PAVEMENT DESIGN for DUMMIES Boulder County Resource Conservation – Glasphalt Research Project prepared by LBA Associates, Inc. – November 2006 (draft) Draft 11/2/06

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

(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

Will have samples to circulate to audience 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

Part I: Road Construction Draft 11/2/06

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

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

Load Bearing by Flexible v. Rigid Pavement Draft 11/2/06

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

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

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

Part II: Materials Draft 11/2/06

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

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

Preparing Aggregate Excavated – dug or blasted Size-reduced – crushed & screened Washed - to remove undesired small particles Stockpiled Draft 11/2/06

Asphalt 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 Draft 11/2/06

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

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

Part III: Pavement Design Draft 11/2/06

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

Pavement Design, con’t 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

Pavement Design, con’t 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

30% of cost of HMA pavement 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

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

HMA Placement Equipment – transfer vehicles & asphalt paver; Paver is self-propelled unit Includes tractor, hopper & floating “screed” Draft 11/2/06

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

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

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

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

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

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

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

Glass Preparation Requirements 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 Draft 11/2/06

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

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

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