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

An investigation into the nonlinear rheological behavior of modified asphalt binders using large amplitude oscillatory shear rheology

Gulzar, S., Castorena, C., & Underwood, S. (2023), INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING, 24(1). https://doi.org/10.1080/10298436.2023.2211211

Asphalt mixture fatigue damage and failure predictions using the simplified viscoelastic continuum damage (S-VECD) model

Zeng, Z., Kim, Y. R., Underwood, B. S., & Guddati, M. (2023), INTERNATIONAL JOURNAL OF FATIGUE, 174. https://doi.org/10.1016/j.ijfatigue.2023.107736

Balanced Mixture Design Framework for Asphalt Mixtures Based on Index- and Performance-Volumetrics Relationships

Rocha, M. L., Aragao, F. T. S., Nascimento, L. A. H., & Underwood, B. S. (2023, April 6), TRANSPORTATION RESEARCH RECORD. https://doi.org/10.1177/03611981231161063

Benchmarking Recycled Binder Blends Using Statistical Analysis: A Case Study of Virginia and North Carolina

Preciado, J., Gulzar, S., Fried, A., Castorena, C., Underwood, B. S., Habbouche, J., & Boz, I. (2023, July 3), TRANSPORTATION RESEARCH RECORD, Vol. 7. https://doi.org/10.1177/03611981231178812

Case Studies of Asphalt Pavement Quality Assurance Specifications, Performance-Related Specifications, and Performance-Based Specifications

Saleh, N. F., DeCarlo, K., Underwood, B. S., Pine, W. J., Huber, G., Tran, N., … Kim, Y. R. (2023, May 4), TRANSPORTATION RESEARCH RECORD, Vol. 5. https://doi.org/10.1177/03611981231166685

Criterion to Select the Maximum Aggregate Size of Fine-Aggregate Asphalt Matrices

Souza, T. D., Enriquez-Leon, A. J., Rocha, M. L., Osmari, P. H., Sacramento Aragao, F. T., Brabo Pereira, A. M., & Underwood, B. S. (2023, March 31), TRANSPORTATION RESEARCH RECORD. https://doi.org/10.1177/03611981231159891

Early Friction and Texture Evolution After an Asphalt Overlay

Goenaga, B., Underwood, B. S., Castorena, C., & Rogers, P. (2023, January 27), TRANSPORTATION RESEARCH RECORD, Vol. 1. https://doi.org/10.1177/03611981221149436

Effect of soil amendments on the compaction characteristics, hydraulic conductivity, and tire sinkage potential of roadside soils

Goenaga, B., Underwood, B. S., Tirkolaei, H., & Neithalath, N. (2023), TRANSPORTATION GEOTECHNICS, 41. https://doi.org/10.1016/j.trgeo.2023.101019

Effect of synthetic fibers on the mechanical performance of asphalt mixture: A review

Jia, H., Sheng, Y., Guo, P., Underwood, S., Chen, H., Kim, Y. R., … Ma, Q. (2023). [Review of , ]. JOURNAL OF TRAFFIC AND TRANSPORTATION ENGINEERING-ENGLISH EDITION, 10(3), 331–348. https://doi.org/10.1016/j.jtte.2023.02.002

Laboratory Performance Evaluation of Alternative Approaches to Incorporate Recycled Binder Availability into Mixture Design Procedures

Mocelin, D. M., Isied, M. M., Alvis, M. C. A., Kusam, A., Underwood, B. S., Kim, Y. R., & Castorena, C. (2023, April 19), TRANSPORTATION RESEARCH RECORD, Vol. 4. https://doi.org/10.1177/03611981231161601

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Grants

Identification and Prioritization of Vulnerable Roadway Segments for Proactive Resilience Planning and Response

NC Department of Transportation(8/01/23 - 7/31/25)

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Identification and Prioritization of Vulnerable Roadway Segments for Proactive Resilience Planning and Response

