A review of changes in composition of hot mix asphalt in the United States

Our plain-English summary of A review of changes in composition of hot mix asphalt in the United States, by D.J. Mundt, K.M. Marano, A.P. Nunes, et al (Journal of Occupational and Environmental Hygiene, 2009).

The study

• Authors: D.J. Mundt, K.M. Marano, A.P. Nunes, R.C. Adams
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2009;6(11):714-25
• Type of article: Historical article
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This review researched the materials, methods, and practices in the hot mix asphalt industry that might impact future exposure assessments and epidemiologic research on road paving workers. Since World War II, the U.S. interstate highway system, increased traffic volume, transportation speeds, and vehicle axle loads have necessitated an increase in demand for hot mix asphalt for road construction and maintenance, while requiring a consistent road paving product that meets state-specific physical performance specifications. We reviewed typical practices in hot mix asphalt paving in the United States to understand the extent to which materials are and have been added to hot mix asphalt to meet specifications and how changes in practices and technology could affect evaluation of worker exposures for future research. Historical documents were reviewed, and industry experts from 16 states were interviewed to obtain relevant information on industry practices. Participants from all states reported additive use, with most being less than 2% by weight. Crumb rubber and recycled asphalt pavement were added in concentrations approximately 10% per unit weight of the mix. The most frequently added materials included polymers and anti-stripping agents. Crumb rubber, sulfur, asbestos, roofing shingles, slag, or fly ash have been used in limited amounts for short periods of time or in limited geographic areas. No state reported using coal tar as an additive to hot mix asphalt or as a binder alternative in hot mix pavements for high-volume road construction. Coal tar may be present in recycled asphalt pavement from historical use, which would need to be considered in future exposure assessments of pavers. Changes in hot mix asphalt production and laydown emission control equipment have been universally implemented over time as the technology has become available to reduce potential worker exposures. This work is a companion review to a study undertaken in the petroleum refining sector that investigated current and historical use of additives in producing petroleum-derived asphalt cements.

In plain English

This review examined materials added to U.S. hot mix road-paving asphalt, to inform future studies of paving workers' exposures. The authors reviewed historical documents and interviewed industry experts from 16 states. The work began in June 2005 and data collection ended in June 2006; survey answers mainly reflected practices from the 1970s on. Participants from all states reported additives, mostly under 2% by weight. No state reported using asbestos in hot mix asphalt for mainline road paving. Eight states reported infrequent, low-volume use, from the 1940s to the 1970s. Where specified, most asbestos use was for small, non-mainline jobs such as curbing and crack sealant. Participants gave no figures for the amount of asbestos in the mix. The authors concluded that asbestos and several other additives were used in limited amounts, periods or places. They wrote that potential current worker exposure would be limited to activities surrounding removal of such pavement, and that exposure to recycled pavement containing asbestos may need consideration in future research. They noted the survey was not tested for reliability and the study could not address personal exposures.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Review of historical documents combined with an interview-based survey of industry experts
• Who was studied: Hot mix asphalt industry practices in 16 U.S. states (Arizona, California, Florida, Indiana, Iowa, Kansas, Kentucky, Maryland, Minnesota, New York, Ohio, Pennsylvania, Texas, Utah, Virginia, Washington). Per Table II, participants were 20 state transportation department representatives, 9 state asphalt paving association representatives, 18 contractors and 3 independent consultants. Representatives of three equipment manufacturers were also interviewed. The work began in June 2005, and data collection was completed in June 2006.
• Exposure: Materials added to hot mix asphalt at the mixing plant. Ten were of primary interest: coal tar, asbestos, sulfur, anti-strip agents, crumb rubber, fly ash, roofing shingles, slag, polymers and reclaimed asphalt pavement. The article does not name an asbestos fiber type.
• Main results:
  • Participants from all states reported additive use, most at less than 2% by weight.
  • No state reported current or historical use of asbestos in hot mix asphalt for mainline road paving.
  • Eight states reported infrequent low-volume asbestos use. The earliest reported use was in the 1940s and the most recent in the 1970s.
  • Survey participants gave no quantitative information on the amount of asbestos in the mix.
  • In most cases where the application was specified, asbestos use was for specific, non-mainline, small-area paving applications, including curbing and as crack sealant.
  • A historical source cited in the document review reported asbestos use for the 1962 paving season: 1000 tons of asbestos fiber in 50,000 tons of hot mix asphalt, in the United States and Canada.
  • The authors noted possible exposure to recycled pavement containing coal tar or asbestos, which may need to be considered in future research.
  • No state reported adding coal tar to the asphalt binder or to hot mix asphalt.
  • All states used recycled asphalt pavement in hot mix asphalt.
  • Crumb rubber, sulfur, asbestos, roofing shingles, slag and fly ash were used in limited amounts, for short periods or in limited geographic areas.
  • Participants reported that the most significant change in laydown practice was the addition of emission capture hoods and taller exhaust stacks on pavers.
• The authors' conclusion: The authors concluded that asbestos use was limited in time and location. They concluded that the potential for current worker exposure would be limited to activities surrounding removal of such pavement from old roads. They also noted that exposure to recycled pavement containing asbestos may need consideration in future research.
• Limitations the authors state:
  • The survey was not tested for reliability.
  • Responses about practices before the 1970s were limited.
  • Survey responses tended to be qualitative rather than quantitative.
  • As a historical review, the study cannot address personal exposures of pavers.
  • Measurement of fumes was outside the scope of the study.

Related studies

• Simulation tests to assess occupational exposure to airborne asbestos from artificially weathered asphalt-based roofing products — P. Sheehan, F. Mowat, et al. (2010)
• Estimating exposures in the asphalt industry for an international epidemiological cohort study of cancer risk — I. Burstyn, P. Boffetta, et al. (2003)
• A case-control study of lung cancer nested in a cohort of European asphalt workers — A. Olsson, H. Kromhout, et al. (2010)
• A case-control study of asphalt and tar exposure and lung cancer in minorities — M.D. McClean, K.T. Kelsey, et al. (2011)
• Historical ambient airborne asbestos concentrations in the United States - an analysis of published and unpublished literature (1960s-2000s) — A. Abelmann, M.E. Glynn, et al. (2015)
• Changes in B-readings over time in the United States Navy Asbestos Medical Surveillance Program — J.G. Muller, W.G. Rudolph, et al. (2007)

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