Determining Asphalt Mixture Properties Using Imaging Techniques

This study introduces imaging technology to determine the bulk specific gravity (Gmb) of compacted asphalt mixture specimens. Using an advanced three-dimensional scanner, a fast, accurate technique for determining compacted asphalt mixture specimen Gmb was developed. The feasibility of this technique was evaluated by testing a collection of asphalt mixtures, including dense-graded and stone mastic asphalt mixtures. The results were compared with those obtained using the currently-specified Gmb measurement methods of AASHTO T166 and CoreLok. The proposed scanning technique was also used for both laboratory-prepared and field-cored specimens to determine its reliability and reproducibility. The study results suggest the proposed imaging technique is effective in decreasing Gmb measurement variation as well as in improving the accuracy and reproducibility. Additionally, the results indicate the proposed technique can be applied to any asphalt specimen, regardless of mixture type, aggregate sizes, or fabrication technique

Quality Control and Quality Assurance of Asphalt Mixtures Using Laboratory Rutting and Cracking Tests

The main objectives of this project were to review the available balanced-mix design (BMD) methodologies, understand the I-FIT and Hamburg Wheel Tracking Test (HWTT) test methods using INDOT asphalt mixtures, and to explore the application of these tests to both a BMD approach and as performance-related Quality Control (QC) and Quality Acceptance (QA) methods. Two QA mixture specimen types, plant-mixed laboratory-compacted (PMLC) and plant-mixed field-compacted (PMFC) were used in the determination of cracking and rutting parameters. Distribution functions for the flexibility index (FI) values and rutting parameters were determined for various mixture types. The effects of specimen geometry and air voids contents on the calculated Flexibility Index (FI) and rutting parameters were investigated. The fatigue characteristics of selected asphalt mixtures were determined using the S-VECD test according to different FI levels for different conditions. A typical full-depth pavement section was implemented in FlexPAVE to explore the cracking characteristics of INDOT asphalt mixtures by investigating the relationship between the FI values of QA samples with the FlexPAVE pavement performance predictions. The FI values obtained from PMFC specimens were consistently higher than their corresponding PMLC specimens. This study also found that FI values were affected significantly by variations in specimen thickness and air voids contents, having higher FI values with higher air voids contents and thinner specimens. These observations do not agree with the general material-performance expectations that better cracking resistance is achieved with lower air voids content and thicker layers. Additionally, PG 70-22 mixtures show the lowest mean FI values followed by the PG 76-22 and 64-22 mixtures. The same order was observed from the ΔTc (asphalt binder cracking index) of INDOT’s 2017 and 2018 projects. Finally, it was found that the HWTT showed reasonable sensitivity to the different characteristics (e.g., aggregate sizes, binder types, and air voids contents) of asphalt mixtures. Mixtures containing modified asphalt binders showed better rut resistance and higher Rutting Resistance Index (RRI) than those containing unmodified binders

Demonstration Project for Asphalt Performance Engineered Mixture Design Testing

The asphalt industry is moving towards performance-based methods for asphalt mixture design. The Federal Highway Administration (FHWA) is supportive of state departments of transportations (DOT) adopting index and predictive performance tests, especially those making use of the Asphalt Mixture Performance Tester (AMPT). The FHWA is therefore encouraging state DOTs to gain experience with the requirements of the procedures and analysis tools for Balanced Mixture Design (BMD). The main objective of this study is to evaluate fatigue cracking on three INDOT mainline pavement projects that have asphalt mixtures designed by the Superpave 5 mixture design, and to better understand the fundamental engineering testing capabilities of the AMPT. A total of four Superpave 5 asphalt mixtures were collected and tested from the three projects. The viscoelastic characteristics and fatigue behavior of plant-mixed, laboratory compacted (PMLC), laboratory-mixed, laboratory compacted (LMLC), and plant-mixed, field compacted (PMFC) specimens were assessed according to the AASHTO TP-132 and AASHTO TP-133 test methods. Two AMPT machines (IPC Controls and PaveTest) were used to conduct the dynamic modulus tests, while all fatigue tests were performed using a PaveTest AMPT. The raw data were analyzed using the FlexMAT software. The dynamic modulus and cyclic fatigue test results indicate that AMPT testing can be used to effectively evaluate INDOT asphalt mixtures during the mixture design and production phases. However, to do so, detailed planning and effective training are needed to help ensure the successful completion of AMPT testing

Implementing the Superpave 5 Asphalt Mixture Design Method in Indiana

Recent research developments have indicated that asphalt mixture durability and pavement life can be increased by modifying the Superpave asphalt mixture design method to achieve an in-place density of 95%, approximately 2% higher than the density requirements of conventionally designed Superpave mixtures. Doing so requires increasing the design air voids content to 5% and making changes to the mixture aggregate gradation so that effective binder content is not lowered. After successful laboratory testing of this modified mixture design method, known as Superpave 5, two controlled field trials and one full scale demonstration project, the Indiana Department of Transportation (INDOT) let 12 trial projects across the six INDOT districts based on the design method. The Purdue University research team was tasked with observing the implementation of the Superpave 5 mixture design method, documenting the construction and completing an in-depth analysis of the quality control and quality assurance (QC/QA) data obtained from the projects. QC and QA data for each construction project were examined using various statistical metrics to determine construction performance with respect to INDOT Superpave 5 specifications. The data indicate that, on average, the contractors achieved 5% laboratory air voids, which coincides with the Superpave 5 recommendation of 5%. However, on average, the as-constructed mat density of 93.8% is roughly 1% less than the INDOT Superpave 5 specification. It is recommended that INDOT monitor performance of the Superpave 5 mixtures and implement some type of additional training for contractor personnel, in order to help them increase their understanding of Superpave 5 concepts and how best to implement the design method in their operation

