Research

Publications

Journal publications

Our researchers have published more than 150 technical papers and journal articles in civil engineering, transportation research and materials journals.

Research reports

View a list of our research reports and access PDFs of our research on ScholarWorks.

Theses and dissertations

To view a complete list of master's theses and Ph.D. dissertations conducted as part of the Western Regional Superpave Center, please visit our list of graduate dissertations and theses on ScholarWorks.

Current research projects

  • Development and Deployment of Innovative Asphalt Pavement Technologies

    Abstract

    The Federal Highway Administration (FHWA) has an ongoing Accelerated Implementation and Deployment of Pavement Technologies (AIDPT) Program, which includes the deployment of innovative technologies to improve pavement performance and reduce agency risk. A constant challenge in the transportation community is timely and efficient deployment of these new and innovative technologies. This is particularly true in the area of asphalt pavements. It often takes years, and sometimes decades, to change business practices, revise specifications, or refine production and construction practices.

    The Pavement Engineering & Science (PES) program in the Civil end Environmental Engineering department was selected to stimulate, facilitate, and expedite the deployment and rapid adoption of new and innovative technology relating to the design, production, testing, control, construction, and investigation of asphalt pavements. The proposed project is a cooperative effort between the FHWA and the University of Nevada, Reno team to improve the quality and performance of asphalt pavements.

    Products will include developing marketing/implementation plans, engaging subject matter experts to aid in conducting forensic investigations pertaining to deployment and in the refinement of specifications and practices, developing web-based training tools, marketing of case studies, data analysis, market analysis, specification tracking, compilation of findings, and supporting stakeholder engagement. This effort will leverage the unique technology capabilities and facilities of the University's team with FHWA’s mission. 

    The University's team consists of the PES program faculty, and two subcontractors: Applied Research Associates (ARA) and Paragon Technical Services, Inc. The project performance period is 5 years.

  • Guide for Flexible Pavement Design and Materials Selection
    • Sponsored by Regional Transportation Commission of Washoe County
    • Peter E. Sebaaly (PI), Adam J. Hand and Elie Hajj (co-PIs)
    • Date: July 1, 2016 - June 30, 2020

    Abstract

    This research is funded by the Regional Transportation Commission (RTC) of Washoe County, Nevada, U.S.A. The Guide was developed by the faculty and graduate students of the pavement engineering and science (PES) Program.

    The Guide has two major parts:

    1. Structural design
    2. Materials selection

    The structural design for flexible pavements was developed to provide uniform pavement design practices for North-Western Nevada agencies and consultant personnel conducting new and rehabilitated flexible pavement designs following the AASHTO 1993 Pavement Design Guide. The structural design part was finalized on October 1, 2019 and presented an all-inclusive process for the structural design of flexible pavements within Nevada’s North-Western Region.

    The Guide covered the following critical aspects of the structural design of flexible pavements:

    1. Definitions of distresses encountered in flexible pavements and in-depth discussions on their potential causes and recommended steps to prevent their occurrence.
    2. Characterization of traffic loads, which play a critical role in the structural design of flexible pavements.
    3. Selection and design of new and rehabilitation strategies along with examples.
    4. Discussion of an effective pavement preservation program to ensure that the designed-constructed flexible pavement will perform at a high level of service throughout its design life.

    The materials selection part is currently being developed and will be incorporated into the final Guide, which will combine the two parts. The objective of the materials selection is to provide guidance for engineers specifying and approving asphalt mixture types and mix designs giving consideration to:

    • Physical location of the mixture defined by functional classification (e.g., arterial, collector, residential roads) and expected traffic level and type.
    • Location of the mixture in the pavement structure (surface course or underlying layer).
    • Mixture design options including nominal maximum aggregate size (NMAS), asphalt binder type, allowable recycled asphalt pavement (RAP) content, compaction level (75 versus 50 blow versus Superpave 50 gyrations) and design air void level (4 versus 3%).

