The DSR is used to characterize the visco-elastic properties of the binder before and after aging. Specifications for test resultscontrol binder stiffness at high and intermediate temperatures. High temperaturespecifications ensure the binder retains adequate stiffness to contributesignificantly to the overall shear strength of an HMA mixture. Intermediatetemperature specifications help ensure the binder does not contribute to fatiguecracking of the HMA.

    Rotational Viscometer (RTV): The RTV is used to determine the viscosity of theoriginal binder at 135 C (275 F). Specifications limit viscosity at 135 C to ensureo o o

    that the binder can be pumped or otherwise handled during HMA manufacturing.

    Bending Beam Rheometer (BBR): The BBR is used to characterize the lowtemperature properties of binders. Specifications limit the low-temperature stiffnessto protect against cracking in cold weather.

    Direct Tension Tester (DTT): The DTT is used to measure the failure strain ofbinders at low temperatures. As with the BBR, the DTT specifications ensure thatthe binders resistance to low temperature cracking is maximized.

    AGGREGATES

    Aggregates are any hard, inert material which are used in graded sizes (fine tocoarse). Aggregates are also referred to as rock, gravel, mineral, crushed stone,slag, sand, rock dust and fly ash. Aggregates may be used alone for base courselayers or as a part of the HMA pavement layers. Several types of aggregate which

    are available are described below. Aggregates, depending on use, have certaindesired physical and chemical properties which are described later in this section.

    Natural Aggregates

    Natural rocks occur either as outcrops at or near the surface or as gravel deposits,usually along an old stream bed. They are classified into three groups: igneous,metamorphic and sedimentary based on the way the rocks were originally formed.Natural aggregates can be Pit or Bank-Run Aggregates or Processed Aggregates.

    Pit or Bank-Run Aggregates - These include both gravel and sand, which are

    taken directly from the deposit without processing.

    Processed Aggregates - These include pit or bank-run aggregates and blastedoutcrops which have been crushed to make them more suitable for usage withinHMA pavements. Crushing pit or bank-run aggregates normally improves theparticle shape by making the rounded particles more angular. Crushing can alsoimprove the size distribution and range.

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    2001 WAPA Design Guide - 8

    Crushed stone is also a processed aggregate. It is created when fragments ofbedrock or large stone are crushed so that all particle faces are fractured. Thecrushed stone can be sized by screening; and the rock dust, which results fromcrushing, can be removed by washing.

    Recycled Aggregates

    Reclaimed asphalt pavements (RAP) and concrete pavements both contain

    valuable aggregates. The aggregate, if of good quality when placed, is most likelystill of good quality and can be recycled into HMA pavement or base course layers.When recycled aggregates are used, it is important that HMA mixtures containingrecycled materials meet all specifications required of an HMA mixture withoutrecycled materials.

    Synthetic Aggregates

    Aggregates produced by altering both the physical and chemical properties of amaterial are called synthetic or artificial aggregates. Two examples of syntheticaggregates are lightweight aggregate, which is produced by heating clay to a very

    high temperature, and slag, which is normally produced in the blast furnace duringsteel production. Synthetic aggregates are sometimes used in HMA.

    AGGREGATES FOR BASE COURSES

    Aggregates used for base courses are largely obtained from local supplies ofprocessed natural rocks. The properties desired for aggregates used as basecourses are given below.

    Desirable Properties of Aggregates used for Base Courses

    Desirable properties of aggregates used for a base course are similar to those givenlater for HMA pavements. These properties, as they apply to aggregates for basecourses, are briefly discussed in this section. See the section on AGGREGATESFOR HMA for a more complete definition of some of the properties.

    Size: The maximum size of an aggregate is the sieve size through whichessentially 100 percent of the material will pass. The maximum size is important toinsure good performance. It is also important that the desired gradation be

    maintained.

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    2001 WAPA Design Guide - 9

    Gradation: Aggregate gradation describes the distribution of aggregate particlesizes. Proper gradation is important for stability, workability and permeability. It isalso desirable to have a base course which will not retain moisture nor becomeunstable when wet. Crushed aggregate base course master gradation bands havebeen established by WISDOT for both crushed gravels and crushed stones, asshown in Table 3.1.

    Cleanliness / Deleterious Materials: Cleanliness refers to the absence of certainforeign or deleterious materials that, when present, make the aggregate undesirablefor use as a base course. Base course aggregates should be substantially freefrom vegetable matter, shale and lumps, or balls of clay.

    Toughness/Hardness: Aggregates are subject to crushing and abrasive wearduring manufacturing, placement, and compaction. Thus they must be hard andtough to resist crushing, degradation, and disintegration when stock piled or placed,compacted with rollers, and traveled over with trucks.

    Durability/Soundness: Aggregates must be resistant to breakdown ordisintegration under action of wetting and drying and/or freezing and thawing.

    Surface Texture: A rough, sand- paper-like surface texture, such as found on theexposed faces of most crushed aggregates, tends to increase strength and stability.

    Particle Shape: Aggregates that are cubical and angular will provide the greatestmechanical stability.

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    2001 WAPA Design Guide - 10

    Table 3.1 WISDOT Master Aggregate Gradations for CrushedAggregate Base Courses(1)

    SieveSize

    Percentage Passing by Weight

    Gradation No. 1 Gradation No. 2 Gradation No. 3

    Crushed Crushed Crushed Crushed Crushed CrushedGravel Stone Gravel Stone Gravel Stone

    1 Inch 100 100 -- -- -- --1 Inch 75-100 -- 100 100 100 1003/4 Inch -- -- -- -- 95-100 95-1003/8 Inch 40-75 30-65 50-85 40-75 50-90 50-90

    No. 4 30-60 22-55 35-65 25-60 35-70 35-70No. 10 20-45 15-40 25-50 15-45 20-55 15-55No. 40 10-30 -- 10-30 -- 10-35 --No. 200 3-10 2-12 3-10 3-12 8-15 5-15(2) (2)

    Unless otherwise specified, Gradation No. 2 should be used for the top layer of(1)

    base course and Gradations No. 1 or No. 2 should be used for lower basecourse layers.

    The percent passing the No. 200 sieve is limited to a maximum of eight percent(2)

    for crushed gravel base courses placed between old and new pavement.

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    AGGREGATES FOR HMA

    Aggregates used in HMA are largely obtained from local supplies of natural rockand recycled asphalt and concrete pavements. Other types of aggregate that aresometimes used in HMA are lightweight aggregates or slag, which are termedsynthetic aggregates. The properties desired for aggregates used in HMA are givenbelow.

    Typically, two or more aggregate supplies are blended together to achieve all of thedesirable properties listed below. The blended aggregates represent about 90%-96% of the weight and about 65%-85% of the volume of a compacted HMApavement layer.

    Desirable Properties of Aggregates for HMA

    Selection of an aggregate for use in HMA depends on the quality of the material, thetype of pavement for which it is intended, availability, and cost. The followingproperties should be evaluated to determine the suitability of an aggregate for use

    in HMA:

    Size: The maximum size of an aggregate is the sieve size through whichessentially 100 percent of the material will pass. The nominal aggregate sizerepresents the smallest sieve size for which at least 90 percent of the material willpass. Aggregate size in a mixture is important to ensure good performance. If thenominal size is too small, the mix may be unstable; if it is too large, workability andsegregation may be a problem.