Sponsor: NC Department of Transportation

Start Date: 8/01/23

End Date: 7/31/25

Abstract

Infrastructure resilience has become an important topic for North Carolina. Recent hurricanes and other extreme events have caused more than $450 million in direct damage to the State’s transportation infrastructure and innumerable indirect damage from losses in mobility, additional travel times needed while repairs were made, and other impacts. Though the North Carolina DOT (NCDOT) has been conducting studies to understand vulnerability and risk to its assets, most of these have focused on hydraulic structures and/or pavements that were located on top of, or adjacent to, hydraulic structures. In light of these issues, the proposed research plan will seek to achieve five objectives. 1) Provide a better understanding of the failure pathways and factors contributing to pavement failures during past events. 2) Identify the gaps and critical data linkages that hinder the use of existing NCDOT information to support resilience-based planning with respect to pavements. 3) Develop a framework for identifying and prioritizing road segments as part of resilience-based improvement plans/programs. 4) Develop a design feature selection and repair strategy decision tree that considers specific features, planned needs, sustainability considerations, and possible extreme event stressors at a given pavement site. 5) Identify data gaps and critical data linkages that hinder the use of existing NCDOT information to support this effort and provide recommendations to improve data collection and information to support resiliency efforts. The primary outcome of the proposed research will be a design feature selection and repair strategy decision tree that considers specific features, planned needs, sustainability considerations, and possible stressors at a given pavement site. Another product will be identification of critical data linkages that hinder the use of existing NCDOT information to support this effort and recommendations to improve data collection and information to support resilience efforts. This research will provide NCDOT personnel with the tools necessary to take a proactive approach to inform pavement resilience project identification and prioritization based upon the as-built and current condition of roadway segments. It will also identify the design and repair options that could be used to improve the pavement performance during and after extreme events such as hurricanes. This research will also improve specifications that are used for design or repair so that pavements are better able to withstand extreme event damage and/or recover more quickly and/or the damage that does occur has a more limited impact on safety and mobility.

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Evaluation of Macrotexture and Friction of Alternative Asphalt Surface Course Material

NC Department of Transportation(8/01/23 - 7/31/25)

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Evaluation of Macrotexture and Friction of Alternative Asphalt Surface Course Material

Sponsor: NC Department of Transportation

Start Date: 8/01/23

End Date: 7/31/25

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. In recent years the NCDOT has conducted different research efforts to characterize the friction and texture characteristics of North Carolina mixes. Most recently, NCDOT RP 2020-11 quantified the impact of new asphalt overlays on friction and texture values and RP 2022-05 has been evaluating preliminary friction and texture performance models. Both projects have evaluated the effect of mixture compositional factors on the short- and long-term performance of both friction and texture. Friction and texture observations collected in both projects suggest that NCDOT dense-graded mixes have initial low texture values because of the fine gradations that are used in the current mix design specifications. Low macrotexture may contribute to reduced skid resistance values in the field. Revising the existing asphalt mixture categories to solve these problems may result in many practical issues due to contractor practices, familiarity with mixture designs, and unintended consequences to durability. On the other hand, a preliminary evaluation of the surface mixture guidelines in South Carolina and Virginia shows important differences with the NCDOT current practice. Both state DOTs use coarser gradations for dense-graded surface mixtures and have SMA mixes as an option to use in roads with high traffic volumes and high friction demand. Therefore, a research study is needed to identify alternative structural mixture designs that can be specified to ensure adequate friction and texture in North Carolina. The primary outcome of the proposed research will include new or improved asphalt mix design specifications updated to include new mixture categories that could be selected by NCDOT pavement designers in situations that warrant higher surface texture and/or friction. Given the existence of specifications for such mixes in other states, it is likely that the recommendations can have immediate impact. These outcomes can be used by the Traffic Safety and Materials and Test Units of the North Carolina DOT, the products of this research will provide immediate indications as to whether pavement mixture design specifications in adjacent states result in asphalt surface mixtures with improved macrotexture and friction.

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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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