Education

Research Description

Dr. Underwood's research and education program focuses on materials and their interaction with society and the natural and built environments. This program pursues research, education, and service activities that evaluate, inform, and shape the science of these interactions, particularly how material decisions influence the use, function, and impact of civil infrastructure. As he and his students pursue these questions both broadly (by expanding the scope or significance of impact assessment) and deeply (by building the methods and models to better explain the physical behaviors that occur) new findings are integrated into his teaching. He and his students pursue this research in two ways. First, they use experimental mechanics and constitutive models to evaluate and understand the behavior of infrastructure materials, principally asphalt concrete. This knowledge is then exploited to better engineer the materials and/or structures to achieve sustainability and resiliency. Second, they use emerging perspectives and analytical tools to assess the role of social constructs in governing the impact of technological advances on infrastructure. Specific attention is given to pavements and with a focus on resilience due to a recognition that pavement engineering and indeed engineering of infrastructure in the built environment is facing great uncertainty.

Publications

Performance of warm asphalt mixtures containing reclaimed asphalt pavement, an anti-stripping agent, and recycling agents: A study using a balanced mix design approach

Yousefi, A. A., Haghshenas, H. F., Underwood, B. S., Harvey, J., & Blankenship, P. (2023), CONSTRUCTION AND BUILDING MATERIALS, 363. https://doi.org/10.1016/j.conbuildmat.2022.129633

Characterization of the permanent deformation of asphalt mixtures based on indexes and on pavement structural performance

Barros, L. M., Nascimento, L. A., Sacramento Aragao, F. T., Underwood, B. S., & Pivetta, F. do C. (2022), CONSTRUCTION AND BUILDING MATERIALS, 326. https://doi.org/10.1016/j.conbuildmat.2022.126555

Correlation of asphalt binder linear viscoelasticity (LVE) parameters and the ranking consistency related to fatigue cracking resistance

Yang, K., Li, R., Castorena, C., & Underwood, B. S. (2022), CONSTRUCTION AND BUILDING MATERIALS, 322. https://doi.org/10.1016/j.conbuildmat.2022.126450

Cracking performance predictions using index-volumetrics relationships with direct tension cyclic fatigue test and Illinois Flexibility Index Test (I-FIT)

Jeong, J., Underwood, S., & Kim, Y. R. (2022), CONSTRUCTION AND BUILDING MATERIALS, 315. https://doi.org/10.1016/j.conbuildmat.2021.125631

Development of an analytical framework for evaluation of critical fiber length in asphalt concrete with a fiber pullout test

Noorvand, H., Mobasher, B., Underwood, S., & Kaloush, K. (2022), CONSTRUCTION AND BUILDING MATERIALS, 360. https://doi.org/10.1016/j.conbuildmat.2022.129561

Effect of laboratory oxidative aging on dynamic shear rheometer measures of asphalt binder fatigue cracking resistance

Yang, K., Li, R., Underwood, B. S., & Castorena, C. (2022), CONSTRUCTION AND BUILDING MATERIALS, 337. https://doi.org/10.1016/j.conbuildmat.2022.127566

Evaluation of Recycling Agent and Extender Dosage Selection Procedures to Restore the High-Temperature Climatic Performance Grade

Fried, A., Xue, L. G., Gulzar, S., Preciado, J., Underwood, B. S., & Castorena, C. (2022, February 5), TRANSPORTATION RESEARCH RECORD, Vol. 2. https://doi.org/10.1177/03611981221074361

Evaluation of Structural Performance of Pavements under Extreme Events: Flooding and Heatwave Case Studies

Matini, N., Gulzar, S., Underwood, S., & Castorena, C. (2022, March 9), TRANSPORTATION RESEARCH RECORD, Vol. 3. https://doi.org/10.1177/03611981221077984

Method to Reduce Uncertainty in the Prediction of Pavement Condition With a Lower Sample Frequency

Goenaga, B., Karanam, D., & Underwood, B. S. (2022, April 12), TRANSPORTATION RESEARCH RECORD, Vol. 4. https://doi.org/10.1177/03611981221086636

Molecular-based asphalt oxidation reaction mechanism and aging resistance optimization strategies based on quantum chemistry

Liu, S., Shan, L., Li, G., Underwood, B. S., & Qi, C. (2022), MATERIALS & DESIGN, 223. https://doi.org/10.1016/j.matdes.2022.111225

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Grants

Balanced Asphalt Mix Design for North Carolina

NC Department of Transportation(8/01/22 - 7/31/24)

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Balanced Asphalt Mix Design for North Carolina