    Gradation: Aggregate gradation describes the distribution of aggregate particlesizes. Gradation affects all the important properties of an HMA, including stiffness,

    stability, durability, permeability, workability, fatigue resistance, skid resistance andresistance to moisture damage. Aggregate master gradation bands have beenestablished by WISDOT for HMA surface and lower layers, as shown in Table 3.2.Further guidance on the selection of a master gradation best suited to each projectis provided in Section 4.0.

    Cleanliness / Deleterious Materials: Cleanliness refers to absence of certainforeign or deleterious materials that, when present, make aggregates undesirablefor HMA. Washing dirty aggregate can usually reduce the amount of undesirablematerials to an acceptable level. Typical objectionable materials include vegetation,shale, soft particles, clay lumps, clay coating on aggregate particles, and sometimesexcess dust from the crushing operation.

    Toughness/Hardness: Aggregates are subject to crushing and abrasive wearduring the manufacturing, placement, and compaction of HMA. They must be hardand tough to resist crushing, degradation, and disintegration when stock piled, fedthrough an HMA facility, placed with paver, compacted with rollers, and traveledover with trucks.

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    Durability/Soundness: Aggregates must be resistant to breakdown ordisintegration under the action of wetting and drying and/or freezing and thawing(weathering).

    Surface Texture: A rough, sandpaper-like surface texture, such as found on theexposed faces of most crushed stones, tends to promote the mechanical bondbetween the asphalt binder and the aggregate and increases stability.

    Particle Shape: Aggregate particles suitable for use in a HMA should be cubicalrather than flat, thin, or elongated. In compacted HMA, angular-shaped particlesexhibit greater interlock and internal friction, and hence result in greater mechanicalstability than do rounded particles.

    Absorption: The porosity of an aggregate permits the aggregate to absorb asphaltbinder, forming a bond between the particle and the asphalt. Some porosity isdesired, but aggregates that are highly absorbent are generally not used since theywould require a high amount of asphalt binder.

    Affinity for Asphalt: Asphalt binder must wet the aggregate surface, stick to theaggregate, and resist stripping in the presence of water (asphalt binder separatesfrom the aggregate surface). Dust coatings on aggregates can cause poor bondingof asphalt binder.

    Table 3.2 Aggregate Gradation for HMA Layers

    Sieve

    Size

    Percentage Passing by Weight (1)

    Nominal Size (2)

    1 1 inch 3/4 inch inch 3/8inch inch

    2 inch 1001 inch 90 - 100 1001 inch 90 max 90-100 100 inch --- 90 max 90 - 100 100 inch --- --- 90 max 90-100 100d inch --- --- --- 90 max 90-100No. 4 --- --- --- --- 90 maxNo. 8 15 - 41 19 - 45 23 - 49 28 - 58 20-65

    No. 200 0 - 6 1 - 7 2 - 8 2 - 10 2 - 10

    Percent passing of total aggregate weight(1)

    Unless otherwise designated, the nominal size of aggregate should be 3/4(2)

    inch for lower pavement layers and inch for upper pavement layers.

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    4.0 HMA MIX DESIGN

    WHAT IS AN HMA MIX DESIGN?

    An HMA mix design includes a series of laboratory tests that are performed on aparticular set of HMA ingredients to determine whether, and in what proportions,these ingredients can be combined to meet project specifications. The Superpave

    method of mix design is the procedure currently used in Wisconsin. Superpavestands forSUperiorPERforming hot mix asphalt PAVEments.

    The Superpave method of mix design was developed to provide a national standardfor HMA pavements. This national standard allows the asphalt industry to measureHMA performance on a national level. Furthermore, the Superpave mix designmethod better simulates expected traffic loads during the mix design process andtherefore produces pavement designs which perform better under actual trafficloadings. The gyratory compactor is the new piece of standardized equipment thatis used to compact asphalt samples during the Superpave mix design method. Thisequipment is used to determine the proper blends of aggregates and binder to

    complete an HMA mix design appropriate for a certain type of traffic.

    Special use HMA mixes may also be designed to meet specific projectrequirements, such as high density, high flexibility, low permeability or high skidresistance.

    PROPERTIES CONSIDERED IN MIX DESIGN

    Quality HMA pavements are achieved when properly designed, produced, placed,and compacted. These steps ensure that desired mix properties are in place after

    construction.

    These desirable properties are:

    ! Durability ! Stability ! Impermeability ! Workability ! Flexibility ! Fatigue Resistance ! Skid Resistance

    Durability: Durability of an HMA pavement includes its ability to resist factors suchas oxidation of the asphalt cement, disintegration of the aggregate, and stripping ofthe asphalt cement from the surface of the aggregate. These factors can resultfrom weather conditions, traffic loadings, aggregate quality, or a combination ofthese factors.

    Typically a durable mixture can be achieved by using the optimum asphalt cementcontent, using well graded quality aggregates, and compacting the designed mixtureto the recommended density to minimize in-place permeability.

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    Stability: Stability of an HMA pavement includes its ability to resist shoving andrutting under repeated traffic loadings. Stable HMA pavements maintain their shapeand smoothness while unstable pavements deform under repeated loadings andmay develop ruts, ripples or other signs of pavement movement. The stability of anHMA pavement is related to the internal friction and cohesion of the mix. Internalfriction is directly related to the angularity and roughness of the aggregates. Incompacted mixes, angular aggregates exhibit greater interlock and internal friction,

    resulting in greater mechanical stability. Rough, sandpaper-like aggregate surfaces,such as found on the exposed faces of most crushed stones, also tends to increasestability. Internal cohesion is related to the thickness of the asphalt films coating theaggregates. Cohesion increases, to a point, with an increase in the asphalt cementcontent.

    Impermeability: Impermeability is the resistance of the HMA pavement to thepassage of air and water into and through it. Impermeability is related to both thequantity and arrangement of the air voids in the mix. HMA pavements withnumerous interconnected voids which connect to the pavement surface have lowimpermeability.

    Workability: Workability is the property of the HMA which describes the ease withwhich it can be placed and compacted. A mix with good workability requires lesscompactive effort to obtain the required density.

    Flexibility: Flexibility is the ability of the asphalt pavement to adjust to gradualsettlements and movements in the subgrade without cracking. This is a desirablecharacteristic since almost all subgrades when subject to loading will settle or thesubgrade may rise due to expansive type soils. Generally, flexibility of an asphaltpaving mixture is improved by using a high asphalt content and relatively open-graded aggregates.

    Fatigue Resistance: Fatigue resistance is the ability of the asphalt pavement towithstand repeated bending caused by the passage of wheel loads without cracking.The fatigue resistance is affected by the asphalt binder content, air-void content,asphalt aging, load magnitude, pavement thickness and strength, and the supportprovided by underlying layers.

