Developement of a framework for asphalt performance-related specification and performance prediction

Traditional asphalt mixtures have generally involved relatively simple combinations of virgin asphalt binder and aggregates to meet load-bearing needs of the roads and surfaces. Accordingly, simple tests such as Marshall Stability and Flow were used in an effective manner for asphalt mixture screening and quality control purposes. In recent years, there has been a proliferation of asphalt ingredients available to designers, especially in the case of recycled materials, compaction aides, and mixture performance and/or sustainability promoting products. These include reclaimed asphalt pavement (RAP), recycled asphalt shingles (RAS), warm mix agents, antistripping agents, rejuvenators, ground tire rubber, and even waste plastic. These modern, heterogeneous asphalt mixtures exhibit more complex behavior as compared to earlier mixes containing fewer ingredients and predominantly virgin materials. As a result, recent asphalt mixes require advanced performance tests to account for these complexities, while factoring in traffic and environmental loads for the given mixture type being designed. In this study, various existing roads including good and bad performing sections were selected in Illinois and Missouri and after conducting site visits. In field investigations, the main distresses on the Tollway in northern Illinois and across the state of Missouri were identified. Also, several field cores were obtained from mainline and shoulder sections to evaluate the laboratory performance of existing asphalt mixtures across a range in-situ aging levels. Analyzing the available field performance data such as international roughness index (IRI), condition rating system (CRS), and rut depths and comparing them with laboratory testing results provided a robust data set to establish updated performance test thresholds for the Tollway mixture design specification. According to recent literature, mixture performance can be evaluated using various tests to mitigate different distress types such as cracking, rutting, and moisture damage. In this study, fourteen different mixtures produced in 2018 on mainline and shoulders sections across the Tollway system, and four mixtures in Missouri were selected to characterize performance testing trends and to study the ability of the different performance tests to predict pavement performance. To this end, performance tests such as the DC(T), I-FIT, IDEAL-CT, IDT, Hamburg, and TSR were conducted on the collected plant produced mixtures. The process of sample fabrication, ease of conditioning and testing, repeatability and ability to correctly rank various Tollway mix types was taken into consideration in selecting the appropriate performance tests to be used in the Tollway's mix design asphalt specification. The DC(T) test was found to possess the best correlation to field performance, and significantly outperformed the I-FIT test in terms of test repeatability. Both the I-FIT and IDEAL tests returned failing results for a number of SMA mixes, and dense-graded mixes with high recycling content, which have traditionally performed well on the Tollway. This provided additional motivation to retain the DC(T) test as the cracking test to be used in the Tollway's asphalt mixture design specification. The analysis presented in this study, in conjunction with field observations, led to the identification of various cracking types as the primary distresses observed on Tollway mainline and shoulder sections surfaced with asphalt. Rutting and stripping were not found on Tollway asphalt surfaces, nor in Missouri at the present time. The Disk-shaped Compact Tension (DC(T)) test was chosen to be retained in the performance related specification (PRS) for the design of crack-resistant mixtures due to its high degree of correlation with field results and best repeatability. A systematic approach was developed, which allowed different reliability levels to be addressed in the specification, along with a consensus step to take advantage of local practitioner experience. Similarly, for high-temperature performance, Hamburg thresholds for binder course mixtures were tailored for different mixture types and use cases. In some cases, by relaxing Hamburg requirements, designers have more leeway in building crack resistance into the mixture and/or to utilize higher amounts of recycled materials. For SMA mixtures, it was observed that low rut depth mixes were sometimes identified as having stripping potential in the Iowa method. However, similar mixtures have not exhibited stripping in the field. As a result, it is recommended that SMA mixtures with rut depths less than or equal to 4.0 mm after 20,000 passes should be characterized as non-stripping and do not need to be checked for stripping potential through the Iowa method. Based on experimental results, it is also recommended to use the Hamburg test in lieu of the TSR stripping test for moisture sensitivity evaluation. In the event of failing results, the TSR test can be used as a secondary method to assess adequate moisture resistance. Using the specification for both cracking and rutting, a novel grading system that takes into account the performance of the asphalt mixture was developed and the Tollway mixtures were graded based on this system. Also, the characterization of the viscoelastic behavior at low temperature through the DC(T) creep test led to validating the performance of the mixtures that could pass the cracking requirements.Includes bibliographical references (pages 219-237)

