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

Chemical Composition and Rheological Characteristics of Binders Containing RAP and Rejuvenator

Mansourkhaki, A., Ameri, M., Habibpour, M., & Shane Underwood, B. (2020), JOURNAL OF MATERIALS IN CIVIL ENGINEERING, 32(4). https://doi.org/10.1061/(ASCE)MT.1943-5533.0003016

Development of a fatigue index parameter, S-app, for asphalt mixes using viscoelastic continuum damage theory

Wang, Y. D., Underwood, B. S., & Kim, Y. R. (2020), INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING. https://doi.org/10.1080/10298436.2020.1751844

Development of environmentally friendly flame retardant to achieve low flammability for asphalt binder used in tunnel pavements

Sheng, Y., Wu, Y., Yan, Y., Jia, H., Qiao, Y., Underwood, B. S., … Kim, Y. R. (2020), JOURNAL OF CLEANER PRODUCTION, 257. https://doi.org/10.1016/j.jclepro.2020.120487

Effect of Speed Bumps on Pavement Condition

Goenaga, B., Underwood, S., & Fuentes, L. (2020), TRANSPORTATION RESEARCH RECORD. https://doi.org/10.1177/0361198120927005

Implementation of the AASHTO M 332 Specification: A Case Study

Gundla, A., Salim, R., Shane Underwood, B., & Kaloush, K. E. (2020), TRANSPORTATION RESEARCH RECORD. https://doi.org/10.1177/0361198120933266

Low-temperature performance grade characterisation of asphalt binder using the dynamic shear rheometer

Underwood, B. S., & Castorena, C. (2020), INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING. https://doi.org/10.1080/10298436.2020.1774766

Molecular weight distribution of asphalt binders from Laser Desorption Mass Spectroscopy (LDMS) technique and its relationship to linear viscoelastic relaxation spectra

Gundla, A., & Underwood, B. S. (2020), FUEL, 262. https://doi.org/10.1016/j.fuel.2019.116444

Nonlinear Viscoelastic Response of Crumb Rubber Modified Asphalt Binder Under Large Strains

Gulzar, S., & Underwood, B. S. (2020), TRANSPORTATION RESEARCH RECORD. https://doi.org/10.1177/0361198120907097

Past and Present Design Practices and Uncertainty in Climate Projections are Challenges for Designing Infrastructure to Future Conditions

Underwood, B. S., Mascaro, G., Chester, M. V., Fraser, A., Lopez-Cantu, T., & Samaras, C. (2020), JOURNAL OF INFRASTRUCTURE SYSTEMS, 26(3). https://doi.org/10.1061/(ASCE)IS.1943-555X.0000567

Relations between colloidal indices and low-temperature properties of reclaimed binder modified with softer binder, oil-rejuvenator and polybutadiene rubber

Mansourkhaki, A., Ameri, M., Habibpour, M., & Underwood, B. S. (2020), CONSTRUCTION AND BUILDING MATERIALS, 239. https://doi.org/10.1016/j.conbuildmat.2019.117800

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Grants

Evaluating Recycling Agents’ Acceptance for Virginia: Test Protocols and Performance-Based Threshold Criteria

US Dept. of Transportation (DOT)(7/01/20 - 1/31/23)

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Evaluating Recycling Agents’ Acceptance for Virginia: Test Protocols and Performance-Based Threshold Criteria

Sponsor: US Dept. of Transportation (DOT)