    Skid Resistance: Skid resistance is the ability of the pavement to minimize theskidding or slipping of the tires of vehicles on the surface. This is of a particularimportance when the pavement surface is wet. The skid resistance can beimproved by selecting an aggregate with a rough surface texture and using the

    proper asphalt content. Hydroplaning can be reduced by proper surface drainageand/or providing an open-graded friction course.

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    WISDOT HMA PAVEMENT TYPES

    Quality HMA pavements must be designed and constructed to withstand a widevariety of traffic and environmental loadings. Pavements which are to be subjectedto repeated, heavy truck loadings must be designed with a maximum internalstability to provide adequate resistance to rutting. In contrast, pavements which areexpected to receive few, if any, heavy loadings should be designed for maximum

    durability to resist the disintegrating effects of climate. It is imperative that theselection of HMA mixture type be matched to the expected loadings to ensure thebest pavement performance over its design life. In other words, do not select anHMA mixture type designed for high traffic loadings if your pavement is expectedto receive only light traffic, and vice versa.

    In 2000, the Wisconsin DOT assembled a new list of mixes that are all Superpavedesigned. These mixes are part of the 2000 Supplemental Specifications amendingthe 1996 Edition of the Standard Specifications for Highway and StructureConstruction. The new mixes, just like the Type HV, MV, and LV mixes theyreplace, are designed towards specific traffic volumes. The Wisconsin DOT

    Superpave specifications include charts that list traffic volumes and appropriate mixselections that are suitable for use when a detailed traffic analysis is performed.

    Table 4.1 provides the Superpave mix type recommended for your everyday needs.If you are specifying a pavement with extreme or unusual traffic conditions, pleasecontact WAPA or your local WAPA contractor for further recommendations.

    Table 4.1 Superpave Mix Design Recommendations

    Superpave Previously Specified Typical ExamplesMix Type Mix Type of Usage

    E - 0.3 LV School areas and playfields

    Residential driveways and streets Parking lots

    Seasonal recreational roads Low volume rural roads

    E - 1 MV Collector streets and other roadways

    Light industrial lots

    E - 3 MV Major arterial streets Local business streets

    Medium industrial lots and streets

    E - 10 HV Major truck terminals Major industrial streets

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    AGGREGATES FOR HMA LAYERS

    Aggregates used for HMA should be hard durable particles of crushed gravel,crushed stone, manufactured sand, natural sand, mineral filler or a combinationthereof. The desirable gradation of the aggregates is based on the nominal size ofthe aggregate, defined as the smallest sieve size for which more than 90 percentof the aggregate passes. Master gradation ranges for aggregates used in HMA are

    specified by the WISDOT, as shown in Table 4.2.

    Table 4.2 WISDOT Master Aggregate Gradations for HMA Layers

    SieveSize

    Percentage Passing by Weight

    Nominal Size

    1 1 inch 3/4 inch inch 3/8inch inch

    2 inch 1001 inch 90 - 100 1001 inch 90 max 90-100 100 inch --- 90 max 90 - 100 100 inch --- --- 90 max 90-100 100d inch --- --- --- 90 max 90-100No. 4 --- --- --- --- 90 maxNo. 8 15 - 41 19 - 45 23 - 49 28 - 58 20-65

    No. 200 0 - 6 1 - 7 2 - 8 2 - 10 2 - 10

    Three nominal aggregate sizes are recognized by WISDOT for normal pavements.They are:

    Upper Layer Mixes - " (12.5 mm) or 3/8" (9.5 mm)Lower Layer Mixes - 3/4" (19 mm)

    The Superpave mix design criteria allows the use of aggregate blends designedtowards the coarse end of the gradation specifications. As a result, a inch upperlayer mix may appear coarser than conventional mixes used to date. A 3/8" upperlayer mix may be selected to provide a more closed surface texture. Other

    aggregate sizes are available for extreme or unusual traffic conditions. Pleasecontact WAPA or your local WAPA contractor for assistance in these situations.

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    HMA LAYER THICKNESS

    To ensure proper compaction of individual HMA layers, the minimum and maximumlayer thickness for Superpave mixes are specified by WISDOT based on thenominal aggregate size, as shown in Table 4.3.

    Table 4.3 WISDOT Thickness Specifications for Individual HMA Layers

    Nominal Minimum Maximum MaximumAggregate Layer Lower Upper

    Size Thickness Layer Layer (inch) Thickness Thickness

    (inch) (inch)

    3/4" 2.25 4.0 3.0

    " 1.75 3.0 2.5

    3/8" 1.5 3.0 2.0

    JOB MIX FORMULA

    The Job Mix Formula (JMF) is the standard to which a produced HMA is comparedduring the Quality Management Program (QMP). The JMF identifies the selectedaggregate gradation, the design binder content, and gyratory test results for thecompacted HMA, including the air voids content and the percent voids in the mineralaggregate (VMA). Since it is not practical to meet the exact JMF values throughout

    production, appropriate tolerances based on the number of tests performed and theprobable error in each test must be established. The current WISDOT QMPSpecifications should be consulted for guidance on establishing appropriatetolerances.

    WISDOT HMA DESIGN SPECIFICATIONS

    WISDOT design specifications for compacted HMA pavements are based on the

    selected HMA mixture type and aggregate gradation. Current specifications forSuperpave mixture designs are provided below in Tables 4.4 and 4.5.Specifications for aggregate gradations are provided in Table 4.2

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    Table 4.4 WISDOT Minimum VMA Requirements

    Nominal Aggregate PercentSize Minimum VMA

    1 " 11.0%

    1 12.0%

    3/4 13.0%

    " 14.0%

    3/8" 15.0%

    Table 4.5 WISDOT Superpave Mixture Requirements

    Mixture Type E - 0.3 E - 1 E - 3 E - 10

    Gyratory CompactionGyrations for N 6 7 7 8iniGyrations for N 40 60 75 100desGyrations for N 60 75 115 160max

    Air Voids, %V 4.0 4.0 4.0 4.0a(%G @ N ) (96.0) (96.0) (96.0) (96.0)mm des

    %G @ N < 91.5 < 90.5

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    5.0 PAVEMENT DESIGN CONSIDERATIONS

    The structural design of a pavement system is a detailed process which must fullyaddress the interactions of materials, traffic loads, and environmental effects. Forthe users of this Design Guide, much of this design work has already been doneduring the preparation of the thickness design charts presented in Section 6.0. Touse these charts effectively, the designer must establish important design inputs,

    including:

    ! Traffic loadings (truck volumes and weights), and! Subgrade support (including drainage considerations)

    TRAFFIC LOADINGS

    Traffic loading information is necessary to establish both the required thickness ofthe pavement structure and the appropriate HMA mix type. Truck or heavyequipment loading on the pavement structure is the principal factor affecting thedesign and performance of an HMA pavement. For example, studies have shown

    that one heavily loaded interstate transport truck can cause pavement damageequivalent to that of 5000 passenger cars. Because of this large discrepancy ininduced damage, automobiles and light trucks are typically not considered duringthe development of required pavement thickness.