Determining Asphalt Mixture Properties Using Imaging Techniques

This study introduces imaging technology to determine the bulk specific gravity (Gmb) of compacted asphalt mixture specimens. Using an advanced three-dimensional scanner, a fast, accurate technique for determining compacted asphalt mixture specimen Gmb was developed. The feasibility of this technique was evaluated by testing a collection of asphalt mixtures, including dense-graded and stone mastic asphalt mixtures. The results were compared with those obtained using the currently-specified Gmb measurement methods of AASHTO T166 and CoreLok. The proposed scanning technique was also used for both laboratory-prepared and field-cored specimens to determine its reliability and reproducibility. The study results suggest the proposed imaging technique is effective in decreasing Gmb measurement variation as well as in improving the accuracy and reproducibility. Additionally, the results indicate the proposed technique can be applied to any asphalt specimen, regardless of mixture type, aggregate sizes, or fabrication technique

Non-contact AC current measurement using vibration analysis of a MEMS piezoelectric cantilever beam

This paper proposes a non-contact system to measure electrical current crossing a wire. To do so, design and simulation of a piezoelectric cantilever beam with a tip mass is presented using mathematical modeling. The sandwich cantilever beam is composed of two piezoelectric layers and a mid-layer made up of steel. For mathematical modeling, the governing differential equation of the beam is extracted and solved by Galerkin method. Then the output voltage is calculated for different values of external forces. The force applied to the tip mass from the magnetic field of wire is used as external excitation force of the beam. According to the response of the output voltage, the current crossing the wire is calculated. Validation of the model is demonstrated compared to other references. In results section, frequency response behavior and influence of the geometric parameters on output voltage are analyzed. Appropriate values of these parameters should be used in design process of this non-contact sensor to have an observable applied force from the current carrying wire

Determining Asphalt Mixture Properties Using Imaging Techniques

SPR-4415This study introduces imaging technology to determine the bulk specific gravity (Gmb) of compacted asphalt mixture specimens. Using an advanced three-dimensional scanner, a fast, accurate technique for determining compacted asphalt mixture specimen Gmb was developed. The feasibility of this technique was evaluated by testing a collection of asphalt mixtures, including dense-graded and stone mastic asphalt mixtures. The results were compared with those obtained using the currently-specified Gmb measurement methods of AASHTO T166 and CoreLok. The proposed scanning technique was also used for both laboratory-prepared and field-cored specimens to determine its reliability and reproducibility. The study results suggest the proposed imaging technique is effective in decreasing Gmb measurement variation as well as in improving the accuracy and reproducibility. Additionally, the results indicate the proposed technique can be applied to any asphalt specimen, regardless of mixture type, aggregate sizes, or fabrication technique

Design and Analysis of a Piezoelectric-Based AC Current Measuring Sensor

Electrical current measurement is a suitable method for the performance determination of electrical devices. There are two contact and noncontact methods in this measuring process. Contact method has some disadvantages like having direct connection with wire which may endamage the system. Thus, in this paper, a bimorph piezoelectric cantilever beam which has a permanent magnet on its free end is used to measure electrical current in a noncontact way. In mathematical modeling, based on Galerkin method, the governing equation of the cantilever beam is solved, and the equation presenting the relation between applied force and beam’s output voltage is presented. Magnetic force resulting from current carrying wire is considered as the external excitation force of the system. The results are compared with other references in order to demonstrate the accuracy of the mathematical model. Finally, the effects of geometric parameters on the output voltage and natural frequency are presented

Investigation of Nonlinear Thermo-Elastic Behavior of Fluid Conveying Piezoelectric Microtube Reinforced by Functionally Distributed Carbon Nanotubes on Viscoelastic-Hetenyi Foundation

In this paper, nonlinear and nonlocal thermo-elastic behavior of a microtube reinforced by Functionally Distributed Carbon Nanotubes, with internal and external piezoelectric layers, in the presence of nonlinear viscoelastic-Hetenyi foundation, and axial fluid flow inside the microtube is studied. Nonlinear partial differential equations governing the system are derived using Reddy’s third-order shear deformations theory along with the Von-Karman theory including the effect of fluid viscosity. Then, the equations are converted to time-dependent ordinary nonlinear equations using the Galerkin method. Afterward, the governing equations of the microtube’s lateral displacements are solved using the multiple scales method. The analysis of the piezoelectric’s parametric resonance is performed by obtaining trivial and nontrivial stationary solutions and plotting characteristic curves of the frequency response and voltage response. At the end, the effect of different parameters including the flow velocity, excitation voltage, parameters of the foundation, viscosity parameter, thermal loading and nanotubes’ volume fraction index on the nonlinear behavior of the system, under parametric resonance condition, is investigated

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

MoDOT project #TR201712A 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 in2016. 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\u2019s 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. Appendices published in separate files attached to this record