Start Date: 7/01/20

End Date: 1/31/23

Abstract

In 2007, the Virginia Department of Transportation (VDOT) introduced specifications to allow higher percentages of reclaimed asphalt pavement (RAP) (i.e., up to 30%) in hot-mix asphalt (HMA) surface mixtures without adjustment of the virgin binder grade. The increased use of RAP was expected to result in a lower cost of produced asphalt mixtures given the continuous rising cost of oil and thus asphalt binders and fuel needed to produce asphalt pavements. By 2013, VDOT had begun to consider the feasibility of allowing the use of surface mixtures containing up to 45% of RAP material. Several trial sections were constructed containing mixtures with 20%, 30%, 40%, and 45% RAP for evaluation (Nair et al., 2019). In general, those trials found that mixtures containing up to 45% RAP could be designed, produced, and constructed if proper procedures are followed. In 2019, the research team at Virginia Transportation Research Council (VTRC) initiated another study to evaluate field trials of high RAP asphalt mixtures (i.e., more than 40%) designed following the Balanced Mix Design (BMD) special provision for VDOT’s surface mixtures. The primary concern with such mixtures has been that the use of high percentage of RAP will overly stiffen mixtures; making them more brittle and prone to premature cracking. The use of high percentage of RAP can lead to numerous construction and performance issues including, but not limited to, compactibility and workability in cool weather, low-temperature cracking with accumulation of thermally induced stresses, fatigue cracking and micro damage accumulation leading to crack initiation and propagation with repeated loading, reflection cracking with repeated loading and daily / seasonal thermal stresses, and raveling with subsequent aging or moisture damage. The challenges arising from the use of high RAP content mixtures can be addressed through the use of softer binders or additives such as recycling agents (RAs). These additives were utilized in HMA in the early period of widespread recycling in the 1970s and 1980s for the purpose of realizing three types of benefits: environmental, economic, and engineering. The use of RAs holds promise as long as there is a proper understanding of how effectively they restore binder rheology and how that effectiveness evolves with aging of mixtures in the laboratory, making them proper additives to be incorporated in mixtures to be placed in field. Hence, there is a need for an engineered framework to evaluate RAs in terms of their stiffness and cracking resistance when incorporated into the binder blends of corresponding mixtures. Currently, there are no unique and / or detailed handy guides or specifications that outline a framework to evaluate acceptability of RAs in the state of Virginia. Therefore, this study aims to identify and / or develop a testing protocol to evaluate the effectiveness of RAs in alleviating the brittleness of high RAP asphalt mixtures. In addition, a performance-based parameter(s) with its threshold limits / criteria will be identified or developed to accept or reject a certain product (i.e., recycling agents). Both objectives will facilitate responsible use of innovative materials as part of Virginia’s Balanced Mix Design (BMD) initiative. In this study, NCSU researchers will conduct experiments on asphalt binder, asphalt from reclaimed asphalt pavement (RAP), rejuvenator agents, mortars, and asphalt mixture.

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TFRS 01: Quality Assurance (QA) Aspects of Performance Related Specifications (PRS)

National Academy of Sciences(4/15/20 - 8/13/22)

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TFRS 01: Quality Assurance (QA) Aspects of Performance Related Specifications (PRS)

Sponsor: National Academy of Sciences

Start Date: 4/15/20

End Date: 8/13/22

Abstract

The objective of this research is to develop guidance to integrate the performance predictive capabilities of the PASSFlexTM software and its suite of tools (FlexPAVETM version 2.0, FlexMATTM, and FlexMIXTM) within a statistically sound QA system in a PRS framework. The research shall address: (a) the use of the cyclic fatigue Sapp and SSR allowable traffic for rutting (ATR) index test parameters, index thresholds, and acceptance limits in support of performance engineered mixture design (PEMD) approaches and to facilitate further implementation of the tests and performance predictions, (b) material selection and mixture design changes that can impact the test results (cyclic fatigue, SSR, and their index parameters) and trends associated with owner agency specified performance thresholds, and (c) the major elements of a QA system (per TRB E-Circular 235, Glossary of Transportation Construction Quality Assurance Terms (http://onlinepubs.trb.org/onlinepubs/circulars/ec235.pdf) and associated buyer/seller and payment risks.

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Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Small Scale Dynamic Modulus

Federal Highway Administration (FHWA)(3/11/20 - 8/23/22)

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Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Small Scale Dynamic Modulus

Sponsor: Federal Highway Administration (FHWA)

Start Date: 3/11/20

End Date: 8/23/22

Abstract

In this research study, NCSU will design, conduct, and provide recommendations relating to a two-phase ruggedness and interlaboratory study on a test method that has been identified as critical to asphalt pavement performance and design practice. AASHTO TP 132 (2019) Standard Method of Test for Determining the Dynamic Modulus for Asphalt Mixtures Using Small Specimens in the Asphalt Mixture Performance Tester (AMPT) has been developed, refined, and recently published as an AASHTO provisional standard; a statistically sound refinement procedure is needed to facilitate widespread adoption and implementation. Not only can this standard be used to obtain inputs to the AASHTO PavementME pavement structural analysis software, the standard is being used in ongoing FHWA efforts as part of a performance-related specification framework which seeks to increase pavement life through fundamental testing and predictive relationships. AASHTO TP 132 is of interest because of its fundamental nature, determination via the AMPT standardized equipment, and its ability to model and predict material performance over a wide range of loading and climate conditions a pavement may experience; resulting in better performing, safe, quiet, durable, long lasting asphalt roadways. Additionally, a draft practice for preparing small-scale specimens has been developed and published as AASHTO PP 99 (2019) Standard Method of Practice for Preparation of Small Cylindrical Performance Test Specimens Using the Superpave Gyratory Compactor (SGC) and Field Cores. This draft practice is of significant interest to the asphalt materials community due to anticipated materials, time, and cost savings associated with preparing and evaluating smaller performance test. 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 – Ruggedness study presentations and webinar – NCSU will present the findings to targeted stakeholders. Task 5 – Publication ready final deliverables – the AASHTO standards will be revised into a final form. Task 6 – Revise work ILS work plan – NCSU will revise the original work plan from Task 1 based on findings from Tasks 3-5 for conducting the ILS study. Task 7 – Perform work plan and document efforts – NCSU will coordinate the ILS according to the approved work plan. This will include identifying participants, sending materials, and analyzing their results statistically. Task 8 – ILS study presentation and webinar – NCSU will present their findings to targeted stakeholders. Task 9 – Publication ready final deliverables – the AASHTO standards revised in Task 5 will be modified to include repeatability and reproducibility statements.

