Simulation, Modeling and Interpretation of Asphalt Rheology

Rheological methods from polymer science such as time-temperature superposition and linear viscoelasticity will be used to model the time, frequency, and temperature dependence of dynamical mechanical properties of asphalts. Experimental data will be taken from the literature and/or will be measured at the Rhode Island Department of Transportation. Master curves for storage and loss modulus and tan will be modeled using fundamental constitutive equations, such as multicomponent Maxwell models. Those same models will be used to interpret other mechanical experiments, such as creep and recovery. Research will involve ongoing participation by a graduate student and an undergraduate researcher. What defines a sustainable road? One aspect would certainly include physical durability across a variety of environmental and loading conditions. The same roadway materials would maintain their structure at high temperatures, without creeping under heavy loads, while they would exhibit flexibility at low temperatures, preventing brittle fracture, and would resist fatigue cracking over the vast number of days spent at more typical temperatures. A transportation system built on poor materials is arguably unsustainable, regardless of the sustainability of the material supply, due to delays resulting from potholes, repairs, reconstruction, etc. Asphalts are complicated mixtures whose properties vary depending on the supplier and the original source. It is difficult to determine specific and effective strategies for attaining targeted properties, such as at the extremes of pavement temperature used in classifications. Adding polymers creates modified asphalts with improved results: polymer-modified asphalts maintain specified creep compliance at yet higher temperatures and failure strain and stiffness at yet lower temperatures. Core asphalts from the Strategic Highway Research Program (SHRP) are well-defined from a highway engineering perspective and have provided a context for research studies into asphalt modification strategies, the different contributions to physical properties from different asphalt components, etc. Despite the resulting knowledge and Superpave recommendations for improved asphalt binders, the question of which chemical process or procedure provides the best modification strategy remains an open question. In addition, a potential problem has been findings that Superpave measurements do not test all of the properties affected in polymer-modified asphalts. For example, polymer-modified control sections in a roadway test showed "significantly less cracking than (shale oil-modified) test sections," despite both modified asphalts having a lower temperature performance grading (PG) of -22ºC.  The proposed work addresses properties of the asphalt binder used in roadways and bikeways. The research will develop self-consistent mechanistic models of asphalt physical properties, such as viscosity and dynamic modulus. The expectation is that such "physics-based" models will function effectively in the extrapolation-derived scenarios that occur when testing the extremes of a pavement design. The ultimate project aim is to develop tests and promote new methods of interrelating asphalt properties that can complement standard methods used currently in the Superpave method. Under Superpave guidelines and the PG grading system, asphalts are selected for pavements based on their rheological performance under a few conditions of temperature, frequency, and time. The complex modulus under shear (|G*|), the phase angle, and the tensile modulus (via stiffness S, its reciprocal) are measured using dynamic shear rheometry and bending beam rheometry in order to predict if the asphalt will display sufficient strength at high temperature to prevent rutting, sufficient flexibility at low temperature to resist thermal cracking, and resistance at intermediate temperatures to fatigue cracking. Beyond these direct relationships, correlations have also been made between pavement cracking and properties such as viscosity and ductility. Theoretically, it is possible to inter-relate these different measurements using mathematical tools such as time-temperature superposition, Boltzmann superposition integrals, and Kramer-Kronig relationships, in conjunction with parameterized rheology models. While current practice does employ time-temperature superposition to some extent, there is additional asphalt property information available from trends in temperature and frequency, beyond the individual data points required to compare with a specification. Such information, when combined with an appropriate mechanical modeling tool, can potentially improve the ability to anticipate pavement failures due to unexpected asphalt mechanical responses that were not assumed when devising the specifications. The proposed work will naturally address asphalt rheology using a multidisciplinary approach, despite there being a single principal investigator. The methods described originate from polymer science. Their application to asphalts was emphasized during the Strategic Highway Research Program (SHRP, the research that led to Superpave) and was reinterpreted through a civil engineering perspective. In the proposed work, a combination of chemical engineering a polymer science perspectives, both held by the PI, will be used to investigate the potential to unify many mechanical tests using a single set of models. The experience will expose chemical engineering undergraduate and graduate students to questions posed by civil engineers. Advice from project End Use Advisors, who are civil engineers at Rhode Island Department o Transportation (RIDOT), will help to ensure that the results are in forms that can truly help to solve problems in the pavement design community. The expected results fall into two categories. The direct result will be parameterized rheological models for asphalts similar to those used by RIDOT in paving applications. Such models can be used in additional research projects about pavement mechanics (e.g. finite element calculations). The indirect result will be increased understanding (both within RIDOT and in the general asphalt community) about how different experiments can be inter-related. Spreadsheets and other programs for doing the modeling will be transferred to RIDOT as part of the modeling effort. The project will initially rely on experimental data available from the literature, through assistance of fellow asphalt researchers. An excellent example is work by Marateanu and co-workers; they measured frequency dependence of complex modulus over a range of temperatures for both RTFO and PAV-aged asphalts. Methods summarized here will be applied initially to their data. Many others have published asphalt rheology data as well. For example, Shenoy presented dynamic shear rheometry studies of polybutadiene/polystyrene and polyethylene modified asphalts, demonstrating superposition of the rheological results. Masson and co-workers have used tools such as infrared spectroscopy and modulated differential scanning calorimetry to study phase behavior and microstructure of polymer modified and unmodified asphalts. Many other data sets are published as well, such as for SBS and polyethylene modified asphalts.

    Language

    • English

    Project

    • Status: Active
    • Funding: $32500.00
    • Contract Numbers:

      DTRT06-G-0038

      001850

    • Sponsor Organizations:

      Research and Innovative Technology Administration

      University Transportation Centers Program
      1200 New Jersey Avenue
      Washington, DC  United States  20590
    • Performing Organizations:

      University of Rhode Island Transportation Center

      University of Rhode Island
      75 Lower College Road
      Kingston, RI  United States  02881
    • Principal Investigators:

      Greenfield, Michael

    • Start Date: 20080101
    • Expected Completion Date: 0
    • Actual Completion Date: 20100630
    • Source Data: RiP Project 20243

    Subject/Index Terms

    Filing Info

    • Accession Number: 01462362
    • Record Type: Research project
    • Source Agency: University of Rhode Island Transportation Center
    • Contract Numbers: DTRT06-G-0038, 001850
    • Files: UTC, RiP, USDOT
    • Created Date: Jan 3 2013 2:02PM