ICT studies investigate warm-mix asphalt technology for more environmentally sound pavements

Warm-mix asphalt technology provides several environmental benefits that result from using lower production and placement temperatures. The Asphalt Institute Technical Working Group reports that WMA requires less energy to produce than hot-mix asphalt and releases fewer greenhouse gases and air pollutants. Another advantage of WMA is its potential for allowing the use of more recycled material, such as recycled asphalt pavement (RAP) and recycled roofing shingles (RAS), when additives are used as a compaction aid. ICT researchers have completed two studies that analyze WMA technology to evaluate its viability:

• R27-SP17: Warm-Mix Asphalt Study for the Illinois Department of Transportation
• ICT-12-001: Short-Term Performance of Stone-Matrix Asphalt Produced with Warm-Mix Additives for the Illinois Tollway

In project R27-SP17, ICT researchers examined the performance characteristics of new asphalt mixtures such as WMA, stone-matrix asphalt (SMA), and RAS with alternative friction aggregates such as diabase, quartzite, and granite. The aim of the study was to evaluate these new mixes and provide IDOT with guidance on the applicability of the mix designs to meet IDOT’s goals of cost-effective, durable, and environmentally friendly pavements.

Permanent deformation was evaluated using the Hamburg Wheel Tracker, and the material was characterized by dynamic modulus testing. The researchers concluded that although WMA specimens are within the allowed permanent deformation limits, the specimens had a higher wheel track displacement than most other hot-mix asphalts with similar composition. The team recommended additional testing on a larger variety of specimens, along with testing of thermal fracture properties.

In project ICT-12-001, the research team looked at the short-term performance of SMA prepared with WMA additives such as Evotherm and Sasobit, as well as foamed asphalt techniques. They conducted extensive laboratory tests and onsite stiffness and deflection measurements from pavement surfaces after construction. The team concluded that SMA containing different WMA additives showed comparable performance with the control SMA. The researchers also evaluated methods to determine an optimal time after construction to open the road to traffic.