    The materials selection will make it possible to consistently and easily select the right mix type for the right project specific conditions, will simplify the process for design engineers, and reduce the potential for specifying mixture(s) that may not optimize pavement performance.

  • Impact of Recycled Tires on the Performance of Asphalt Concrete Pavements
    • Sponsored by U.S. Polyco Company
    • Peter E. Sebaaly (PI)
    • Date: October 1, 2017 - September 30, 2020

    Abstract

    This research project is sponsored by the U.S. Polyco Company, Ennis, Texas, U.S.A. The objective of the research is to evaluate the properties of asphalt binders that are modified with rubber from recycled tires and assess their impacts on the performance of asphalt mixtures and asphalt concrete pavements. The U.S. produces 300 million used tire each year. Using some of the used tires into the construction of asphalt concrete pavements would reduce some landfills around the country. Preliminary data from this research showed that up to 4,700 used tires can be recycled into the construction of every lane-mile of asphalt concrete pavement.

    In this research, graduate students in the Pavement Engineering and Science (PES) Program work under the direct supervision of the faculty to assess the engineering properties and performance characteristics of tire rubber modified asphalt binders and mixtures. The engineering property of the asphalt mixture is measured in terms of its dynamic modulus while the performance characteristics are measured in terms of the asphalt mixture resistance to rutting, fatigue cracking, thermal cracking, and reflective cracking. The various experiments are conducted using state of the art equipment in the PES laboratory facilities.

    Once these evaluations are conducted, the impact of the tire rubber modified asphalt mixtures on the performance life of the asphalt concrete pavement will be evaluated through advanced dynamic analyses, which takes into consideration the unique features of the moving vehicle and the complex behavior of the pavement structure. Finally, life cycle cost analyses will be conducted to determine the benefit-cast ratio of using tire rubber modified asphalt mixtures in the construction of asphalt concrete pavements.

Past research projects

  • Analysis Procedures for Evaluating Superheavy Load Movement on Flexible Pavements (DTFH61-13-C-00014)
    • Sponsored by Federal Highway Administration
    • Elie Y. Hajj (PI), Raj V. Siddharthan (Co-PI), and Sherif Elfass (Research Engineer)
    • Date: August 19, 2013 - January 31, 2018
    • GovTribe Record

    Abstract

    The movement of superheavy load (SHL) has become more common over years since it is a vital necessity for many important industries. Superheavy load (SHL) hauling units are much larger in size and weight compared to the standard trucks. SHL vehicles may involve gross vehicle weights in excess of a few million pounds often requiring specialized trailers and components with non-standard spacing between tires and axles. Such moves require the determination of whether the pavement is structurally adequate to sustain the SHL movement and involves the analysis of the likelihood of instantaneous or rapid load-induced shear failure.

    In this study, a comprehensive mechanistic-based methodology was developed which consisted of the following analysis procedures:

    1. Segmentation of SHL analysis vehicle
    2. Subgrade bearing failure analysis
    3. Sloped shoulder failure analysis
    4. Buried utility risk analysis
    5. Localized shear failure analysis
    6. Deflection-based service limit analysis
    7. Cost allocation analysis

    This report presents a summary of these developed analysis procedures associated with SHL movement on flexible pavements. Further details of these procedures are presented in their respective standalone appendix reports.

    Complementary verification and calibration processes of a number of important theoretical-based aspects that were incorporated in the analysis approach were conducted. To this end, a comprehensive experimental program that included five full-scale pavement/soil testing performed at the University's large-scale box facility was designed and carried out. Supplementary numerical modeling as well as measured data from Accelerated Pavement Testing (APT) facilities provided additional justifications to the procedures adopted in this study. The developed analysis procedures were then implemented into a user-friendly software package called SuperPACK (Superheavy Load Pavement Analysis PACKage) to evaluate SHL movements on flexible pavements.

