Projects

Research Assistants Working on Project: Jose Medina, Ramadan Salim, Ashraf Alrajhi Description: Modification of asphalt concrete mixtures to achieve enhanced engineering performance is common. The most often used methodologies involve either chemical or polymer modification, but a less often recognized form of modification involves mechanical reinforcement. This type of modification carries some advantages over other techniques particularly with respect to compatibility across materials of varying chemical composition and structural configuration. Fiber reinforced asphalt concrete (FRAC) is a technology that provides mechanical reinforcement to asphalt concrete mixtures and enhances the performance of these materials. Within FRAC there are two broad classes of materials; 1) reinforcement to improve the viscosity of the binding materials and prevent drain down in open graded friction courses (OGFC), porous friction courses (PFC), and stone mastic asphalt (SMA) and 2) reinforcement to improve the performance of the asphalt concrete with respect to fatigue cracking, permanent deformation, and/or thermal cracking. Cellulose and mineral fibers are most often used for the first class and synthetic fibers (polypropylene, aramid+polypropylene, etc.) are often used for the second purpose. ASU has conducted a series of projects to investigate and improve upon the performance of asphalt concrete mixtures containing synthetic fibers. In these projects the researchers investigate the material by linking together mixture level performance tests that identify underlying mechanical behaviors of the FRAC with pavement performance and life cycle cost modeling. ASU is also conducting studies to investigate, refine, and develop fiber blends that better address the needs of highway agencies. Related Publications: 2008 ASU Final Report – FORTA Evergreen Drive Estimation of FRAC Layer Coeffecient Based On MEPDG Performance Extraction of Aramid Fibers from FRAC Fiber MEPDG Guideline FORTA Boeing Report I-81 Field Performance (PCI) PCI Comparison of Sections With and Without Fibers Resilient Modulus and Pavement Reduction White Paper on Fatigue Ratio Analysis  

Research Assistants Working on Project: Gonzalo Arredondo   Description: The design and construction of asphalt pavements with Recycled (or Reclaimed) Asphalt Pavement (RAP) have been encouraged nationwide as a sustainable pavement practice and currently more than 100 million tons of the material are used in pavement related activities every year. Typically, recycling projects use between 10 and 40% RAP, and best practices at these contents exist, and  many research studies show that performance and environmental benefits of using RAP exist when these practices are followed. Nevertheless failure occur and there are still concerns that higher RAP contents will result higher mixture stiffness and pavements that are more susceptible to cracking; although higher mixture stiffness also provide better performance to protect against rutting development.  The factors that lead to failure are often related to local practice and material streams. Concerns are related to the variability of the RAP materials being stored from various projects within the same stockpiles. The use of higher percentage of RAP also complicates the complete understanding of the physio-chemical interactions between the RAP and the virgin binder in the asphalt mixture. Therefore, the percentage and effect of using RAP on the long term pavement performance has to be carefully evaluated and quantified for each local agency. The City of Phoenix is interested to evaluate the use of RAP as part of its maintenance and rehabilitation program. Arizona State University is proposing to identify how to most effectively incorporate RAP into the City of Phoenix pavement program.  

Research Assistants Working on Project: Akshay Gundla, Jose Medina, Padmini Gudipudi, Ryan Stevens, Ramadan Salim, and Waleed Zeiada (postdoctoral scholar) Description: The process of oxidation can cause stiffening and embrittlement of asphalt concrete, which may result in increased cracking and ultimately reduced pavement life. This phenomenon has been studied extensively with respect to asphalt binder where researchers have proposed conceptual, chemical, and rheological models to describe the oxidation process. While these efforts have made considerable headway towards explaining the fundamental process of oxidation at the asphalt binder scale, an equivalent understanding of the effects of these binder changes on the mechanical behaviors of asphalt concrete has not been achieved. The reasons for this lack of a fundamental link may be due to; 1) the aging kinetics are highly binder specific and dependent upon temperature; 2) physico-chemical interactions between asphalt binder and aggregate may be significant but are not very well understood, 3) particle contact and interaction are mixture dependent and not well understood; 4) thermal exposure during the mixing and placement operations can be highly variable and in some cases not very well controlled; and 5) void content can vary. Coincidently, there has been substantially less research to understand the aging phenomenon of asphalt mixtures. Some of these works conclude that without a fundamental link the only way to determine the impact of aging on mixture properties is direct experimentation of the mixtures The properties of asphalt concrete are the result of many interdependent physical and chemical mechanisms occurring across multiple length scales. Admixtures such as hydrated lime (HL) and portland cement (PC) are known to affect the behaviors of asphalt concrete at the macroscale, but their contribution at other scales and influences on overall performance of the material are not well understood. This study investigates the potential for HL and PC for mitigating the effects of asphalt concrete aging with respect to modulus and fatigue resistance. The properties of interest are being evaluated at multiple scales which involve binder, mastic, and mixture testing. Rheological analyses of aged and un-aged control, HL modified, and PC modified mastics indicate that HL possesses greater potential to mitigate aging than PC. In mixture testing, the modulus results showed trends similar to that of mastics wherein the HL modified samples were the stiffest and also showed greater potential to mitigate aging. As expected, the relative increase in stiffness and relative potential to mitigate aging, averaged across temperatures, was found to be higher in mastics than the mixtures. The results from uniaxial fatigue test show that HL mixtures possess higher fatigue resistance when aged, thus less negative impacts from the oxidation process. Magnification of aging mitigation potential at the mastic scale and its direct correlation to fatigue behavior, explains why multiple scale evaluations can be useful in evaluating the true benefits of the admixtures. Publications: Gundla, A., P. Gudipudi, J. Medina, R. Salim, W. Zeiada, and B.S. Underwood (2016). “Multiscale Evaluation of Aging in Asphalt Concretes Containing Hydrated Lime and Cement Additives,” Journal of Materials in Civil Engineering, doi: 10.1061/(ASCE)MT.1943-5533.0001501

