Asphalt is the black, sticky binder refined from crude oil, and it's also the everyday name for the pavement made with it. In the U.S., the binder is often called asphalt cement; much of the world calls it bitumen. When it's heated and mixed with crushed stone and sand, it becomes asphalt concrete (the hot or warm mix that paves roads, parking lots, and driveways). In this article, "binder" means the refinery product and "asphalt mix" or "pavement" means the finished material. It's flexible, water-resistant, quick to install, and recyclable, which is why it remains the most common paving material in Connecticut and across the country.
Composition of Asphalt
Paving mixtures combine aggregate, including fine mineral material, with asphalt binder. Proportions and production methods vary with the specified mix, but as a rough introductory guide:
- Aggregates: Crushed stone, gravel, sand, and fine mineral filler make up roughly 95% of a typical mix by weight.
- Binder: Asphalt cement (bitumen), roughly 5% by weight, coats the aggregate and glues it together.
- Additives: Some mixes also include polymers, anti-strip agents, or warm-mix additives to improve performance or workability.
How Asphalt Is Made
Refining
Asphalt binder is what's left after crude oil is distilled at a refinery and the lighter fuels are removed. Because it's a refinery product, binder prices follow crude oil and refinery supply. ConnDOT publishes the binder price it uses for contract price adjustments on its material price adjustments page.
Heating
At the asphalt plant, binder is stored hot so it flows, and aggregates are dried and heated in a drum. Warm-mix production uses lower temperatures than traditional hot mix.
Mixing
Heated binder and aggregate are combined in precise proportions. The recipe, or mix design, depends on the intended use, from thick base courses on highways to finer surface mixes for driveways.
Transporting
The finished mix is loaded into dump trucks, usually tarped to hold heat, and hauled to the job site.
Laying
A paving machine spreads the mix over a prepared base designed for the site and its expected loads, and rollers compact it to the right density. Good asphalt compaction is one of the biggest factors in how long pavement lasts.
Cooling and Hardening
As the asphalt cools, it stiffens into a durable surface. When it's ready for traffic depends on the weather, the thickness, and the loads involved, and the binder continues to age over time; your crew will give you reopening guidance for your site.
Types of Asphalt
- Hot Mix Asphalt (HMA): Produced at high temperatures, often around 300°F depending on the mix, and widely used for roads, parking lots, and driveways.
- Warm Mix Asphalt (WMA): Made with warm-mix technologies, additives or foaming processes that allow production at lower temperatures, which can reduce fuel use and fumes at the plant and on the job.
- Cold Mix Asphalt: Used mainly for patching, especially in winter when hot-mix plants are closed. Conventional cold patch is usually a temporary repair, though some specialty cold-applied products are sold for permanent repairs when their instructions are followed. You can read more in the difference between hot mix and cold mix asphalt.
Applications of Asphalt
- Road construction: Highways, local streets, and bridges.
- Driveways and parking lots: An economical, long-lasting surface for homes and businesses.
- Roofing: Asphalt shingles and roll roofing.
- Paths and recreation: Walking and bike paths, playgrounds, and other recreational surfaces.
Benefits of Asphalt
- Durability: A flexible pavement that handles traffic well when properly designed and built. (Concrete can also serve driveways and heavy-traffic facilities when properly designed; the right choice depends on the site, loads, budget, and maintenance expectations.)
- Cost-effectiveness: Often less expensive to install than concrete, depending on the site and scope.
- Recyclability: Old asphalt can be milled and reused in new pavement.
- Smoothness and quick repair: A smooth, quiet surface that can be patched and opened to traffic quickly.
The Manufacturing Process in Detail
Material Selection
Aggregates are chosen for size, hardness, and shape, and binder is selected by performance grade (PG) to suit the climate and traffic.
Proportioning
Accurate proportioning of aggregate and binder produces the intended properties. Modern plants control this with automated systems.
Mixing Techniques
Plants are either batch plants, which make one batch at a time, or drum plants, which mix continuously.
Quality Control
Producers test aggregate gradation, binder content, and mix temperature throughout production to meet the specifications for each job.
Environmental Considerations
Asphalt production uses energy and fuel. Recycled materials conserve resources, and warm-mix technology can reduce energy use when a mix is actually produced at a lower temperature; the net benefit depends on the mix and how it's made.
Recycling
Asphalt pavement is widely reported as America's most recycled material. According to the National Asphalt Pavement Association's survey with FHWA, producers put about 101.4 million tons of reclaimed asphalt pavement (RAP) back into new mixes during the 2024 construction season, and more than 99 percent of reclaimed asphalt pavement was put back to use. That doesn't mean new pavement is mostly recycled: the same survey put average RAP content at about 22.9 percent of new asphalt mixture. Learn more in our article on recycling asphalt.
Emission Control
Modern asphalt plants use dust collection and emission control systems to limit what's released during production.
Conclusion
Asphalt is a versatile, durable, and cost-effective material, and understanding how it's made explains why base preparation, mix quality, and compaction matter so much. If you're planning a new driveway installation or a parking lot paving project, Maisano Brothers Inc. has been paving Connecticut since 1967 and is happy to walk you through the options.
