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/georgeh@uwyo.edu(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