Collaborators: Nichols Consulting Engineers Research Assistants Working on Project: Akshay Gundla and Ramadan Salim Description: The Arizona Department of Transportation (ADOT) asphalt binder purchase specifications are based largely on the AASHTO M320 standard that was developed during the Strategic Highway Research Program (SHRP). During this time modified binder systems (polymeric and chemical) were not as widespread as they are today and the grading parameters developed provided an accurate indication of binder performance. Since the development of this standard, modified systems have become more prevalent and practitioners have identified certain limitations in the M320 parameters. The development of the Multiple Stress Creep and Recovery (MSCR) test (AASHTO T 350) and the release of AASHTO M332are two recent advances that address these shortcomings. The MSCR test measures the non-recovered creep compliance, J_nr, which is characterized at strain levels that exceed the linear viscoelastic limit of the material and produces enough deformation to capture some of the benefits of binder modification. In AASHTO M332, J_nr replaces the ratio of the dynamic shear modulus to the sine of the phase angle (|G*|/sind) as the grading parameter for short term aged asphalt. It also assigns binder grades with two designations, one for temperature (as in AASHTO M320) and the other for traffic (S = standard, H = heavy traffic, V = very heavy traffic; and E = extreme traffic). The objectives for this research project are:

• Determine if the MSCR test parameter is a better indicator of the rutting performance of Arizona asphalt pavements than the currently used M320 parameter.
• Determine whether there are other undesirable performance impacts associated with using the MSCR test parameter. Specifically, does adopting the MSCR test parameter correlate to any undesirable results in performance?
• Confirm the applicability of the MSCR test to Arizona binders and conditions.
• Determine how key industry representatives anticipate possible economic effects to Arizona asphalt binder suppliers if ADOT chooses to adopt M332.

Presentations: Stempihar, J., A. Gundla, and B.S. Underwood (2017). “Alternate Interpretation of Stress Sensitivity in AASHTO T 350 (MSCR Test),” Annual Meeting of the Transportation Research Board 

Research Assistants Working on Project: Ryan Stevens Description: The objective of this study is to evaluate the Arizona Department of Transportation (ADOT) Multiple Stress Creep Recovery (MSCR) test database. This study examines the impacts of a change to MSCR based asphalt grading for the state of Arizona and seeks to provide ADOT and local suppliers with the necessary information to participate in regional MSCR/ AASHTO M332 task groups. The information obtained through this study will benefit ADOT, asphalt binder suppliers, and the Arizona State University (ASU) civil engineering students and faculty. The MSCR test specified in AASHTO T350 forms the basis for a revised and alternative performance grading specification that is described in AASHTO M332. The test is thought to better classify modified asphalt systems. A recent Asphalt Institute survey indicates that 26 states have implemented, will implement, or are considering implementing the protocol at least partially. Although Arizona is not among these 26 states, MSCR testing has been performed periodically since 2008 and currently ADOT has a database of more than 340 asphalt binder samples from across the state. This study is not intended to evaluate the MSCR test itse lf, but rather the expected impacts of the MSCR based grading system (AASHTO M332) if applied to the currently available asphalt cements in Arizona. Publications: Stevens, R., J. Stempihar, B.S. Underwood, and D. Pal (2015). “Evaluation of Multiple Stress Creep and Recovery (MSCR) Data for Arizona,” International Journal of Pavement Research and Technology. 8(5), pp. 337-345. doi: 10.6135/ijprt.org.tw/2015.8(4).337 

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Research Assistants Working on Project: Sathish Nagarajan Description: The major challenge for any pavement is the freight transport carried by the structure. This challenge is expected to increase in the coming years as freight movements are projected to grow and because these movements account for most of the load related distresses for the pavement. The problem is not simple in that the prediction of future freight traffic movements depends on current traffic conditions and an accurate prediction of economic and population growth of the different regions of the United States. The prediction of pavement deterioration also involves along with the future freight traffic, an assessment of the existing pavement and soil conditions and also the part played by the environment. In this project the issue of freight on the pavement infrastructure is explored by combining freight movement predictions with pavement performance prediction models. This work uses current traffic, climate, soil, and the pavement construction details of major interstate routes in the United States to assess the impacts from freight projections. Interstates are divided into smaller segments and analyzed using the mechanistic-empirical analysis method, to explicitly identify the impacts to fatigue, rutting and IRI of the pavement segments. Pavement segments are classified based on the severity levels of these combined distresses, which represents the segments that are most susceptible to future freight traffic. Under the scenarios examined, it is found that interstates in the Mountain and South-Atlantic regions of the United States are particularly prone to trends in freight movement. Conversely, pavements along the Pacific coast and West-Central regions are expected to sustain projected freight movements better. The results of this study provide a unique perspective on the issue of freight movement, particularly with respect to its impacts on the pavement infrastructure. It provides a forward looking view of the impact from freight movement and may lead to further research towards a more efficient pavement preservation/maintenance/rehabilitation program that is cognizant of future trends in freight. 

