A LABORATORY INVESTIGATION AND MODELING OF DYNAMIC MODULUS OF ASPHALT MIXES FOR PAVEMENT APPLICATIONS

Traditionally, stiffness of hot mix asphalt (HMA) has been used as a measure of the pavement's ability to carry vehicular traffic loads without undergoing excessive deformation. Early deterioration of pavements due to rutting, fatigue cracking, and other type of distresses may be attributed to inadequate stiffness. The mechanistic empirical pavement design guide (MEPDG) emphasizes the use of dynamic modulus of asphalt mixes at all three levels of flexible pavement design. HMA mixes and aggregates that are commonly used in Oklahoma for the construction of flexible pavements were characterized in this study.A database of dynamic modulus and master curves was developed for the mixes used in this study, which is expected to be useful in the implementation of the MEPDG for the design and analysis of flexible pavements. In addition, the effect of plant production and sample preparation methods on different aggregate shape parameters was evaluated. The results indicate that texture and form of coarse aggregates can change significantly during plant production and compaction in a gyratory compactor. No significant differences were observed for fine aggregates. The present study also compared the shape properties of three different types and sizes of coarse aggregates. The larger size aggregates were found to be rougher and more cubical compared to the smaller size aggregates, indicating that aggregate particles become smoother and elongated with a reduction in size.Three different input levels of the MEPDG for modified and unmodified mixes were compared in this study. It was found that the accuracy of Level 2 and Level 3 depend on the mix type. The current study also evaluated the strengths and weaknesses of four empirical models (i.e., Witczak 1999, Witczak 2006, Hirsch, and Al-Khateeb) that are commonly used in estimating dynamic modulus. Analyses of the results show that the performance of a model varies with air voids and temperature. Statistical and neural network (NN) models were developed to estimate dynamic modulus including angularity, texture, form, and sphericity of aggregates as variables. Inclusion of shape parameters is found to enhance the predictive capability of a model significantly. It was found that the long-term oven (LTO) aging resulted in approximately a 42% to 60% increase in dynamic modulus, depending upon the amount of reclaimed asphalt pavement (RAP) in the mix and air voids. Overall, enhanced characterization of aggregates and asphalt mixes is found to be extremely important for pavement design applications

Field Performance Monitoring and Modeling of Instrumented Pavement on I-35 in McClain County

Phase 1 of this project was conducted to better understand the cause of pavement failure under actual traffic loading and environmental conditions. A 1,000-ft. long experimental pavement section was constructed on I-35 in McClain County and was instrumented for field data collection. The test section was designed to fail in a relatively short period of time under heavy interstate traffic. After approximately four years (from 2008 to 2012) of exposure to continuous interstate traffic and environment, the test section experienced significant rutting but no fatigue cracking. Therefore, the funding agency decided to monitor the test section for two additional years (from 2012 to 2014) as part of Phase 2 of the project. Additionally, a need for predicting distresses (i.e., rut, based on the site-specific data) using the Mechanistic Empirical Pavement Design Guide (MEPDG) software was expressed. In Phase 2 of this project, the quarterly field testing (FWD, rut measurements, roughness measurements, and crack mapping) was performed on a quarterly basis. Also, the weekly downloading of traffic data and data processing were performed to allow updating of the rut prediction models developed in Phase 1 of this study. Site-specific (Level 1) input parameters for traffic, climate and materials were developed in this study. Furthermore, the rut prediction models in the MEPDG software were calibrated using the developed input parameters and measured rut depths from the test section. Laboratory tests (Hamburg rut, four point beam fatigue, volumetric properties, etc.) were performed on the extracted samples from the test section. Moreover, the contribution of different pavement layers to total rutting was assessed by a forensic investigation involving cutting full-depth trenches at three selected locations of the test section.Final report, October 2012-December 2014N

Quality control of subgrade soil using intelligent compaction

Intelligent Compaction (IC) of subgrade soil has been proposed to continuously monitor the stiffness of subgrade during its compaction. Modern IC rollers are vibratory compactors equipped with (1) an onboard measuring system capable of estimating the stiffness of the pavement material being compacted, (2) Global Positioning System (GPS) sensor to precisely locate the roller, and (3) an integrated mapping and reporting system. Using IC, the roller operator is able to evaluate the entire subgrade and address deficiencies encountered during compaction. Continuous monitoring of quality during construction can help build better quality and long-lasting pavements. However, most of the commercially available IC rollers report stiffness in terms of Original Equipment Manufacturer (OEM) specified indicator, known as Intelligent Compaction Measurement Value (ICMV). Although useful, additional tests are required to establish the correlation between these ICMV values and the resilient modulus of subgrade (M-r). Since the mechanistic design of the pavement is performed using M-r, it is important to know if the design M-r is achieved on the entire subgrade during compaction. This paper presents a systematic procedure for monitoring the level of compaction of subgrade in real time using intelligent compaction (IC). Specifically, the Intelligent Compaction Analyzer (ICA) developed at the University of Oklahoma was used for estimating the modulus of the subgrade. Results from two demonstration studies show that the ICA is able to estimate subgrade modulus with an accuracy that is acceptable for quality control activities during the construction of pavements

