Warm Mix Asphalt Richard Bessom, P.E., CCM Program Manager, Horizontal Projects Capital Programs & Environmental Affairs Francis Skip Parker Associate, Director of Construction Services
1937
2007
Logan Airport Today 2,400 Acres Six (6) Runways Fifteen Miles of Taxiways 102 Aircraft Gate Positions 204 Acres of Pavement 12,000 Workers Employed Regional Economy Stimulated by $7B / year 88,000 Direct and Indirect Jobs
Airport Statistics Passengers Logan is the 19th Busiest Airport in the Nation Logan is the 41st Busiest Airport in the World Operations Logan is the 16th Busiest Airport in the Nation Logan is the 24th Busiest Airport in the World Cargo Logan is the 19th Busiest Airport in the Nation Logan is the 60th Busiest Airport in the World Based on ACI Worldwide Traffic Rankings By Passenger, Cargo and Movements 2007 (Preliminary)
Present Passenger Loads Logan was Built to Handle a Peak of 50-60,000 Passengers per Day Logan Airport Averages: 77,000 Passengers/Day or 28.1 Million Passengers/Year
Background of Pavement Issues Prior to mid 1980s, pavements were rehabilitated for cracking and oxidation Starting late 1980s rutting began Volume of wide body aircraft Additives in the 1990s to stiffen the mix TLA, polymers, larger aggregate Late 1990s stripping began
Asphalt Stripping In recent polymer modified surface courses and underlying layers Pavement Consortium Stripping Test Protocol Rut and Strip Resistant HMA Lime Effective anti-strip agent Stiffens binder Slows aging process
Good Core
Bad Core
Really Bad Core
Screening - Accelerated Load Test Pavement Consortium Test to identify moisture susceptible mixes under traffic at high temperatures. Tensile Strength Ratio (TSR) Applies to freeze-thaw, not hot/wet conditions Equipment choice MMLS3 thru Worcester Polytechnic Institute (Model Mobile Load Simulator 3)
MMLS3 Massport Model Mobile Load Simulator - 3
MMLS Samples Model Mobile Load Simulator - 3 16
Current Everyday Mix ( November Mix ) P401 PG64-28 (Mass Highway Dept Binder) Styrene-butadiene-rubber (SBR at 4% of binder weight) Lime @ 1% of aggregate weight Recycled Asphalt Pavement (RAP @ 18%) PG76-28 equivalent
Other Products Densiphalt Rosphalt Citgoflex FR Stone Matrix Asphalt (SMA) Portland Cement Concrete (PCC) P401 w/ PG64-28, PG70-28, PG76-28
Logan International Airport - Alleyway B & C, 4 Densiphalt
Terminal B/C Alleyway
Rosphalt Used as wearing course on PCC bridge decks: Eliminates waterproofing On Tobin Bridge & Terminal E Upper Level Road Very expensive, $400/ton
Citigoflex Citgoflex FR used for special applications Very tough, fuel resistant First 400 of Runway 22L Terminal alleyways
Stone Matrix Asphalt (SMA) Stone on stone contact for resisting loads with high asphalt content for durability. Logan JMF added lime and fiber for resisting draindown, anti-stripping agent, & latex to lessen temperature susceptibility. Terminal D installation: Batched hotter than normal. Slight rutting initially, patch not cooled. Surface is very textured.
Sustainable Construction of Asphalt Pavements Recycled asphalt pavement (RAP) Asphalt shingles Glass Crumb rubber from old tires Warm Mix Asphalt (WMA)
What is WMA? Hot Mix Asphalt (HMA) with an additive and/or modification of the asphalt mixing process to lower the viscosity of asphalt binder Enables the production of asphalt mixes at a relatively lower temperature (Reductions of 50 to 100 degrees Fahrenheit have been documented) Used throughout Europe over the past decade
Types of WMA Technologies Logan Airport: Organic additives such as Sasobit, a Fischer-Tropsch paraffin wax and Asphaltan B, a low molecular weight esterified wax. Other Products: Synthetic zeolite called Aspha-Min (Advera) during mixing at the plant to create a foaming effect in the binder. WAM-Foam (Warm Asphalt Mix Foam), which introduces a soft binder and hard foamed binder at different stages during plant production. Asphalt emulsion product, Evotherm, which uses a chemical additive technology and a "dispersed asphalt technology" delivery system.
How Does WMA Work? Warm Mix Asphalt additives reduce the viscosity of asphalt binder at lower temperatures thus allowing production of mix and construction of asphalt pavements at relatively lower temperatures
Comparisons - HMA vs. WMA WMA is the combination of aggregates and liquid asphalt, just like HMA. WMA requires less heat to produce than HMA due to the incorporation of an additive to the mixing process. Hot Mix Asphalt - 275-325ºF Warm Mix Asphalt - 250-275ºF
Construction Benefits of WMA The construction season in many parts of the world which have colder climates in winter can be extended Offers the potential of recycling larger amounts of RAP materials Ability to haul paving mix for longer distances Ease of compaction during cooler temperatures Less wear and tear on plant equipment Thicker lift means quicker construction
Operational Benefits of WMA Lower production temperature means less oxidative aging Better compaction leads to better density and hence performance Lower batch temperatures means thicker lifts Consensus of European countries that WMA should provide equal or better performance than HMA Severely aged mixes are more susceptible to cracking The aging can be reduced significantly by lowering the mixing temperature
Environmental Benefits of WMA Reduced fuel consumption (10-55%) Decreasing emission (20-55%) visible and non-visible Reduced worker exposure; improved working conditions for crew
Cost Benefits of WMA Fuel at plant Crew time Increased production Thicker lifts Ease of compaction Reduced equipment operating time Reduced cooling time
WMA Research & Development Area Taxiway A
WMA Control Area Taxiway A
WMA Pavement Section Taxiway A -
WMA at Logan Airport Set-1: Virgin Mix, with Citgoflex PG 82-22 binder+1% Sasobit Set-2: 18.5% RAP Mix with Citgoflex PG 82-22+1% Sasobit Set-3: November Mix with PG 64-28+1% Hydrated Lime+4% Latex+1.5% Sasobit
Test Results Cores from all three sets show good results in the different tests Set 2 is the best of the three sets of mixes Set 2 cores are also found to have the lowest variability of in-place air voids in most cases
The Good, The Bad, The Ugly Environment Friendly; Reduces Carbon Footprint Costs Benefits Operational Benefits Used throughout Europe Great Upside Potential in US WMA meets FAA P-401 Specifications Possible Wave-of-the-Future?
WMA Research & Development Contributors Massport Stantec Worcester Polytechnic Institute (WPI) ATC Associates, Inc. Aggregate Industries, Inc.