Collaborators: North Carolina State University, Dr. Richard Kim (PI), Dr. Cassie Castorena, Western Research Institute Research Assistants Working on Project: Akshay Gundla and Padmini Gudipudi Description: Aging has long been recognized as a major distress mechanism for asphalt concrete and, by extension, asphalt pavements. Aging causes the material to stiffen and embrittle, which leads to a high potential for cracking. The term aging with regard to asphalt concrete can have multiple interpretations. The term has been applied to mean the overall deterioration of an asphalt pavement from exposure to both climatological and load factors. In other cases, aging refers only to the effects of climate, which includes oxidative aging, ultraviolet radiation, and moisture-related damage. The most common usage of the term aging, and the one used herein, is as a descriptor for the process of asphalt binder oxidation. A review of the pertinent literature shows that although significant research has been devoted to understanding and modeling the aging phenomenon of asphalt binder, relatively little has been devoted to the aging of asphalt mixtures. The lack of significant research in this area, particularly in the years since the Strategic Highway Research Program (SHRP) concluded, reflects the complexities involved in studying the mixture aging. When factors such as the physico-chemical interactions between asphalt binder and aggregate occur, and when the material becomes structured and contains air voids, the aging process becomes more complex than the process with the binde r alone. To date, no comprehensive study exists that links the known behavior of an asphalt binder to the tendencies of an asphalt mixture, which is affected by these and other interacting factors. Without such a study, and given the current state of understanding of the relationship between the properties of an asphalt binder and an asphalt mixture that consists of that asphalt binder, it is argued that the only way to determine the impact of aging on mixture properties is direct experimentation of the mixtures. In this project ASU is investigated the accuracy with which laboratory aging must replicate in-service oxidation by quantifying the sensitivity of asphalt concrete properties to changes in asphalt binder rheology. It is well known that the properties of asphalt concrete mixture are affected due to oxidation of asphalt. In the present study, effort is made to evaluate the sensitivity of mechanical properties of asphalt concrete mixture to asphalt binder oxidation through a multiscale evaluation approach. The study involves temperature and frequency sweep experiments on unaged and aged asphalt binder (to establish baseline properties), asphalt mastic (to consider physico-chemical aspects), and fine aggregate matrix (FAM – to consider air voids and aggregate interaction effects). The multiscale approach separates effects of aggregate-binder physico-chemical interactions from those caused by air voids and physical aggregate interactions. Also, all binders were pre-aged to specific aging levels before incorporating to prepare respective aged mastics or FAM samples. The methodology adopted for assessment of sensitivity was based on the theory of crossover modulus and second order rate kinetics of asphalt binder oxidation.

Collaborators: Texas A&M University, Dr. Maryam Sakhaeifar (Prime), Dr. David Newcomb, Mona Nobakht Research Assistants Working on Project: Padmini Gudipudi, Waleed Zeiada (post-doctoral), Jeff Stempihar (Research Professor) Description: Preserving the current pavement network has become one of the top priorities for many highway agencies. There are many pavements on important routes that have exceeded their design lives and are in need of cost-effective and sustainable rehabilitation. A well-conceived preservation plan will help agencies ensure overall enhancement of the system’s functional ability with a multi-year maintenance and rehabilitation (M&R) treatments program. Such a program will help the agency optimize the allocations of annual investment in pavement rehabilitation at the network (and probably project) level. In this study it will be attempted to offer procedures to assess the current pavement conditions and investigate the historical data for selecting an appropriate rehabilitation treatment so that the use of available funding can be optimized. This study introduces a life-cycle cost analysis (LCCA) to quantify the benefits of selecting long-lasting rehabilitation treatments compared to the long term cost of more conventional treatments. For the purpose of this study, the use of RealCost 2.5 software for conducting LCCA will be followed. This user friendly software is in Microsoft Excel format and available through FHWA. It can be utilized to determine quantitative estimates of construction schedule, work zone user costs, and agency costs for initial construction and rehabilitation activities. Texas A&M University is leading the pavement and LCCA analysis. ASU has been involved in experimental characterization (axial fatigue and indirect tensile creep compliance and strength) of Oklahoma Department of Transportation materials as well as Falling Weight Deflectometer analysis of the study pavements. Publications: Nobakht, M., M.S. Sakhaeifar, D. Newcomb, B.S. Underwood, T. Freeman (2014). “Techniques for Selecting Cost-Effective Pavement Rehabilitation Strategies: Two Case Studies,” Proceedings 2014 Airfield and Highway Pavements Conference, ASCE, Orlando, Florida. Nobakht, M., M. S. Sakhaeifar, D. Newcomb, B. S. Underwood,  and T. Freeman (2015). “Techniques for Selecting Cost-Effective Pavement Rehabilitation Strategies,” ASCE T&DI 2015 Annual Meeting, Miami, Florida, June 2015.

Research Assistants Working on Project: Akshay Gundla Description: Over 90% of U.S highways and roads are surfaced with hot mix asphalt (HMA). As the country’s infrastructure ages, these roads and highways have to be maintained and rehabilitated. Reclaimed asphalt pavement (RAP) is the term given to asphalt pavement materials that have been removed from an existing pavement structure during re-construction, re-surfacing and/or other utility/maintenance works and processed so that they can be incorporated into new asphalt concrete or be used as a granular base, subbase, embankment material, or fill material. When properly crushed and screened the final product consists of high quality well graded asphalt coated aggregates. Depleting supply of raw materials, coupled with increased demand and limited supply and emphasis on sustainable infrastructure has necessitated use of RAP more now than ever before. Traditionally, the use of RAP in pavements has been restricted to a maximum of 15%. The main concern among the contractors and the states with using higher dosage rates is the increase in stiffness of the mix that comes with the addition of RAP. This increase in stiffness makes the pavement rut resistant but also makes it more brittle and prone to cracking. Past research has emphasized the importance and influence of physicochemical interaction on the behavior of regular asphalt concrete mixtures. These influences are likely present in RAP mixtures as well albeit in a more complicated way. Recent research has supported this hypothesis and suggests that the difference in performance of non-modified and RAP modified asphalt concrete mixtures to the possible difference in physicochemical interactions due to presence of RAP. The hypothesis behind this study is that a better understanding of physicochemical interactions of RAP modified mixtures will provide more insight into the performance of these mixtures. The present research seeks to study these physicochemical interactions at the mastic scale due to relatively simpler interactions present in mastics when compared to the mixtures. A locally sourced RAP material was screened and sieved to separate the coated fines (passing #200) from the remaining sizes. These binder coated fines were mixed with virgin filler at proportions commensurate with 0%, 10%, 30%, 50% and 100% RAP dosage levels. Mastics were prepared with these blended fillers and a PG 64-22 binder at a filler content of 27% by volume. Rheological experiments were conducted on the resulting composites as well as the constituents, virgin binder, solvent extracted RAP binder. The results from the dynamic modulus experiments showed an expected increase in stiffness with increase in dosage levels. These results were used to model the hypothesized structure of the composite. The study presented discusses the different micromechanical models employed, their applicability and suitability to correctly predict the blended mastic composite. Related Publications: Gundla, A. and B.S. Underwood (2015). “Evaluation of in situ RAP Binder Interaction in Asphalt Mastics using Micromechanical Models,” International Journal of Pavement Engineering. In Press. doi: 10.1080/10298436.2015.1066003 Gundla A. (2014). “Use of Micromechanical Models to Study the Mastic Level Structure of Asphalt Concrete Containing Reclaimed Asphalt Pavement,” M.S. Thesis. Arizona State University, Tempe, AZ.  

