Dust Control on County Roads 1 53 rd Annual County Judges and Commissioners’ Continuing Education Conference and Educational Exposition Conference Austin, Texas February 16, 2011 George Huntington, PE University of Wyoming (307) 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 lost Washboards Potholes Fly Rock Broken windshields Money Lost Drainage & Safety Shape and Materials: Goals Shed water Carry loads Limit dust

2 Dust Control on County Roads Plasticity Stickiness Binding 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 wet Holds together when dry Aggregate Angularity 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.

3 Dust 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] < 400 To avoid lack of strength due to high fines and plasticity Dust Suppressants MaterialsApplicationMaintenancePerformanceFinances

4 Dust Control on County Roads 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 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 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

5 Dust 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 MgCl 2 – Magnesium Chloride, Mag Chloride, Mag Water CaCl 2 – 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. MgCl 2 and CaCl 2 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, Dust Palliative Selection and Application Guide, USDA Forest Service, Dust Control for Unpaved Roads, Canada, Dust Scan Report, 2011 (planned), Western Transportation Institute, Montana State University Controlling Highway Related Dust, Iowa DOT and Iowa State University, Control of Dust Emissions from Unpaved Roads, University of Alaska – Fairbanks, Cost Effectiveness of Dust Control, Alaska DOT, Laboratory Study of Dust Palliatives, Texas A&M University, &idtype=cvips Eco-Road Building for Emerging Economies: An Initial Scan for Promising Alternative Technologies, global Transport Knowledge Partnership, 2008, accessed May 11, 2010 USEPA National Emissions Inventory Booklet, US Roads: Road Management and Engineering Journal, Dust: Don’t Eat It, Control It, Dust Control on County Roads References