Types of Asphalt Mix: A Practical Guide

"Asphalt" covers many different mixes. Each is designed for a particular layer, load and climate. This guide explains the main asphalt mix types, what labels like 9.5 mm and PG 64-22 mean on a quote, and which mix suits a driveway, parking lot, road or patch.

How Asphalt Mixes Are Classified

Asphalt paving mix is crushed stone, sand and filler held together by a small percentage of asphalt binder. Mixes are described in five ways, and a single mix has a label for each:

• Production temperature: hot, warm or cold.
• Gradation (how the stone sizes are blended): dense-graded, gap-graded (SMA) or open-graded.
• Stone size: the nominal maximum aggregate size (NMAS), such as 9.5 mm or 19 mm.
• Binder grade: a Superpave performance grade such as PG 64-22, and whether it is polymer-modified.
• Recycled content: the percentage of reclaimed asphalt pavement (RAP).

Hot Mix Asphalt (HMA)

Hot mix is made at a plant at more than 300°F (FHWA), hauled hot, and placed and compacted before it cools. It comes in three gradations.

Dense-graded

This is the standard mix, with a well-blended range of stone sizes. Pavement Interactive describes it as the general-use mix: suitable for every pavement layer and traffic level, and "relatively impermeable" when properly designed and built.

Stone matrix asphalt (SMA)

SMA is a gap-graded mix. It has a coarse stone skeleton with stone-on-stone contact, filled with a rich mortar of binder and mineral filler. Fibers keep the binder from draining off during hauling. FHWA says SMA costs more than conventional mix because it needs better aggregate, more binder and usually a modified binder. FHWA also says a 20 to 30 percent longer service life is expected. It is used mainly as a surface course on interstates and busy highways, and rarely on driveways.

Open-graded

Open-graded mixes leave out most of the fine material so water can drain through them. They include open-graded friction course (OGFC), a highway surface about an inch thick with typically around 15 percent air voids that cuts spray and tire noise. They also include asphalt-treated permeable base, a drainage layer under other pavement, and porous asphalt (covered below).

Warm Mix Asphalt (WMA)

Warm mix is made with additives or foaming technology that let it be produced and placed 30 to 120°F cooler than hot mix (FHWA). FHWA lists these benefits: a longer paving season, longer haul distances, easier compaction and lower emissions. According to NAPA's industry survey, mix made with warm-mix technology was 40.2 percent of all U.S. asphalt in 2024. For homeowners, warm mix is ordered, priced and calculated like hot mix.

Cold Mix Asphalt

Cold mix uses asphalt emulsion or cutback (solvent-thinned) asphalt, so it can be stockpiled and placed without heating. It is the material in bagged cold patch and in the stockpiles road crews use for winter pothole repair. It is softer than hot mix and gains strength slowly as water or solvent evaporates, so it is best for patches rather than whole surfaces.

An FHWA-sponsored study of more than 1,250 pothole patches found that quality cold-mix patches "can remain in service for several years." It also found that simple throw-and-roll patching was as effective as more labor-intensive methods in most situations. Material quality made the difference. The cold patch calculator converts hole sizes into bags.

Porous (Permeable) Asphalt

Porous asphalt is an open-graded surface with roughly 16 to 22 percent air voids. It sits on a deep bed of clean crushed stone with about 40 percent voids, which stores rainwater until it soaks into the soil (FHWA Tech Brief HIF-15-009). It is used for stormwater control in parking lots, low-volume streets and some driveways.

• Life: FHWA reports porous lots lasting more than 20 years with no maintenance other than cleaning. The EPA cites cold-climate porous lots lasting over 30 years, against about 15 years for conventional lots.
• Care: Vacuum or power-wash it 2 to 4 times a year. Never sealcoat or crack-seal it, and don't use sand on it in winter, because all three clog the pores.

Recycled Asphalt (RAP) Mixes

Reclaimed asphalt pavement is old asphalt that has been milled or crushed and mixed into new asphalt, reusing both its stone and its binder. NAPA's 2024 survey found new mixes averaged 22.9 percent RAP, with 101.4 million tons reused. Most plant mixes, including driveway mixes, contain some RAP. RAP mixes are designed to meet the same specifications as all-virgin mixes.

Plant mix containing RAP is different from asphalt millings, which are loose RAP spread and rolled as a gravel-style surface. Millings cost less but do not perform like paved asphalt. Price them with the asphalt millings calculator.

Polymer-Modified Asphalt (PMA)

Polymer-modified mixes add a polymer, most often SBS, to the binder. FHWA says conventional polymer-modified binders contain about 2.5 to 3 percent polymer, and "highly modified" binders 7 to 8 percent. Modification makes the binder more elastic, improving resistance to rutting under heavy, slow or stopped traffic and to cracking. It costs more and is rarely used on home driveways.

