Select Publications

Knott JF, Sias JE, Dave EV, Jacobs JM. Seasonal and Long-Term Changes to Pavement Life Caused by Rising Temperatures from Climate Change. TRANSPORTATION RESEARCH RECORD [Internet]. 2019;2673 (6) :267–278. Publisher's Version
Mallick RB, Kottayi NM, Veeraragavan RK, Dave E, DeCarlo C, Sias JE. Suitable Tests and Machine Learning Approach to Predict Moisture Susceptibility of Hot-Mix Asphalt. JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS [Internet]. 2019;145 (3). Publisher's Version
Oshone M, Dave EV, Sias JE. Asphalt mix fracture energy based reflective cracking performance criteria for overlay mix selection and design for pavements in cold climates. Construction and Building Materials [Internet]. 2019;211 :1025 - 1033. Publisher's VersionAbstract
This study investigates the dependence of overlay field cracking performance on overlay thickness and fracture energy of asphalt mixture. A total of 15 pavement sections in Minnesota for which Disk-shape Compact Tension (DCT) testing was performed on field cores from overlays were used for the study. Due to the difference in the overlay lives, different cracking performance measures such as average transverse cracking rate (ATCR), maximum transverse cracking rate (MTCR) and transverse cracking performance index (TCTotal) were calculated. These cracking performance measures were compared with asphalt overlay thicknesses and DCT fracture energies. The analysis indicated the dependence of TCTotal on both overlay thickness and fracture energy. The observed relationship was assessed for reliability using a statistical analysis and a new performance parameter that combines overlay thickness with fracture energy is proposed to provide measure of total fracture resistance of the overlay. Preliminary thresholds are also proposed for selection of overlay thicknesses and material types in new overlays.
© 2019 Elsevier Ltd
Oshone M, Dave EV, Daniel JS, Rowe GM. Assessment of various approaches to determining binder bending beam rheometer low temperature specification parameters from dynamic shear rheometer test, in Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions. Vol 87. Jacksonville, FL, United states ; 2018 :345 - 374.Abstract
The current asphalt binder performance grading system employs Dynamic Shear Rheometer (DSR) testing to determine high and intermediate temperature Theological properties. In recent years, the ability to measure DSR instrument compliance has allowed researchers to reliably measure low temperature binder properties as well. Low temperature characterization using DSR requires substantially smaller amount of binder as compared to the currently employed binder testing method, Bending Beam Rheometer (BBR). For these reasons and the possibility of using one piece of equipment for full characterization of asphalt binders, previous research has investigated DSR as an alternative to replace BBR testing by determining equivalent creep stiffness (S) and slope (m-value) from shear complex modulus. Different methods have been proposed to determine BBR specification parameters from DSR data and their viability has been evaluated primarily for virgin binders. The objective of this paper is to further assess the applicability of different methods to determine S and m-values from DSR data for four neat binders as well as extracted and recovered binders from eighteen different mixture samples. The variables within the matures include lab versus plant production, aggregate size and gradation, binder PG and source, and recycled material type and content. The methods employ different interconversion methods, ranging from exact interconversions to regression-based estimates. The shear relaxation modulus or creep stiffness and slope are correlated to S and m-value measured from BBR testing. The study also investigates the impact and differences due to use different interconversion methods. The results show that the Christensen approximate interconversion is adequately able to predict parameters from DSR results that are equivalent to S and m-value determined from BBR testing. The exact interconverted shear creep stiffness and shear relaxation modulus using generalized Maxwell model are compared to lab measured S and m values, results show that a linear relationship exists between these parameters. Finally, a simple equation is developed to enable estimation of BBR S and m-value from a single point measurement of complex shear modulus and phase angle. This contribution is expected to have a practical use by providing a platform to estimate low temperature specification parameters from a single point DSR measurement.
© 2019 Association of Asphalt Paving Technologist. All Rights Reserved.
Oshone M, Ghosh D, Dave EV, Daniel JS, Voels JM, Dai S. Effect of mix design variables on thermal cracking performance parameters of asphalt mixtures. Transportation Research Record [Internet]. 2018;2672 (28) :471 - 480. Publisher's VersionAbstract
