Performance Characteristics of Modern Recycled Asphalt Mixes in Missouri, Including Ground Tire Rubber, Recycled Roofing Shingles, and Rejuvenators

A comprehensive lab and field investigation was carried out to evaluate the performance of recycled asphalt mixtures in Missouri by researchers at the University of Missouri-Columbia, in collaboration with the Missouri Department of Transportation and the Midwest Transportation Center.  Sixteen field sections were evaluated, including a number of sections from the recent Long-Term Pavement Performance (LTPP), Special Pavement Sections (SPS-10) project in Osage, Beach, MO, which was constructed in 2016. Binder testing and mix performance tests were carried out on field cores and laboratory compacted specimens.  Based on the findings of the study, the following conclusions were drawn: (1) Missouri’s practices for the responsible and effective use of recycled materials is sound, and continues to improve over time - recent mix designs demonstrate more appropriate balancing between recycled material levels and virgin binder selection, resulting in better performance tests results when compared to older recycled mix designs; (2) Opportunities exist for further improving recycled mix design methods and recycling optimization in Missouri, including (a) Moving to higher ABR levels, by implementing mixture performance tests (balanced mix design); (b) Increasing the use of recycled ground tire rubber (GTR) in Missouri mixes, by using balanced mix design to certify mixes using new, more economical GTR recycling methods, and; (c) Researching the use of recycled materials in stone-mastic-asphalt (SMA) designs. It is recommended to further evaluate and fine-tune mix performance tests for use in balanced mix design, which is particularly important for modern, heterogeneous recycled mixes.

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Report number: cmr19-002
Published: January 2019
Project number: TR201712
Authors: William G. Buttlar, Jim Meister, Behnam Jahangiri and Hamed Majidifard
Performing organization: University of Missouri-Columbia

Field Implementation of Super-Workable Fiber-Reinforced Concrete for Infrastructure Construction

A fiber-reinforced super-workable concrete (FR-SWC) made with 0.5% micro-macro steel fibers and 5% CaO-based expansive agent was used for the new deck slab of Bridge A8509. The selected FR-SWC had a targeted slump flow of 20 in. at the casting location. Multiple trial batches were performed, in collaboration with the concrete supplier, to adjust the mixture composition to meet the targeted performance criteria. This was followed up by casting the fibrous concrete in a mock-up slab measuring 10 x 10 ft that was prepared to simulate the tight rebar and the roadway crown slope in the transverse direction. The results indicated the necessity to lower the concrete slump from the intended value for FR-SWC to hold the 2% crown slope of the bridge deck in the transverse direction. The final mixture that was selected following the trial batches and mock-up placement had a slump consistency of 8 plus or minus 2 in. (FRC). Six sensor towers were installed in the slab within 18 ft to the East and West sides of the intermediate bent to monitor in-situ properties of the concrete. Each tower had three humidity sensors, three thermocouples, and 12 concrete strain gauges. The slump values varied between 6 and 10 in. Slump values were around 8.5 in. The fresh air volume ranged from 4.4% to 5.8%, and the concrete temperature ranged from 85 to 97 degrees F. At 56 days, the compressive strength ranged from 7,020 to 8,360 psi and had a mean value of 7,770 psi. Data up to 260 days are reported at the time of the preparation of this report.

A strain model was proposed to evaluate the strain data collected from the embedded sensors. The model represents the total strain as a summation of strains due to thermal deformation, drying and autogenous shrinkage, and structural deformation. The model was used to evaluate strains and estimate values of the concrete shrinkage during the first 30-36 hours, which corresponded to the time of demolding of the shrinkage samples as well as the load distribution factor between the concrete slab and the steel corrugated sheet that varied with concrete age. Findings indicated that the load distribution factor increased with concrete age reaching a value of 0.98 at 260 days. The concrete shrinkage during the first 30-36 hours was then estimated to be 75 micro-strain.

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Report number: cmr19-001
Published: January 2019
Project number: TR201705
Authors: Kamal Khayat and Ahmed Abdelrazik
Performing organization: Missouri University of Science & Technology