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Evolution of Pavement Friction and Macrotexture after Asphalt Overlay

NC Department of Transportation(8/01/19 - 7/31/21)

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Evolution of Pavement Friction and Macrotexture after Asphalt Overlay

Sponsor: NC Department of Transportation

Start Date: 8/01/19

End Date: 7/31/21

Abstract

Vehicle collisions and increases in collisions rates during wet conditions are one of the major safety concerns for the NCDOT. Wet collision rates increase because skid resistance reduces under wet 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. Although the NCDOT actively addresses skid resistance issues as they are identified, a recent study involving a small subset of North Carolina roadways has suggested that wet crash rates may increase after pavements are overlaid. That study concluded that NCDOT needed to consider characterization of both friction and macrotexture as part of its pavement friction measurement and management plan. While the current studies have successfully identified the potential for issues in recently overlaid projects, they did not identify whether these effects are temporary, and if so, how long they may last. In addition, past studies have not been able to identify any specific causative effects that may increase or decrease the impact of overlays on skid resistance. Since the primary change after an overlay is placed is the driving surface, there is a need to better understand how the asphalt mixture composition may affect the overall skid resistance of the roadway under wet conditions.

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Evaluation of Inverted Pavement for NC Roadways

NC Department of Transportation(8/01/19 - 7/31/21)

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Evaluation of Inverted Pavement for NC Roadways

Sponsor: NC Department of Transportation

Start Date: 8/01/19

End Date: 7/31/21

Abstract

North Carolina current allows two basic types of pavement design on NCDOT roadways; 1) those whose structural capacity comes primarily from asphalt concrete (flexible pavements) and 2) those whose structural capacity comes primarily from portland cement concrete (rigid pavements). These designs have been used successfully in many applications throughout the State; however, they utilize a large amount of relatively expensive and difficult to produce materials (asphalt concrete and portland cement concrete). A third technique, inverted pavement design that requires less of these materials and is purported to provide equivalent or superior performance is not currently allowed with the NCDOT specifications. Inverted pavements consist of a 2 - 3.5-inch asphalt concrete surface, supported by a 6 – 10-inch layer of unbound aggregate base and then by 8 - 12 inches of a cement treated subbase. Literature and experience have shown that these pavements can be designed and used in many applications at a substantial cost savings. However, there are many unknowns when directly adopting design specifications from elsewhere as local materials, practices, and experience may not be fully accounted for. Thus, there exists a need to gain state specific experience in the engineering and performance of these structure before their adoption can be considered.

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Evaluation of New Asphalt Concrete Job Mix Formula Specifications

NC Department of Transportation(8/01/19 - 1/31/21)

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Evaluation of New Asphalt Concrete Job Mix Formula Specifications

Sponsor: NC Department of Transportation

Start Date: 8/01/19

End Date: 1/31/21

Abstract

The North Carolina Department of Transportation (NCDOT) has recently modified the asphalt mixture design procedures in part, to increase the asphalt content and address observed cracking issues with asphalt mixtures. These changes have reduced the number of asphalt mixture types, changed compaction levels and the volumetric limits for some mixtures, and adjusted how recycled materials are considered. Given the complexity of the interactions between material parameters, the procedural changes do not guarantee that the resultant asphalt mixture designs have actually achieved the intended goal of improved durability.

