Rafiqul A. Tarefder

Nanoscale Evaluation of Moisture Damage in Polymer Modified Asphalts

The moisture damage in polymer modified asphalts has been studied for decades, yet the effects of chemical functional groups on moisture sensitivity are not known. In this study, a nanoscale experiment is conducted to measure these effects in terms of adhesive/cohesive forces using an atomic force microscopy (AFM). A base asphalt binder and two polymers such as styrene-butadiene (SB) and styrene-butadiene-styrene (SBS) modified asphalts are used to prepare an AFM sample on glass substrates. The AFM samples are conditioned under dry and wet conditions. In the AFM, these samples are probed by silicon nitrite ( Si3 N4 ) , carboxyl ( —COOH ) , methyl ( — CH3 ) , and hydroxyl ( —OH ) functionalized AFM tips and nanoscale pull-off or adhesion/cohesion forces between asphalt and tip molecules are measured. Based on the ratio of wet to dry adhesion/cohesion forces, it is shown that the polymer modification makes binders less susceptible to moisture damage. Among the four tips, the —COOH tip shows almost no differ...

Determining Hardness and Elastic Modulus of Asphalt by Nanoindentation

Nanoindentation is a relatively new technique which has been used to measure nanomechanical properties of surface layers of bulk materials and of thin films. In this study, micromechanical properties such as hardness and Young’s modulus of asphalt binders and asphalt concrete are determined by nanoindentation experiments. Indentation tests are conducted on a base binder and two polymer-modified performance grade (PG) binders such as PG-70-22 and PG76-28. In addition, two Superpave asphalt mixes such as SP-B and SP-III are designed using these PG binders, and the corresponding mixes are compacted to prepare asphalt concrete. Aggregate, matrix (Materials Passing No. 4 sieve) and mastic (Materials Passing No. 200 sieve) phases of each asphalt concrete sample are indented using both Berkovich and Spherical indenters. In nanoindentation, an indenter penetrates into asphalt material and the load (milli-Newton) and the depth (nanometers) of indentation are recorded continuously. Indentation load versus displacem...

A Multinomial Logit Model-Bayesian Network Hybrid Approach for Driver Injury Severity Analyses in Rear-End Crashes

Rear-end crash is one of the most common types of traffic crashes in the U.S. A good understanding of its characteristics and contributing factors is of practical importance. Previously, both multinomial Logit models and Bayesian network methods have been used in crash modeling and analysis, respectively, although each of them has its own application restrictions and limitations. In this study, a hybrid approach is developed to combine multinomial logit models and Bayesian network methods for comprehensively analyzing driver injury severities in rear-end crashes based on state-wide crash data collected in New Mexico from 2010 to 2011. A multinomial logit model is developed to investigate and identify significant contributing factors for rear-end crash driver injury severities classified into three categories: no injury, injury, and fatality. Then, the identified significant factors are utilized to establish a Bayesian network to explicitly formulate statistical associations between injury severity outcomes and explanatory attributes, including driver behavior, demographic features, vehicle factors, geometric and environmental characteristics, etc. The test results demonstrate that the proposed hybrid approach performs reasonably well. The Bayesian network reference analyses indicate that the factors including truck-involvement, inferior lighting conditions, windy weather conditions, the number of vehicles involved, etc. could significantly increase driver injury severities in rear-end crashes. The developed methodology and estimation results provide insights for developing effective countermeasures to reduce rear-end crash injury severities and improve traffic system safety performance.

Investigating driver injury severity patterns in rollover crashes using support vector machine models

Rollover crash is one of the major types of traffic crashes that induce fatal injuries. It is important to investigate the factors that affect rollover crashes and their influence on driver injury severity outcomes. This study employs support vector machine (SVM) models to investigate driver injury severity patterns in rollover crashes based on two-year crash data gathered in New Mexico. The impacts of various explanatory variables are examined in terms of crash and environmental information, vehicle features, and driver demographics and behavior characteristics. A classification and regression tree (CART) model is utilized to identify significant variables and SVM models with polynomial and Gaussian radius basis function (RBF) kernels are used for model performance evaluation. It is shown that the SVM models produce reasonable prediction performance and the polynomial kernel outperforms the Gaussian RBF kernel. Variable impact analysis reveals that factors including comfortable driving environment conditions, driver alcohol or drug involvement, seatbelt use, number of travel lanes, driver demographic features, maximum vehicle damages in crashes, crash time, and crash location are significantly associated with driver incapacitating injuries and fatalities. These findings provide insights for better understanding rollover crash causes and the impacts of various explanatory factors on driver injury severity patterns.

Effects of Dwell Time and Loading Rate on the Nanoindentation Behavior of Asphaltic Materials

In a nanoindentation test, a test sample is indented or loaded by an intender tip and then unloaded, and the load-displacement data are recorded. Load-displacement data are then analyzed using a common method to determine elastic modulus and hardness of materials. The slope of the unloading curve is positive and typically follows the slope of the loading curve for hard samples such as aluminum and silicon. The analysis method is not applicable if the unloading curve follows a negative slope, which is the case for soft viscous materials, such as asphalt binders and polymers. However, past studies have not attempted to examine the effects of dwell time and loading rate on viscous materials, such as asphalt binders, which are performed in this study. It is shown in this paper that an increase in dwell time shows a decrease in the bowing out or nose effect of the unloading portion of the load-displacement curve. At very low loading rates, asphalt binder shows a high viscous effect, which creates a large negative slope of the unloading curve.

Examining driver injury severity outcomes in rural non-interstate roadway crashes using a hierarchical ordered logit model.

