Select Publications

In Press
Daniel JS, Corrigan M, Jacques C, Nemati R, Dave EV, Congalton A. Comparison of asphalt mixture specimen fabrication methods and binder tests for cracking evaluation of field mixtures . Road Materials and Pavement Design [Internet]. In Press :1-17. Publisher's VersionAbstract

One of the most influential variables in determining the performance-based properties of the asphalt mixtures is the specimen fabrication method. This study investigates the impact of specimen fabrication methods through a comprehensive study of six test sections constructed in 2011that include a range of RAP contents and two different virgin binders. Complex modulus and fatigue characterisation was conducted on asphalt binders and mixtures. Three specimen fabrication methods were evaluated: specimens compacted from plant sampled loose mix with and without reheating, and specimens fabricated from raw materials in the laboratory. Predicted performance from lab tests were compared to field performance. The mixtures with PG 58-28 binder showed expected trends with increasing RAP content (higher modulus, lower phase angle); however, mixes with PG 52-34 did not. Similar trends were observed for specimens fabricated with plant mix (not reheated), and the specimens fabricated with raw materials in the lab. Binder results and performance prediction using the plant mix agree with the observations in the field.

daniel_et_al_rmpd_2018.pdf
2018
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. 

 

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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.

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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.

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2017
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.

yue_et_al_rmpd_2017.pdf
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°.