Research Assistants Working on Project: Ramadan Salim Sponsor: Arizona Pavement and Materials Conference Description: One of the least studied and hence least understood phenomena in asphalt concrete pavements are durability cracks. These cracks are generally associated with low volume, rural roadways (though not always) and manifest principally as cracks that run transverse to the direction of travel. This pattern of failure suggests a type of thermally induced, but they occur in regions where temperatures rarely drop below freezing. One theory suggests a combination of factors including thermal fatigue brought on by relatively large temperature variations, oxidation induced stiffening and embrittlement of the binder, and possibly other support condition related mechanisms all combine to yield this distress. Other mechanisms related to the aggregate skeleton resistance to thermal contraction may also have an important role in the extent and severity of this distress.   In spite of not having a coherent or consistent explanation of the cause, many agencies are now faced with management and maintenance of roadways that exhibit these durability cracks. It is believed that a comprehensive, quantified explanation of this distress will lead to 1) better decisions at the planning/design phase so as to avoid the development of this distress and 2) management solution that yields the most appropriate set of strategies to best mitigate the impacts of durability cracking. The first step in this process is compilation of area experiences, documentation of examples, and a system by which these cracks can be documented.   At the request of the Arizona Pavement/Materials Conference Committee, funds are being requested to study and compile local experiences with durability cracks and to create a mechanism to allow agencies to share technical details on projects that show this distress.   The technical brief produced from this study will highlight the most likely causes of the distress (from existing knowledge coupled to what is learned through the interview and documentation process). It will also discuss any relevant findings from the interview process and propose a common set of ranking and terms that can be used to document the distress and share resources and information across local agencies. Any useful findings regarding the maintenance of this distress will be identified. A tentative outline and brief explanation of content is:

• Introduction: Explanation of what a durability crack is and how it differs from other more commonly described distresses like fatigue cracking, rutting, and thermal cracking.
• Causes of Durability cracking: Explanation of how durability cracking occurs with specific attention to why it is a particularly relevant problem to Arizona (or surrounding regions)
• Study method: Summary of the tasks and procedures taken to build the knowledge that went into the tech brief
• Extent of the problem in Arizona: Summary of results from interviews, documentation of extent and severity in Arizona (or specific to the Phoenix Metropolitan region), contributing factors that were identified, and proposed terminology and classification system for the distress.
• Maintenance strategies: Documentation of maintenance strategies being used and their success at mitigating the failures.     

Collaborators: Fugro-BRE, Inc., Austin, TX Research Assistants Working on Project: M El-Basyouny Description: Major changes in the asphalt pavement industry have occurred in the last 10 years. Potential changes in the next 10 years will be substantial and highly positive to technology. This paper presents an overview of recent research efforts undertaken to recommend a fundamentally based laboratory “Simple Performance Test” (SPT) for permanent deformation evaluation of asphalt mixtures. The test is intended to be used within the newly adopted “Superpave” volumetric mixture design procedure, and to provide accurate correlation to field rutting performance. The laboratory testing program included mixtures and performance data from three major experimental sites: the Minnesota Road Project (MnROAD), the Federal Highway Administration (FHWA) Accelerated Loading Facility Study (ALF), and the FHWA Performance Related Specifications Study (WesTrack). Eleven test types and over eighty test response parameters were evaluated. This paper focuses on three selected candidate tests for the rutting evaluation: the dynamic modulus, static creep, and the repeated load permanent deformation tests.

Collaborators: Arizona Department of Transportation, Ford Motor Company, Recycled Tires Engineering and Research Foundation, FNF Construction, City of Phoenix, Hanson Aggregates, and the Arizona Cement Association Research Assistants Working on Project: Goutham Lingannagari, Aleksander Zborowski Description: Crumb rubber is a material produced by shredding and commutating used tires. There is no doubt that the increasing piles of used tires create environmental concerns. The long-term goal of this research is to find means to dispose of the crumb rubber by placement of the rubber in portland cement concrete and still provide a final product with good engineering properties. The Arizona Department of Transportation and Arizona State University have initiated several crumb rubber concrete (CRC) test sections throughout Arizona over the past few years. Laboratory tests were conducted to support the knowledge learned in the field and enhance the understanding of the material properties of CRC. Concrete laboratory tests included compressive, flexural, indirect tensile strength, thermal coefficient of expansion, and microscopic matrix analyses. The unit weight and the compressive and flexural strengths decreased as the rubber content in the mix increased. Further investigative efforts determined that the entrapped air, which caused excessive reductions in compressive strength, could be reduced substantially by adding a deairing agent. The higher tensile strains at failure observed from the tests were indicative of more ductile, energy-absorbent mix behavior. The coefficient of thermal expansion test results indicated that CRC was more resistant to thermal changes. The CRC specimens tested remained intact after failure and did not shatter as a conventional mix did. Such behavior may be beneficial for a structure that requires good impact resistance properties. If no special considerations are made to maintain higher strength values, the use of CRC mixes in places where high-strength concrete is not required is recommended.