Analysis of fission product revaporization in a BWR Reactor Coolant System during a station blackout accident

This paper presents an analysis of fission product revaporization from the Reactor Coolant System (RCS) following the Reactor Pressure Vessel (RPV) failure. The station blackout accident in a BWR Mark I Power Plant was considered. The TRAPMELT3 models for vaporization, chemisorption, and the decay heating of RCS structures and gases were used and extended beyond the RPV failure in the analysis. The RCS flow models based on the density-difference or pressure-difference between the RCS and containment pedestal region were developed to estimate the RCS outflow which carries the revaporized fission product to the containment. A computer code called REVAP was developed for the analysis. The REVAP code was incorporated with the MARCH, TRAPMELT3 and NAUA codes from the Source Term Code Package (STCP) to estimate the impact of revaporization on environmental release. The results show that the thermal-hydraulic conditions between the RCS and the pedestal region are important factors in determining the magnitude of revaporization and subsequent release of the volatile fission product into the environment. 6 refs., 8 figs

Feedback Control Systems for Non-Linear Simulation of Operational Transients in LMFBRs

Feedback control systems for non-linear simulation of operational transients in LMFBRs are developed. The models include (1) the reactor power control and rod drive mechanism, (2) sodium flow control and pump drive system, (3) steam generator flow control and valve actuator dynamics, and (4) the supervisory control. These models have been incorporated into the SSC code using a flexible approach, in order to accommodate some design dependent variations. The impact of system nonlinearity on the control dynamics is shown to be significant for severe perturbations. Representative result for a 10 cent and 25 cent step insertion of reactivity and a 10% ramp change in load in 40 seconds demonstrate the suitability of this model for study of operational transients without scram in LMFBRs

A simplified model for calculating atmospheric radionuclide transport and early health effects from nuclear reactor accidents

During certain hypothetical severe accidents in a nuclear power plant, radionuclides could be released to the environment as a plume. Prediction of the atmospheric dispersion and transport of these radionuclides is important for assessment of the risk to the public from such accidents. A simplified PC-based model was developed that predicts time-integrated air concentration of each radionuclide at any location from release as a function of time integrated source strength using the Gaussian plume model. The solution procedure involves direct analytic integration of air concentration equations over time and position, using simplified meteorology. The formulation allows for dry and wet deposition, radioactive decay and daughter buildup, reactor building wake effects, the inversion lid effect, plume rise due to buoyancy or momentum, release duration, and grass height. Based on air and ground concentrations of the radionuclides, the early dose to an individual is calculated via cloudshine, groundshine, and inhalation. The model also calculates early health effects based on the doses. This paper presents aspects of the model that would be of interest to the prediction of environmental flows and their public consequences

Statistical competencies for medical research learners: What is fundamental?

IntroductionIt is increasingly essential for medical researchers to be literate in statistics, but the requisite degree of literacy is not the same for every statistical competency in translational research. Statistical competency can range from 'fundamental' (necessary for all) to 'specialized' (necessary for only some). In this study, we determine the degree to which each competency is fundamental or specialized.MethodsWe surveyed members of 4 professional organizations, targeting doctorally trained biostatisticians and epidemiologists who taught statistics to medical research learners in the past 5 years. Respondents rated 24 educational competencies on a 5-point Likert scale anchored by 'fundamental' and 'specialized.'ResultsThere were 112 responses. Nineteen of 24 competencies were fundamental. The competencies considered most fundamental were assessing sources of bias and variation (95%), recognizing one's own limits with regard to statistics (93%), identifying the strengths, and limitations of study designs (93%). The least endorsed items were meta-analysis (34%) and stopping rules (18%).ConclusionWe have identified the statistical competencies needed by all medical researchers. These competencies should be considered when designing statistical curricula for medical researchers and should inform which topics are taught in graduate programs and evidence-based medicine courses where learners need to read and understand the medical research literature

A sensitivity analysis technique for application to deterministic models

An important element of any uncertainty analysis consists of evaluating the sensitivity of the output uncertainty distributions to the input assumptions. These sensitivity analyses require extensive information regarding mathematical correlations between input and output variables which are generally obtained through repeated computer runs of a physical model. However, in predicting uncertainties associated with severe accident sources terms using contemporary methods, techniques must be devised which reduce the need for extensive commutation using large computer codes. The purpose of the current paper is to propose a new method for sensitivity analysis which does not utilize response surface methods, but instead relies directly on the results obtained from the original computer code calculations. 3 refs., 1 fig

Environmentally Tuning Asphalt Pavements Using Phase Change Materials

Environmental conditions are considered an important factor influencing asphalt pavement performance. The addition of modifiers, both to the asphalt binder and the asphalt mixture, has attracted considerable attention in potentially alleviating environmentally induced pavement performance issues. Although many solutions have been developed, and some deployed, many asphalt pavements continue to prematurely fail due to environmental loading. The research reported herein investigates the synthetization and characterization of biobased Phase Change Materials (PCMs) and inclusion of Microencapsulated PCM (μPCM) in asphalt binders and mixtures to help reduce environmental damage to asphalt pavements. In general, PCM substances are formulated to absorb and release thermal energy as the material liquify and solidify, depending on pavement temperature. As a result, PCMs can provide asphalt pavements with thermal energy storage capacities to reduce the impacts of drastic ambient temperature scenarios and minimize the appearance of critical temperatures within the pavement structure. By modifying asphalt pavement materials with PCMs, it may be possible to tune the pavement to the environment