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Determining Structural Number for Forta-FI

FORTA Corporation (8/31/19 - 12/15/20)

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Determining Structural Number for Forta-FI

Sponsor: FORTA Corporation

Start Date: 8/31/19

End Date: 12/15/20

Abstract

We propose to perform experimentation and analysis to develop AASHTO design compatible structural layer coefficients for mechanically fiber reinforced asphalt concrete (M-FRAC). These studies would be coordinated with a new project from the North Carolina Department of Transportation (NCDOT), which aims to recalibrate the structural layer coefficients for their materials. Other studies have been conducted to calibrate these coefficients, but none have been coordinated with a state transportation agency’s own, larger calibration effort. Thus, we believe that the proposed effort, in addition to being somewhat more comprehensive than the previous work, would also carry greater credibility to other state and local highway agencies. The estimated cost for this study would be between $53,014 and $45,003 depending on the contracting mechanism, and the work would be carried out between August, 2019 and May, 2020.

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TOPR for Performance Related Specifications Advances Quality Assurance for Pavements

Federal Highway Administration (FHWA)(8/02/18 - 8/01/20)

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TOPR for Performance Related Specifications Advances Quality Assurance for Pavements

Sponsor: Federal Highway Administration (FHWA)

Start Date: 8/02/18

End Date: 8/01/20

Abstract

The Federal Highway Administration (FHWA) has fully supported Quality Assurance (QA) and advancing components of QA for many years. One of those components is Performance-Related Specifications (PRS). As the PRS efforts have advanced additional needs have been identified in order to complete an further advance the research further. This project will serve to further develop, improve, and validate the developed relationships for the PRS. A number of tasks will be completed in order to meet the following specific objectives: • Development of Level 1 Performance Engineered Mix Design (PEMD) method and threshold values for Level 2 PEMD index parameters • Performance testing for transfer functions to support PEMD for PRS • Comparison of Balance Mix Design (BMD) and PEMD testing for PRS • Advance in a collaborative approach for FLEXPave™ PRS models utilizing existing calibrations for AASHTOware Pavement ME™. • PRS training and shadow projects. • Coordination with existing PRS research for the development of a comprehensive written marketing plan. • Interim stakeholders PRS Status Meeting. • Under this task, the team shall create a system of tools including guidelines and sample specifications for agencies to transition from the traditional QA standard specifications to standard PRS.

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Calibration of Structural Layer Coefficients for North Carolina Asphalt Pavements

NC Department of Transportation(8/01/18 - 1/31/21)

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Calibration of Structural Layer Coefficients for North Carolina Asphalt Pavements

Sponsor: NC Department of Transportation

Start Date: 8/01/18

End Date: 1/31/21

Abstract

The North Carolina Department of Transportation (NCDOT) uses the AASHTO Guide for Design of Pavement Structures 1993 to determine the minimum pavement stiffness that ensures pavement longevity. During design, this stiffness is first determined using an iterative design process, charts, or software. Then, the engineer selects materials and layer thicknesses that provide the required stiffness by summing the contributions of individual layers. The contribution from any given layer is calculated by the product of that layer’s thickness and a structural layer coefficient that captures the overall quality and structural benefit of the material. In the NCDOT procedure, the structural layer coefficient for asphalt concrete (AC) is 0.44 (surface and intermediate mixtures) or 0.30 (base mixtures), while other material types are lower, e.g., the structural layer coefficient for unbound aggregate base materials is 0.14. While the NCDOT has had success with these structural layer coefficient values, they are based on a test road constructed and evaluated in one climate zone and with one set of materials. Modern material selection and design have resulted in substantial changes in AC and aggregate base since this time. These improvements have likely resulted in different structural contributions from these materials, which means the structural layer coefficients should be reviewed and possibly changed. Proper characterization of these layer coefficients could result in substantial cost savings to the NCDOT by reducing the required pavement thickness and/or leading to pavements that require less frequent rehabilitation and reconstruction.

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Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Cylcic Fatigue test

Federal Highway Administration (FHWA)(9/28/17 - 12/26/20)

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Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Cylcic Fatigue test

Sponsor: Federal Highway Administration (FHWA)

Start Date: 9/28/17

End Date: 12/26/20

Abstract

AASHTO TP 107 enables the practical, mechanistic performance characterization of asphalt concrete using cyclic fatigue testing in the Asphalt Mixture Performance Tester (AMPT). AASHTO TP 107 was initially developed for the use of 100-mm diameter specimens, which yield a single test specimen per gyratory sample. Recently, a modified version of AASHTO TP 107 was proposed for the testing of 38-mm diameter small specimens that improves the efficiency of specimen fabrication and enables the testing of field cores extracted from as-built pavement layers. The objective of the proposed research is to improve AASHTO TP 107 by conducting ruggedness and interlaboratory studies using both small and large specimens. The ruggedness evaluation will identify controllable experimental factors that significantly affect the test results and to establish limits for their control. The interlaboratory study will lead to precision statements that define the repeatability and reproducibility of small and large cyclic fatigue the test results.

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