oshone_et_al_rmpd_2017.pdf
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.
2016
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.
2015
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.
Dailey J, Dave EV, Musselman E, Kostick R. Laboratory evaluation of partial depth patching materials for use in winter climates. Transportation Research Record [Internet]. 2015;2481 :56 - 64. Publisher's VersionAbstract
Over the course of their service life, concrete pavements undergo significant traffic and climatic loads, which lead to a gradual accumulation of damage. This accumulation of damage and distress comes from the effects of changing weather conditions (e.g., temperature, moisture) and continuous vehicular traffic. Repeated environmental and traffic loading leads to cracking and spalling of the concrete at the joint edges. States in the northern portion of the United States and the provinces of Canada have climates that fluctuate greatly in temperature throughout the seasons. Greater temperature differentials cause greater deflections in rigid pavements; these deflections lead to more prevalent spalling and a greater need for partial depth repair. Many U.S. state departments of transportation (DOTs) use partial depth repair as routine practice to maintain concrete pavements (e.g., the DOTs of Minnesota, North Dakota, South Dakota, Idaho, Montana, Washington, and Wisconsin). Enhanced acceptance criteria of rapid set cementitious materials for use in partial depth repair are needed. The purpose of this study was to investigate laboratory tests, recommended by ASTM C928 and others, for inclusion in the acceptance specifications for patching materials.
2014
Tebaldi G, Dave EV, Marsac P, Muraya P, Hugener M, Pasetto M, Graziani A, Grilli A, Bocci M, Marradi A, et al. Synthesis of standards and procedures for specimen preparation and in-field evaluation of cold-recycled asphalt mixtures. Road Materials and Pavement Design [Internet]. 2014;15 (2) :272–299. Publisher's Version
DeDene CD, Voller VR, Marasteanu MO, Dave EV. Calculation of particle heating times of reclaimed asphalt pavement material. Road Materials and Pavement Design [Internet]. 2014;15 (3) :721 - 732. Publisher's VersionAbstract
Recycling aged asphalt pavements into new asphalt pavements is a common practice in the pavement industry. The process involves adding the reclaimed asphalt pavement (RAP) into a superheated asphalt mixing drum, where the binder contained within the RAP is expected to melt and be incorporated into the new hot-mix asphalt. Since the RAP is added part way through the mixing process, the amount of time spent inside the mixing drum is short and possibly insufficient for the RAP binder to melt and mix with the new asphalt binder. To address this issue, a numerical model is developed using the thermal properties of asphalt materials to investigate the melting potential of the RAP inside an asphalt mixing drum. Through a dimensionless analysis, the proposed model allows for the practice-ready calculation of the minimum time needed for any spherical particle to heat to a desired temperature given the initial temperature, ambient temperature, thermal diffusivity, and particle radius. Using the resulting equation, it is shown that there may be cases in which the RAP is not sufficiently heated inside an asphalt mixing drum. © 2014 Taylor & Francis.
Dave EV, Hanson C, Helmer B, Johanneck L. Effect of asphalt binder content and grade on transverse field cracking performance of Minnesota's Roadways, in Asphalt Pavements - Proceedings of the International Conference on Asphalt Pavements, ISAP 2014. Vol 2. Raleigh, NC, United states ; 2014 :1209 - 1217.Abstract
Cracking is a major distress mechanism in asphalt pavements. Thermal cracking is especially prevalent in Northern Minnesota and other areas with cold climates. Developing asphalt mix designs that are more resistant to cracking distresses is necessary to reduce maintenance and rehabilitation expenditures. The present study involves analysis of over 32,000 asphalt mixes and approximately 12,000 field sections available from Minnesota Department of Transportation (MnDOT). The main objective of this work is to identify the effects of asphalt binder content and binder grade on the actual field cracking performance. A comprehensive database has been developed that includes mix design information (design traffic level, mix size, binder type, wear versus non-wear course), mix volumetrics and gradation (air voids, voids in mineral aggregates, voids filled with asphalt, adjusted asphalt film thickness, percent passing on control sieves, recycled fractions), and actual field performance data from MnDOT's pavement management system. This database has made it possible to quantify the effects of binder content and grade on the actual field performance. A series of statistical tests were conducted to determine if significant relationships exist between the binder content and grade, and the field cracking performance. The results show that both binder content and grade have a significant effect on the transverse cracking of pavements and for Minnesota the PG XX-34 grade may be better suited than the PG XX-28 binder grade. © 2014 Taylor & Francis Group, London.
Carlson A, Jensen T, Lund AF, Dave EV, Saftner DA. MS projects from partnership with city government, in ASEE Annual Conference and Exposition, Conference Proceedings. Indianapolis, IN, United states ; 2014 :Dassault Systemes (DS); et al.; Kaplan; National Instruments; NCEES; Quanser -.Abstract
This paper describes graduate student projects that were conducted through cooperation between University of Minnesota Duluth and the City of Duluth. While graduates students at the University of Minnesota Duluth can complete a traditional thesis-based MS, they also have the option of completing additional course work and a MS project. The graduate projects are designed to be realistic engineering problems that allow students gain and apply higher level civil engineering analysis and design knowledge. This paper describes two of these projects resulting in three MS projects. The first project determined a method of using fine dredge material from the harbor as engineered fill using locally available additives. The second project focused on transportation and structural issues in a neighborhood revitalization. These projects were evaluated using recently developed graduate student learning outcomes. The MS projects from this partnership were successful in meeting the graduate student learning outcomes when compared to MS projects from other sources. © American Society for Engineering Education, 2014.
2013
Ahmed S, Dave EV, Buttlar WG, Exline MK. Cracking resistance of thin-bonded overlays using fracture test, numerical simulations and early field performance. International Journal of Pavement Engineering [Internet]. 2013;14 (6) :540 - 552. Publisher's VersionAbstract
Thin-bonded bituminous overlays are becoming an increasingly popular pavement maintenance treatment, which can be used to restore smoothness, seal and renew the pavement surface and increase skid resistance. Thin-bonded overlays (TBOs) are constructed using a specialised type of paving equipment called a spray paver. A spray paver combines the operation of applying a tack coat and laying down asphalt concrete in a single pass. This allows for the application of a high rate of polymer-modified asphalt emulsion tack coat. Due to reduced thickness, cracking distress is more of a concern in this type of system. This paper describes a new approach for the evaluation of the cracking performance of TBO systems through fracture mechanics-based testing of laboratory and field specimens. Computer simulations and early field performance data are also used in the evaluation. This study is conducted in the context of three field projects which encompass seven different pavement test sections. The test sections allowed a number of variables to be studied, including type and application rate of tack coat emulsion and type of hot-mix asphalt gradation structure (gap graded vs. dense graded). Comparisons are also made between overlays constructed using spray paver and conventional paving process. All seven sections were computationally simulated to evaluate their performance in the context of thermal and reflective cracking potential. Fairly good agreement is observed between laboratory tests, computer simulations and field performance data. The results indicate that good thermal and reflective cracking resistance are expected from TBOs. Furthermore, it was observed that the cracking performance of TBOs depends on the type of gradation for the overlay mixture and the tack coat emulsion type and its application rate. © 2013 Taylor and Francis Group, LLC.
Saftner DA, Ojard SD, Dave EV, Johnson NW, Kwon E, Teasley R. Development of a civil engineering capstone design course for a new program, in ASEE Annual Conference and Exposition, Conference Proceedings. Atlanta, GA, United states ; 2013.Abstract
The University of Minnesota Duluth's Department of Civil Engineering accepted its first students in 2008, graduated its first class in 2012, and first offered a capstone design course in the spring semester, 2012. Groups of five to six students designed a building on a local site. Students organized their teams based on interest in a particular branch of civil engineering, allowing individual students to focus their efforts on a particular subject. Based on feedback from faculty, practicing engineers, and students, several changes were implemented prior to the fall 2012 semester. These changes included making the group size smaller, modifying the graded submissions, and changing the project location. Most significantly, the course was reorganized to prevent students from working the entire semester in one area of civil engineering while doing little to no work in other areas. This paper compares the different capstone design experiences. Results from the analysis are part of a larger comparison between narrow, in-depth and broad, general approaches to design experiences for undergraduate civil engineering students. ©American Society for Engineering education, 2013.
Dave E, Baker J. Moisture damage evaluation of Asphalt mixes that contain mining byproducts. Transportation Research Record [Internet]. 2013;(2371) :113 - 120. Publisher's VersionAbstract
The availability of mineral aggregates for pavement construction is continuously depleting. The aggregate manufacturing process requires significant amounts of energy, which ranges from 10 to 30 MJ/ton. The process also produces 5 kg/ton of carbon dioxide (CO<sub>2</sub>), which causes significant amounts of greenhouse gas emissions. With the annual consumption of approximately 1.2 billion tons of aggregates in the United States, the environmental impact is significant. More than 125 million tons of fine-grained, crushed siliceous material is generated annually through iron ore mining in northern Minnesota. Typically, this material is referred to as "taconite tailings" and usually ends up as landfill near mining operations. This paper describes a moisture damage evaluation of asphalt mixes that contained significant fractions of aggregate as taconite tailings. The evaluation was conducted with the use of the conventional AASHTO T 283 test procedure as well as an approach with a fracture energy basis. The paper presents comparative results for two mixes: one made with taconite tailings and the other with conventional granite aggregates. The results indicated that a mix that contained taconite had acceptable moisture-damage resistance. The results also pointed out the limitations of the AASHTO T 283 procedure, especially the process of moisture conditioning. The fracture energy results indicated that, although mixes underwent reduced tensile strength, the overall capability of mix to strain without cracking significantly increased after the AASHTO-recommended moisture conditioning process. The study also included a set of samples that were field-conditioned over the winter and spring months. The mechanical behavior of field-conditioned samples was quite different from the behavior of samples conditioned in the laboratory with the AASHTO procedure.

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