Dust Control on County Roads

1. 1 Dust Control on County Roads George Huntington, PE University of Wyoming http://wwweng.uwyo.edu/wyt2/ georgeh@uwyo.edu (307) 766-6783 • 53rd Annual County Judges and Commissioners’ Continuing Education Conference and Educational Exposition Conference • Austin, Texas • February 16, 2011 “Onecar making onepass on onemile of dirt or gravel road oncea day for oneyear creates onetonof dust.” Why is road dust a problem? Air Quality Human Health Crops and Livestock Equipment Visibility Aggregate Loss Ride roughness Increased maintenance costs Consequences of losing dust: Shape and Materials: Goals Shed water Carry loads Limit dust Aggregate lost Washboards Potholes Fly Rock Broken windshields Money Lost Drainage & Safety

2. 2 Dust Control on County Roads Plasticity Ideal Surfacing Aggregate: Stickiness Binding capacity Carries loads without rutting or slipperiness when wet Holds together when dry Plasticity Index = Liquid Limit – Plastic Limit Flowable Liquid Limit Plastic Plastic Limit 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. 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. Semi-Solid Aggregate Angularity 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. A flattened crown causes potholes, increased maintenance, and, therefore, increased dust. A worn cutting edge may cause a flattened crown.

3. Dust Control on County Roads 3 Sample Driving Surface Aggregate Specifications Dust Control: Step 1 • Good quality aggregate • Strong • Binds together • Performs well when wet and when dry Step 2 • Don’t break up the crust • Don’t over-maintain Australian Criteria ¤ <20” annual rainfall § >20” annual rainfall 300 < PI*[% passing #40] < 400 To avoid lack of strength due to high fines and plasticity Step 3 • Dust suppressants • Soil stabilizers

4. 4 Dust Control on County Roads Liquid/Brine Application Topical Shallow Dust Control Solid/Flakes/Pellets Application Blended Deeper Stabilization • Shape and dampen the road • Scarify or Windrow • Add product • Blend • Reshape • Compact • 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 Performance Less More Maintenance • Less distress • Loose aggregate • Dust • Washboards • Potholes • More distress • Slippery • Ruts Issues • Leaching and Durability • Appropriate Application • Surfacing materials • Climate • Traffic • Timing • Costs • Application rates • Application frequency • Ease of application • Environmental impacts • MSDS (Material Safety Data Sheets) • Negligible industry regulation Finances • 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

5. Dust Control on County Roads 5 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

6. 6 Dust Control on County Roads References 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