Reading a PG binder grade

In a grade such as PG 64-22, the first number is the average 7-day maximum pavement temperature in °C the binder is designed for. The second is the lowest pavement temperature it is designed for (Pavement Interactive). PG 64-22 suits pavement that reaches 64°C (147°F) in summer and drops to −22°C (−8°F) in winter. Pavement Interactive notes a rule of thumb: grades whose two numbers are 90°C or more apart usually need polymer modification.

Superpave and NMAS Sizes Explained

Superpave is the standard U.S. mix design system for dense-graded hot mix, and the NAPA/FHWA selection guide recommends it. Superpave mixes are named by their nominal maximum aggregate size (NMAS), which is roughly the largest stone size in the mix. Smaller NMAS mixes give a smoother, tighter surface. Larger ones are stronger and cost less per ton but must be laid thicker. Research summarized by NCAT recommends a lift thickness of at least 3 times the NMAS for fine-graded mixes and 4 times for coarse-graded mixes. Thinner lifts are hard to compact.

The NAPA/FHWA mix selection guide says to consider appearance as well. A 9.5 or 12.5 mm surface looks better on a city street, while a 19 mm mix may suit an industrial area. It adds: "never substitute performance for appearance."

Which Asphalt Mix to Use

For driveway thickness choices, see how to choose the right asphalt thickness. For how the mix affects longevity, see how long an asphalt driveway lasts. For a cheaper rural option, compare tar and chip vs. asphalt.

Asphalt Mix Comparison Table

Densities below are the planning values used in our calculator, or a description where we have no single value. Your supplier's job-mix density always takes priority.

Pick the mix in the asphalt calculator to apply these densities automatically. To convert a known volume or area to tons, use the asphalt tonnage calculator with your supplier's density.

Frequently Asked Questions

What type of asphalt is best for a driveway?

A dense-graded hot mix or warm mix is best for nearly every driveway, typically a 9.5 or 12.5 mm surface course. Thicker builds can use a 19 mm base course under it. Ask the contractor which plant mix they use, and confirm the compacted thickness of each layer in writing.

What is the difference between hot mix and cold mix asphalt?

Hot mix is made at over 300°F and compacted while hot, producing a dense, durable pavement. Cold mix uses emulsion or cutback binder so it can be stored and used without heating. It is softer and sets slowly, which makes it suited to patches and temporary repairs rather than full driveways.

What does 9.5 mm or 12.5 mm mean in asphalt?

It is the nominal maximum aggregate size: roughly the largest stone in the mix. Smaller sizes give a smoother surface and can be laid thinner. As a rule, lay each lift at least 3 times the NMAS for fine-graded mixes and 4 times for coarse-graded mixes.

Is recycled asphalt as good as new asphalt?

Plant mix that contains RAP is designed to meet the same specifications as virgin mix, and U.S. mixes averaged 22.9 percent RAP in 2024 (NAPA). Loose asphalt millings spread as a driveway surface are different. They are cheaper but do not form the same sealed, paved surface.

What is the most durable type of asphalt?

For heavy traffic, stone matrix asphalt and polymer-modified mixes are the most rut-resistant, and FHWA expects 20 to 30 percent longer life from SMA. For a home driveway, a well-compacted dense-graded mix over a solid, well-drained base lasts longest per dollar.

Can porous asphalt be used for a driveway?

Yes, where stormwater rules or soils favor it, but it needs a stone reservoir designed for your site. It must be vacuumed rather than sealcoated, and sand can't be used on it in winter.

Sources

• Pavement Interactive: HMA Mix Types
• Pavement Interactive: Open-Graded HMA
• Pavement Interactive: Superpave Performance Grading
• NAPA/FHWA Information Series 128: HMA Pavement Mix Type Selection Guide
• NCAT (Auburn University): lift thickness and NMAS
• FHWA: Stone Matrix Asphalt How-To Document (FHWA-HIF-23-002)
• FHWA: Highly Modified Asphalt How-To Document (FHWA-HIF-22-058)
• FHWA Every Day Counts: Warm Mix Asphalt
• FHWA: Warm Mix Asphalt Technologies and Research
• NAPA IS-138: Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage, 2024
• FHWA Tech Brief: Porous Asphalt Pavements with Stone Reservoirs (HIF-15-009)
• U.S. EPA: Stormwater Best Management Practice, Permeable Pavements
• FHWA Focus: A Better Fix for Potholes
• Colorado Asphalt Pavement Association: "Best Practices" for the Use of Asphalt Driveways