Fatigue Performance of Asphalt Pavements Containing RAS and RAP

Rising oil and gas prices spurs development of methods and technologies for reducing fuel consumption and increased use of recycled materials. With increased environmental awareness, using reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in pavements have been gaining momentum nationally and globally. However, despite their advantages, there are national concerns associated with fatigue and low-temperature cracking potential of pavements when containing increased amounts of RAS and RAP. Therefore, this study was undertaken to evaluate the fatigue performance of hot-mix asphalt (HMA) containing RAS and RAP. Specifically, changes in fatigue resistance and cycles to fatigue failure with changes in the amount of RAS and RAP were examined using both flexural fatigue (four-point beam) and axial fatigue (cyclic direct tension) tests on laboratory compacted specimens. Effect of virgin binder grade on the fatigue performance was also examined. In addition, the effect of RAS and RAP in HMA on its creep compliance and dynamic modulus was investigated. These properties are used in the evaluation of fatigue resistance based on the axial cyclic direct tension test. For this purpose, eight fine surface course mixes (S4) with different types of asphalt binders (i.e., PG 64-22 OK and PG 70-28 OK) containing different amounts of RAS and RAP were designed and tested in the laboratory. The amount of RAS and RAP in HMA mixes varied, but the total amount of replaced binder was kept within certain specifications (i.e., RAP and/or RAS limited to 30% binder replacement). It was concluded that the fatigue life of asphalt mixes with a PG 64-22 OK binder increased with use of RAP or a blend of RAP and RAS. Using a blend of 5% RAP and 5% RAS in a mix led to the maximum increase in fatigue life. However, it was observed that the fatigue life of the mix decreased when 6% RAS was used compared to that of virgin mix with the same type of asphalt binder (PG 64-22). Also, it was found that when a PG 70-28 OK asphalt binder was used, use of RAP and/or RAS in a mix resulted in a decrease in fatigue life. Using 6% RAS resulted in the maximum decrease in fatigue life, compared to that of virgin mix with the same type of asphalt binder (PG 70-28 OK). Use of a polymer-modified asphalt binder (PG 70-28 OK) was found to be an effective way to increase the fatigue life of virgin mixes. More specifically, if RAP and/or RAS was used fatigue life was a concern. Furthermore, it was concluded that high coefficient of variation values of the cycles to failure found for four-point beam fatigue test show that the repeatability of this method was not very good. The dynamic modulus and creep compliance test results revealed that addition of RAP and/or RAS to asphalt mixes increased their stiffness, for cases in which PG 64-22 OK or PG 70-28 OK asphalt binders were used. This may result in a better rutting performance, but may lead to a mix with a higher low-temperature cracking potential versus the virgin mixes. Finally, it was found that indirect tensile strength (IDT) of the asphalt mixes increased with use of RAP and/or RAS compared to those of virgin mixes. Use of 6% RAS resulted in the maximum increase in IDT values. Also, a comprehensive survey was conducted among the state departments of transportation for gathering data on the current practices including the methods and specifications associated with the use of RAS and RAP in pavements. The results from this study can be used to develop/update guidelines/special provisions for design of HMA containing RAP and RAS in Oklahoma.Final report, October 2012-January 2015N

Field performance monitoring and modeling of instrumented pavement on I-35 in McClain county - phase I

Flexible pavements comprise about 93 percent of paved roads in the United States. Although flexible pavements are widely used for reasons such as cost, constructability and consistent performance, they are often subject to severe cracking and rutting. This combined laboratory and field study is conducted to better understand the mechanisms that cause pavement failure under actual traffic loading and environmental conditions. A 1,000-ft. long experimental pavement section was constructed on I-35 in McClain County and instrumented in collaboration with the National Center for Asphalt Technology (NCAT) and the Oklahoma Department of Transportation (ODOT) for field data collection. The test section was designed to fail in a relatively short amount of time under heavy interstate traffic. The field data collection focused on pavement response data (longitudinal and transverse strains at the bottom of the asphalt layer, Falling Weight Deflectometer testing), environmental data (temperature within the pavement), performance data (rut and cracks on the surface of the pavement) and actual traffic data (number of trucks, axles, and axle load). From the field data, fatigue and rut prediction models were developed. A separate statistical rut prediction model was also developed from the laboratory rut tests using the Asphalt Pavement Analyzer (APA). Additionally, from the laboratory four-point fatigue tests data, fatigue cracking susceptibility towards temperature was analyzed.Final Report October 2006 - December 2012N