    For the purposes of this Design Guide, design traffic is defined as the average dailynumber of equivalent 18,000 pound Single Axle Loads (Design Daily ESALs) thepavement is expected to carry in the design lane. Procedures for estimating DesignDaily ESALs, ranging from detailed analyses of truck types, volumes, and axleweights, to simplified estimations based on pavement usage classification, areprovided in this Section. The collection of detailed traffic data may not be practical

    for all pavement jobs but these data may be required for specific projects. The useris encouraged to use as detailed a procedure as the available data allows.

    TRAFFIC CLASSIFICATIONS

    For the user of this Design Guide, traffic has been classified and designated perWISDOT guidelines as shown below.

    Truck Type Designation

    Heavy Single Unit Trucks:

    2 Axles, 6 Tires 2D3 Axles 3SUTractor-Semitrailer:

    3 or 4 Axles 2S-1, 2S-25 Axles and Above 3S-2

    Tractor-Semitrailer-Trailer:5 Axles and Above 2-S1-2

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    ESAL FACTORS

    Normal traffic streams consist of a random mixture of vehicles with different axleloads and number of axles. For ease of computation, vehicle and axle weight datamay be reduced to a common denominator known as the Equivalent Single AxleLoad (ESAL). Table 5.1 below illustrates the ESAL factors appropriate for eachtruck designation used within this Design Guide.

    DESIGN DAILY ESALs

    The Design Daily ESALs are calculated based on the average daily traffic mix thepavement is expected to carry over its design life. On multi-lane facilities, DesignDaily ESALs are determined only for the design lane, which is the outermost laneof the facility that typically carries the majority of the heavy truck loadings.

    Table 5.1 Pavement ESAL Factors

    Truck Type Designation Application ESAL Factor

    Local delivery2D School Buses 0.3

    General Delivery3SU Refuse 0.8

    2-S1, 2-S2 General Delivery 0.5

    Interstate Transport3S-2 Mass Transit Busses 0.9

    2-S1-2 Interstate Transport 2.0

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    ESAL CALCULATIONS

    Calculation Procedure 1

    For detailed calculations, the average daily total number of each truck designationmust be established for the design lane. These totals are multiplied by theirrespective ESAL factors to determine the daily ESALs applied by each truck

    designation. These daily ESALs are then summed up to arrive at the Design DailyESALs for the design lane, as shown below.

    Example Calculation Procedure 1

    Truck Truck Number of ESAL DailyType Designation Trucks Factor ESALs(1)

    3-Axle SingleUnit Truck 3SU 25 x 0.8 = 20

    4-Axle Semi-Trailer 2S-2 15 x 0.5 = 7.5

    5-Axle Tractor-Semitrailer-Trailer 2-S1-2 10 x 2.0 = 20

    DESIGN DAILY ESALs Sum = 47.5 = 48

    Example average daily truck count, by designation, within design lane.(1)

    Calculation Procedure 2

    When detailed truck classification data is not available, the Design Daily ESALs maybe estimated by assuming each truck can be represented by a single ESAL factor.In these instances the average daily total number of trucks, excluding light pick-uptrucks, in the design lane should be multiplied an ESAL factor of 0.9 to determinethe Design Daily ESALs, as shown below.

    Example Calculation Procedure 2

    Truck Number of ESAL Design DailyType Trucks Factor ESALs(1)

    All Trucks 50 x 0.9 = 45

    Example average total daily trucks within design lane.(1)

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    Simplified Procedure

    The simplified procedure assigns Design Daily ESAL values based solely on thetype or usage classification of the pavement. Five traffic classes are used in thisDesign Guide, each corresponding to a range of Design Daily ESALs. Guidancefor selecting Traffic Class and Design Daily ESALs based solely on usageclassification is provided in Table 5.2 and Figure 5.1.

    The user must exercise caution when using this simplified procedure because 1) thepavement may experience significantly higher truck loadings than those assumedand thus may experience premature failure, or 2) the pavement may experiencesignificantly fewer truck loadings than those assumed and thus will be overdesigned and more costly to construct.

    Table 5.2 Simplified Assignment of Traffic Class and Design Daily ESALs

    Traffic Design DailyClass ESAL Range Typical Usage Classification

    I < 1 ! School areas and play fields ! Residential driveways

    ! Parking lots, 50 stalls or less ! Seasonal recreational roads

    II 1-5 ! Residential streets and low volume ruralroadways ! Parking lots, more than 50 stalls

    III 6 - 50 ! Light industrial lots ! Collector streets and other roadways

    IV 51 - 275 ! Local business streets(1) ! Major arterial streets

    ! Medium industrial streets/lots

    V 276 - 1000 ! Heavy industrial drives/lots(2) ! Heavy truck terminals/truck stops

    ! Bus Stops

    Under certain traffic conditions at the high end of the ESAL range, i.e., heavy loads at slow(1)

    speeds or lots of stop and go conditions, consideration should be given to changing theSuperpave mix type or binder properties. Contact WAPA or your local WAPA contractor formore information.

    Designs for extreme traffic conditions not covered by the table are available by contacting(2)

    WAPA or your local WAPA contractor.

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    Figure 5.1 Multiple Zone Traffic Classes

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    SUBGRADE SUPPORT

    Drainage and soil-support values are major factors in pavement life; it is importantto know the supporting soil. Thickness design recommendations are provided inthis Design Guide only for soils classified into three broad classes: Excellent-Good,Medium, and Poor. Soil descriptions and typical California Bearing Ratios (CBR)(1)

    ranges for each class are provided herein. Design values for Soil Support Values

    (SSV) used within this Guide are also provided.

    Organic soils or soils with CBR values less than 2 should either be avoided,removed and replaced with suitable materials, or stabilized with an appropriatestabilizing agent to ensure a good compaction platform. A geotechnical engineershould be consulted in these instances to determine the most appropriate courseof action.

    Subgrade Soil Classification

    When possible, field or laboratory tests should be used to evaluate the load

    supporting capabilities of subgrade soils. One common method for determining therelative strength of the subgrade is the CBR method. However, it is realized thatthis or other tests may not be readily available or may be too costly for small jobs.In these instances, a field evaluation should be conducted by a geotechnicalengineer, who can then assign the subgrade soils to the appropriate categoriesgiven below.

    Excellent - Good Soils: Excellent soils retain a substantial amount of their loadsupporting capacity when wet and are little affected by frost. Excellent soils includeclean and sharp sands, sands and gravels, particularly those that are well graded.Good soils retain a substantial amount of the load-supporting capacity when wet.Included are clean sands and sand-gravels, and soils that are free of detrimentalamounts of plastic materials. A soil classified as Excellent would have a CBR > 20while Good soils would have a CBR of from 10 to 20. For the purposes of thisDesign Guide, Excellent to Good Soils have been assigned an SSV = 5.0.

    Medium Soils: These soils retain a moderate degree of firmness under adversemoisture conditions. Included are such soils as loams, silty sands, and sand-gravelmixtures containing moderate amounts of clay and fine silt. Soils classified asMedium Soils would have a CBR of 6 to 10 and have been assigned an SSV = 4.0.

    Poor Soils: These soils become quite soft and plastic when wet. Included are

    those soils having appreciable amounts of clay and fine silt (50% or more passingNo. 200 sieve). The coarser silts and sand loams also may exhibit poor bearingproperties in areas where frost penetration into the subgrade or base is a factor.

