The smell of a freshly paved road comes from a construction process that begins long before asphalt reaches the street. At hot-mix asphalt plants, stone aggregate is heated and combined with asphalt binder before the mixture is loaded into trucks and transported to paving crews. Along the way, heating, material handling, diesel equipment, and paving operations can all affect the surrounding air.
Road paving takes place outdoors, but that does not automatically prevent workers from encountering concentrated pollutants. People standing close to hot asphalt, engines, or dusty equipment can experience much higher concentrations than someone farther away, even when the surrounding atmosphere appears open and well ventilated.
Heating Asphalt Creates Fumes and Aerosols
Asphalt binder is a petroleum-based material that must be heated so it can coat aggregate and remain workable during paving. Heating releases a complex mixture of vapors, while some of those vapors cool and condense into very small airborne particles known as fumes or aerosols.
Workers exposed to asphalt fumes may experience irritation of the eyes, nose, throat, and respiratory system, along with symptoms such as headaches. The exact mixture in the air can change with asphalt composition, temperature, work practices, and the equipment being used, which makes controlling the source especially important.
Air Quality Starts at the Asphalt Plant
A hot-mix asphalt plant handles large amounts of crushed stone before paving material ever reaches a road. Aggregate must be stored, moved, dried, heated, and mixed, and these activities can create particulate matter from stockpiles, conveyors, transfer points, dryers, and truck traffic.
The plant also uses fuel to heat and dry the aggregate. Combustion can produce carbon monoxide, nitrogen oxides, and other gases, while the heated asphalt can release volatile organic compounds and fine organic aerosols during mixing, storage, and truck loading.
Dust collectors and other emission-control systems are commonly used to capture particles from plant equipment. Controlling material transfer points and maintaining the plant’s ventilation and collection systems can reduce both visible dust and much smaller particles.
Recycled Pavement Returns to the Process
Old pavement does not always become waste when a road is replaced. Reclaimed asphalt pavement, often called RAP, can be milled from existing roads, processed, and incorporated into new asphalt mixtures.
RAP is commonly crushed and screened before reuse, which means recycling introduces its own material-handling and dust-control needs. The recycled material can then replace part of the new aggregate and asphalt binder required for another pavement mixture, allowing old roadway material to become part of a new road.
Recycling changes where some emissions occur rather than eliminating air-quality concerns completely. Crushing, screening, transporting, reheating, and mixing reclaimed pavement all involve processes where dust or other emissions may need to be controlled.
The Paver Creates a Local Exposure Zone
At the road, hot asphalt is delivered into the front of a paving machine and carried toward the rear. Augers spread the material across the roadway, while the screed levels and partially compacts the hot mixture into a smooth layer.
Workers stationed around the rear of the paver may spend much of their shift close to hot material. Asphalt fumes released near the auger and screed can therefore enter a worker’s breathing zone before outdoor air has enough distance to disperse them.
Wind can help dilute emissions, but it can also push them toward workers depending on direction and speed. Outdoor work should therefore not be treated as if unlimited ventilation automatically exists wherever the worker is standing.
Pavers Can Capture Fumes at the Source
NIOSH worked with equipment manufacturers, labor groups, and the paving industry to develop engineering controls for hot-mix asphalt pavers. These systems use exhaust ventilation near the auger and screed area to capture fumes close to where hot asphalt is being distributed.
Source capture follows the same principle used in laboratories and industrial facilities. Removing contaminants before they spread through the surrounding air is generally more effective than relying entirely on dilution after the emissions have already reached workers.
The performance of these systems depends on maintenance and airflow. Damaged ducts, malfunctioning fans, blocked openings, or poorly maintained equipment can reduce how effectively the system captures fumes.
Diesel Equipment Adds Another Pollutant Source
Paving operations involve much more than the asphalt itself. Haul trucks, rollers, milling machines, loaders, and other diesel-powered equipment may operate near workers for hours at a time.
Diesel exhaust contains gases and fine particulate matter, adding another air-quality concern to the paving environment. Workers near idling trucks or equipment may therefore encounter a combination of asphalt emissions and engine exhaust rather than a single pollutant source.
Reducing unnecessary idling and maintaining engines can help limit these emissions. Equipment placement also matters because an exhaust pipe positioned close to a work area can create a localized exposure even on a wide-open roadway.
Air Quality Does Not Stop at the Building Wall
Asphalt paving illustrates an important point about air pollution: being outdoors does not mean every contaminant immediately disappears. The distance between a worker and a source can matter greatly, particularly when hot material or an engine is producing pollutants only a few feet away.
From aggregate dust at the plant to fumes around the screed and diesel exhaust on the roadway, paving creates several different air-quality environments during a single construction process. Engineering controls, dust collection, equipment maintenance, source capture, and good work practices help keep the air above a newly paved road from becoming another occupational hazard.