  • Structural Coefficient for High Polymer Modified Asphalt Mixes (BE321)
    • Sponsored by Florida Department of Transportation
    • Peter E Sebaaly (Co-PI), Elie Y. Hajj (Co-PI), Adam J. T. Hand, and Rajaratnam Siddharthan
    • Date: March 7, 2017 - March 6, 2019
    • TRID database record

    Abstract

    The overall objectives of this research study are to determine the structural coefficient for asphalt mixes that contain high polymer modified binder (specified by FDOT as PG76-22 (HP) and containing approximately 7.5% SBS or SB polymer). With this determination, the Flexible Pavement Design Manual will be modified to adopt the structural value for mixtures containing this binder type. The proposed approach combines advanced laboratory testing and characterization of PMA and HP mixes from Florida with an array of dynamic modeling of flexible pavement responses under different traffic conditions simulating urban roads, intersections, and off ramps. Initial structural coefficients (SCs) for HP modified asphalt mixes will be developed for new and overlay pavement designs based on respective identified critical distresses. The dynamic modeling will be completed through a computer model for flexible pavements (3D-FAST) that has been developed by the researchers and validated using several field measured pavement responses. The 3D-FAST software will allow researchers to account for the mix-specific viscoelastic properties of the PMA and HP AC layers, varying vehicle travel speeds, braking and decelerating effects, and non-uniform contact stress distributions at the tire-pavement interface. This effort will be followed by a verification experiment with the full scale laboratory testing of flexible pavement structures in the indoor 10.3 feet by 10.3 feet by 7 feet high PaveBox at the University of Nevada, Reno. The full-scale laboratory testing using the PaveBox will serve as an intermediate step between the laboratory and the APT experiments by helping researchers in refining the initially determined SCs before making final recommendations.

  • Mechanistic-Based Pavement Damage and Associated Cost from Overweight Vehicles in Nevada (No. 609-13-803)
    • Sponsored by Nevada Department of Transportation
    • Elie Y. Hajj (PI), and Raj V. Siddharthan (Co-PI)
    • Date: January 7, 2014 - September 30, 2017
    • TRIS Database Record

    Abstract

    The movement of overweight (OW) vehicles has become more common over the years due to its vital necessity for many important industries such as chemical, oil, defense, etc. Using OW vehicles reduces the number of vehicles on highways, potentially decreasing traffic congestion and emissions. However, the operation of large and heavy vehicles can lead to a speedy deterioration of the roadway system; hence necessitating additional resources to maintain the conditions of roadway pavements at an acceptable level.

    The approach presented in this study allows for the estimation of pavement damage associated costs (PDAC) attributable to OW vehicle moves. The PDAC can be estimated for different OW axle loadings and configurations with due considerations given to locally-calibrated pavement distress models, existing pavement condition, different pavement repair options, and vehicle miles traveled (VMT). The approach uses the same information currently requested by NDOT during the OW permit application process and provides a realistic methodology to assess pavement damage from single-trip and multi-trip OW scenarios. In the methodology, the damage from OW vehicles is compared to that caused by a standard vehicle. It should be noted that the costs associated to the pavement damage caused by lighter vehicles (GVW up to 80,000 lb) is assumed to be already covered by fuel taxes and will be reflected in a PDAC of zero dollars.

    As part of this study a ten-year NDOT over-dimensional permit database containing 367,595 entries was analyzed. Along with the ten-year permit database, thousands of actual over-dimensional permit forms which described GVW and the entire axle and load configurations of the permitted vehicles were analyzed. The purpose of the analysis was the identification and classification of trends, GVW, axle loads/tire loads and other important characteristics of the OW movements in Nevada. This analysis enabled the design of a comprehensive experimental plan of pavement analyses required to model OW vehicles under the different loading, pavement temperature, and speed conditions found in Nevada.

    The presented methodology provides useful ways to assess pavement damage from OW vehicles, eliminating the need for conducting individual deterministic pavement analysis assessments. Through comparative analysis it was found that the proposed methodology produces PDAC values that are comparable to those levied by other SHAs that implement distance and weight-distance fee structures. It was also estimated that the PDAC methodology could produce significant increase in revenue when assuming average input values. However, such increase in revenue is mostly associated to OW vehicles in the heaviest categories.