    Soils classified as Poor Soils would typically have CBR values of 2 to 5 and havebeen assigned an SSV = 2.5.

    The California Bearing Ratio (CBR) test provides a measurement of the strength and support(1)

    value of an aggregate base or subgrade soil.

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    DRAINAGE

    An important consideration in designing a high quality pavement is providingadequate drainage. Good drainage helps ensure the success of durablepavements. Any drainage deficiencies should be corrected prior to construction.To provide adequate drainage it is necessary that sufficient slope be provided in thedesign of the pavement surface and that the water which enters the base or

    subbase is not retained. There are two basic categories of drainage: surface andsubsurface.

    Surface Drainage

    Surface drainage includes the removal of all water present on the pavement,shoulder, and adjacent ground surfaces. For good surface drainage, the pavementand shoulders must be properly crowned or cross-sloped to ensure the rapid flowof water off the roadway to curbs and gutters or to adjacent drainage ditches.Roads and longer driveways with two or more lanes should be crowned with across-slope of at least two percent.

    For parking and play areas, a minimum cross-slope of one percent is necessary toensure adequate drainage of surface water and to avoid standing water that mayseep into the soil. Cross-slopes greater than one percent may be advisable ifsurfaces to be paved cannot be checked to close tolerances.

    Where minimum cross-slopes are used, proper consideration must be given to planelevation data at key intersection, cross-overs, and transitions between grade linesto ensure that this minimum slope is maintained during construction and to avoidstanding water. It is important that bird baths (leeching basins) not be created.Pavements in these locations will typically fail in a short time unless internaldrainage is provided to drain the low spots.

    Subsurface Drainage

    Subsurface water is water that seeps through the pavement or is contained in thesoil beneath the surface. When it emerges or escapes from the soil, it is referredto as seepage water. Subsurface water usually is present as free water that flowsunder the force of gravity or as capillary water that moves under capillary action inthe soil.

    Subdrains are required in areas where water may collect in the structural elementsof the pavement. The technical expertise of an engineer is required to identify theseareas and to design adequate drainage provisions.

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    GEOTEXTILE FABRICS

    Geotextiles are part of a broad class of geosynthetics, which are fabric-likematerials made from polymers such as polyester, polyethylene, polypropylene,nylon, and others. Geosynthetic use in civil engineering construction is about 15years old and growing at a very rapid pace.

    Geotextiles are available in woven, knitted, or non-woven form in thicknessesranging from about 0.01 to 0.3 in. The engineering properties of geotextiles varysignificantly from one form to another and also vary within form classes based onthe polymer used, thickness, and bonding technique. The proper choice and designof a geotextile fabric requires special skills; a geotechnical engineer should becontacted.

    Geotextiles are used to perform one or more of the following functions:

    ! Separation! Reinforcement!

    Filtration! Drainage

    Separation: Geotextiles may be used to keep various soil or aggregate layersseparate after construction. For example, a clayey subgrade soil can be keptseparate from an aggregate base course by placing a geotextile over the subgradeprior to base course placement.

    Reinforcement: The tensile strength of geotextiles can be advantageously usedto increase the load bearing capacity of the soil.

    Filtration: When placed between fine-grained and coarse-grained material layers,the fabric allows free seepage of water from one layer to the other while at the sametime protecting the fine-grained materials from being washed into the coarse-grained materials.

    Drainage: The fabrics can rapidly channel water from soils to various outlets.

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    6.0 THICKNESS GUIDES FOR HMA PAVEMENTS

    The following pages provides pavement thickness recommendations for the variouscombinations of traffic class and subgrade type. The pavement layer thicknessesprovided were developed to be adequate for the combinations of maximum designdaily ESALs within each traffic class and minimum subgrade support value within

    each subgrade rating.

    An interactive thickness design process is also available on the WAPA website at:

    http://www.wispave.org

    An example output from this interactive process is provided below.

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    TRAFFIC CLASS I

    ! Design Daily ESALs < 1! Residential Driveways! School areas and play fields!

    Parking lots, 50 stalls or less! Seasonal recreational roads

    HMA With Crushed Full-Depth Subgrade Type

    Aggregate Base HMA

    Equivalent

    HMA

    Mixture

    TypeHMA Base HMA

    Thickness Thickness Thickness Rating Description(Inch) (inch) (Inch)

    3.0 8.0 5.5 E - 0.3 Poor plasticity. SSV = 2.5 to 3.9.Clays and silts with high

    3.0 6.0 4.5 E - 0.3 Medium plasticity. SSV = 4.0 toClays and silts with low

    4.9.

    3.0 6.0 4.0 E - 0.3 Excellent SSV > 5.0Good to Sands and gravels.

    Use of Design Tables

    1. Determine the Design Daily ESALs (18,000 pound Equivalent Single Axle

    Loads) or Traffic Class which best describes the use of the intended pavement(See Section 5).

    2. Determine the Subgrade Support. (See Page 24)

    3. Select the HMA pavement thickness from the table above which includes layerthickness for HMA pavements with crushed aggregate bases and well as full-depth HMA thickness equivalencies.

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    TRAFFIC CLASS II

    ! 1 to 5 Design Daily ESALs! Residential streets! Low volume rural roadways!

    Parking lots, more than 50 stalls

    HMA With Crushed Full-Depth Subgrade Type

    Aggregate Base HMA

    Equivalent

    HMA

    Mixture

    TypeHMA Base HMA

    Thickness Thickness Thickness Rating Description(Inch) (inch) (Inch)

    4.0 9.0 6.5 E - 0.3 Poor plasticity. SSV = 2.5 to 3.9.Clays and silts with high

    3.5 6.0 5.5 E - 0.3 Medium plasticity. SSV = 4.0 toClays and silts with low

    4.9.

    3.0 6.0 5.0 E - 0.3 Excellent SSV > 5.0Good to Sands and gravels.

    Use of Design Tables

    1. Determine the Design Daily ESALs (18,000 pound Equivalent Single AxleLoads) or Traffic Class which best describes the use of the intended pavement(See Section 5).

    2. Determine the Subgrade Support. (See Page 24)

    3. Select the HMA pavement thickness from the table above which includes layerthickness for HMA pavements with crushed aggregate bases and well as full-depth HMA thickness equivalencies.

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    TRAFFIC CLASS III

    ! 6 to 50 Design Daily ESALs! Collector streets and other roadways! Light industrial lots

    HMA With Crushed Full-Depth Subgrade Type

    Aggregate Base HMA

    Equivalent

    HMA

    Mixture

    TypeHMA Base HMA

    Thickness Thickness Thickness Rating Description(Inch) (inch) (Inch)

    6.0 10.0 9.5 E - 1 Poor plasticity. SSV = 2.5 to 3.9.(1)Clays and silts with high

    5.0 9.0 8.0 E - 1 Medium plasticity. SSV = 4.0 to(1)Clays and silts with low

    4.9.

    4.0 9.0 7.0 E - 1 Excellent SSV > 5.0(1)Good to Sands and gravels.

