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PAVEMENT DESIGN for DUMMIES

PAVEMENT DESIGN for DUMMIES. Boulder County Resource Conservation – Glasphalt Research Project prepared by LBA Associates, Inc. – November 2006 (draft). U.S. Highways (2001 data). 8.21M lane miles in place Truck traffic increasing faster than passenger vehicle traffic 93% asphalt pavement

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PAVEMENT DESIGN for DUMMIES

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  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 County’s project. Draft 11/2/06

  3. 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 (Paved) Roadway Functions 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 ¾”) & 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. 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 Asphalt Pavement Draft 11/2/06

  11. 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 HMA Draft 11/2/06

  12. Part II: Materials Draft 11/2/06

  13. Aggregate • Found in floodplains, stream terraces and alluvial fans – also excavated from quarries • 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, con’t • 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. Excavated – dug or blasted Size-reduced – crushed & screened Washed - to remove undesired small particles Stockpiled Preparing Aggregate Draft 11/2/06

  16. Also called asphalt binder or bitumen 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 Asphalt Draft 11/2/06

  17. Asphalt, con’t • 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. 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) Pavement Design Considerations Draft 11/2/06

  21. 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 Pavement Design, con’t Draft 11/2/06

  22. Drainage Surface HMA relatively impermeable if well compacted Need cross slopes of 2% Subsurface – facilitate good permeability with subgrade soils and base course design Pavement Design, con’t Draft 11/2/06

  23. Aggregate + Asphalt 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, con’t • 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, con’t 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 Colorado’s 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 with glass in surface Draft 11/2/06

  33. Blended w/ Aggregate Crushing - most states require all glass at minus 3/8” (but < 8% passing No. 200 sieve) Cleaning – debris threshold may be < 5% Transporting - to aggregate production site Blending with aggregate Used in HMA All of above – except that gradation & debris threshold may be tighter Mix glass/aggregate w/ binder (also req’d w/o glass) Add anti-stripping agent May require adjustments during pavement placement Note: health & safety issues associated with crushing glass Glass Preparation Requirements Draft 11/2/06

  34. Glasphalt Economics • Many pilot project in 1970s to 1990s - earliest projects findings were promising • Several states allowed glass to be used with roadway aggregate (a few also allowed in HMA) • As alternative glass markets developed economics were less favorable • Today very few state/federal roads utilize glass in roadways Feasibility still exists in areas where public agencies are building roads, limited local glass markets exist and/or regional climates require additional road base fill Draft 11/2/06

  35. Questions to Ask • Are there any obstacles to using natural aggregate in the region? (availability, cost, engineering properties or other) • Are there significant advantages to using a new material? (same reasons, plus the ability to develop an end market for glass) • Are there net benefits with using glass? • Are enough quantities of glass produced to make the investigation worthwhile for both recyclers & aggregate/HMA producers? Draft 11/2/06

  36. Thanks To The following references were used to develop this presentation: • The Washington Asphalt Pavement Association’s Asphalt Pavement Guide • USGS’ Front Range Infrastructure Resources Project • Bicycling Magazine (September, 2006) • MidAmerica Recycling & Strategic Materials websites Draft 11/2/06

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