HLA-DQA1*05 carriage associated with development of anti-drug antibodies to infliximab and adalimumab in patients with Crohn's Disease

Anti-tumor necrosis factor (anti-TNF) therapies are the most widely used biologic drugs for treating immune-mediated diseases, but repeated administration can induce the formation of anti-drug antibodies. The ability to identify patients at increased risk for development of anti-drug antibodies would facilitate selection of therapy and use of preventative strategies.This article is freely available via Open Access. Click on Publisher URL to access the full-text

The Outsourcing of Legal Service to India: Trends, Challenges and Potential

The outsourcing of legal services to India is becoming increasingly popular among U.S. and U.K. law firms and corporations. This thesis seeks to discuss three main topics surrounding legal process outsourcing (LPO): its emerging trends, the legal challenges it raises and the hitherto unrecognized potential it holds. Firstly, this thesis clarifies concepts of LPO and its operating models practiced by U.S. and U.K. law firms and corporations. Whenever there is outsourcing in the manufacturing or service sectors, concerns over job losses in the domestic territory are raised by politicians and policy-makers. Accordingly, this research critically discusses the impact of outsourcing on unemployment with a particular focus on legal sector jobs. Secondly, the outsourcing of legal services creates significant challenges for ethics rules and data protection laws. The act of sending legal work overseas by U.S. lawyers may violate American legal ethics rules including those related to conflicts of interest, supervision, fee- sharing, client confidentiality, and attorney-client privilege. Self-regulation is the hallmark of the U.S. legal profession. This thesis therefore reflects, in the first instance, upon the issue of the independence of lawyers who have established a ‘sheltered’ industry for themselves by creating rules that prevent non-lawyers from practicing law. Thereafter, acknowledging the presence of the U.S. legal ethics rules, this thesis provides an explanation as to how a U.S. lawyer could outsource legal works to India without compromising core legal ethics rules. Thirdly, this research explores the hidden potential of LPO to improve access to justice. The outsourcing of legal services to India suffers from a negative image among certain sections of the American legal profession, but has only been discussed so far in the context of law firms and corporations. This thesis develops an altogether new proposal where Indian LPO professionals could help alleviate the access to justice problem among indigent and low-income populations of the United States

Understanding effects of RAP on rheological performance and chemical composition of SBS modified binder using series of laboratory tests

The present study aims to evaluate rutting, fatigue, and rheological performances of a SBS co-polymer modified binder (PMB40) blended with different percentages (i.e., 0%, 15%, 25% and 40%) of reclaimed asphalt pavement (RAP) binder. The change in viscosity, mixing and compaction temperatures, and temperature susceptibility of PMB40 binder mixed with RAP were measured using Brookfield viscometer. Furthermore, linear viscoelastic range (LVE) and time-temperature sweep tests were conducted to characterize binders. The rutting and fatigue performance of PMB40 binder with varying percentages of RAP was evaluated using multi stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests, respectively. The change in chemical composition of PMB40 binder with addition of RAP was determined by Fourier transform infrared (FTIR) spectroscopy. The results showed that addition of RAP makes PMB40 binder stiff and less temperature susceptible, however, it did not change mixing and compaction temperatures significantly. Furthermore, high temperature performance grade (PG) of PMB40 binder was unaltered with addition of RAP, which is contrary to findings reported in literature. The MSCR test showed significant reduction in recovery and increment in non-recoverable creep compliance of PMB40 binder with addition of RAP, indicating a poor rutting resistance of the binder with inclusion of RAP. The LAS test showed that rate of damage increases and number of cycles to fatigue failure of PMB40 binder decreases with addition of RAP. The FTIR test confirmed increase in sulfoxide and carbonyl content with addition of RAP. A good correlation was found for ICO and ISBS indices obtained from FTIR with rheological properties of PMB40 binder. It is to be noted that the findings presented in this paper are based on one modified binder and one RAP source, thus it is recommended that effects of different RAP sources on performance of SBS modified binder be studied in detail. Further, effects of ageing (short term and long term) should be studied to have insight into characterization of RAP blended binders. It is also recommended that binder’s rheological performance tests be validated by conducting laboratory tests on asphalt mixes. Keywords: Reclaimed asphalt pavement, Polymer modified binder, MSCR, LAS, FTIR, Ruttin