    Mixture type E - 0.3 should be used if Design Daily ESALs < 41.(1)

    Use of Design Tables

    1. Determine the Design Daily ESALs (18,000 pound Equivalent Single AxleLoads) or Traffic Class which best describes the use of the intended pavement(See Section 5).

    2. Determine the Subgrade Support. (See Page 24)

    3. Select the HMA pavement thickness from the table above which includes layerthickness for HMA pavements with crushed aggregate bases and well as full-depth HMA thickness equivalencies.

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    TRAFFIC CLASS IV

    ! 51 to 275 Design Daily ESALs! Local business streets! Major arterial streets!

    Medium industrial streets/lots

    HMA With Crushed Full-Depth Subgrade Type

    Aggregate Base HMA

    Equivalent

    HMA

    Mixture

    TypeHMA Base HMA

    Thickness Thickness Thickness Rating Description(Inch) (inch) (Inch)

    8.0 14.0 12.5 E - 3 Poor plasticity. SSV = 2.5 to 3.9.Clays and silts with high

    7.0 11.0 10.5 E - 3 Medium plasticity. SSV = 4.0 toClays and silts with low

    4.9.

    6.0 10.0 9.5 E - 3 Excellent SSV > 5.0Good to Sands and gravels.

    Use of Design Tables

    1. Determine the Design Daily ESALs (18,000 pound Equivalent Single Axle

    Loads) or Traffic Class which best describes the use of the intended pavement(See Section 5).

    2. Determine the Subgrade Support. (See Page 24)

    3. Select the HMA pavement thickness from the table above which includes layerthickness for HMA pavements with crushed aggregate bases and well as full-depth HMA thickness equivalencies.

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    TRAFFIC CLASS V

    ! 276 to 1000 Design Daily ESALs! Heavy truck terminals! Truck stops!

    Heavy industrial drives/lots! Bus stops

    HMA With Crushed Full-Depth Subgrade Type

    Aggregate Base HMA

    Equivalent

    HMA

    Mixture

    TypeHMA Base HMA

    Thickness Thickness Thickness Rating Description(Inch) (inch) (Inch)

    10.5 14.0 15.0 E - 10 Poor plasticity. SSV = 2.5 to 3.9.(1)Clays and silts with high

    9.0 11.0 12.5 E - 10 Medium plasticity. SSV = 4.0 to(1)Clays and silts with low

    4.9.

    8.0 10.0 11.5 E - 10 Excellent SSV > 5.0(1)Good to Sands and gravels.

    Mixture type E - 3 should be used if Design Daily ESALs < 411.(1)

    Use of Design Tables

    1. Determine the Design Daily ESALs (18,000 pound Equivalent Single Axle

    Loads) or Traffic Class which best describes the use of the intended pavement(See Section 5).

    2. Determine the Subgrade Support. (See Page 24)

    3. Select the HMA pavement thickness from the table above which includes layerthickness for HMA pavements with crushed aggregate bases and well as full-depth HMA thickness equivalencies.

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    7.0 PAVEMENT MANAGEMENT SYSTEMS

    ESTABLISHING A PAVEMENT MANAGEMENT SYSTEM

    Many agencies and owners have developed informal procedures for identifying,

    budgeting, and scheduling pavement maintenance needs. These ad hocapproaches may have been successful because of the knowledge, good judgement,and most importantly the experience of those in decision-making positions. Today,however, due to higher traffic volumes and increasingly tighter budgets, a moresystematic approach is warranted.

    Implementing a structured Pavement Management Systems (PMS) can help toestablish and prioritize maintenance needs and to plan budget allocations. ThesePMS need not be overly complex nor expensive to acquire and operate. Many PMSprograms, such as the PASER software developed by the TransportationInformation Center at the University of Wisconsin-Madison, only need a portable

    computer to run efficiently. Implementing a PMS is cost-effective, regardless of thesize of the pavement network being managed. Networks as large as a statewideprimary road system or as small as a single parking lot can be better managed witha PMS. A PMS can provide easy access to information such as:

    ! What is the condition of all pavements within the network?! When is the best time to schedule repair?! What is the most cost-effective repair or reconstruction procedure?! What is the cost if repairs are delayed?

    A structured PMS has the following basic components:

    ! Record-keeping database! Condition rating system! Condition rating projection! Correlations of repair procedures and costs based on pavement condition rating! Priority ranking! Budget planning

    Record Keeping Database: Record keeping methods can be simple or complexdepending on the resources available to the agency. It is important that onceestablished, pavement records be up-dated on a regular basis.

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    Condition Rating Systems: Condition rating systems are necessary so thatpavement distress is properly evaluated. Some types of distress have more effecton the pavement performance than others. Therefore, it is necessary that a ratingsystem be established which will properly score the various types of pavementdistress. The PASER Manual provides such a system. In the PASER system, a 10is assigned to new construction and a 1 is assigned to a pavement surface withsevere distress and with extensive loss of surface integrity.

    All that is needed to establish a pavement rating is to have an individual withknowledge of the types of pavement distress walk the road and assign a numberbased on the PASER rating scale. Once this has been done for all pavementsurfaces in an agency's jurisdiction, a numerical value is available upon which tocompare pavement surfaces.

    Condition Rating Projection: The future condition of a pavement section can beprojected based on the age, pavement type, and present condition of the sectionusing a variety of techniques. These projections are necessary to determine theoptimum time to repair a pavement or to determine the effectiveness of applied

    maintenance treatments.

    Correlation of Repair Procedure and Cost with Pavement Condition Rating:The PASER Manual can serve as a guide as to the type of repair or reconstructionthat is recommended for a pavement based on the type and severity of existingdistress.

    Priority Ranking: The numerical score (PASER number) can be used as oneparameter in the priority ranking of pavements. This ranking may also include otherfactors such as traffic volume, budget, effect of delaying maintenance on pavementdeterioration, and other factors.

    The cost of rehabilitating a pavement will increase with use (traffic) and age(weathering). Figure 7.1 illustrates the cost implications of delaying therehabilitation of a pavement until it has reached the end of its useful life. As shown,costs can be significantly reduced if repairs are applied while the pavement is stillin good to fair condition.

    Budget Planning: A planned maintenance and rehabilitation program shouldinclude budget considerations. Financial resources available over a period of x-years (5, 10, etc. years) should match year by year the projected cost ofmaintenance and rehabilitation work proposed. The ultimate goal is to maintain the

    entire pavement network in good condition at the lowest cost. To do this, it isessential that work completed at the optimum time and that all repairs be of highquality. Stretching budget dollars by providing a lesser quality job that covers morepavement surface is not, in the long run, an effective strategy.

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    Figure 7.1 - Pavement Deterioration/Rehabilitation Relationship

    DEFINITION AND USE OF PASER MANUAL

    General: The PAvement Surface Evaluation and Rating (PASER) system is astructured procedure for visually rating pavement conditions that can be usedindependently or within a structured pavement management system. The PASERSystem also provides guidance for determining the required level of maintenanceor rehabilitation based on the obtained pavement rating. A copy of the AsphaltPASER manual can be obtained at nominal charge by contacting:

    Transportation Information CenterUniversity of Wisconsin-Madison432 N Lake StreetMadison, WI 53706Ph: (800) 442-4615Fax: (608) 263-3160Email: [email protected]

    How to Use the PASER System: The first step in establishing a rating for apavement section is to identify the types of defects which exist. The PASER

    System provides photographs of those types of surface defects which can occur inHMA pavements.

