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 mix that paves roads, parking lots, and driveways). 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
Asphalt pavement is made of three main components:
- Aggregates: Crushed stone, gravel, and sand make up roughly 95% of the mix by weight.
- Binder: Asphalt cement (bitumen), about 5% by weight, coats the aggregate and glues it together.
- Additives and fillers: Fine mineral filler, polymers, anti-strip agents, or warm-mix additives may be added to improve performance.
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, and they have been volatile in 2026. 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.
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 hot 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, compacted stone base, 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. It can usually take light traffic within a few days, but it continues to harden over the following months.
Types of Asphalt
- Hot Mix Asphalt (HMA): Produced at around 300°F, give or take, and the standard for roads, parking lots, and driveways.
- Warm Mix Asphalt (WMA): Produced at lower temperatures using additives or foaming, which reduces fuel use and fumes at the plant and on the job.
- Cold Mix Asphalt: Used mainly for pothole patching and temporary repairs, especially in winter when hot-mix plants are closed. 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: Handles traffic and flexes with freeze–thaw movement better than rigid pavement.
- Cost-effectiveness: Usually less expensive to install than concrete.
- 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, but warm-mix technology and recycled materials reduce emissions and conserve resources.
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 million tons of reclaimed asphalt pavement (RAP) back into new mixes during the 2024 construction season. 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, we've been paving Connecticut since 1967 and are happy to walk you through the options.