Collaborators: Decorative Paving Solutions, American Asphalt, Vulcan Materials, CEMEX, and For Ever Lawn, Dr. Soe Myint, Dr. Waleed Zeiada Research Assistants Working on Project: Jeffrey Stempihar, Tina Pourshams-Manzouri, , Maria Rodezno, David Ramsey, Sam Enmon, Jiachuan Yang, and Jiun Song Description: Increased nighttime temperatures caused by retained heat in urban areas is a phenomenon known as the urban heat island (UHI) effect. Urbanization requires an increase in pavement surface area, which contributes to UHI as a result of unfavorable heat retention properties. In recent years, alternative pavement designs have become more common in an attempt to mitigate the environmental impacts of urbanization. Specifically, porous pavements are gaining popularity in the paving industry because of their attractive storm water mitigation and friction properties. However, little information regarding the thermal behavior of these materials is available. This study explores the extent to which porous asphalt pavement influences pavement temperatures and investigates the impact on UHI by considering the diurnal temperature cycle. A one-dimensional pavement temperature model developed at Arizona State University was used to model surface temperatures of porous asphalt, traditional dense-graded asphalt, and portland cement concrete pavements. Scenarios included variations in pavement thickness, structure, and albedo. Thermal conductivity testing was performed on porous asphalt mixtures to obtain values for current and future analysis. In general, porous asphalt exhibited higher daytime surface temperatures than the other pavements because of the reduced thermal energy transfer from the surface to subsurface layers. However, porous asphalt showed the lowest nighttime temperatures compared with other materials with a similar or higher albedo. This trend can be attributed to the unique insulating properties of this material, which result from a high air void content. As anticipated, the outcome of this study indicated that pavement impact on UHI is a complex problem and that important interactions between influencing factors such as pavement thickness, structure, material type, and albedo must be considered.

Collaborators: Decorative Paving Solutions, American Asphalt, Vulcan Materials, CEMEX, and For Ever Lawn, Dr. Soe Myint, Dr. Waleed Zeiada Research Assistants Working on Project: Jeffrey Stempihar, Tina Pourshams-Manzouri, , Maria Rodezno, David Ramsey, Sam Enmon, Jiachuan Yang, and Jiun Song Description: In recent years, an increase of environmental temperature in urban areas has raised many concerns. These areas are subjected to higher temperature compared to the rural surrounding areas. Modification of land surface and the use of materials such as concrete and/or asphalt are viewed to be the main factors influencing the surface energy balance and therefore the environmental temperature in the urban areas. Engineered materials have relatively higher solar energy absorption and tend to trap a relatively higher incoming solar radiation. They also possess a higher heat storage capacity that allows them to retain heat during the day and then slowly release it back into the atmosphere as the sun goes down. This phenomenon is known as the Urban Heat Island (UHI) effect and causes an increase in the urban air temperature. Several studies in the literature focus on the pavement albedo as a key factor affecting the UHI. However, studies conducted at Arizona State University (ASU) have shown that the problem is more complex and that solar reflectivity alone should not be the only factor considered for UHI pavement mitigation measures. The main objective of this study was to analyze and research the influence of pavement materials on the near surface air temperature. In order to accomplish this effort, test sections consisting of Hot Mix Asphalt (HMA), Porous Hot Mix asphalt (PHMA), Portland Cement Concrete (PCC), Pervious Portland Cement Concrete (PPCC), artificial turf, and landscape gravels were constructed in the Phoenix, Arizona area, near the ASU campus. Air temperatures at different elevations, pavement albedo, wind speed, solar radiation, and wind direction were recorded, analyzed and compared above each pavement material type. The results showed that there was no significant difference in the air temperature at 3-feet and above, regardless of the pavement type. Near surface pavement temperatures were also measured and modeled. The results indicated that for complete UHI analysis, it is important to consider the interaction between pavement structure, material properties, and environmental factors. Overall, this study demonstrated the complexity of evaluating pavement structures for UHI mitigation; it provided great insight on the effects of material types and properties on surface temperatures and near surface air temperature. Data will be continued to be collected for one year; future analysis and verification will be reported on in a separate study effort.

Collaborators: James Delton, State Materials Engineer and Paul Burch, Pavement Design Engineer. Research Assistants Working on Project: Atish Nadkarni, Waleed Zeiada, Krishna Biligiri Description: The stripping in of hot-mix asphalt (HMA) is assessed by AASHTO T283 by means of the indirect tensile strength test. The tensile strength ratio (TSR) is used as the criterion for strength retention after sample conditioning. In recent years, the dynamic modulus (|E*|) test, conducted according to AASHTO TP62-03, has gained wider use in the pavement community for two reasons: it is a major input into the Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures and is being used as a simple performance test indicator. The objective of this study was to assess whether the E* laboratory test can be used as a replacement test property for indirect tensile strength in AASHTO T283. Because the E* test is nondestructive, unlike the indirect tensile strength test, the advantage would be that the same specimens could be used before and after moisture conditioning. The scope of work in this research included conducting a laboratory testing program on several types of asphalt mixtures by means of both test procedures. All mixtures were obtained from construction projects in the field. A unique aspect of this study was that some of the mixtures failed in the field after stripping. The E* tests were used to determine the percent of retained stiffness, a term referred to as E* stiffness ratio (ESR). Results of both TSR and ESR conducted on the same mixtures were compared and statistically analyzed. The analysis indicated that there was no statistically significant difference between the measured TSR and ESR values for the same mixture. The correlation obtained between the two ratios had good measures of accuracy. It was concluded that the ESR can potentially replace TSR testing to assess field moisture damage for asphalt mixtures. The recommendation was to continue the testing program and expand the database for future analysis.