    The second step is to select a rating. The rating scale established is from 10(excellent) to 1 (failed). Photographs and Tables are provided to assist in theselection of a pavement rating.

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    8.0 PAVEMENT REHABILITATION

    Pavement rehabilitation can be accomplished using a variety of methods. Thissection is intended to provide only a general overview of rehabilitation methodsavailable for pavements and is not intended as a guide on how to do the work.These rehabilitation methods are not applicable to every pavement surface,therefore it is highly recommended that a person with experience in pavement

    rehabilitation should be contacted to determine the rehabilitation technique mostappropriate for your pavement.

    This section presents information on HMA overlays and methods for surfacepreparation, including:

    HMA Overlays! Thin HMA Overlays! Structural HMA Overlays! Open-Graded Friction Courses

    Surface Preparations! Localized Surface Preparation! HMA Cold Milling! In-Place HMA Recycling! Concrete Pavement Preparation

    The complete rehabilitation of a pavement will typically involve one or more of theabove procedures. For example, it may be necessary to crack and seat a concretepavement prior to placing a structural overlay.

    HMA OVERLAYS

    HMA overlays are commonly used to restore an aged pavement to like-newcondition. HMA overlays can be placed with minor traffic disruptions and whenproperly designed and constructed, the overlaid pavement will provide a smooth,durable surface for many years. The overlay thickness, which is related to itsintended function, may be determined based on a number of analysis techniqueswhich will not be discussed here. Further information on the design of HMAoverlays is available in Section XI, Credits and References.

    The performance of an HMA overlay is significantly affected by movements in the

    underlying pavement layer. Because it is not possible to completely arrest thismovement, procedures to provide an HMA overlay which is more tolerant ofpavement movements have been investigated, including:

    ! Use of softer asphalt binders or rubber or polymer modified asphalt binders! Use of reinforcement interlayers within the HMA overlay! Use of synthetic fabrics within the HMA overlay as reflection crack arresters

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    The use of softer asphalt binders has proven not to be suitable for use on high-volume roadways due to potential stability problems. Additives and reinforcementinterlayers are still being researched and some potential advantages have beenobserved.

    Thin HMA Overlays

    Thin HMA overlays, commonly placed in thicknesses less than 2 inches, are usedto protect a deteriorated pavement, reduce roughness, and/or restore skidresistance. When thin HMA overlays are used, it is important to ensure that 1) themaximum aggregate size is appropriate for the overlay thickness, 2) a proper tackcoat is applied, 3) work is carried out in warm weather so that desired level ofcompaction is achieved, and 4) good HMA construction quality control ismaintained.

    Structural HMA Overlays

    Structural overlays are used to increase or restore the structural integrity of a

    pavement. Structural overlays may be required where there is a dramatic increasein heavy truck traffic or where existing pavements are approaching the end of theirdesigned service life. Overlays will increase pavement life, reduce maintenancecost, provide a smoother riding surface and improve skid resistance.

    Open-Graded Friction Courses

    An open-graded friction course (OGFC) is a high-void HMA wearing course whichcontains a high percentage of one-sized aggregates. OGFC can rehabilitateasphalt pavements which have lost their skid resistance as a result of aggregatepolishing and/or flushing of asphalt binder. They are effective in reducing

    hydroplaning and wet pavement accidents and can also help to reduce road noise.

    SURFACE PREPARATION METHODS

    To ensure good performance of an HMA overlay, the existing pavement surfacemust be properly prepared. In general, uncorrected problems existing in thepavement surface will become problems in the HMA overlay. The type and extentof surface preparation should be carefully matched to the existing pavementcondition and the HMA overlay type.

    Localized Surface Preparation

    Localized surface preparation includes patching of deteriorated pavement areasand treatment of existing cracks.

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    Patching Deteriorated Pavement Areas: Patching is one of the most commonmethods for repairing localized areas with intensive cracking as a result ofexcessive loadings (alligatoring) or other factors. Patching can be either partial orfull depth. Partial depth patching involves the removal of only the surface layer andreplacement with HMA. Full depth patching involves complete pavement removaldown to the subgrade or an intermediate base layer which is intact.

    Regardless of the patch depth, it is important to remove all deteriorated areas of the

    existing pavement. Some areas of deterioration may not be visible on the surfacebut will become exposed during the removal process. In these cases, it is importantto extend the patch boundaries to include these previously unseen areas ofdeterioration.

    Treatment of Existing Cracks: In this procedure, transverse and longitudinalcracks which are opened up between to inch are cleaned and filled with asealant material. Larger cracks should be cleaned and filled with an HMA patchmaterial.

    HMA Cold Milling

    Cold milling is the process of removing a desired pavement thickness with aspecially designed milling machine. A milling machine has a rotating drum mountedwith carbide bits. These bits strike the pavement surface and remove the material(concrete or asphalt) to a predetermined depth. Any desired pavement thicknesscan be removed and any size material desired can be produced. The size of thematerial may be important if it is to be recycled since it may not be necessary tocrush to obtain the desired size.

    Milling provides a level, roughened surface which has good skid resistance andprovides an excellent bond with the overlay. Most pavement distortions, such as

    rutting, bumps, and shoving, can be removed. This process does not harm theunderlying material. Milling makes it possible to maintain the original pavementelevations. By removing material at the surface, no adjustments are required in theelevation at manholes, curbs and gutters, storm sewer inlets and other connectingpavement surfaces.

    In-Place Recycling (Pulverizing)

    In-place recycling is the pulverization of the existing pavement followed byreshaping and compaction. A stabilizer (asphalt binder, emulsified asphalt, fly ash,lime, cement, or other chemical) may be added to the pulverized material prior to

    compaction. The process does not require the use of new aggregate and surfacedeficiencies can be eliminated.

    After compaction the resulting mixture is covered by a structural layer of HMA. Therecycled base can provide a structural capacity greater than the original base;thereby making the pavement capable of carrying a higher level of traffic.

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    Concrete Pavement Preparation

    Cracks will typically develop in a HMA overlay placed on a concrete pavement.Reducing or minimizing the occurrence of these cracks is generally a high priorityif the service live of the pavement is to be extended. Cracks which develop in aHMA overlay directly above existing cracks and joints in the concrete pavement aretermed reflection cracking. Almost any joint or crack spacing in the concretepavement produces localized high stress in the HMA overlay. This results from

    temperature induced movements and vertical displacements due to load. Thetemperature induced movements are more likely to be the most significant of thetwo.

    Many methods have been tried in an attempt to eliminate the reflection cracks. Oneconcept in trying to eliminate or retard reflection cracking is to spread the strainwhich would occur over one crack to several cracks. In this way, no one cross-section of the pavement is subjected to large strains. Described below are severalmethods that have been used over the past 30 years to retard or eliminate reflectioncracking.

