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Code of Practice for the Reduction of VOC Emissions from the Use of Cutback and Emulsified Asphalt

1 Preface

1.1 Background

Canada has approximately 1 million kilometres of roads and highways, of which just under half are paved.Footnote1 With more than 20 million road vehicles registered in Canada, the transportation system also includes large areas of parking lots and private driveways. Asphalt is the material of choice for road and parking lot pavement. It is used for construction, maintenance and repairs. With such a large paved surface across Canada, the asphalt sector (manufacturing, distribution, supply and use) is an important industry sector in Canada.

Emulsified asphalt (EA) and cutback asphalt (CA) are used for various applications associated with road construction, maintenance and repairs. Examples include:

  • Plant mix (open-graded, dense-graded, sand);
  • Road mix (mixed in place), including mining with open- and dense-graded aggregate, sand, sandy soil;
  • Surface treatment, including fog, sand, chip, sandwich, and slurry seals, micro-surfacing and cape seal;
  • Asphalt applications including prime and tack coat, dust palliative, crack filler;
  • Maintenance mix;
  • Cold in-place recycling; and
  • Full-depth reclamation.

In preparing these products, asphalt cement is mixed with either a petroleum diluent to produce CA or with emulsifiers, water and sometimes a small quantity of petroleum diluent to produce EA. Once the liquefied asphalt cement is applied to the surface of the road, the diluent (petroleum solvent in the case of asphalt cutbacks and primarily water in the case of asphalt emulsions) evaporates, leaving the residual asphalt cement to perform its function.

The application of asphalt causes emissions of volatile organic compounds (VOC) through the evaporation process described above and contributes to the creation of ground-level ozone and particulate matter, which are major components of smog.

In 2013, some jurisdictions in Canada and 30 jurisdictions in the United States have adopted practices to control the level of VOC emissions from this sector. All of the jurisdictions include restrictions of CA during the ozone season, which is typically the summer months, while many of the jurisdictions also include restrictions of VOC content in both EA and/or CA product manufacturing.  Some jurisdictions also prohibit CA throughout the year.

1.2 Asphalt use in Canada and VOC emissions

The level of VOC emissions depends on a number of factors, including the type of asphalt used and the ambient temperature. New formulations of asphalt using bio-products instead of petroleum solvents are being developed and are becoming more available. The hardening of this type of asphalt is done through polymerization of the bio-diluent rather than through evaporation, thereby eliminating VOC emissions.

The majority of asphalt used in Canada is the EA type. Based on a study conducted for Environment Canada in 2010, 301 kilotonnes (kt) of liquefied asphalt were used in Canada in 2009, 85% of which was EA while 15% was CA.Footnote2 The total VOC emissions associated with this usage are estimated to be 8.8 kt (5.2 kt for CA and 3.6 kt for EA). While CA represented only 15% of asphalt use in Canada in 2009, it was responsible for 59% of the VOC emissions associated with the use of asphalt. The same study estimated that VOC emissions from asphalt could reach 10.8 kt in 2020 in the absence of an environmental framework to guide the use of asphalt in Canada.

Footnotes

Footnote 1

U.S. Central Intelligence Agency (2008).  The World Factbook, accessed March 2013.

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Footnote 2

Environmental Health Strategies Inc. Technical and Economic Study on VOC (Volatile Organic Compound) Emissions from Emulsified and Cutback Asphalt Use in Canada. October 2010. Prepared for Environment Canada.

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