Collaborators: FORTA Corporation: Clifford MacDonald, John Lindh, Jeff Lovett, and George Sadowski; Teijin Aramid: Jorg Willing, City of Tempe: John Osgood, Denise Brewer, Toby Crooks and Derik Winkle; CEMEX (formally Rinker West, Central Region): Donald Green; MACTEC: Sam Huddleston and Brian Waterbury; ASU: Kenneth Witczak, Matthew W. Witczak and Michael S. Mamlouk. Research Assistants Working on Project: Krishna Prapoorna Biligiri, Waleed Abdelaziz Zeiada, Maria Carolina Rodezno, Jordan Xavier Reed, Ravi Kantipudi, Atish Nadkarni Description: The objective of this study was to evaluate the material properties of a conventional (control) and fiber reinforced asphalt mixtures using advanced material characterization tests. The laboratory experimental program included: triaxial shear strength, dynamic (complex) modulus, repeated load permanent deformation, fatigue, crack propagation, and indirect tensile strength tests. The data was used to compare the performance of the fiber modified mixture to the control. The results showed that the fibers improved the mixture’s performance in several unique ways against the anticipated major pavement distresses: permanent deformation, fatigue cracking, and thermal cracking.

Collaborators: FORTA Corporation Research Assistants Working on Project: Krishna Prapoorna Biligiri, Waleed Abdelaziz Zeiada, Maria Carolina Rodezno, Jordan Xavier Reed, Ravi Kantipudi, Atish Nadkarni, Ramadan Salim, Jose Medina, Ashraf Alrajhi Description: This study highlights findings from several research efforts on Fiber Reinforced Asphalt Concrete (FRAC) mixtures. The fibers are a blend of polypropylene and aramid fibers. The reinforcing strength contribution of fibers was evident in several mechanical tests. Flexural and fracture tests also indicated that the FRAC mixture is better able to resist the development and propagation of cracks when compared to the control mixture. The stiffness properties also showed that the FRAC mixture will provide better rutting and fatigue cracking resistance. Recommendations on the use of FRAC mixture moduli and/or structural layer coefficients in pavement desi gn analysis are also discussed.

Collaborators: National Center of Excellence on SMART Innovations Research Assistants Working on Project: J Carlson, R Bhardwaj, D Morris Description: The current method of measuring thermal conductivity requires flat plates. For most common civil engineering materials, creating or extracting such samples is difficult. A prototype thermal conductivity experiment had been developed at Arizona State University (ASU) to test cylindrical specimens but proved difficult for repeated testing. In this study, enhancements to both testing methods were made. Additionally, test results of cylindrical testing were correlated with the results from identical materials tested by the Guarded Hot-Plate method, which uses flat plate specimens. Several recommendations were made for the future implementation of both test methods. The work in this study fulfills the research community and industry desire for a more streamlined, cost effective, and inexpensive means to determine the thermal conductivity of various civil engineering materials.

Collaborators: Arizona Department of Transportation, National Center of Excellence on SMART Innovations Research Assistants Working on Project: Joby Carlson Description: The main objective of this research study was to provide understanding, supporting documentation, and tools on how pavement designs and materials selection contribute to surface and subsurface temperature fluctuations. This objective was achieved through two focus areas that outlined the scope of work of this research: thermal properties and reflectance evaluation, and heat absorption and transfer modeling. In the first focus area, the reflectance “albedo” characteristics of various concrete pavement surfaces / mix types were identified. Surface and in-depth pavement temperatures of several field sections were collected to help validate modeling efforts. Perhaps one of the most notable accomplishments in this focus area was the development of a simplified laboratory test procedure to measure the thermal conductivity of paving materials using cylindrical specimens. Laboratory tests were also conducted to measure key thermal properties of the different paving materials. These properties were used as input parameters for the pavement heat absorption and transfer model. In the second focus area, a pavement heat absorption and transfer model was developed and validated. This fundamental model accounts for the surface rates of solar radiation absorption and heat transmission of various pavements designs. It can be used for comparative evaluation for the different pavements designs in mitigating the Urban Heat Island Effect. The outcome of the two focus areas outlined above are envisioned to play a key role aiding future decision makers and designers when choosing appropriate pavement materials for their particular application. It will provide further awareness of urban heat island, and drives further municipal ordinances and building codes that incorporate environmentally appropriate materials into development and rehabilitation projects.

Collaborators: National Center of Excellence on SMART Innovations Research Assistants Working on Project: Jiachuan Yang Description: Studies on urban heat island (UHI) have been more than a century after the phenomenon was first discovered in the early 1800s. UHI emerges as the source of many urban environmental problems and exacerbates the living environment in cities. Under the challenges of increasing urbanization and future climate changes, there is a pressing need for sustainable adaptation/mitigation strategies for UHI effects, one popular option being the use of reflective materials. While it is introduced as an effective method to reduce temperature and energy consumption in cities, its impacts on environmental sustainability and large-scale non-local effect are inadequately explored. This study provides a synthetic overview of potential environmental impacts of reflective materials at a variety of scales, ranging from energy load on a single building to regional hydroclimate. The review shows that mitigation potential of reflective materials depends on a set of factors, including building characteristics, urban environment, meteorological and geographical conditions, to name a few. Precaution needs to be exercised by city planners and policy makers for large-scale deployment of reflective materials before their environmental impacts, especially on regional hydroclimates, are better understood. In general, it is recommended that optimal strategy for UHI needs to be determined on a city-by-city basis, rather than adopting a “one-solution-fits-all” strategy.

