An Asphalt Plant in Your Community?
What’s going on here?
Glad you asked. More than 94 percent of the nation’s 2 million miles of paved streets and highways are surfaced with asphalt. That’s because state and federal highway departments have long known that asphalt pavements are smooth, cost-effective to construct and maintain, exceptionally durable, environmentally friendly, and 100 percent recyclable.
Actually, the asphalt pavement industry usually speaks of asphalt facilities, not asphalt plants — because these are mixing facilities. Around the country, asphalt facilities are placed next to homes, businesses, golf courses, and farms. Chances are good that there has been an asphalt facility not far from you for years, and you didn’t even know it was there.
By the way, you may think we’re nitpicking, but asphalt “plant” (the most commonly used term) is misleading in that it implies the production of petroleum asphalt itself, which implies an oil refinery.
So what exactly is asphalt?
What most people mean when they say “asphalt” — also known as blacktop, macadam, or tarmac — is actually a particular product, known in our industry as asphalt pavement. Engineers might refer to it as asphalt concrete, and it is sometimes specified as hot-mix asphalt (HMA) pavement.
It sounds complicated
It’s really pretty simple. There are two basic ingredients in an asphalt pavement. The first is aggregates (crushed stone, gravel, and sand). The aggregates used are almost always locally available stone. About 95 percent of the total weight of an asphalt pavement consists of aggregates.
The remaining 5 percent is asphalt cement, the black liquid that acts as the glue to hold the pavement together. Asphalt cement (AC), sometimes called binder or bitumen, is a petroleum product generally obtained from the same refineries that produce gasoline for your car and heating oil for your house. Asphalt cement is one of the heaviest, most viscous parts of petroleum, and it is processed to meet certain standards for different types of pavements.
Some mixes also require small amounts of additives, which can range from chemicals that improve mix performance to natural fibers that strength specialty mixes. The use and storage of these materials is carefully monitored and regulated.
Mix the ingredients together, and you get asphalt paving mix.
So, that’s all that happens at an asphalt facility?
Basically, yes. The paving aggregates are dried and heated, then mixed and coated with asphalt cement. The resulting asphalt pavement mix is put in silos for short-term storage, then trucked to the paving site.
Why do we need an asphalt facility in my community?
Asphalt pavement mixtures are usually mixed at temperatures between 300°F and 325°F — cooler than what you’d use to bake a pie. And it has to be laid hot, no less than about 250°F. Getting HMA from the facility to the paving site is like delivering a pizza. The farther you have to carry it, the cooler it gets. If it gets too cool, it is no longer useful for paving. The industry is also adopting "warm-mix" technologies that allow asphalt paving mixes to be created and used at lower temperatures without sacrificing quality.
I’m concerned about the health risks.
If you visit an asphalt mixing facility, you’ll see that the people working there wear typical construction clothes such as hard hats, gloves, and long-sleeved shirts. The greatest risk is from getting burned. What you won’t see is anybody wearing a respirator. There is no evidence that the very low levels of emissions from an asphalt mixing facility pose health risks to humans.
But don’t you have to keep hazardous chemicals on site?
Liquids that must be handled with care at an asphalt facility are: 1) fuel oil for the burner, which is the same kind of fuel oil you may be using to heat your home; 2) fuel for vehicles, which the same product you buy at the gas station; and 3) at some facilities, solvents for the quality control lab. These solvents are used in small quantities with great care, and new lab procedures are quickly making solvents obsolete.
By federal law, an asphalt facility must keep these products, including the fuel oil, either in underground tanks that meet strict EPA standards, or in above-ground tanks surrounded by berms that would hold ALL the contents in the event of a spill.
What happens if there is a spill or leak?
Asphalt cement starts to harden the moment it cools. Unless it’s 250°F outside, it simply cannot travel over the ground more than a few feet. It will not penetrate the soil more than an inch or two before solidifying. Asphalt cement does not mix with, or become soluble, in water.
What about the environment?
More than 30 years ago, asphalt mixing facilities often generated noticeable levels of dust, smoke, odors, and noise. But two things have brought big changes. One was the EPA’s New Source Performance Standards, which went into effect in 1973. These required asphalt mix producers to pass strict emission standards and install control systems to prevent the release of dust and smoke into the air. A facility must also meet stringent “visible emissions” tests in order to comply with regulations. EPA now acknowledges that asphalt mixing facilities are not a major source of emissions.
An even stronger incentive for clean operation is economic. It’s in the owner’s best interest to make sure that all the equipment is operating at peak efficiency — which means producing very little in the way of emissions.
Hot Mix Asphalt producers want to be good neighbors. They strive to build clean, quiet facilities compatible with the rest of the neighborhood.
It sounds like this would be okay.
You’re right. When people get the facts about modern asphalt facilities, they understand the need for having one community. And they appreciate their critical role in building and maintaining the nation’s infrastructure.
For more information on the environmental impact of asphalt facilities, download our guide, “The Environmental Impact of Asphalt Plants.”