Kamil E. Kaloush

Rational Modeling of Tertiary Flow for Asphalt Mixtures

The objective of this research study was to evaluate several mathematical models to be used in calculating the onset of tertiary flow [referred to as the flow number (FN) parameter] for asphalt mixtures. The FN indicates the onset of shear deformation in asphalt mixtures, which is a significant parameter in evaluating rutting in the field. The FN is obtained from the repeated load permanent deformation (RLPD) laboratory test. Current modeling techniques in determining the FN use a polynomial model fitting approach, which works well for most conventional asphalt mixtures. However, analysis and observations on the use of this polynomial model for rubber-modified asphalt mixtures showed problems in identifying the true FN values. The scope of the work included the collection and analysis of more than 300 RLPD test data files, which comprised more than 40 mixtures, a wide range of test temperatures, and several stress levels. A new comprehensive mathematical model was recommended to accurately determine the FN. The results and analysis were evaluated through manual calculations and found to be accurate, rational, and applicable to all mixture types, whether a tertiary stage was reached or not.

Mesoscale and microscale evaluation of surface pavement impacts on the urban heat island effects

The global phenomenon of rapid urbanization is forcing the transition of native vegetation to man-made engineered surfaces resulting in the urban heat island (UHI) effect. The UHI can adversely impact the sustainability of regions by increasing the dependence of mechanical cooling which results in increased greenhouse gas emissions, consumption of water in the thermoelectric process and increased costs of living for regional residents. The UHI can also increase the incidence and severity of heat related illnesses as well as alter sensitive ecological systems. Mesoscale remote sensing was acquired and reviewed to identify the role of surface pavements on the UHI in the Phoenix region. The imagery provided coarse visual representation of the paved surfaces, including local roads, highways and parking lots pavements; they showed a noteworthy role in regards to the UHI as well as distinguishing variability of surface temperatures related to spatial patterns, pavement material type, location and surrounding landscape. Remote sensing was also used to demonstrate the usefulness of capturing and analyzing surface materials, comparing soil and vegetation indices, albedo and surface temperatures. Handheld IR thermography was also utilized in examining contributing factors and mitigation techniques to the UHI. The findings of this study indicated that both mesoscale satellite remote sensing imagery and microscale handheld IR thermography are useful tools for defining and evaluating pavement surfaces temperatures and their contribution to the UHI. However, both have limitations in their use based on the study of interest.

Properties of crumb rubber concrete

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 ...

Porous Asphalt Pavement Temperature Effects for Urban Heat Island Analysis

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 paper 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.

Evaluation of Fiber-Reinforced Asphalt Mixtures Using Advanced Material Characterization Tests

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.

Evaluation of asphalt mixtures' viscoelastic properties using phase angle relationships

A recent study at Arizona State University has shown that the phase angle, φ, was a good laboratory parameter to distinguish the asphalt mixtures tyre/pavement noise characteristics in the field. The phase angle is obtained simultaneously from the E* dynamic complex modulus test (AASHTO TP 62-03). In particular, the peak or maximum phase angle obtained from the range of the E* test frequencies provided the best indication of the mixtures noise-dampening response. The objective of this study was to utilise the φ–E* relationships to develop appropriate master curves for the phase angle parameter. In addition, the objective was to develop predictive phase angle models so that they can be used to assess the dampening response, and therefore the tyre/pavement noise characteristics of the different asphalt mixtures. E*–φ results from 217 conventional and crumb rubber-modified asphalt mixtures were used in the analysis. The beta distribution was found to best fit the phase angle master curve relationship and the statistical goodness-of-fit parameters were found to be excellent. Phase angle predictive equations were modelled with combinations of mixture properties such as aggregate gradations, binder viscosity–temperature susceptibility parameters, asphalt content, mixture air voids, temperature and loading frequency. Over 6510 data points were included in the development of the phase angle predictive equations. They included equations for both conventional and crumb rubber-modified mixtures. The predictive equations had very good to excellent goodness-of-fit statistics.

