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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 Historical documents were reviewed, and industry experts from 16 states were interviewed to obtain relevant information on industry practices.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. [ABSTRACT FROM AUTHOR]

Asphalt has been widely used as the primary bound road construction material, both as road base material and wearing course. Polycyclic aromatic hydrocarbons (PAHs) have commonly been observed in soils near and under roads. However, the contribution from PAH leaching from asphalt to the actual contamination of the soil adjoined to the road has been poorly described. Leaching of the 16 U.S. EPA PAHs from bitumen-based asphalt was investigated for four asphalt specimens and modeled for general road constructions scenarios. The total content of PAHs in the asphalt specimens was for three of four asphalt specimens below the Danish soil quality criteria. The availability of the sum of the 16 U.S. EPA PAHs was found to be in the range 3–11% of the total content. The experiments involved a 64-day tank leaching test based on the Dutch NEN 7345 standard and a new column-based availability test corresponding to a liquid-to-solid ratio of 100 L kg−1. The tank leaching test indicated that leaching of PAHs was diffusion controlled, although our experiment statistically could document this for only 7 of the 16 U.S. EPA PAHs. Overall, the effective diffusion coefficients for all specimens were within a factor of 100 (one exception) showing no correlation with the number of rings in the PAHs. This suggests that for practical purposes it might be acceptable to use one single diffusion coefficient for all PAHs in asphalt. Scenario calculations indicated that only a minor part of the PAHs present in the asphalt is leached out during 25 years of leaching (0.004–1.1% for five PAHs) corresponding to only of 0.5 mg m−2 of surface in contact with water. Concentrations of PAHs that are found above the Danish soil quality criteria near roads paved with bitumen-based asphalt in Denmark are very unlikely to be caused by leaching of PAHs from the asphalt. [ABSTRACT FROM AUTHOR]

Traces the introduction of asphalt paving in urban U.S. in the 1800s. Development of stone-crushing machinery for paveway construction; Structural component of asphalt material; Impact of the demand on the discovery of asphalt sources.

Polymer-modified asphalts are used in Alaska to address problems with rutting, cracking, and premature aging. This usage raises two important issues—the improvement of the pavement performance with polymer modification while maintaining the ability to properly place and compact polymer-modified mixes. This study addresses both issues. Base asphalts and polymer-modified binders were analyzed for storage stability, compatibility, and consistency using traditional and Superpave tests. Thermal stress restrained specimen tests and Georgia wheel rutting tests were conducted for asphalt-aggregate mixtures. The test results indicate that polymer-modified asphalts should always be an end result of an extensive product development program. The premanufactured binders had the best performance and workability. The polymer modification improved the performance of all base asphalts in several polymer-asphalt combinations. Some binders smoked excessively during mixing, which warrants further research. A storage stability test should be added to specifications or the contractor should address the storage stability with techniques such as tank circulation. On the basis of the test results, the Superpave PG grading needs to be adjusted for polymer-modified asphalts. [ABSTRACT FROM AUTHOR]

The U.S. asphalt paving industry, which includes both the refining and hot mix sectors, has evolved over time to meet various performance specifications for asphalt (known as bitumen outside the United States). Additives to asphalt produced in the refinery, as well as changes in temperatures, equipment used, and materials added in the hot mix asphalt process - which are likely to vary by state - may affect exposures to workers in the asphalt paving industry. The purpose of this investigation was to document the changes in the refining, manufacturing, and hot mix of paving asphalt in the United States since World War II. The approach taken for the investigation of both the refining and hot mix sectors was similar. Historical documents, as available, were reviewed and individual experts in each industry sector were interviewed to identify current and historic practices. In general, of the refining facilities surveyed, the number reporting use of any material within a particular class ranged from none to more than half the respondents. Sixteen states were included in the review of the hot mix sector. All states reported addition of materials to hot mix asphalt currently or historically, but concentrations were generally small (less than 10% per unit weight of asphalt). Changes to paving asphalt in the United States over the past 50 years appear to have occurred, but are generally not consistent by geography or over time. Modifications that have been made to asphalt were to improve performance, and were dictated by state specifications. [ABSTRACT FROM AUTHOR]