Performance testing of asphalt pavements with recycled asphalt shingles from multiple field trials

Outline

• Highlights
• Abstract
• Keywords
• 1. Introduction
• 2. Experimental Plan
• 3. Results and Discussion
• 4. Conclusions
• Acknowledgments
• References

Conclusions

The Transportation Pooled Fund (TPF)-5(213) demonstration projects show that pavements with RAS can be successfully produced and meet state agency quality assurance requirements for asphalt content, gradation, and volumetrics. This includes the SMA mixes produced in Illinois which used 5% RAS in place of fibers; the RAS mixes produced in Indiana and Wisconsin that used foaming and Evotherm WMA technologies, respectively; and the RAS mixes produced in Missouri which used RAS, RAP, and GTR.

When RAS is used in HMA, the shingle binder increases the high and low temperature performance grade (PG) of the base binder. For every 1% increase in RAS, the low temperature grade of the base binder will increase 1.9 C; and for every 1% increase in RAP, the low temperature grade of the base binder will increase 0.3 C. Therefore, on average, 3% RAS or 20% RAP would be the maximum amount of recycled material allowed without requiring a low temperature grade bump (6 C) in the base binder. This corresponds to a 14% binder replacement when using RAS and a 20% binder replacement when using RAP, when considering the average asphalt content values for all the mix designs. When estimating how RAS will affect an HMA binder, agencies should consider the RAS source (post-manufacturer versus post-consumer) and whether a modifier is used in the base asphalt.

The flow number and dynamic modulus results from the demonstration project mixes show that using RAS or a combination of RAS/RAP in HMA improves its rutting resistance. The pavement condition surveys confirmed the high rutting resistance of the mixes as there was no measurable amount of wheel path deformation in the pavements that were evaluated for multiple years.

All the mixes, with or without RAS, performed well with respect to fatigue cracking in the four-point bending beam test. The K2 coefficients ranged from 4.19 to 9.95 and the estimated fatigue endurance limits ranged from 53 to 359 micro-strain. The SMA mixes from Illinois which used 5% RAS and no added fibers exhibited good fatigue characteristics. In the case of the Indiana demonstration project, the RAS mixes performed the same as the RAP mix; and in the case of the Iowa, Missouri, Minnesota, and Colorado demonstration projects, the RAS mixes exhibited slightly better fatigue lives than the non-RAS mixes. Fibers in the RAS could be contributing to the improved mix performance.

The SCB test results were evaluated by comparing the low temperature fracture energy group means of the mixtures for each demonstration project. There were no differences in fracture energy for the projects in Missouri, Minnesota, Indiana, Wisconsin, and Colorado. However, there were differences in fracture energy for the projects in Iowa and Illinois. For the Iowa mixes, the 4% RAS mix had a statistically higher fracture energy than the 0% RAS mix which suggests that RAS can improve the fracture resistance of HMA prior to long-term aging. For the Illinois mixes, adding 11% RAP to the mixes with 5% RAS decreased the fracture energy. The increase in recycled binder content from the RAP likely caused the fracture energy to drop since the asphalt binder replacement increased from 21% to 35% due to RAP. Based on these results, it is possible for recycled mixes with RAS to have acceptable resistance to fracture, but a combination of RAS and RAP and a high asphalt binder content replacement can result in a lower fracture resistance.

The pavement condition surveys in Missouri revealed the pavement containing coarsely ground RAS exhibited more transverse cracking than the pavement containing finely ground RAS. In both the Missouri and Colorado demonstrations projects, the RAS pavements exhibited slightly more cracking than the non-RAS pavements. In contrast, the RAS pavements exhibited the same amount of cracking or less than the non-RAS pavements for the Iowa, and Indiana demonstration projects. In the Indiana project, more cracking was observed for the RAS mix produced with foaming WMA technology than the RAS mix produced without foaming. In the Minnesota project, slightly more cracking was also observed in the mix using post-manufacturer RAS compared to the mix using post-consumer RAS. However, when taking into consideration the variability of the existing pavement condition beneath the asphalt overlays and the small difference in crack length among the different mix types for some projects, definitive conclusions about RAS pavements solely based on the surveys should be reserved.