Comprehensive Data Analysis for AMPT Tests on MO 740 and Hwy 54

In this study, the S&T research team conducted comprehensive data analysis from the Asphalt Mixture Performance Tester (AMPT) samples collected in the Highway 54 and MO 740 projects. The MO 740 project in Boone County contained test sections with five mix designs, i.e., control mix, ground tire rubber (GTR)-modified mixture, and three mixtures containing recycled plastic. The Highway 54 project had ten samples collected at different times during the production of the surface mix. The data were analyzed on both the material and structural scales, and for the MO 740 project, field performance was also used to verify the research findings. The fatigue performance index Sapp and the Rutting Strain Index (RSI) were calculated, and the mixture performance in pavement structures with realistic traffic loads and climate was predicted. The research found that the mixture performance in the Highway 54 project has a good correlation with the mixture volumetric properties. In terms of the different mix designs in the MO 740 project, the AMPT tests suggested that the GTR-modified mixture had the lowest modulus but had the highest cracking resistance. However, the mixture might have a higher rutting susceptibility than the other mixtures. On the other hand, the addition of plastic increased the mixture stiffness and did not have a great impact on the fatigue and rutting performance compared with the control mixture.

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Report number: cmr 23-017
Published: December 2023

Project number: TR202417
Authors: Jenny Liu and Yizhuang David Wang

Performing organization: Missouri University of Science & Technology

Evaluation of Recycled Components in Stone Matrix Asphalt Mixes

Currently, Missouri DOT (MoDOT) does not allow use of recycled materials in SMAs although the HMAs are routinely incorporated with them. MoDOT commissioned this study to investigate the effect of incorporation of recycled materials such as RAP and GTR in SMAs. In Phase 1 of the study, plant-produced mixtures were collected, and recreated in the lab under BMD methodology to determine acceptable upper-limit on RAP for initial implementation. In Phase 2, friction properties of mixtures were obtained by testing aggregate stockpiles, lab and plant produced mixtures, and a field section containing GTR. Based on the results, the following conclusions were drawn: 1) The current use of conglomerate (non-homogeneous), unfractionated RAP stockpiles poses practical limitations in achieving passing BMD thresholds at higher levels of RAP, 2) Suitable frictional characteristics were achieved at lower levels of RAP but results indicated that the softer aggregates present in current RAP stockpiles tended to reduce skid resistance, and 3) Use of GTR appears to be promising option for incorporating recycled materials into Missouri pavements, based on lab BMD and skid resistance results in the lab and field. Based on the findings, the following recommendations were made :1) MoDOT should consider allowing RAP in SMA mixtures but, an upper limit of 15% asphalt binder replacement (ABR) from RAP is recommended at this time, 2) If greater than 15% ABR by RAP is considered, a value engineering proposal should be provided, accompanied with BMD tests, 3) The research supports the continued and increased usage of GTR as a possible approach towards achieving good mixture durability, skid resistance, and mixture sustainability.

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Report number: cmr 23-016
Published: December 2023

Project number: TR202020
Authors: William G. Buttlar, Magdy Addelrahman, Punyaslok Rath, Jim Meister, Nandita Gettu, and Ahmed S. El-Ashwah

Performing organization: University of Missouri-Columbia and Missouri University of Science and Technology