What is Rubber Asphalt?
In 2015, the Illinois Tollway Authority commissioned a demonstration project of dry process rubber asphalt pavements. This project designed to evaluate mix performance in the lab and field production of the mixes. ElastikoTM Engineered Crumb Rubber Asphalt selected as the mix modifier in the project because of extensive field experience. This joint project included both the Tollway and the Wisconsin DOT.
Working in conjunction with STATE Testing of East Dundee, IL, WIDOT and The Tollway commissioned two mix designs that had modification with ElastikoTM ECR. They included a 12.5 mm N80 SMA mix design and a WIDOT WI-12.5 N75 SMA mix. Both mix designs showed moderately high levels of ABR (40%), including both RAS and RAP. The mix designs included the use of 10% rubber additions by weight of virgin binder (58 -28), which translated to about 6 lbs. of rubber per mix ton.
Both mixes were produced in a lab setting in order to evaluate the mix performance. The Tollway SMA got compared to a similar mix design using a 70 -28 PMA binder with no ECR, and the WIDOT mix design was compared to an unmodified 58 -28 hot mix asphalt of similar design.
ECR and Polymer Comparison
In a comparison with a polymer modified mix design, the ECR-modified mix exhibited similar rutting and cracking resistance. With the standard hot mix design, the ECR-modified mix out-performed the standard mix in both rutting and cracking resistance.
Since the ECR modification process was significantly less expensive than other traditional forms of modification (less expensive than terminal blend rubber, polymer modification) with comparable or better performance, the mixes got approved for plant production and laydown.
Curran Construction produced materials that they used to pave several miles of I-88 shoulder in 2015. They reported that the modified mixes similar to standard hot mix designs in production and laydown, and they had no issues in any portion of the project.