Sponsor: NC Department of Transportation

Start Date: 8/01/22

End Date: 7/31/24

Abstract

Current procedures for asphalt mixture design in North Carolina require contractors to conform to volumetric requirements on the air void content, voids in mineral aggregate, and other parameters at a fixed, traffic- and layer-specific compaction effort. The presumption in this case is that the mixtures produced under the same guidelines will have similar properties. However, recent findings by NCSU suggests that this presumption may be inaccurate and may have substantial implications in the design, performance, and management of roadways. This research study will address this issue by: i) identifying the most appropriate durability related testing protocol for incorporation into mix design and quality assurance/control operations; ii) establishing initial threshold limits for the test identified; iii) developing a draft balanced mix design (BMD) procedure for North Carolina, and iv) developing a draft protocol for integrating the identified performance tests into quality assurance and quality control operations. The primary outcome of the proposed research will be a test method and procedure that the NCDOT can deploy in asphalt mixture design and production to ensure that the mixtures delivered in the state have an acceptable level of performance.

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Evaluation of RAP/RAS Stockpiles in North Carolina and Changes in these Stockpiles Over Time

NC Department of Transportation(8/01/22 - 7/31/24)

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Evaluation of RAP/RAS Stockpiles in North Carolina and Changes in these Stockpiles Over Time

Sponsor: NC Department of Transportation

Start Date: 8/01/22

End Date: 7/31/24

Abstract

The vast majority of asphalt mixtures produced in North Carolina contain recycled materials, including Reclaimed Asphalt Pavement (RAP) and/or Recycled Asphalt Shingles (RAS). This research project seeks to identify how asphalt plant processing and stockpiling variables affect the consistency of RAP and RAS materials with time in a given stockpile and across different plants in North Carolina. Furthermore, the project will assess how changes in recycled material properties affects asphalt mixture performance is needed to understand the practical implications of variability. Collectively, the results of this research will inform improved measures within the NCDOT specifications to mitigate variability of recycled material sources and, in turn, improve the reliability of asphalt mixture performance.

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Mechanistic-Based Evaluation of Performance Thresholds for Engineered Surface Asphalt Mixtures

US Dept. of Transportation (DOT)(2/01/22 - 6/29/24)

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Mechanistic-Based Evaluation of Performance Thresholds for Engineered Surface Asphalt Mixtures

Sponsor: US Dept. of Transportation (DOT)

Start Date: 2/01/22

End Date: 6/29/24

Abstract

In 2018, an initial effort was undertaken by Virginia Transportation Research Council (VTRC) to provide benchmark indications of performance for a number of “typical / everyday” asphalt surface mixtures produced and sampled in 2015 in anticipation of this new approach. Three fast, simple, practical, but empirical performance tests addressing different modes of distresses were selected for use as part of the BMD method. The selected tests were Cantabro test, the Indirect Tensile cracking test (IDT-CT), and the Asphalt Pavement Analyzer (APA) rut test for assessing durability, cracking and rutting potentials of asphalt mixtures, respectively. VDOT has been so far extensively building upon its BMD initiative based on Approach I, the empirical tests (for rutting and cracking) and associated thresholds have never been verified through the use of Approach II. This study would provide an opportunity to: • Establish links between laboratory performance-related asphalt mixtures empirical and fundamental properties (on one hand) and M-E structural pavement design (on the other hand). This is a vital step to a practical integration of mixture design and structural design. • Verify (or refine) the performance thresholds on the basis of mechanistic approach, rather than empirical approach. • Establish and verify initial traffic-based performance thresholds for the empirical tests tied /correlated to the fundamental tests and mechanistic analyses. In order to fulfill the objectives of this research study, the following six primary tasks are proposed. First, the existing literature on similar efforts by other state agencies will be summarized and reported. Then, the research team will conduct a laboratory experimental program with three major parts: material selection (18 different mixtures), performance testing on reheated mixtures, and performance testing on extracted and recovered binder. NCSU researchers will assist in all three tasks, but take the primary lead in the performance testing on asphalt mixtures and binders. Third, the laboratory measured engineering and performance properties will be coupled in a full mechanistic analysis framework. This is a vital step to quantify and effectively evaluate the impact of using BMD asphalt surface mixture on the overall performance of pavements. This will include the use of AASHTOWare® Pavement ME and FlexPaveTM. The mechanistic-based simulations will be executed using real existing and most commonly encountered pavement structures in Virginia (referred to herein as pseud-hypothetical pavement structures). NCSU researchers will lead the analysis of this task and carry out the requisite simulations. Fourth, links and correlations between BMD and mechanistic-based fundamental tests. In Task 5, NCSU researchers will VDOT personnel at the VTRC (or other approved site in Virginia) to perform AASHTO TP 132 (dynamic modulus), AASHTO TP 133 (cyclic fatigue) and AASHTO TP 134 (stress sweep rutting). In Task 6, a final report will be developed. VTRC personnel will lead this effort, but NCSU researchers will support the task.