Collaborators: National Center of Excellence on SMART Innovations Research Assistants Working on Project: Mark Belshe, Maria Rodezno Description: Curling stresses of concrete pavement can be very damaging, and reducing the temperature swings would be very beneficial. This study includes a field instrumentation effort with pavement temperature sensors to quantify the thermal behavior of concrete pavement with and without an open-graded asphalt rubber friction course. The study shows a nonlinear temperature profile across slab thickness, with a large change in temperature between day and night at the top of the concrete slab, and little change at the bottom of the slab. Adding an open-graded friction course over the concrete pavement reduces the temperature fluctuation between day and night as a result of the aeration effect, which is increased by traffic. A three-dimensional (3D) finite-element analysis with a nonlinear temperature gradient shows that adding the friction course reduces the curling stresses in the summer. Furthermore, since traffic increases the aeration effect, sections without traffic show lower effect of friction course on reducing the temperature differentials between the top and bottom of the slab.

Collaborators: Arizona Department of Transportation: James Delton, Paul Burch, Ali Zareh, George Way, Alex Durazo, Scott Weinland, Russell DiVincenzo, and Michael Kondelis. Arizona State University: Jay Golden, Kenny Witczak. Research Assistants Working on Project: Maria Carolina Rodezno, Joby Carlson, Kiran Mohanraj and Atish Nadkarni Description: An experimental laboratory study was undertaken to evaluate the engineering properties for four different concrete mixtures: a control mixture with no fibers and mixtures with polypropylene fibers using the following dosages: 3, 5, and 8 lb/yd3 (1.78, 2.97, and 4.75 kg/m3). Various samples were collected during construction and tested for compressive strength, flexural strength, and toughness using cylindrical, prismatic, and round panel specimens. Because the toughness results cannot be taken into account using common concrete pavement design methodologies, which is especially true for the round panel test, an analysis was performed that took into account the additional benefit of the polypropylene fibers using a residual strength approach. It was concluded that the effect of the addition of fibers was best captured using the round panel test. It was also concluded that the use of 5 lb/yd3 (2.97 kg/m3) fiber dosage had the best value-added benefit to the mixture.

Collaborators: Arizona Department of Transportation: Dale Buskirk, Arnold Burnham, Beverly Chenausky, Kathleen Sommer, Mark Wheaton, James Delton, Dennis Rusher, Ernie Johnson, Edward Walsh, John Kruger, and George Way. Research Assistants Working on Project: Maria Rodezno, Qinyue Sun, and Daniel Gonzales Description: Tire wear contributes to atmospheric particulate matter (PM) and is regulated by the U.S. Environmental Protection Agency because PM has been shown to affect human health. Vehicle emissions are a significant source of both PM2.5 and PM10. Vehicle fleet emissions per mile traveled have been reduced significantly in the past 30 years as a result of improved engine operation and tailpipe controls. However, “zero emission” vehicles will continue to generate PM from tire wear, road wear, brake wear, and resuspended road dust. In this study, aerosol measurement techniques at Arizona State University were applied to evaluate tire wear emissions from the vehicle fleet by using the Deck Park Tunnel in Phoenix, Arizona. The Deck Park Tunnel highway surface was portland cement concrete (PCC) and was resurfaced with an asphalt rubber friction course (ARFC) layer as part of the Arizona Department of Transportation Quiet Pavements Program. This study took advantage of a rare opportunity to sample tire wear emissions at the tunnel before and after the ARFC overlay. The hypothesis was that an ARFC surface results in less tire wear than the existing PCC road surface. This paper reports on the measured PM emissions from the on-road vehicle traffic during typical highway driving conditions for the two different roadway surfaces. It presents the analysis of representative tire tread samples for tire wear marker compounds and a comparison of roughness and frictional surface characteristics as measured before and after the ARFC overlay. The study found that emission rates of tire wear per kilometer driven on PCC road surfaces were 1.4 to 2 times higher than emission rates of tire wear on ARFC road surfaces.

Collaborators: CEMEX, the Portland Cement Association (PCA), Progressive Concrete Works Inc., and the J. Russell and Bonita Nelson Fine Arts Center at Arizona State University. Research Assistants Working on Project: Joby Carlson, Mohamed Arab Description: Pervious Portland cement concrete has gained recent momentum in industry and local governments for being an environmentally preferred alternative to conventional impermeable pavement materials. Pervious concrete is best known for its benefits for storm water management in parking lots and low volume roads. It is also hypothesized to aid in mitigating the Urban Heat Island effect although no research has documented such a benefit in hot arid-climates. In this study, a pervious concrete parking lot constructed in the Phoenix, Arizona metropolitan area is evaluated. The facility was instrumented with temperature and soil moisture sensors, and was monitored for several months. The in situ data was used to calibrate a pavement thermal model and run several different design scenarios. The findings suggested that pervious concrete pavements can provide night time minimum surface temperatures that are lower than conventional impermeable pavements. The moisture results and regional soil analyses also indicated that these permeable materials provide an effective alternative means to capture and retain storm water runoff from parking lots and are applicable for the majority of soil types found in Arizona.

Collaborators: ADOT Materials Group Research Assistants Working on Project: A Zboroswki, Andres Sotil Description: This study focused on conducting experimental program on several Asphalt Rubber (AR) mixtures to obtain their typical engineering properties and understand their field performance. Most of the labora tory program was based on tests recommended by the National Cooperative Highway Research Program, NCHRP 9-19 Project, which dealt with recommending Simple Performance Tests (SPT) for the evaluation of asphalt mixes. The laboratory tests included: consistency binder tests, triaxial shear strength, repeated load permanent deformation, dynamic modulus, flexural beam fatigue, and indirect tensile tests. The results obtained for the AR mixtures were also compared, when possible, with results obtained for conventional mixtures. The AR mixes were those typically used in Arizona, along with an experimental mixture that was constructed by Alberta Transportation, in Canada. All laboratory test specimens were prepared using mixes that were collected during construction. The tests also included sensitivity studies of the mixtures to air voids, temperatures, and influence of confinement level. It was concluded that many parameters obtained from the above tests were successful in describing the observed good field performance of AR mixes.

