Polymer Modified Asphalt: SBS, EVA and When to Use It
Polymer modified asphalt (PMA) is regular asphalt binder with a plastic or rubber-like polymer blended in. The polymer changes how the binder reacts to heat, cold and repeated loads. Plain asphalt gets soft in summer and brittle in winter; a good polymer blend narrows that swing so the pavement resists rutting on hot days and cracking on cold ones. Highway agencies use it on busy roads, intersections and special mixes. This guide explains why binders get modified, the main polymer families, how PMA is graded and when it is worth the extra step.
Asphalt tonnage calculator →Why modify asphalt at all?
Pavement Interactive's overview of asphalt modifiers lists a few big reasons modification became common:
- Heavier demands: more traffic, heavier loads and higher tire pressures push pavements toward rutting and cracking.
- Superpave specs: the Superpave performance grade system sets stiffness limits at both high and low temperatures. In extreme climates, unmodified binder often cannot meet both.
- Recycling: some modifiers come from waste streams such as ground tires.
- Life-cycle thinking: modified binder usually costs more up front but is meant to last longer with less maintenance.
The same source says a good modifier should make binder easier to pump and mix at plant temperatures, stiffer at high service temperatures, softer and quicker to relax at low temperatures, and, for some additives, better at sticking to stone when wet.
The main polymer families
| Type | Examples | What it mainly does |
|---|---|---|
| Elastomers | SBS, SBR, SEBS, natural or synthetic latex | Stretch and spring back, improving rut resistance and elastic recovery |
| Plastomers | EVA, polyethylene, polypropylene | Add stiffness and early strength |
| Rubber | Crumb rubber from tires | Elastic behavior at higher dosages; see rubberized asphalt |
A Western Transportation Institute review prepared for New Mexico DOT describes those three groups and notes some trade-offs. Elastomers like SBS improve resistance to permanent deformation because they stretch under load and recover when it is removed, but they can be more prone to breaking down with age unless the pavement gets periodic fog seals. Plastomers give high early strength but, according to the studies it reviews, can raise the risk of rutting and cracking failures.
How much polymer goes in
The same review found plastomer and elastomer contents usually sit at low to medium levels, no more than about 7 percent by weight of binder, while crumb rubber runs higher, typically 15 to 20 percent. Getting the blend right matters: the polymer has to be compatible with the base asphalt or it separates in storage. Suppliers often add sulfur or other cross-linking agents to keep SBS blends stable.
How PMA is graded and checked
- PG grades with a wide spread. Grades like PG 76-22 usually need modification, because few plain binders hold up at 76°C and still pass at −22°C.
- "PG plus" tests. Many states added elastic recovery, toughness or tenacity checks on top of the base PG tests to confirm the polymer is doing its job.
- MSCR. The multiple stress creep recovery test measures how much the binder recovers after repeated loading, and many agencies now use it to grade modified binders for traffic level.
- Lab aging quirks. Very stiff modified binders can be awkward in the rolling thin film oven, where they may not flow normally in the rotating bottles.
What the field record shows
The WTI review cites several studies. A 2005 Asphalt Institute study of 84 sites across North America found polymer modified pavements had significantly less rutting and less thermal and fatigue cracking than pavements with unmodified binder. Texas research found many elastomer-modified binders hardened as much as 40 percent more slowly than neat binders. Arizona's PG 76-22 TR+ binder requires at least 2 percent SBS and 8 percent crumb rubber, and its elastic recovery at 10°C must be 55 percent or more. Results vary by project, so these are examples, not guarantees.
Where polymer modified asphalt is used
- Interstates and heavy truck routes where rutting is a concern.
- Intersections and bus stops with slow, stopping traffic.
- Specialty mixes such as stone mastic asphalt and open-graded friction courses.
- Very hot or very cold climates that push a plain binder past its limits.
What about driveways and parking lots?
Most home driveways are paved with whatever standard mix the local plant runs that day, and light car traffic rarely justifies a special binder. For a commercial lot with delivery trucks, or a driveway that sees heavy equipment, it is fair to ask the contractor which binder grade the mix uses and whether a modified grade is available. The bigger wins on a driveway are usually a solid base, proper compaction and good drainage. To estimate tonnage for any mix, use the asphalt tonnage calculator or the driveway asphalt calculator.
You will also see "polymer modified" on some driveway sealers and crack fillers. That label means polymer was added to an asphalt emulsion or rubberized base. Formulas differ, so go by the product's directions for coverage and cure.
Questions people ask
What is polymer modified asphalt?
It is asphalt binder blended with a polymer, most often an elastomer like SBS, a plastomer like EVA, or rubber, to change how the binder behaves with temperature and load. The goal is a binder that is stiffer in summer heat and more flexible in cold weather than plain asphalt.
What does SBS do in asphalt?
SBS (styrene-butadiene-styrene) is a rubbery polymer that lets the binder stretch and recover under load. That elastic recovery improves resistance to rutting and to some kinds of cracking. Research summarized for New Mexico DOT notes elastomers can be more prone to aging without periodic fog sealing.
How much polymer is added to asphalt?
A Western Transportation Institute review for New Mexico DOT found plastomer and elastomer contents are usually at low to medium levels, no more than about 7 percent by weight, while crumb rubber is used at higher levels, typically 15 to 20 percent.
Is polymer modified asphalt worth it for a driveway?
Usually not needed. Residential driveways see light loads, and most local plants supply their standard mix. Polymer modified binders earn their keep on highways, intersections, heavy truck routes and thin overlays where rutting or cracking is a known problem.
What PG grades are polymer modified?
High-spread grades such as PG 76-22 or PG 70-28 are commonly made with polymer, because plain asphalt often cannot meet both the high and low temperature limits. The exact recipe depends on the supplier and the agency's spec.
What is a polymer modified asphalt emulsion sealer?
It is a driveway or pavement sealer that uses an asphalt emulsion base with polymer added. Product formulas differ, so read the label for coverage, cure time and temperature limits rather than assuming one polymer sealer works like another.
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