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BMD+ and PEM+ Advances Mixture Performance Comparison and Next Generation Pavement Design

Federal Highway Administration (FHWA)(11/11/21 - 5/29/23)

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BMD+ and PEM+ Advances Mixture Performance Comparison and Next Generation Pavement Design

Sponsor: Federal Highway Administration (FHWA)

Start Date: 11/11/21

End Date: 5/29/23

Abstract

The objective of this task order is the continued advancement of the performance specification continuum for BMD+ and mechanistic pavement design. Advancement of efforts will be accomplished by the following tasks: 1. Development of Level 1 BMD+ methods and threshold values for Level 2 BMD index parameters (Sapp and RSI) 2. Performance testing for transfer functions to support BMD+ and advanced pavement design 3. Comparison of BMD and BMD+ testing for mixture performance comparisons and analysis 4. Advance in a collaborative approach for FlexPAVE pavement design methods 5. BMD+ training and parallel field construction projects 6. Interim stakeholders status meeting 7. Create a system of tools including guidelines and sample specifications for agencies to transition from their traditional standard specifications to BMD+ specifications using performance tests and advanced mechanistic pavement design

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Development of Friction Performance Models

NC Department of Transportation(8/01/21 - 7/31/23)

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Development of Friction Performance Models

Sponsor: NC Department of Transportation

Start Date: 8/01/21

End Date: 7/31/23

Abstract

Vehicle collisions and increases in collisions rates during wet conditions are one of the major safety concerns for the NCDOT. Collision rates increase when the surface is wet because skid resistance reduces under these conditions. The precise amount of loss is dependent on many factors, but the consensus among experts is that pavement friction and macrotexture are important factors that affect the skid resistance and changes in this resistance under wet conditions. This research will achieve three objectives; 1) characterize friction and texture performance models, 2) develop friction and texture performance thresholds, and 3) identify asphalt mixture compositional factors (gradation, asphalt content, presence of modified versus non-modified asphalt, etc.) that affect the as-constructed macrotexture and friction. The primary outcome of the proposed research will be an initial set of performance models that can be used to assess immediate and potentially long-term friction/macrotexture issues. The research will also produce a set of threshold limits for friction/macrotexture where investigatory and intervention steps need to be taken to control for safety. Finally, the research will produce information on the mixture design factors that contribute to higher or lower friction/macrotexture. These outcomes can be used by the Traffic Safety and Materials and Test Units of the North Carolina DOT to predict and manage friction and texture performance on roadways and to understand when measurements represent a potential hazard exists. It will also be used to help identify asphalt mixtures with potential friction and macrotexture issues and develop better guidelines, specifications, and operational controls (if necessary) for recently overlaid pavements. This could lead to reduced collision rates on these pavements. Thus, this research will result in overall improved procedures for flexible pavement overlay operations.

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TSA: TESTING SERVICES AGREEMENT: MICHELIN RUBBER COMPOUND TESTING USING MICHELIN STANDARD TRIBOLOGY TEST PROTOCOL

Michelin(2/01/21 - 3/31/21)

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TSA: TESTING SERVICES AGREEMENT: MICHELIN RUBBER COMPOUND TESTING USING MICHELIN STANDARD TRIBOLOGY TEST PROTOCOL

Sponsor: Michelin

Start Date: 2/01/21

End Date: 3/31/21

Abstract

TSA: TESTING SERVICES AGREEMENT: MICHELIN RUBBER COMPOUND TESTING USING MICHELIN STANDARD TRIBOLOGY TEST PROTOCOL

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Modifying Existing Asphalt Mix Design Procedures for RAP/RAS Surface Mixtures

NC Department of Transportation(1/01/21 - 8/15/23)

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Modifying Existing Asphalt Mix Design Procedures for RAP/RAS Surface Mixtures

Sponsor: NC Department of Transportation

Start Date: 1/01/21

End Date: 8/15/23

Abstract

The use of high Recycled Binder Replacement Percentages (RBRs%) in asphalt surface mixtures is increasing. The asphalt binders in recycled materials are generally hardened and embrittled from oxidization and may not fully mobilize and blend with virgin materials. Consequently, high recycled content mixtures may be prone to cracking if appropriate measures to consider this effect are not taken during the mixture design process. The objectives of the proposed research project are to: (1) modify the NCDOT’s procedures for the design of surface mixtures containing RAP and RAS to improve performance and (2) modify the NCDOT’s specifications to improve the consistency within and across RAP and RAS stockpiles within North Carolina. 1. To achieve these objectives, an operational review will be conducted to identify how contractors process, stockpile, characterize and use RAP and RAS under the current NCDOT guidelines. In addition, relationships between asphalt content and performance will be developed for recycled mixtures sourced from North Carolina. These relationships will be used to identify the maximum virgin binder content allowable and to maximize cracking performance without having the rutting performance fall below a critical performance threshold for each mixture. The collective results will be used to identify appropriate revisions to the NCDOT’s current recycled mixture design procedure to ensure reliable performance. The research results will lead improved specifications that will facilitate the design of better-performing surface mixtures containing recycled materials. These specifications will improve the durability of NCDOT pavements and consequently decrease life-cycle costs.