    Cracking and Seating: In this method, a drop hammer or similar device is usedto develop tight cracks in the concrete pavement, typically at about 24-30 inches oncenter. Tight cracks are those in which the aggregate still interlocks and load canbe transferred through the crack. After cracking, a 10 ton steel drum vibratory rollermakes several passes over the cracked pavement to seat the concrete. This willeliminate voids which may have existed below the concrete pavement. It isimportant that the roller not be oversized for the field site since it is possible to overstress the subbase. Cracking and seating is most applicable to jointed concretepavements which are structurally sound but have high roughness and significantamounts of patching and spalling.

    Breaking and Seating: In this method, a drop hammer or similar device is usedto develop cracks in the concrete at least 12 inches on center. Steel reinforcementwithin the concrete is broken and/or the bond between the concrete and thereinforcement is destroyed. After breaking, the concrete blocks are seated by usingseveral passes of a 10 ton steel drum vibratory roller. Breaking and seating is mostapplicable to jointed reinforced concrete pavements which are structurally sound buthave high roughness and a significant amount of patching and spalling.

    Rubblizing: In this method, specially designed equipment essentially reduces theconcrete pavement to crushed aggregate. The slab action is completely destroyedand the concrete-to-steel bond is destroyed. Rubblizing is applicable to plain

    jointed, jointed reinforced and continuously reinforced concrete pavements thathave deteriorated to the point that there is little potential to retain slab integrity andstructural capacity. After rubblizing, the materials are compacted with two passesof a 10-ton steel drum vibratory roller (a Z-Grid steel drum roller is used in someinstances), followed by single passes of a 10 ton rubber tire roller and a 10 ton steeldrum vibratory roller.

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    9.0 HMA FOR RECREATIONAL AND OTHER USES

    This section provides general information and suggestions on the use of HMA forrecreational or other uses, including sidewalks and walkways, bicycle and golf cartpaths, play areas, tennis courts, running tracks, curbs, reservoir liners, and railroadtrack beds. If more detailed information is desired, you are urged to contact the

    Wisconsin Asphalt Pavement Association or a member contractor. To achievesatisfactory results, the designed HMA mix must be matched to the pavement use.For example, and HMA mix designed for a highway is most likely not appropriate forused as a tennis court.

    SIDEWALKS AND WALKWAYS

    Sidewalks and walkways of HMA can be blended into the contours of the existingground to preserve aesthetics and to reduce impact on the environment. Wheneverpossible, it is desirable to have surface drainage flow from these pathways. The

    width will typically be dictated by the expected foot traffic. Where access formaintenance or repair vehicles, construction equipment or emergency vehicles maybe a problem, a wider pavement surface may be required.

    BICYCLE AND GOLF CART PATHS

    The construction of bicycle and golf cart paths is essentially the same except thatthey are usually built in different widths. A bicycle path should be at least 8 feetwide to allow bicycles to pass in two directions. Golf cart paths should be at least

    five feet wide. It may be necessary in remote areas, difficult terrain, or wheredamage to grounds may occur, to construct wider pavements to allow formaintenance or emergency vehicle passage.

    Bicycle and golf cat paths should have a minimum slope of 2 percent ( inch perfoot) and should be constructed so that water will not collect at the pavement edge.It may be necessary to construct an underdrain system to carry water away.

    PLAY AREAS

    Play areas may include basketball courts and paved surfaces surrounding playground equipment. Both surface and subsurface drainage should be investigatedto ensure that excessive moisture is not allowed to accumulate under the pavementand shorten the life of the play area surface.

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    CURBS

    Hot mix asphalt curbs can be an integral part of the pavement or they can be laidseparately on an existing pavement by use of a slip form paver. These curbs serveto control drainage, delineate the pavement edge, help prevent vehicularencroachment on adjacent areas, maintain edge of pavement, and enhance the

    overall appearance of streets and highways.

    TENNIS COURTS

    It is most important that both surface and subsurface drainage be thoroughlyinvestigated to ensure a smooth, non-cracked playing surface is maintained. Ifsubsurface drainage is not satisfactory, it is recommended that perimeter drains beinstalled or that an HMA base on a suitable subgrade soil be used.

    It is also important that tennis court surfaces properly drain. To accomplish this, the

    court surface should have a minimum slope of 1 inch per 10 feet on a true planefrom side to side, end to end, or corner to corner. The surface should not slopeaway in two directions from the net.

    ASPHALT-RUBBER RUNNING TRACKS

    High school and colleges are increasingly using asphalt-rubber surfaces for outdoorand indoor running tracks and for long jump, high jump and pole vault runways. Itis recommended that these be constructed over an HMA or coarse aggregate base.

    Rubber for use in asphalt-rubber mixes is available from several manufacturers.Information on these manufacturers can be obtained from WAPA member firms.

    HMA FOR HYDRAULIC STRUCTURES

    HMA may be used to line reservoirs, dams, retention ponds, and for potable waterstorage since HMA does not contaminate the water. Special care is required in thepreparation of the soil surface prior to paving and it is necessary that a proper

    drainage system be installed to prevent excessive hydrostatic pressures.

    HMA mixtures for hydraulic linings can differ significantly from HMA for pavementsor roadways. It is necessary that a dense mix be used if the lining is to beimpervious, typically requiring a higher asphalt binder content and increased minus200 sieve material. The higher asphalt binder content increases the durability of themix and the additional minus 200 sieve material increases the impermeability towater.

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    Conventional pavers and rollers are used to construct HMA linings on mild slope.On steep slopes cables may be necessary to winch equipment up and down theslope and special pavers and rollers may be required. It may also be necessary touse a performance graded (PG) binder to ensure that adequate HMA stability isobtained.

    RAILROAD TRACKBEDS

    HMA has been used successfully as an underlayment system for railroad trackbeds. The asphalt layer is topped by a ballast which supports the ties and the rails.The asphalt underlayment helps to spread the load, confine the ballast, waterproofthe subgrade, and prevent pumping. It can be cost-effective, especially where apoor base course exists.

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    10.0 REFERENCES

    Wisconsin Department of Transportation (WISDOT):Standard Specifications for Road and Bridge Construction, 1996 Edition.Supplemental Specifications to the Standard Specifications for Road and BridgeConstruction, 2000 Edition.

    Facilities Development Manual.Construction and Materials Manual.

    Transportation Information Center, University of Wisconsin-Madison:Pavement Surface Evaluation and Rating (PASER MANUAL), 1987, Madison, WI.

    National Asphalt Pavement Association (NAPA) Information Series (IS):IS-20, Guide to Thickness EquivalenciesIS-21, Placing & Compacting Thick LiftsIS-77, Are Hot Mix Tarps Effective?IS-97, Blistering in Asphalt Pavements

    IS-98, Cracking & Seating of PCC PavementsIS-99, Simplified Design Guide for HMA Railroad TrackbedsIS-103, Large Stone Mixes: A Historical InsightIS-105, Design & performance Study of a Large Stone HMA Under Concentrated

    Punching Shear ConditionsIS-107, Estimating User Costs of Asphalt Concrete Pavement RehabilitationIS-109, Design of HMA Pavements