An Asphalt Plant in Your Community?
More than 94 percent of the nation’s two million miles of streets and highways are paved 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, or sometimes, Hot Mix Asphalt (HMA) pavement.
There are two basic ingredients in Hot Mix Asphalt. 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 five percent is Asphalt Cement, the black liquid that acts as the glue to hold the pavement together.
Asphalt Cement (AC) 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. Mix the two ingredients together, and you get Hot Mix Asphalt.
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 Hot Mix Asphalt is put in silos for short-term storage, then trucked to the paving site.
Why do we need an asphalt facility in my community?
Hot Mix Asphalt is usually mixed at temperatures between 300 and 325 degrees-cooler than what you’d use to bake a pie. And it has to be laid hot, no less than about 250 degrees. 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.
Health risk concerns?
If you visit an HMA 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 HMA 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 a Hot Mix 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 is 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, a Hot Mix 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 degrees Fahrenheit 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, Hot Mix Asphalt 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 HMA 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 HMA 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.
When people get the facts about modern HMA facilities, they understand the need for having one in their community. And they appreciate their critical role in building and maintaining the nation’s infrastructure.