What is a Warm Mix Asphalt (WMA) Additive?

A warm mix asphalt (WMA) additive is a material that lets asphalt mix be produced and placed at lower temperatures than hot mix asphalt (HMA).

What it does

Asphalt binder must be fluid enough to coat the aggregate and to compact. HMA gets this fluidity from heat. The FHWA states that HMA is typically produced above 300°F (about 150°C). WMA technologies aim to give the same coating and workability at a lower temperature.

Technology groups

The FHWA lists four groups:

• Synthetic zeolites. They foam the binder. Aspha-Min and Advera WMA are examples.
• Two-component binder systems. WAM-Foam is the example.
• Organic wax additives. Sasobit and Asphaltan B are examples.
• Chemical additives. An asphalt emulsion carries them. Evotherm is the example.

Stated benefits

The FHWA says WMA may use less fuel to heat the mix. It may also give fewer fumes and odors at the plant and the paving site. It calls these benefits promising and says that further research must confirm them. It gives no single temperature reduction. The reductions it lists are vendor claims for each product, and it considers the products experimental.

Airfield context

FAA Item P-401 sets the mix design criteria for airfield asphalt. These include a tensile strength ratio (TSR), shown in brackets as “not less than 80”. The job mix formula lists the supplier-recommended mixing and compaction temperatures. The text of P-401 in AC 150/5370-10H does not name warm mix asphalt.

This page does not state how WMA performs on a runway. No source that TarmacView opened supports a performance claim for airfield use.