To address asphalt pavement thermal cracking, researchers have developed performance-based evaluation tools for asphalt mixtures. A minimum fracture energy obtained from a disc-shaped compact tension test and Black space parameters determined by the stiffness and relaxation properties of asphalt mixtures are two such methods to ensure good thermal cracking resistance. Mix specifiers and producers strive to meet the requirements set by these performance-based criteria by adjusting their mix designs. However, there is a lack of information and consensus on the effect of mix design variables (such as binder grade and mix volumetrics) on thermal cracking performance of mixtures as it relates to fracture energy and Black space location. This study strives to fill this gap by quantifying the effect of: (1) recycled asphalt content, (2) effective binder content, (3) air voids, (4) asphalt film thickness, (5) voids in mineral aggregates, and (6) PG low and high temperature grades on thermal cracking resistance. A large dataset, 90 mixtures from the Minnesota Department of Transportation and 81 mixtures from University of New Hampshire database, was used for the study. The results indicate a strong correlation between binder related properties (binder content, asphalt film thickness, PG spread) and fracture energy. The correlation coefficients obtained from this study for PG spread, effective binder content, and air void can be confidently employed to achieve targeted fracture energy thresholds. The same can be achieved for the Glower-Rowe parameter at 15ºC by employing the correlation coefficients obtained for PG low temperature, virgin asphalt content, and voids in the mineral aggregate.
© National Academy of Sciences: Transportation Research Board 2018
Rahbar-Rastegar R, Daniel JS, Dave EV. Evaluation of viscoelastic and fracture properties of asphalt mixtures with long-term laboratory conditioning. Transportation Research Record [Internet]. 2018;2672 (28) :503 - 513. Publisher's VersionAbstract
Aging affects the properties of asphalt mixtures in different ways; increase of stiffness, decrease of relaxation capability, and the increase of brittleness, resulting in changes in cracking behavior of asphalt mixtures. In this study, ten plant-produced, labcompacted mixtures with various compositions (recycled materials, binder grades, binder source, and nominal maximum aggregate size) are evaluated at different long-term aging levels (24 hours at 135°C, 5 days at 95°C, and 12 days at 95°C on loose mix and 5 days at 85°C on compacted specimens). The asphalt mixture linear viscoelastic properties (|E*| and d) and master curve shape parameters measured from complex modulus testing and fracture properties (measured from discshaped compact tension and semi-circular bending fracture testing) are compared at different levels of aging. The results indicate that the mixture exposure time to aging is proportional to the dynamic modulus and phase angle changes. Generally, the fracture parameters of mixtures become worse when aging level changes from 5 to 12 days aging. In spite of the similar viscoelastic properties, the mixtures with 24 hours at 135°C and 12 days at 95°C aging do not show similar fracture parameters.
© National Academy of Sciences: Transportation Research Board 2018.
Nemati R, Dave EV. Nominal property based predictive models for asphalt mixture complex modulus (dynamic modulus and phase angle). Construction and Building Materials [Internet]. 2018;158 :308 - 319. Publisher's VersionAbstract
Dynamic modulus (|E|) and phase angle (δ) are necessary for determining the response of asphalt mixtures to in-service traffic and thermal loadings. While a number of |E| and δ predictive models have been developed, many of them require lab measured properties (e.g. binder complex modulus). The majority of previous work has focused only on prediction of |E|, limited models exist for prediction of δ. This research utilized generalized regression modelling of lab measurements (from 81 asphalt mixtures) to develop and verify prediction models for |E| and δ using only nominal asphalt mix properties that are readily available during the initial mixture design and specification process.
© 2017 Elsevier Ltd
Tebaldi G, Dave E, Cannone Falchetto A, Hugener M, Perraton D, Grilli A, Lo Presti D, Pasetto M, Loizos A, Jenkins K, et al. Recommendation of RILEM TC237-SIB on cohesion test of recycled asphalt. Materials and Structures/Materiaux et Constructions [Internet]. 2018;51 (5). Publisher's VersionAbstract
This recommendation describes how to evaluate the presence of potentially active bitumen in recycled asphalt (RA) materials through the cohesion test. The experimental protocol is designed according to the research performed by the RILEM Technical Committee 237-SIB ‘‘Testing and characterization of sustainable innovative bituminous materials and systems’’ with the purpose, to develop a new, simple and fast method for the characterization of RA while limiting the need for conventional rheological tests. The guidelines in this recommendation focus on the testing procedure including specimen preparation, data analysis and provide information on the preparation of a tests report.
© 2018, RILEM.
Tebaldi G, Dave EV, Cannone Falchetto A, Hugener M, Perraton D, Grilli A, Lo Presti D, Pasetto M, Loizos A, Jenkins K, et al. Recommendation of RILEM TC237-SIB: protocol for characterization of recycled asphalt (RA) materials for pavement applications. Materials and Structures/Materiaux et Constructions [Internet]. 2018;51 (6). Publisher's VersionAbstract
This recommendation proposes an experimental protocol to characterize recycled asphalt materials. The guidelines presented in this document are based on the results of a round robin test organized by the RILEM Technical Committee 237-SIB “Testing and characterization of sustainable innovative bituminous materials and systems” and provide information on the testing procedure, data analysis and indications for the preparation of a test report.
© 2018, RILEM.
Dave EV, Botella R, Marsac P, Bodin D, Sauzeat C, Nguyen ML. Cracking in Asphalt Pavements . In: Mechanisms of Cracking and Debonding in Asphalt and Composite Pavements: State-of-the-Art of the RILEM TC 241-MCD. Vol. 28. Springer International Publishing ; 2018. pp. 33-102. Publisher's VersionAbstract

