This project expands upon ongoing research, which is focused on creating model asphalt mixtures comprised of only 5-10 compounds that replicate several physical properties of SHRP core asphalts while possessing chemical functionalities consistent with those of real asphalts, as based on experimental characterizations available from the literature. It will first target examples from the experimental asphalt literature in order to check the simulation predictions and to explain the underlying reasons for successful additive effects. An intermediate-term step, which will commence during this project, is to establish collaborations with a lab-experiment-based transportation research group (or groups), and/or with asphalt suppliers. Over the long-term, we would jointly propose strategies and improvements, assess them using the modeling tools developed, and finally test them experimentally. The result of this follow-up project will be a demonstration that model asphalt compositions, when combined with model additives such as polymers or rubber, lead to overall mixtures that display the same modifications from pure asphalt properties as those found to occur in real asphalt/modifier samples. This validation will enable the model asphalt compositions to be used in subsequent property prediction studies.
Highway
Asphalts are complicated, poorly defined, and inexpensive mixtures of hundreds of chemical compounds. Even with well-documented samples, such as the Strategic Highway Research Program-sponsored "core" asphalts, determining specific and effective strategies for attaining targeted properties is a difficult process. This project expands upon ongoing research, which is focused on creating model asphalt mixtures comprised of only 5-10 compounds that replicate several physical properties of SHRP core asphalts while possessing chemical functionalities consistent with those of real asphalts, as based on experimental characterizations available from the literature. It is planned that the model asphalt mixtures be expanded to test their ability to predict effects of asphalt modification using common additives, such as polymers or rubber. The mixture effects will be tested using molecular simulation techniques: statistical mechanics-based tools for predicting microscopic and macroscopic properties based on the details of molecule-molecule interactions. The direct outcome of the work will be initial evaluations of a future opportunity: using molecular-scale calculations to predict how different additives or new additive strategies can affect overall asphalt mechanical properties, using modeling tools in advance of experiments. The molecular-level detail will enable assessing why particular additive strategies succeed or fail, allowing for further science- and engineering-based improvements.
Task 1. Asphalt Modifier Selection
The first task is to choose asphalt modifiers of most interest to the Rhode Island Department of Transportation and its contractors. The focus will be on additives appropriate for unmodified asphalts similar to those modeled using the simplified asphalt mixtures. The availability of literature data for modified asphalt mechanical properties will also be taken into account during this selection process.
Task 2. Simulations of Asphalt/Modifier Mixtures and Comparisons with Literature Data
The second task is to conduct molecular simulations on the selected model asphalt/modifier mixtures. The predicted results will be compared to experimental data. The simulation results are expected to reproduce the expected additive effects.
Task 3. The "Whys" of Additive Function
The third task is to deepen the interpretation of the asphalt/modifier simulations. In particular, the specific molecular-level interactions that change overall modified asphalt properties will be sought out. This will enable exploring and interpreting the "whys" of asphalt function. Such results and consequent new knowledge will be used to improve and optimize model asphalt and asphalt/modifier compositions.
Below lists the original dates and milestones:
December 2004 Completion of current project to determine model asphalt mixtures that replicate mechanical behaviors of unmodified asphalts. New project begins.
February 2005 Select set of target asphalts and modifier combinations of interest. Find appropriate literature data that describe modification effects.
May 2005 Attain first model asphalt/modifier combination that replicates, in molecular simulations, physical property modifications for a modified asphalt of interest.
August 2005 Complete studies of other mixtures and address "why" questions. Research portion of project completed at start of fall semester.
November 2005 Present completed work at American Institute of Chemical Engineers (AIChE).
January 2006 Present completed work at Transportation Research Board (TRB).
$64,887.94
Research assistantship for Ph.D. student, including summer research; paid employment for an undergraduate researcher.
Extends project titled "Developing Model Asphalts using Molecular Simulation" by considering how such model asphalts respond to the presence of common asphalt modifiers, such as polymers.
The principal investigator's research focuses on molecular simulations of polymers, liquids, and additives. One graduate student in the group is working on the first phase of this project. The other graduate student in the group is using Monte Carlo, molecular dynamics simulations, and geometric analysis calculations to study packing and function of polythiophene polymers. Independently, the principal investigator is conducting simulations of molecular tribology and of diffusion through polymers. While the research content is separate from these other projects, the methodologies are similar. This has already allowed the graduate student conducting asphalt simulations (in the previous phase of the project) to benefit from intra-group mentoring, discussions, and interactions.
Results will be presented to a chemical engineering audience at the Annual Meeting of the American Institute of Chemical Engineers (AIChE) and possibly via the American Chemical Society (Fuel and Petroleum chemistry divisions). Results will be communicated to a transportation audience at the Transportation Research Board (TRB) Annual Meeting and/or at the Association of Asphalt Paving Technologists (AAPT) Annual Meeting, as well as via URITC and RIDOT. Project reports will be converted into journal articles for widespread long-term accessibility.
One key application of creating model asphalt and modified asphalt mixtures is developing and screening different proposed modification strategies. Why do certain additives affect high or low temperature properties? Is it possible to provide low-temperature flexibility and high-temperature rutting resistance simultaneously? What kinds of polymers, copolymers, or plasticizers might be most compatible? Do time-temperature superposition concepts developed in polymer science apply to original or modified asphalt systems? This follow-up study will begin with base cases from the initial research project and will target examples from the experimental asphalt literature in order to check the simulation predictions and explain the underlying reasons for successful additive effects.
The results will ultimately be useful to the materials area within the Research and Technology section of the RIDOT Transportation Development section. Research progress will be shared with Colin Franco and Francis Manning, RIDOT Research and Technology Development, on an ongoing basis. Franco and Manning will help to identify the most promising findings that can move towards direct highway tests via continued laboratory testing.
Research groups that conduct asphalt property experiments will be contacted early in the research process to lay groundwork for collaborations. This will ensure that a framework exists for simulating promising asphalt additives in follow-up work. We would jointly propose strategies and improvements, assess the proposed improvements using the modeling tools developed, and finally test them experimentally. The long-term application is thus creating modified asphalts that exhibit superior physical property characteristics for highway use.
Asphalt, asphalt chemistry, asphalt composition, asphalt model, glass transition, molecular simulation, molecular dynamics, Monte Carlo