Development of a Flow Number Predictive Model

The NCHRP 9-19 panel recommended the repeated load permanent deformation test as a laboratory procedure that could be used to evaluate the resistance of a hot-mix asphalt (HMA) to tertiary flow. No standard test protocol addresses the required laboratory stress to be applied. The test can take several hours until tertiary flow is reached and in many cases the sample may never fail. A model capable of predicting or providing general guidance on the flow number characteristics of a mix can be of great value. The model can be ideally used as a guideline to determine the stress–temperature combination that will yield tertiary flow within a reasonable testing time. In this study, an effort was undertaken to develop a flow number predictive model. The model uses HMA mixture volumetric properties and stress–temperature testing conditions as predictor variables. The laboratory test data used are a combination of two valuable databases. The first one included tests conducted at Arizona State University; the second one included tests conducted by the FHWA Mobile Asphalt Material Testing Laboratory. Ninety-four mixtures were evaluated, and 1,759 flow number test results were available. Various regression models were evaluated by combining several independent variables. The final model selected had fair statistical measures of accuracy, and it covered a wide range of mixtures, gradations, and binder properties, as well as laboratory-applied stress. As more testing data become available, the model could be refined and recalibrated for better accuracy.

Determination of Thermal Properties of Asphalt Mixtures

Rational analyses of pavement response require knowledge of the thermal properties of asphalt mixtures. These properties have not been reported thoroughly in the literature and researchers typically depend on assumed values. In the first part of this study, a laboratory test was developed to determine the thermal coefficients of expansion and contraction of several types of asphalt mixtures. The thermal coefficient values were dependent on material type and method of compaction. The coefficients of thermal expansion were slightly larger than the coefficients of thermal contraction. Hot mix asphalt (HMA) showed lower thermal coefficients than the asphalt rubber mix. In the second part of the study, a heat flow computer program was used to simulate lab temperature measurements and calculate the volumetric heat capacity (C) and thermal conductivity (k) values of HMA. No unique C and k values were found, but a linear relationship between C and k values was obtained. A band of possible optimum C and k values was developed. The program was used to estimate the required stabilization times to change test specimen temperatures according to the dynamic modulus (E*) test protocols.

Using Dynamic Modulus Test to Evaluate Moisture Susceptibility of Asphalt Mixtures

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.

Predictive Equations to Evaluate Thermal Fracture of Asphalt Rubber Mixtures

ABSTRACT Thermal cracking is a serious type of pavement distress and its prevention is a critical issue for many transportation agencies around the world. The indirect tensile (IDT) creep and strength tests were developed during the Strategic Highway Research Program (SHRP) to characterize the resistance of Hot Mix Asphalt concrete (HMA) to low-temperature cracking. Currently, the IDT creep and strength tests are considered one of the most promising tests for predicting the low-temperature performance of asphalt concrete mixtures. The IDT tests are used as the material characterization tests for thermal fracture in the Mechanistic-Empirical Pavement Design Guide (MEPDG) of New and Rehabilitated Pavement Structures (also known as the 2002 Design Guide) developed during the National Cooperative Highway Research Program (NCHRP) Project 1–37A. The existing Thermal Cracking Model (TCMODEL) that is currently an integral part of the MEPDG has proved to adequately predict low temperature cracking of asphalt concrete mixtures utilizing conventional binders. Thermal fracture characterization studies conducted at Arizona State University (ASU) concluded that the IDT procedures need certain refinements and revisions. In addition, experience from testing several asphalt rubber mixtures have shown that the existing TCMODEL in the MEPDG falls short in properly characterizing the exceptional thermal cracking resistance of the asphalt rubber mixtures in the field. The objective of this research was to develop a new method for evaluation of the thermal cracking potential in HMA, with focus on asphalt rubber mixtures. Necessary revisions and refinements of the existing IDT test protocol were made, and an IDT test results database was created and used in the development of the fracture energy prediction model. The new development utilizes the fracture energy parameter instead of the tensile strength maximum limit of the material and the slope of the creep compliance—the “m” parameter. The results of the total fracture energy measured during the IDT strength test in the lab were correlated with volumetric properties of the mixtures and a regression model was developed.