This chapter provides a comprehensive review of both laboratory characterization and modelling of bulk material fracture in asphalt mixtures. For the purpose of organization, this chapter is divided into a section on laboratory tests and a section on models. The laboratory characterization section is further subdivided on the basis of predominant loading conditions (monotonic vs. cyclic). The section on constitutive models is subdivided into two sections, the first one containing fracture mechanics based models for crack initiation and propagation that do not include material degradation due to cyclic loading conditions. The second section discusses phenomenological models that have been developed for crack growth through the use of dissipated energy and damage accumulation concepts. These latter models have the capability to simulate degradation of material capacity upon exceeding a threshold number of loading cycles.

Buttlar WG, Chabot A, Dave EV, Petit C, Tebaldi G ed. Mechanisms of Cracking and Debonding in Asphalt and Composite Pavements: State-of-the-Art of the RILEM TC 241-MCD . Springer International Publishing; 2018 pp. 237. Publisher's VersionAbstract


Premature cracking in asphalt pavements and overlays continues to shorten pavement lifecycles and creates significant economic and environmental burden. In response, RILEM Technical Committee TC 241-MCD on Mechanisms of Cracking and Debonding in Asphalt and Composite Pavements has conducted a State-of-the-Art Review (STAR), as detailed in this comprehensive book.  Cutting-edge research performed by RILEM members and their international partners is presented, along with summaries of open research questions and recommendations for future research.


This book is organized according to the theme areas of TC 241-MCD - i.e., fracture in the asphalt bulk material, interface debonding behaviour, and advanced measurement systems. This STAR is expected to serve as a long term reference for researchers and practitioners, as it contributes to a deeper fundamental understanding of the mechanisms behind cracking and debonding in asphalt concrete and composite pavement systems. 


Nemati R, Dave EV. Nominal property based predictive models for asphalt mixture complex modulus (dynamic modulus and phase angle) . Construction and Building Materials [Internet]. 2018;158 (Supplement C) :308 - 319. Publisher's VersionAbstract

Abstract Dynamic modulus (|E∗|) and phase angle (δ) are necessary for determining the response of asphalt mixtures to in-service traffic and thermal loadings. While a number of |E∗| and δ predictive models have been developed, many of them require lab measured properties (e.g. binder complex modulus). The majority of previous work has focused only on prediction of |E∗|, limited models exist for prediction of δ. This research utilized generalized regression modelling of lab measurements (from 81 asphalt mixtures) to develop and verify prediction models for |E∗| and δ using only nominal asphalt mix properties that are readily available during the initial mixture design and specification process.

