What is Rubber Asphalt?
In 2015, the Illinois Tollway Authority commissioned a demonstration project of asphalt pavements modified with dry process rubber. This project was designed to evaluate mix performance in the lab and field production of the mixes. ElastikoTM Engineered Crumb Rubber Asphalt was selected as the mix modifier in the project because of extensive field experience that included multiple state DOTs and many private contractors. This was a joint project that 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 were modified 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 had 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 was 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.
In a comparison with a polymer modified mix design, the ECR-modified mix exhibited similar rutting and cracking resistance, while in the comparison 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 were approved for plant production and laydown.
Curran Construction produced materials that were used to pave several miles of I-88 shoulder in 2015. They reported that the modified mixes were similar to standard hot mix designs in production and laydown, and they had no issues in any portion of the project.