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American Society of Landscape Architects


October 2006 Issue

Greening the Blacktop
Strategies for improving the environmental and health performance of asphalt paving.

By Meg Calkins, ASLA

Greening the Blacktop Budrovic

Conventional asphalt pavement, or asphalt concrete, is the most commonly used site and road construction material, used on 90 percent of new roads. It is inexpensive, flexible, easily placed without formwork, relatively long lasting, and durable. In addition, a wide range of surface finishes and overlays can be applied to fit any design setting and extend the pavement’s life cycle without removing the full paving section. However, asphalt pavement does pose some environmental and human health risks: the most serious from the asphalt binder during extraction and refining and, to a lesser degree, during manufacture and placement.

The human health effects of asphalt binders from mixing, heating, and placement stages are controversial, and there is much criticism of research methods used to determine quantities of fumes and emissions. Uncaptured emissions and fumes from heating asphalt binders can pose both mild and severe health impacts during plant mixing and placement of asphalt pavement, yet the degree of exposure and the severity of the impacts are still debated.

Emissions of hazardous air pollutants (HAPs) from asphalt processing and placement are also an environmental concern. However, the asphalt industry has made efforts to reduce these emissions, and in 2002, hot-mix asphalt (HMA) plants were removed from the Environmental Protection Agency’s list of “major” sources of hazardous air pollutants to be regulated.

In addition to health impacts, an environmental impact of hot-mix asphalt is the energy consumed in heating the asphalt binder and aggregates and keeping them hot during transport and placement.

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