Dave EV, Behnia B. Cohesive zone fracture modelling of asphalt pavements with applications to design of high-performance asphalt overlays . International Journal of Pavement Engineering [Internet]. 2018;19 (3) :319-337. Published OnlineAbstract

Mechanism of fracture in a viscoelastic heterogeneous composite with thermo-rheological properties such as, asphalt mixture is quite involved and cannot be correctly simulated with simpler linear elastic fracture mechanics constitutive laws. Over the last decade and half, a number of researchers have adopted use of cohesive zone (CZ) fracture models for simulation of fracture in asphalt mixtures. CZ interface elements are utilised in finite element (FE) models for representation of crack path, these elements follow traction–displacement relationships that allow for gradually degrading traction capabilities along the crack path with increasing level of crack opening. This paper presents a review of CZ modelling approach for simulation of asphalt pavement and overlay cracking performances. Suitability of CZ modelling approach for capturing discrete fracture in asphalt mixtures at low temperatures is presented through simulation of lab scale test. An example is also presented to demonstrate applicability of CZ-based modelling effort in capturing the crack initiation and propagation in asphalt mixtures at low temperatures. Thereafter, an FE-based pavement simulation approach is discussed that can be utilised in design of asphalt overlays to lower the propensity of reflective cracking. A case study of designing asphalt overlay systems for four real-life pavements in Minnesota is presented to demonstrate the applicability of the CZ-based modelling approach in conducting mechanistic design of asphalt overlays.

Zhu Y, Dave EV, Rahbar-Rastegar R, Daniel JS, Zofka A. Comprehensive evaluation of low-temperature fracture indices for asphalt mixtures . Road Materials and Pavement Design [Internet]. 2017;18 (Sup 4) :467-490. Published OnlineAbstract

For performance-based specifications and design processes, a number of cracking-related index parameters have been proposed for asphalt mixtures in recent years. A number of these parameters have been developed to utilise results from fracture tests. This study conducted a comprehensive evaluation of various fracture index parameters including fracture energy, Illinois flexibility index, stress intensity factor and toughness index. Over 200 tests from 61 distinct test data sets representing 21 asphalt mixtures are included. The focus of this study is on low-temperature cracking and all indices were evaluated using test results from the disk-shaped compact tension fracture tests conducted at low temperatures. The objective of this study was to determine if there is a relationship between various fracture index parameters as well as to determine typical measurement variability associated with each parameter. Comparisons were made between different indices and correlations were determined for the mix rankings provided by individual indices. The results indicate that fracture energy successfully captured the mix rankings and showed a strong correlation with other indices. In order to better capture post-peak softening behaviour of asphalt mixtures, the flexibility and toughness indices have been utilised; however, these parameters were found to have high variability. A new index called fracture strain tolerance has been proposed that was shown to provide the same level of distinction between mixtures as the flexibility and toughness indices while having considerably lower variability. Finally, several areas were identified for future extension of this research.

Oshone M, Dave E, Daniel JS, Rowe GM. Prediction of phase angles from dynamic modulus data and implications for cracking performance evaluation . Road Materials and Pavement Design [Internet]. 2017;18 (Sup 4) :491-513. Published onlineAbstract

The need for a viscoelastic characterisation of hot mix asphalt is increasing as advanced testing and modelling is incorporated through mechanistic-empirical pavement design and performance-based specifications. Viscoelastic characterisation includes measurement of the mixture stiffness and relative proportion of elastic and viscous response. The most common method is to measure the complex modulus, where dynamic modulus represents the stiffness and the phase angle represents the relative extent of elastic and viscous response. Determination of phase angle from temperature and frequency sweep tests has been challenging, unreliable and prone to error due to a high degree of variability and sensitivity to signal noise. There are also large amounts of historical dynamic modulus data that are either missing phase angle measurements or have poorly measured phase angle data that inhibit their use in further evaluation. This paper evaluates the robustness of phase angle estimation from stiffness data for asphalt mixtures. The objectives of the study are to: (1) evaluate the procedure of estimating phase angle from the slope of log-log stiffness master curve fitted with a generalised logistic sigmoidal curve and compare it with lab measurements and the Hirsch model; (2) assess the effect of measured and predicted phase angles on a mixture Black Space diagram; (3) evaluate the effect of using predicted phase angles on SVECD fatigue analysis particularly regarding damage characteristics curves and fatigue coefficients and (4) evaluate the impact on layered viscoelastic pavement analysis for critical distresses (LVECD) pavement fatigue performance evaluation due to the use of predicted phase angles. Three sets of independent mixtures were evaluated in this study comprising a wide range of mixture conditions. The results indicate good agreement between measured and predicted phase angle values in terms of shape and peak master curve values. In terms of magnitude, the values from both matched very well for certain sets of mixtures and subsequently manifested in similar performance predictions. However, for other sets of mixtures, a considerable difference was observed between measured and predicted phase angle values as well as SVECD and LVECD results. The differences may be attributed to the use of different types of linear variable displacement transducers (loose core versus spring loaded). Another possible explanation for the difference could be the contribution of plastic strain, which may create a difference in phase angles of 1–2°.

