“Warm Mix” is a misnomer as this product is still produced at a high temperature in order to bring the oils to the proper viscosity and achieve acceptable mixing of the materials. Warm mix asphalt concrete (WMAC) is similar to hot mix asphalt concrete (HMAC) but is produced with a different process that is used to lower its mixing temperature by 50° to 100°F degrees compared to conventional HMAC (or a processing temperature of between 212° - 275° F). This reduction in process temperature reduces the quantity of fuel required to produce a single unit of asphalt concrete thereby reducing the carbon intensity of production as well as production costs.
There are two general methods to achieve WMAC – the “water foaming” process that uses plant modifications to inject a controlled amount of water into the hot oil and the additive process that uses a chemical additive to allow production of the mix at lower temperatures. Generally, the chemical additive method results in lower temperatures.
WMAC Specification best practices include:
- Be aware of the availability of WMAC in local area and the method(s) used to produce the WMAC. If WMAC is not available, contact local suppliers to determine the reason.
- Adopt a specification that achieves the desired quality and is available in the area.
- Require quality control and quality assurance to verify the quality of the materials and the placement of pavement.
Selecting the appropriate mix design and specifications for the conditions is necessary regardless of the type of asphalt pavement used. Oftentimes, perceived failures of materials can be traced back to mix design selection rather than the materials themselves.