Last year, Asphalt Plus conducted a trial project of dry process crumb rubber modified asphalt on Interstate 88 near Rochelle, Illinois. The project included the laboratory evaluation of two asphalt mix design and placement of two lane-miles of pavement on I-88.
The first mix was:
- Friction SMA (ILDOT)
- 34% ABR (5% RAS and 8 lbs of rubber mix per ton)
- No RAS content
Tests suggest comparable Hamburg and DCT performance between dry process CRM asphalt and PMA.
- 2 vs. 2.5 mm rut respectively
- 602 vs. 566 DCT respectively
The second mix was:
- 12.5 N75 Fine Surface Graded Mix (WIDOT)
Lab testing of the WIDOT mix with and without engineered dry process rubber showed the rubber additions significantly improved mix performance.
Presence of rubber improved:
- Hamburg rutting from 8.2 mm at 10,000 passes to 3.4 mm at 20,000 passes
- Increased DCT results from 358 to 482
Modifying The Plant
The Curran DeKalb plant was modified for dry process asphalt production in a matter of a few hours.
Using a loss-in-weight feeder system:
- Engineered crumb rubber was injected into production with a high degree of accuracy
- Plant production of CRM asphalt at full production rates occurred without interruption
- Two mix designs were produced in sequence with minimal waste
The asphalt mixes were trucked 40 miles on a cool day (55 F at start), and placement temperatures ranged from 235 to 280 F off the trucks.
The Finished Product:
- Finished without any tearing
- Vibratory rollers produced specified compaction without special effort and without stopping plant operations
Performance evaluations will continue in the field following a winter of service. The existing record of technology field performance in colder climates strongly suggests that the use of dry process engineered rubberized asphalt mix designs will be permitted as a competitive alternative to other forms of modified asphalt. The cost advantage suggests this process will benefit both producers and road owners.
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