Dave EV, Kostick RD, Dailey J. Performance of High Friction Bridge Deck Overlays in Crash Reduction. Journal of Performance of Constructed Facilities [Internet]. 2017;31 (2). Publisher's VersionAbstract
In recent history, a number of State Departments of Transportation have looked at providing safer driving conditions on bridges. One improvement method is placing high friction overlays on bridge decks. This study analyzed crash data to evaluate the performance of high friction overlays in reducing crashes. This study was completed by analyzing 10 years of data for nine bridges encompassing four different proprietary overlay systems. Within one of the overlay systems, three different aggregate types were also compared. Crash characteristics analyzed included the crash time, weather conditions, bridge surface conditions, average annual daily traffic, and severity of crashes. This study is part of a comprehensive study that includes extensive field evaluation and comparative performance analysis between different systems to evaluate their effectiveness on bridge decks in Minnesota. While the data presented herein is from bridge sites located in Minnesota, the findings apply to most of the northern tier states in the United States as well as other countries with colder climatic conditions. The analysis of data suggests that although there is a reducing trend in overall number of crashes; a reduction in crashes on bridges cannot be completely attributed to the use of high friction overlays. Furthermore, the presence of high friction overlays are unable to play a role in winter crash prevention. Thus this study shows that forensic evaluation of accident data does not support commonly anticipated crash reduction benefit of high friction overlays.
Dave EV, Hoplin C, Helmer B, Dailey J, Van Deusen D, Geib J, Dai S, Johanneck L. Effects of mix design and fracture energy on transverse cracking performance of asphalt pavements in Minnesota. Transportation Research Record [Internet]. 2016;2576 :40 - 50. Publisher's VersionAbstract
Asphalt pavements in colder climates encounter significantly shortened service lives because of excessive transverse cracking. This paper presents the results for 26 pavement sections in Minnesota that were studied to evaluate the effects of asphalt mix designs on pavement cracking performance. The field performance is presented with various cracking measures and compared with mix design aspects such as amount of asphalt binder, binder grade, and amount of recycling. The disk-shaped compact tension (DCT) fracture energies measured on the field cored samples are also compared with cracking performance. In this study, asphalt pavement sections from several locations were evaluated to encompass various types of asphalt mixtures and asphalt construction types that were commonly used in Minnesota. The amount of transverse cracking for each section was converted into a newly proposed cracking performance measure that accounted for the amount, rate, and timing of cracking. The comparisons between asphalt mixture attributes and cracking performance measures showed that the amounts of total asphalt binder and recycled asphalt binder may not be sufficient. Performance testing, in addition to currently used controls (mix volumetrics and constituent properties), is recommended to ensure good cracking performance. The DCT fracture energy results for companion sections show that mixtures with higher fracture energies exhibit lower amounts of transverse cracking. © 2016, National Research Council. All rights reserved.
Behnia B, Dave EV, Buttlar WG, Reis H. Characterization of embrittlement temperature of asphalt materials through implementation of acoustic emission technique. Construction and Building Materials [Internet]. 2016;111 :147 - 152. Publisher's VersionAbstract
The present study focuses on the application of an acoustic emission (AE) based laboratory test to evaluate low-temperature cracking performance of several types of asphalt materials in the context of a recently completed national pooled fund study on low-temperature cracking (LTC). Comparisons are made between AE test results and the critical cracking temperature of asphalt binders determined from Bending Beam Rheometer (BBR) test and Direct Tension Test (DTT), which are in turn compared to field observed thermal cracking in the corresponding test sections. Based upon our findings, recommendations are made as to the potential use of the AE-based technique in asphalt binder specification. © 2016 Published by Elsevier Ltd.
