Bituminous concrete is a type of construction material used for paving roads, driveways, and parking lots. It's made from a blend of stone and other forms of aggregate materials joined together by a binding agent. This binding agent is called "bitumen" and is a by-product of petroleum refining. It has a thick, sticky texture like tar when heated, then forms a dense solid surface once it dries. Bituminous concrete is also widely known as asphalt in many parts of the world.
Despite its name, this material is quite different than standard concrete, and contains no cement. While most cement-based surfaces are white or gray, bituminous concrete is known for its distinctive black appearance. It is often laid right over a gravel base layer to form new roads and parking lots, but may also be poured over existing concrete to repair or smooth out bumps and voids. Once the bituminous concrete has been poured onto the roadway, installers use large paving machines to smooth and compact the surface.
While asphalt paving doesn't offer the same strength as traditional concrete, it's still the most popular material for most paving applications. Bituminous concrete is strong enough to handle years of vehicle traffic, and is relatively easy to repair or refinish. It also provides a smoother and quieter ride than cement surfaces, which helps to reduce noise pollution around highways and other busy roads. Asphalt paving is also fully recyclable, though recycled products may not be as strong as raw materials. Some manufacturers add recycled tires or glass aggregate to recycled asphalt to increase its strength and resilience.
Many of the drawbacks associated with bituminous concrete concern its impact on the environment. The bituminous binding agents in asphalt are derived from fossil fuels. Not only are fossil fuels non-renewable and in limited supply, they also contribute to pollution in a number of ways. The process of deriving the fuels releases toxic fumes into the air, which contribute to poor air quality as well as global warming.
Asphalt also gives off a distinct smell during and after the paving process. This smell comes from the bituminous binding agents, which off-gas over time to release even more harmful fumes into the air. Rain and stormwater runoff may also cause pollutants from the concrete to wash off into area streams and waterways. Some of the negative environmental effects of bituminous concrete can be reduced by alternative paving techniques, including reducing the temperature of the hot asphalt before pouring.