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  • Draft 11/2/06 1

    PAVEMENT DESIGN

    for DUMMIES

    Boulder County Resource Conservation Glasphalt Research Project

    prepared by LBA Associates, Inc. November 2006 (draft)

  • Draft 11/2/06 2

    U.S. Highways (2001 data)

    8.21M lane miles in place

    Truck traffic increasing faster than passenger vehicle traffic

    93% asphalt pavement

    7% concrete pavement

    Note: pavement discussions in this presentation are limited

    to asphalt pavement as glasphalt research is the ultimate goal of Boulder Countys project.

  • Draft 11/2/06 3

    (Paved) Roadway Functions

    Carries vehicle loads that unpaved roads cannot

    Provides drainage away from driving surface

    Add smoothness to allow higher vehicle speeds and greater drivability

    Provide skid resistance for vehicles

    Provides a relatively dust-free surface

    High-speed surface

  • Draft 11/2/06 4

    Definitions

    Aggregate = natural sand, gravel & stone

    Asphalt = petroleum residue (naturally occurring or from distillation of crude oil)

    Asphalt pavement = aggregate + asphalt + air

    Concrete pavement = aggregate + cement + water + air

    Will have samples to circulate to audience

  • Draft 11/2/06 5

    Part I: Road Construction

  • Draft 11/2/06 6

    Subgrade

    Existing materials quality based on strength, gradation & drainage capacity good soils will retain most of their load-bearing capacity when wet

    If poor soil (e.g., swelling soils); Remove to reach better soils

    below

    Replace with better material

    Stabilize to increase stiffness

    Compaction of subgrade materials is key

  • Draft 11/2/06 7

    Base Courses

    Provides load distribution, drainage & frost resistance

    Materials are moderately stiff to help carry traffic & minimize deflection of pavement materials

    Subbase Course is optional - typically includes relatively fine aggregate (minus ) & 12 thick

    Base Course - typically includes moderately coarse aggregate (minus 1-1/2) & 6-12 thick Can be aggregate only (loose, unbound) OR

    Aggregate bound with asphalt (pavement)

  • Draft 11/2/06 8

    Load Bearing by

    Flexible v. Rigid Pavement

  • Draft 11/2/06 9

    Surface Course

    (in contact with traffic)

    Surface Course = aggregate + asphalt

    Includes highest quality & stiffest materials to

    absorb loads

    Aggregate is typically

    minus 3/8

    Placed in 8 layers

    prior to compaction

  • Draft 11/2/06 10

    Asphalt Pavement

    Also known as blacktop, flexible

    pavement or

    bituminous concrete

    Typically used in

    lower load

    applications

    Less construction

    costs than concrete

    pavement may have

    shorter life & greater

    maintenance

    Support loads by

    flexing & distribution

    through bottom layers

  • Draft 11/2/06 11

    HMA

    Hot Mix Asphalt

    (HMA) is the most

    common type of

    asphalt pavement

    HMA is made

    principally from

    aggregate and

    asphalt binder at

    elevated temper-

    atures at plant

  • Draft 11/2/06 12

    Part II: Materials

  • Draft 11/2/06 13

    Aggregate

    1. Found in floodplains, stream terraces and alluvial fans

    also excavated from quarries

    2. Described in terms of size gradation

    Well graded aggregate (preferred) = wide range of

    sizes

    Fine aggregate = minus 3/16

    Coarse aggregate = > 3/16

  • Draft 11/2/06 14

    Aggregate, cont

    3. Other Characteristics

    Toughness resists crushing or disintegration when tested, stockpiled, transported or made into HMA

    Durability resists damage from wetting & drying

    Particle Shape/Texture cubic & angular with rough surfaces

    Clean free of contaminants (vegetation, clay lumps, soft particles, dust)

    U.S. produced more than 3B tons in 2001 at value of $14.2B highways consumed 40% of this material

  • Draft 11/2/06 15

    Preparing Aggregate

    Excavated dug or

    blasted

    Size-reduced

    crushed & screened

    Washed - to remove

    undesired small

    particles

    Stockpiled

  • Draft 11/2/06 16

    Asphalt

    1. Also called asphalt

    binder or bitumen

    2. Natural Characteristics

    Waterproof

    Thermoplastic

    Elastic

    Adhesive

    U.S. produced more than 35M tons in 2001 at value of $6B highways consumed 85%

    of this material

  • Draft 11/2/06 17

    Asphalt, cont

    3. Other Characteristics Durable - ages well with time

    Rheology or deformation with temperature

    Too warm/too much flow can cause rutting

    Too cold/too little flow can cause cracking

    Purity pure bitumen

    Most current asphalt pavement design approach is based on specifying asphalt in terms of maximum & minimum

    temperatures it will be exposed to

  • Draft 11/2/06 18

    Asphalt Modifiers

    May be added to:

    Lower viscosity (thickness) & increase

    workability

    Increase viscosity & decrease rutting

    Increase adhesion between aggregate and

    binder (especially in presence of moisture)

    decrease stripping

  • Draft 11/2/06 19

    Part III: Pavement Design

  • Draft 11/2/06 20

    Pavement Design Considerations

    Loads penetrate 2-3

    Quantity/repetition of traffic

    Type of traffic passenger,

    trailer, construction

    Type of vehicles tire

    pressure, load, wheel configuration

    Vehicle speed

    Road configuration (curvatures)

  • Draft 11/2/06 21

    Pavement Design, cont

    Environment

    Temperature impacts on binder rheology (extremes lead to rutting & cracking)

    Frost action subgrade heaves, thaw weakening

    Moisture

    Design mitigation = increase pavement to frost depth, replace frost-susceptible &

    weak (expansive) subgrade soils, increase drainage

  • Draft 11/2/06 22

    Pavement Design, cont

    Drainage

    Surface HMA relatively

    impermeable if well

    compacted

    Need cross slopes of 2%

    Subsurface facilitate

    good permeability with

    subgrade soils and base

    course design

  • Draft 11/2/06 23

    Aggregate + Asphalt

    Aggregate Asphalt Binder

    92-96% by weight 4-8% by weight

    30% of cost of HMA pavement

    25-30% cost of HMA pavement

  • Draft 11/2/06 24

    HMA Manufacturing

    Manufacturing = blending & heating components to job specifications Batch plant (older technology)

    Continuous drum plant (can product 100-900 tph)

  • Draft 11/2/06 25

    HMA Placement

    Equipment transfer vehicles & asphalt

    paver;

    Paver is self-propelled unit

    Includes tractor, hopper & floating screed

  • Draft 11/2/06 26

    Placement, cont

    Compaction most important factor for performance

    75-85% maximum density achieved by screed

    Remainder achieved by rollers steel or pneumatic tires, may use vibration

    Must compact prior to cooling (rutting)

  • Draft 11/2/06 27

    Part IV: Other Asphalt

    Pavement Applications Pavement Placement improve placement

    success Leveling layer

    Tack coat

    Surface Treatment increase smoothness, appearance, safety; reduce noise; correct defects Fog & slurry seals

    Overlays

    Repair address specific defects Crack & slurry seals (crack seals often contain crumb

    rubber)

    Patching

  • Draft 11/2/06 28

    Other Applications, cont

    Rehabilitation improve strength or salvage stressed pavement

    Overlays

    Hot In Place Recycling old pavement is heated, scarified/removed, modified, placed & compacted

    Cold in Place Recycling old pavement removed, pulverized, modified, placed & compacted

  • Draft 11/2/06 29

    Recycled Asphalt Pavement (RAP)

    The most recycled materials in U.S. -

    approximately 80M tpy

    Can be used to make new HMA (10-30% by

    weight), in cold mix, as fill or other

    Recycled in place used to resurface

    existing pavement or pulverized for base

    material

  • Draft 11/2/06 30

    Part V: The Glass Alternative

    Colorado Aggregate

    80% of Colorados aggregate is sand & gravel found in drainage areas along the Front Range

    20% is crushed rock mined from quarries in the mountains

    Haul costs significant where source is not located near aggregate plant or project

    How long before land use & environmental constraints cause an aggregate shortage?

  • Draft 11/2/06 31

    Glass Blended w/ Aggregate

    Characteristics similar

    to natural aggregate

    (hard, durable, drains

    well & dries fast)

    Higher heat retention

    (good with frost

    penetration but may

    take longer to cure

    during placement)

  • Draft 11/2/06 32

    Glass in HMA

    Reflective properties (good & bad)

    Decreased skid resistance if gradation

    is too large

    Does not stay bound to asphalt well

    without anti-stripping agent (raveling)

    Real & perceived issues wi

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