Ghasemi P, Podolsky J, Christopher Williams R, Dave E. Performance Evaluation of Coarse-Graded Field Mixtures Using Dynamic Modulus Results Gained from Testing in the Indirect Tension Mode, in International Conference on Transportation and Development 2016: Projects and Practices for Prosperity - Proceedings of the 2016 International Conference on Transportation and Development. Houston, TX, United states ; 2016 :1111 - 1121. Publisher's VersionAbstract
Historically, asphalt mixtures in Minnesota have been produced with fine gradations. However, recently more coarse-graded mixtures are being produced as they require less asphalt binder. Thus, it is important that pavement performance for coarse gradations be evaluated. Within this research work, performance evaluation took place with the use of the dynamic modulus test in indirect tension mode on coarse-graded mixtures consisting of field cores from 9 different pavements located in five districts of Minnesota. From each pavement's surface layer, 3 specimens were tested at three temperatures; 0.4°C, 17.1°C, and 33.8°C each at nine frequencies ranging between 0.1 Hz and 25 Hz. Additional volumetric characterization of the field mixtures was done to determine asphalt content, air voids, and blended aggregate gradations. Asphalt binders were extracted and recovered for use in determining binder shear complex master curves. Through this information the modified Witczak model was used to create |E∗| master curves which were then compared against the indirect tension (IDT) test | E∗| experimentally created master curves. From the results the modified Witczak model needs to be modified for IDT collected dynamic modulus data. © ASCE.
Dave EV, Hoplin C. Flexible pavement thermal cracking performance sensitivity to fracture energy variation of asphalt mixtures. Road Materials and Pavement Design [Internet]. 2015;16 :423 - 441. Publisher's VersionAbstract
Thermal cracking in asphalt pavements continues to be a significant pavement distress mechanism in cold climate regions. The formation of discontinuities due to thermal cracking causes extensive damage to the integrity of the pavement and forms pathways for intrusion of water into the base and subgrade layers. Current use of the performance-based binder specifications has not been shown to effectively lower the propensity for this distress. When this is combined with advent of newer asphalt mix manufacturing and construction technologies as well as desire for incorporation of greater amounts of recycled materials in paving mixtures, it has led to significant research and implementation efforts on asphalt mixture performance-based specifications. On the basis of various past research studies on low temperature cracking, a performance specification that utilises fracture energy of asphalt mixtures through use of disk-shaped compact tension (DCT) test has been developed. A significant number of present studies are underway to implement these specifications including two states which are in the pilot implementation stage. A major question that has been raised during the implementation of these specifications has been in the lack of information on sensitivity of pavement thermal cracking performance to the variations in fracture energy of the mixture. The present study focused on determining the effects on thermal cracking performance of pavements for variations in DCT fracture energy of asphalt mixtures. The sensitivity was determined through use of the IlliTC thermal cracking simulation system. The IlliTC system utilises asphalt mixture's fracture and viscoelastic properties to conduct finite element-based simulations using realistic pavement thermal loading conditions. Although this system has been validated in the past, the present study conducted further validation through comparison of predicted cracking performance with field-measured cracking performance. For sensitivity analysis, three types of asphalt mixtures for three climatic conditions and three pavement structures were evaluated. Apart from other things, the fracture mechanics in asphalt concrete at lower temperatures depend on the material's fracture energy as well as its tensile strength. In order to ensure that the effects of fracture energy variations were the focus, a critical tensile strength value was determined for each scenario (for each mix for each climate), which allowed researchers to conduct the simulations with varying fracture energies (six different levels). The results show that a variation of 25J/m<sup>2</sup> in the fracture energy could lead to significantly different pavement thermal cracking performances. This is a significant finding that will aid in continued implementation of the fracture energy-based material specifications and provides guidance to transportation agencies in development of the final version of their material specifications. © 2015 Taylor & Francis.