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Pavement Performance Impacts Predicted by Climate Change Models in Arizona

Arizona Department of Transportation (ADOT)(1/01/21 - 12/31/21)

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Pavement Performance Impacts Predicted by Climate Change Models in Arizona

Sponsor: Arizona Department of Transportation (ADOT)

Start Date: 1/01/21

End Date: 12/31/21

Abstract

General circulation models for the global climate (generally referred to as climate change models),have predicted wide ranging changes over the next several decades. Some of these changes relate to roadways and pavement infrastructure. Researchers and government entities have identified temperatures (extreme and mean levels of change) and precipitation as primary drivers for these impacts. In the proposed work, NCSU will work with the Arizona Department of Transportation to develop long-term climate model data in connection with future heat and precipitation to the year 2100 and beyond. The specific emphasis of the proposed work is on impacts to pavements.

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Asphalt Pavement Reflective Cracking Model to Better Address Rehabilitation

Federal Highway Administration (FHWA)(9/27/21 - 7/26/23)

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Asphalt Pavement Reflective Cracking Model to Better Address Rehabilitation

Sponsor: Federal Highway Administration (FHWA)

Start Date: 9/27/21

End Date: 7/26/23

Abstract

The Federal Highway Administration (FHWA) has developed mechanistically based performance comparison models to evaluate the cracking and rutting performance of asphalt pavement mixtures. These models form the basis of an asphalt performance comparison development effort and are being implemented into a FlexPAVETM software program for analyzing pavements and predicting distress. In this research study, NCSU will assess current asphalt pavement cracking models that can be applied to reflective cracking and further research, develop, calibrate, train, and validate a mechanistically based asphalt pavement reflective cracking model that is consistent with existing FlexPAVETM methodology and performance tests; incorporate it into the FlexPAVETM software and the FlexMATTM and FlexMIXTM data analysis tools, and assess and incorporate run time improvements to the model, software, and analysis tools.

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Seasonal Effects due to Moisture Variation and Investigation of Cyclic Fatigue Temperature and End Failure on Pavement Performance

US Dept. of Transportation (DOT)(8/12/20 - 2/10/23)

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Seasonal Effects due to Moisture Variation and Investigation of Cyclic Fatigue Temperature and End Failure on Pavement Performance

Sponsor: US Dept. of Transportation (DOT)

Start Date: 8/12/20

End Date: 2/10/23

Abstract

In this research study, NCSU will conduct experiments and analysis to improve the AASHTO TP 133 protocol by incorporating more scientifically based temperature selection guide and providing guidance on the maximum air void content for specimens that are subjected to this standard test method. In addition, NCSU will update the FlexPAVETM software to incorporate seasonal effects into the base layer and the user guides for improved usability. This research supports ongoing FHWA efforts as part of a performance-related specification framework which seeks to increase pavement life through fundamental testing and predictive relationships. Recent developments in these performance tests, adoption of standards, FlexMATTM, FlexMIXTM, and FlexPAVETM provide highway agencies and asphalt paving community with a unique opportunity to use performance tests and mechanistic models for asphalt PEMD, asphalt pavement design, and performance related specifications to integrate these different phases in pavement construction using the same test methods and mechanistic principles. These tools help link material characteristics from testing with mechanistic models to predict performance; and ultimately identify how to best design, construct, and accept a pavement. NCSU will carry out the following tasks. Task 1 – Develop final research plans and project schedule – The proposed plan will be revised based on feedback from the FHWA. Task 2 – Kickoff meeting – NCSU will meet with the project panel to review the statement of work and work plans. Task 3 – Perform work plan and document efforts – NCSU will carry out the approved work plan by following the appropriate ASTM standard test methods to develop a rugged test method. Task 4 – Draft Final Revised FlexPAVETM Software, Installation, and User Guides – NCSU will update the user interface, installation guide, and user guide for the FlexPAVETM software. Task 5 –Presentation and webinar – NCSU will present their findings to targeted stakeholders. Task 6 – Publication ready final deliverables – the reports will be revised and finalized and AASHTO standards will be revised into a final form.

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