Collaborators: ADOT Materials Group Research Assistants Working on Project: Aleksander Zboroswki Description: The existing Thermal Cracking Model (TCMODEL) that is currently an integral part of the Mechanistic Empirical Pavement Design Guide (MEPDG) has been shown to adequately predict low temperature cracking of asphalt concrete mixtures utilizing conventional binders. However, test results from several asphalt rubber mixtures in this research study showed that the TCMODEL in the MEPDG falls short in predicting the observed thermal cracking resistance of these mixtures in the field. This paper presents development and findings of a new method for thermal cracking potential evaluation in asphalt mixtures, with a focus on asphalt rubber mixtures. Refinements of the existing IDT test protocol are presented, and a new Crack Depth Fracture Model is proposed to include a fracture energy parameter. The new fracture energy model is evaluated with laboratory test results and rationality corresponding with field observations. The new model proved to be satisfactory in predicting the thermal cracking performance for both conventional and asphalt rubber mixtures. Its use in future MEPDG models is recommended.

Collaborators: ADOT Materials Group Research Assistants Working on Project: Maria Carolina Rodezno Description: The development and validation of a rutting prediction model based on input of the flow number test is presented in this study. Along with the construction of field test sections, the authors realized that such a model would require a very large laboratory testing program. Therefore, as one of the important tools used in this paper, together with the Mechanistic Empirical Pavement Design Guide (MEPDG, now DARWin-ME), a flow number predictive equation, as developed and published by the authors in a previous study, was utilized. The generation of hundreds of rutting values for different pavement structures, climatic locations, and traffic levels was allowed by the MEPDG. This analysis used a total of 1440 asphalt pavement sections. A power model form was recommended for this rutting – flow number relationship that also included traffic and layer thickness as input variables; it had a very good statistical goodness of fit. The model was additionally validated using actual laboratory flow number testing and field rutting data from 10 test sections which were installed at the National Center for Asphalt Technology (NCAT) Test Track in 2006. Regarding prediction of field rutting of the NCAT test sections, the results showed that the model had very good accuracy.

Collaborators: ADOT Materials Group, George Way Research Assistants Working on Project: Aleksander Zborowski, Andres Sotil, Maria Carolina Rodezno, Mohammad Abojaradeh. Description: Asphalt rubber mixtures continue to receive great attention from many transportation agencies world-wide because of their ability to improve pavement performance c ompared to conventional designs. A number of studies reported on the unique properties and characteristics of asphalt rubber mixtures in terms of improved permanent deformation and fatigue cracking. Several states in the US and countries around the world have used, or are in the process of using asphalt rubber mixtures in new pavement designs and rehabilitation programs. This paper summarizes findings from several research studies conducted at Arizona State University in the areas of binder and mixture performance. The unique engineering properties of asphalt rubber mixtures are discussed along with recommendation on how to use them in current pavement design procedures.

Collaborators: ADOT Materials Group, George Way Research Assistants Working on Project: Luis de Mello Description: The Continuum Damage Theory (CDT) has been used by many researchers to study the fatigue performance of conventional Asphalt Concrete (AC) mixtures. The theory is based on Schapery`s constitutive model for viscoelastic materials subjected to damage. It uses the elastic-viscoelastic correspondence principle, as well as the Work Potential Theory (WPT) and a damage evolution law. Besides its fundamental mechanistic principles, which help the understanding of the fatigue phenomenon, the main benefit of this approach is the possibility of using numerical codes to visualize the damage evolution on AC layers during cyclic loads. This study shows the applicability of the CDT on flexural fatigue tests for both conventional and Asphalt Rubber (AR) mixtures. The results show that the characteristic curves of AR mixtures could be determined for different levels of loading and yielded a unique relation between damage and stiffness. The characteristic curve represents the damage evolution within the mix during the fatigue test. Furthermore, compared to conventional mixtures, the characteristic curves for asphalt rubber mixtures show lower damage accumulation.

Collaborators: Thorsten Nordgren, Mats Wendel Research Assistants Working on Project: Krishna P Biligiri, Waleed A. Zeiada, Maria C. Rodezno, Mena I. Souliman, Jordan X. Reed, Jose M. Rodriguez, Jeffrey Stempihar Description: The objective of this study was to conduct an advanced laboratory experimental program to obtain typical engineering material properties for reference, asphalt-rubber (AR), and polymer-modified (PM) gap graded asphalt concrete mixtures placed in the Stockholm area of Sweden. The advanced material characterization tests included: Dynamic (Complex) Modulus for stiffness evaluation; triaxial shear strength test to evaluate shearing resistance; repeated load for permanent deformation characterization; beam fatigue for crack evaluation; Indirect Diametral Tensile test for thermal cracking mechanism evaluation; and C* Integral test to assess crack growth and propagation. Furthermore, conventional binder consistency tests were performed to complement other material mixture characteristics. The data was used to compare the performance of the AR gap graded mixture with respect to reference and PM gap graded mixtures. The results showed that the AR gap graded mix would provide better resistance to low temperature cracking and permanent deformation. The expected fatigue life for the AR gap graded mixture was higher than the reference and PM mixtures for the existing highway conditions. Furthermore, the crack propagation tests showed that the AR gap graded mixture had highest resistance to crack propagation than the other two mixtures.

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