Rural non-interstate crashes induce a significant amount of severe injuries and fatalities. Examination of such injury patterns and the associated contributing factors is of practical importance. Taking into account the ordinal nature of injury severity levels and the hierarchical feature of crash data, this study employs a hierarchical ordered logit model to examine the significant factors in predicting driver injury severities in rural non-interstate crashes based on two-year New Mexico crash records. Bayesian inference is utilized in model estimation procedure and 95% Bayesian Credible Interval (BCI) is applied to testing variable significance. An ordinary ordered logit model omitting the between-crash variance effect is evaluated as well for model performance comparison. Results indicate that the model employed in this study outperforms ordinary ordered logit model in model fit and parameter estimation. Variables regarding crash features, environment conditions, and driver and vehicle characteristics are found to have significant influence on the predictions of driver injury severities in rural non-interstate crashes. Factors such as road segments far from intersection, wet road surface condition, collision with animals, heavy vehicle drivers, male drivers and driver seatbelt used tend to induce less severe driver injury outcomes than the factors such as multiple-vehicle crashes, severe vehicle damage in a crash, motorcyclists, females, senior drivers, driver with alcohol or drug impairment, and other major collision types. Research limitations regarding crash data and model assumptions are also discussed. Overall, this research provides reasonable results and insight in developing effective road safety measures for crash injury severity reduction and prevention.

Evaluating the Relationship between Permeability and Moisture Damage of Asphalt Concrete Pavements

AbstractLimiting the presence of water inside an asphalt concrete (AC) pavement can slow down the process involved in water diffusion, hydration, adhesion loss, and other mechanisms of moisture damage. In the past, numerous studies have been conducted on the topic of moisture damage and permeability, but very few studies have related permeability with moisture damage in AC. This study evaluates whether such relation exists. In essence, a field survey is conducted to identify a set of pavements (bad) that suffer from moisture damage and a set of pavements (good) that do not exhibit moisture damage. Field permeability tests and coring are conducted on the pavements. Laboratory permeability tests are performed on the field cores. An indirect tensile strength ratio (TSR) of wet- to dry-conditioned core samples is determined in the laboratory and used as a moisture damage potential parameter. Wet conditioning is performed by using a recently developed moisture-induced sensitivity test (MIST) device and a well-...

Exploratory multinomial logit model–based driver injury severity analyses for teenage and adult drivers in intersection-related crashes

ABSTRACT Objective: Teenage drivers are more likely to be involved in severely incapacitating and fatal crashes compared to adult drivers. Moreover, because two thirds of urban vehicle miles traveled are on signal-controlled roadways, significant research efforts are needed to investigate intersection-related teenage driver injury severities and their contributing factors in terms of driver behavior, vehicle–infrastructure interactions, environmental characteristics, roadway geometric features, and traffic compositions. Therefore, this study aims to explore the characteristic differences between teenage and adult drivers in intersection-related crashes, identify the significant contributing attributes, and analyze their impacts on driver injury severities. Methods: Using crash data collected in New Mexico from 2010 to 2011, 2 multinomial logit regression models were developed to analyze injury severities for teenage and adult drivers, respectively. Elasticity analyses and transferability tests were conducted to better understand the quantitative impacts of these factors and the teenage driver injury severity models generality. Results: The results showed that although many of the same contributing factors were found to be significant in the both teenage and adult driver models, certain different attributes must be distinguished to specifically develop effective safety solutions for the 2 driver groups. Conclusions: The research findings are helpful to better understand teenage crash uniqueness and develop cost-effective solutions to reduce intersection-related teenage injury severities and facilitate driver injury mitigation research.

Rheological Examination of Aging in Polymer-Modified Asphalt

AbstractPolymers are commonly used to modify asphalt binder in order to satisfy the performance-grade binder’s rheological properties, such as shear, storage, loss, and bending stiffness. However, it is not known what types and percentages of polymers affect these properties under conditions of aging. To this end, base asphalt binders were modified with styrene-butadiene and styrene-butadiene-styrene polymers at 3, 4, and 5% and then aged in the laboratory using a rolling thin film oven for short-term aging, a pressure aging vessel for long-term aging, and a draft oven for intermediate aging. The stiffness properties of the modified binders were determined using dynamic shear rheometer (DSR), multiple-stress creep recovery (MSCR), Brookfield rotational viscometer (RV), and bending beam rheometer (BBR) tests. Comparison of aging indexes for storage and loss modulus indicated that aging increases the elastic or storage component more than the viscous or loss component of the complex shear modulus. It was sh...

Evaluation of Subgrade Strength and Pavement Designs for Reliability

Reliability is an important factor in flexible pavement design to consider the variability associated with the design inputs. In this study, subgrade strength variability and flexible pavement designs are evaluated for reliability. Six existing pavement sections design data are studied using probabilistic, AASHTO, and mechanistic-empirical pavement design guide (MEPDG). Parameters such as mean, maximum likelihood, median, coefficient of variation, and density distribution function of subgrade strength (R value) are determined. Design outputs are compared in terms of reliability and thickness using these design procedures. It is shown that the AASHTO provides higher reliability values compared to the probabilistic procedure. All the existing pavements fail in the MEPDG distress reliability such as rutting and top-down cracking reliabilities. Currently, New Mexico Department of Transportation uses a single design R value to deal with variability associated with subgrade strength in flexible pavement design. It is shown in this study that single design R value for a roadway section does not yield an effective design regarding target reliability, while the subsectioning procedure based on coefficient of variance of R value is a better way to deal with the subgrade variability. An assessment of minimum R value for making the decision of subexcavation is also presented. It is shown that increasing the minimum R value for subexcavation is not always the proper solution to meet design reliability; rather it yields an inefficient design for requiring higher frequencies of subexcavation. Finally, the reliability of the flexible pavement design is evaluated by varying hot mix asphalt properties. Alternative designs are recommended for the existing pavement thicknesses by modifying material and subgrade properties to mitigate different distresses.