Dust Control on County Roads1
53rd Annual County Judges and Commissioners’ Continuing
Education Conference and Educational Exposition
Conference
Austin, Texas
February 16, 2011
George Huntington, PEUniversity of Wyominghttp://wwweng.uwyo.edu/wyt2/[email protected](307) 766-6783
Why is road dust a problem? Air Quality Human Health Crops and Livestock Equipment Visibility Aggregate Loss Ride roughness Increased maintenance costs
“One car making one pass on one mile of dirt or gravel road once a day for one year creates one ton of dust.”
Consequences of losing dust:Aggregate lostWashboardsPotholesFly Rock Broken windshieldsMoney Lost
Drainage & Safety
Shape and Materials: GoalsShed waterCarry loadsLimit dust
2 Dust Control on County Roads
PlasticityStickinessBinding capacity
Plasticity Index = Liquid Limit – Plastic Limit
Liquid Limit
Plastic Limit
Flowable
Plastic
Semi-Solid
Without enough plasticity, roads are vulnerable to raveling, washboards, and dust loss since a good crust is not formed. With too much plasticity, a road may become slippery and develop ruts when it is wet. The overall crust-forming capacity and rutting vulnerability of a road is a function of both the plasticity of the fines – the material passing a #200 screen – and the amount of fines in the aggregate.
A well graded surfacing material produces less dust by carrying loads, shedding water and preventing raveling. Its tight matrix provides plenty of rock-on-rock contact to carry traffic loads; its tightly packed structure prevents water infiltration; and the presence of fines holds the aggregate together while the coarser material carrying the loads protects the fines from raveling and creating dust.
Ideal Surfacing Aggregate:Carries loads without rutting or slipperiness when wetHolds together when dry
Aggregate Angularity
Rounded• Low strength• Poor aggregate interlock• Pit run• Screened
Angular• High strength• Good aggregate interlock• Scalped and crushed• Quarried
A flattened crown causes potholes, increased maintenance, and, therefore, increased dust. A worn cutting edge may cause a flattened crown.
A consistent 4% crown sheds water from the entire surface, reducing trapped water, thereby reducing ruts and potholes which decreases dust by decreasing the need for maintenance.
3Dust Control on County Roads
Step 2• Don’t break up the crust• Don’t over-maintain
Step 3• Dust suppressants• Soil stabilizers
Step 1• Good quality aggregate
– Strong– Binds together– Performs well when wet and
when dry
Dust Control:
Sample Driving Surface Aggregate Specifications
Australian Criteria ¤ <20” annual rainfall
§ >20” annual rainfall
300 < PI*[% passing #40] < 400To avoid lack of strength due to high fines and plasticity
Agency Min Max Min Max
Utah LTAP 15 25 6 1512 188 12 4 12
New Zealand 10 20 8 12Pennsylvania Center for Dirt
and Gravel Road Studies 10 20
New York State DOT 8 15 2 9Louisiana DOTD 3 15
<12 §
Passing #200 Plasticity Index
100% crushed, no added clay or silt
<4USDA Forest Service - Montana
<4
Australia 10 40<20 ¤
Dust Suppressants
Materials
Application
MaintenancePerformance
Finances
4 Dust Control on County Roads
Leaching and Durability
Appropriate ApplicationSurfacing materials
Climate
Traffic
Timing
CostsApplication rates
Application frequency
Ease of application
Environmental impactsMSDS (Material Safety Data Sheets)
Negligible industry regulation
Issues
Charge residents
Agree to pay only if it works
Application frequency and rates
Save on maintenance
Blading/Smoothing
Reshaping/pulling shoulders
Regravel
Drainage
Public image
Finances
Less distress
Loose aggregate
Dust
Washboards
Potholes
More distress
Slippery
Ruts
Performance Asphalt Treated Aggregate
Untreated Aggregate
Maintenance MoreLess
• Shape the road– Crown
• Dampen the road– Natural or Added– Better penetration
• Apply the liquid– Not so much that it runs off– May want more than one application
• Compact
Liquid/Brine Application Topical Shallow Dust Control
• Shape and dampen the road• Scarify or Windrow• Add product• Blend• Reshape• Compact
Solid/Flakes/Pellets Application Blended Deeper Stabilization
5Dust Control on County Roads
Materials: Dust Control and Stabilization(for more information, see the USDA Forest Service publication Dust Palliative Selection and Application Guide)
• There is no ‘silver bullet’• Often by-products of manufacturing processes
Hygroscopic Salts: Available as brine, pellets, flakes MgCl2 – Magnesium Chloride, Mag Chloride, Mag Water CaCl2 – Calcium Chloride NaCl – Sodium Chloride, table salt These salts modify the chemical properties of aggregates, particularly fines, helping them absorb and retain water, much as table salt does in humid climates. NaCl is not effective in dry climates since it does not absorb water at less than 79% relative humidity. MgCl2 and CaCl2
continue to absorb water down to about 30% relative humidity, though they, too, may dry out when humidity gets very low, leading to dust problems.
Natural Polymers Physically bond or glue particles together. May or may not re-bond after maintenance. Lignin sulfonate Tall oils Vegetable oils
Petroleum Resins Similar to natural polymers
Clay Only in dry climates when sufficient binder is not present. If over-applied, may get very slippery and cause severe rutting when wet.
Asphalt Including emulsions, cutbacks and conventional asphalt. May set up and be impossible to maintain if over-applied. Reclaimed asphalt pavement (RAP) blended about 50%/50% with virgin aggregate helps keep dust down.
Enzymes and Biological Agents Produce glue-like substances that hold particles together.
Motor Oil Used motor oil is a hazardous material and must not be used on roads.
Proprietary Products
Blends…and Many More
Gravel Roads Maintenance and Design Manual, South Dakota Local Technical Assistance Program, 2000
http://www.epa.gov/owow/NPS/gravelroads/intro.pdf
Dust Palliative Selection and Application Guide, USDA Forest Service, 1999
http://www.ecy.wa.gov/programs/air/pdfs/Dust_Palliative.pdf
Dust Control for Unpaved Roads, Canada, 2005
http://gmf.fcm.ca/files/Infraguide/Roads_and_Sidewalks/dust_control_unpaved_rd.pdf
Dust Scan Report, 2011 (planned), Western Transportation Institute, Montana State University
http://www.roaddustinstitute.org/
Controlling Highway Related Dust, Iowa DOT and Iowa State University, 2005
http://publications.iowa.gov/archive/00002804/01/tr506.pdf
Control of Dust Emissions from Unpaved Roads, University of Alaska – Fairbanks, 1992
http://www.dot.state.ak.us/stwddes/research/assets/pdf/fhwa_ak_rd_92_05.pdf
Cost Effectiveness of Dust Control, Alaska DOT, 1988
http://www.dot.state.ak.us/stwddes/research/assets/pdf/ak_rd_88_07.pdf
Laboratory Study of Dust Palliatives, Texas A&M University, 2002
http://ascelibrary.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=JMCEE7000014000005000427000001&idtype=cvips
Eco-Road Building for Emerging Economies: An Initial Scan for Promising Alternative Technologies, global Transport Knowledge Partnership, 2008,
http://www.gtkp.com/uploads/20100506-122335-3531-gtkp_report02_final.pdf, accessed May 11, 2010
USEPA National Emissions Inventory Booklet, 2002
http://www.epa.gov/ttn/chief/net/2002neibooklet.pdf
US Roads: Road Management and Engineering Journal, Dust: Don’t Eat It, Control It, 1998
http://www.usroads.com/journals/rmej/9806/rm980603.htm
6 Dust Control on County Roads
References