Superpave Asphalt Explained: What "9.5 mm Superpave" Means on Your Quote

Superpave (short for Superior Performing Asphalt Pavements) is the system most U.S. highway agencies use to pick asphalt binder and design hot mix. It came out of federally funded highway research in the late 1980s and early 1990s and has three main parts: Performance Graded (PG) binders chosen for the local climate, a volumetric mix design built around a gyratory compactor, and mix names based on stone size and traffic level. When a paving quote says "9.5 mm Superpave surface" or "19 mm Superpave base," it's telling you the nominal maximum stone size in the mix and that it was designed under this system.

Asphalt mix types chart →

Why Superpave Replaced Older Methods

Before Superpave, many agencies designed mixes with the Marshall or Hveem methods and graded binders by penetration or viscosity. Those methods worked, but they weren't tied as directly to how pavement behaves in hot and cold weather or under heavy truck traffic. Superpave aimed to match the binder to the climate and the mix to the traffic, reducing rutting in heat and cracking in cold. It's now the standard in most states, though each agency writes its own version of the specifications.

Part 1: Performance Graded Binders

A Superpave binder is labeled like PG 64-22. The first number is the high pavement temperature in degrees Celsius the binder is designed to handle without excessive softening; the second is the low temperature (minus 22°C here) it's designed to resist cracking at. Hotter climates and heavier or slower traffic push the high number up; colder climates push the low number down. Our asphalt binder guide explains PG grades in more detail.

Part 2: Mix Names and Stone Size

Superpave mixes are named by their nominal maximum aggregate size (NMAS), which roughly describes the largest stone size that makes up a meaningful share of the mix.

Mix size	Typical use	Feel on a driveway
4.75 mm	Thin leveling or overlays in some states	Very fine and smooth
9.5 mm	Surface (wearing) course, thin lifts	Tight, fine texture; common residential top
12.5 mm	Surface course on roads and lots	Slightly coarser texture
19 mm	Intermediate or binder course	Stronger, coarser; usually covered by a surface lift
25 mm and larger	Base courses on heavy-duty pavements	Rarely used on driveways

A common rule of thumb is that each lift should be at least a few times thicker than the NMAS so the stones can pack together. That's one reason fine 9.5 mm mixes are popular for the top of driveways laid in thinner lifts. Our article on 19 mm asphalt mix covers the larger binder-course size.

State names vary. You might see "SP 9.5," "SM-9.5," "9.5 mm wearing course," or a letter code for the traffic level. Ask your contractor or plant what their product code means if the quote isn't clear.

Part 3: Volumetric Design and the Gyratory Compactor

In the lab, technicians compact samples of a trial mix in a Superpave gyratory compactor, a machine that squeezes the mix in a mold while tilting and rotating it to imitate the kneading action of rollers and traffic. The number of gyrations used for design goes up with the expected traffic. The mix is then checked for key volumetric properties:

• Air voids: the small air spaces left in compacted mix. Superpave designs typically target about 4 percent air voids at the design gyration level.
• VMA (voids in mineral aggregate): the space between stones available for binder and air. Minimums get higher as stone size gets smaller, so fine mixes carry enough binder to be durable.
• VFA (voids filled with asphalt): how much of that space binder fills.
• Dust-to-binder ratio: keeps fine dust and binder in balance.

The approved recipe becomes the job mix formula the plant follows. See what a JMF is for how plants hold to it.

What This Means for a Homeowner

• You don't need to specify Superpave yourself. Local plants run approved mixes; your contractor chooses from what's available.
• Surface mix size affects texture. A 9.5 mm top is smoother and tighter looking than a 12.5 mm top.
• Some highway mixes are stiff for hand work. Mixes designed for heavy traffic can be harder to rake and compact on a small job. Many plants also run lower-traffic mixes that are more workable for driveways and lots.
• Temperature still rules. Any mix needs to be placed and rolled hot. An infrared thermometer is a quick way to check delivered mix and mat temperature.

Superpave and Tonnage

Mix design changes density slightly, but for planning, most dense-graded hot mixes are estimated at roughly 145 pounds per cubic foot compacted. That's what our asphalt tonnage calculator uses. Measure the area carefully with a measuring wheel, choose thickness, and confirm the density with the plant if you need precision.

Placing Superpave Mix on Small Jobs

Coarser Superpave mixes can segregate or look rough if they're overworked by hand. Tips for small crews:

• Dump close to where the mix is needed to reduce shoveling
• Spread with an asphalt lute rather than tossing mix with a shovel
• Keep lifts thick enough for the stone size
• Roll promptly while the mix is in its compaction window

Bottom Line on Superpave

Superpave is the framework behind most modern U.S. hot mix: PG binders matched to climate, mixes designed volumetrically with a gyratory compactor, and names based on stone size and traffic. On a residential quote, "9.5 mm" usually means a smooth surface mix and "19 mm" means a stronger binder course underneath. You don't need to design it, but knowing the terms helps you compare bids and ask the right questions.