Asphalt Binder: What It Is and How PG Grades Work

Asphalt binder is the black, sticky material that glues crushed stone and sand together to make asphalt pavement. In the US it's also called asphalt cement, and in much of the world it's called bitumen. It makes up only a small share of a hot mix by weight, but it controls how the pavement handles heat, cold, and aging, and it's the ingredient whose price swings the most.

What asphalt is made of → Asphalt cost per ton →

Where Asphalt Binder Comes From

Most binder is refined from crude oil. It's what remains after the lighter fractions (gasoline, diesel, and so on) are distilled off, then processed to meet grade specifications. Natural asphalt deposits exist, but paving binder in the US comes overwhelmingly from refineries. Because of that link, binder prices tend to follow crude oil and refinery economics.

How Much Binder Is in Hot Mix?

A typical dense-graded hot mix contains roughly 4 to 7 percent binder by weight of total mix, with the rest being aggregate. The exact amount comes from the mix design, which balances durability against the risk of a mix that's too rich and ruts or bleeds. For a quick sense of scale:

• One ton of mix at 5.5 percent binder contains 0.055 × 2,000 = 110 pounds of binder.
• A 12-ton driveway job at that rate contains about 1,320 pounds, or roughly two-thirds of a ton, of binder.

Mixes using recycled asphalt pavement (RAP) get some of their binder from the recycled material, which reduces the amount of new binder needed. See what asphalt is made of for the full recipe.

Performance Grades: What PG 64-22 Means

US agencies specify binder mostly with the Performance Grade (PG) system that came out of the Superpave research program. A grade has two numbers, both in degrees Celsius:

• First number (for example, 64): the high pavement temperature the binder is designed to handle without getting too soft and rutting.
• Second number (for example, -22): the low pavement temperature the binder is designed to handle without getting too stiff and cracking.

So a PG 64-22 binder is meant for pavements that reach up to about 64°C (147°F) and down to about -22°C (-8°F). Pavement temperatures, not air temperatures, are what matter; dark asphalt in summer sun runs much hotter than the air.

Situation	Grade tendency
Hot climates	Higher first number
Very cold climates	More negative second number
Heavy, slow traffic (truck stops, intersections)	Often "bumped" to a stiffer high-temperature grade
Wide temperature range	Often needs a polymer-modified binder

Grades step in 6-degree increments, and which grades are standard varies by state. Your paver will use what local plants make for the local climate.

Older Grading Systems

Before PG grades, binders were classified by penetration (how far a needle sinks into a sample) or by viscosity (names like AC-10 or AC-20). You may still see these terms in older documents, other countries, or some specialty products.

Polymer-Modified Binder

Adding polymers such as SBS, or ground tire rubber, widens the temperature range a binder can handle and improves its elasticity. Modified binders cost more and are common on highways and heavy-duty pavements. On residential driveways, unmodified binders are typical. Our rubberized asphalt guide covers the rubber route.

How Binder Is Tested

Labs test binder at conditions that mimic its life: as delivered, after short-term aging (simulating the heat of mixing and paving), and after long-term aging (simulating years in service). Common test names you may hear are the dynamic shear rheometer (for high and intermediate temperatures) and the bending beam rheometer (for low temperatures). The results determine whether a binder meets a given PG grade.

Why Binder Matters for Your Paving Quote

Binder is a small share of the weight but a meaningful share of the cost of a ton of mix. When crude oil prices rise, plants' costs rise, and quotes follow. Many state transportation departments publish a monthly asphalt binder price index used to adjust road contracts, which shows how much the price can move over a season. For homeowners, the practical points are:

• Quotes may be good only for a limited time for this reason.
• Per-ton prices can change between spring and fall.
• Our cost per ton page gives planning ranges, but only a current local quote counts.

Binder vs. Binder Course

"Binder" can also mean a layer. The binder course is the lower asphalt layer placed under the surface course, usually with larger stone. It contains asphalt binder, but the term refers to the layer, not the material. See binder course vs surface course.

Bottom Line on Asphalt Binder

Asphalt binder is the refined, sticky glue that holds a hot mix together, usually around 4 to 7 percent of the mix by weight. PG grades tell you the high and low pavement temperatures it's built for. Its price follows oil, which is why asphalt quotes change over time.