Ali Behnood

High-Temperature Properties of Asphalt Binders: Comparison of Multiple Stress Creep Recovery and Performance Grading Systems

The Superpave® high-temperature test protocol has been shown to be inadequate for characterizing the high-temperature behavior of asphalt binders, particularly those that are polymer modified. Recently, a specification based on the multiple stress creep recovery (MSCR) test was proposed to address the shortcomings of the Superpave high-temperature binder specifications. This study aimed to investigate the merits of implementing the current MSCR test protocol as a replacement for the performance-graded high-temperature test. A statistical analysis was conducted on a data set from the Indiana Department of Transportation to see how MSCR and performance grading procedures differ in grading various binders. In addition, an experimental study was conducted with 16 modified and unmodified binders. The results indicated that the MSCR test was a suitable replacement for the performance grade test because it provided a better tool to rank modified asphalt binders as well as unmodified ones. That is, creep compliance from the MSCR test more fundamentally represented binder behavior at high temperatures compared with the performance grade rutting parameter. In addition, the simplified approach—known as grade-bumping—used in the current Superpave mix design system to account for high traffic levels and low speed limits can be eliminated when the MSCR test is used.

Determining the Moisture Content of Pre-Wetted Lightweight Aggregate: Assessing the Variability of the Paper Towel and Centrifuge Methods

Internally cured (IC) concrete is frequently produced in North America using pre-wetted lightweight aggregate (LWA). One important aspect associated with the production of quality IC concrete is the accurate determination of the moisture content, including absorbed moisture and surface moisture of the LWA. Knowledge of the moisture content enables aggregate moisture corrections to be made for the concrete mixture, thereby enabling an accurate water-to-cement ratio to be maintained. Two methods for determining the moisture content of LWA include the specified ASTM C1761-13b “paper towel method” and a method that uses a centrifuge (Miller, Barrett, Zander, & Weiss, 2014). There are limited data available on the variability associated with either of these approaches when the test is performed by multiple users. In this study, the absorption of four commercially available LWAs was tested by a single operator in a single laboratory using the centrifuge method. In addition, the absorption of three commercially available LWAs was tested by 25 users performing both experimental methods. This article provides an estimation of precision associated with both a single operator and multiple operators performing both the paper towel method and the centrifuge method to find the absorption of pre-wetted lightweight fine aggregate.

Review of Thaumasite Sulfate Attack on Cement Mortar and Concrete

AbstractDurability is one of the most important considerations regarding the design of new concrete structures in aggressive environments. Thaumasite sulfate attack (TSA) is one durability consideration. This paper reviews the features of TSA, factors affecting TSA, thaumasite formation mechanisms, and prevention measures. Finally, some needs for future studies are also suggested. TSA can completely destroy the cementitious binding ability of concrete by transforming it into a mush. Many factors affect thaumasite formation and TSA. The four primary factors affecting TSA on portland cement-based materials are low temperatures (below 15°C) and the presence of sulfates, carbonates, and moisture. Apparently, the dissolution–precipitation mechanism can be used to explain most phenomena during TSA. A procedure for field studies is also proposed. Both material compositions and surrounding environments should be considered for the prevention of TSA in concrete structures.

The effects of drug and alcohol consumption on driver injury severities in single-vehicle crashes

ABSTRACT Objective: It is well known that alcohol and drugs influence driving behavior by affecting the central nervous system, awareness, vision, and perception/reaction times, but the resulting effect on driver injuries in car crashes is not fully understood. The purpose of this study was to identify factors affecting the injury severities of unimpaired, alcohol-impaired, and drug-impaired drivers. Method: The current article applies a random parameters logit model to study the differences in injury severities among unimpaired, alcohol-impaired, and drug-impaired drivers. Using data from single-vehicle crashes in Cook County, Illinois, over a 9-year period from January 1, 2004, to December 31, 2012, separate models for unimpaired, alcohol-impaired, and drug-impaired drivers were estimated. A wide range of variables potentially affecting driver injury severity was considered, including roadway and environmental conditions, driver attributes, time and location of the crash, and crash-specific factors. Results: The estimation results show significant differences in the determinants of driver injury severities across groups of unimpaired, alcohol-impaired, and drug-impaired drivers. The findings also show that unimpaired drivers are understandably more responsive to variations in lighting, adverse weather, and road conditions, but these drivers also tend to have much more heterogeneity in their behavioral responses to these conditions, relative to impaired drivers. In addition, age and gender were found to be important determinants of injury severity, but the effects varied significantly across all drivers, particularly among alcohol-impaired drivers. Conclusions: The model estimation results show that statistically significant differences exist in driver injury severities among the unimpaired, alcohol-impaired, and drug-impaired driver groups considered. Specifically, we find that unimpaired drivers tend to have more heterogeneity in their injury outcomes in the presence potentially adverse weather and road surface conditions. This makes sense because one would expect unimpaired drivers to apply their full knowledge/judgment range to deal with these conditions, and the variability of this range across the driver population (with different driving experiences, etc.) should be great. In contrast, we find, for the most part, that alcohol-impaired and drug-impaired drivers have far less heterogeneity in the factors that affect injury severity, suggesting an equalizing effect resulting from the decision-impairing substance.

Pavement Patching Practices

Pavement patching is one of the most extensive and expensive pavement maintenance activities undertaken by highway agencies at all levels. Because of the costs and resources involved in this massive undertaking, there are significant benefits to be attained by managing patching programs in the most cost-effective manner. This synthesis summarizes current practices for patching both concrete and asphalt pavements. The intent is to document the state of the practice for patching relatively small-scale surface defects in concrete and asphalt pavements. Both reactive and planned patching are addressed. The synthesis covers management or administrative issues, materials, methods, equipment, specifications and tests, traffic control, and other aspects of patching operations. The information in this synthesis was collected through extensive literature reviews of U.S. and international sources and electronic surveys and followup phone and e-mail interviews.

Automatic regression methods for formulation of elastic modulus of recycled aggregate concrete

Abstract The use of recycled concrete aggregate to produce new concrete can assist the sustainability in construction industry. However, the mechanical properties of this type of aggregate should be precisely investigated before its using in different applications. The elastic modulus of concrete is one of the most important design parameters in many construction applications. Because of various mix designs, the existing formulas for the elastic modulus of concrete cannot be used for recycled aggregate concrete (RAC). In recent years, there have been a few attempts for predicting the elastic modulus of RAC, especially, with various types of artificial intelligence (AI) methods: In this paper, three automatic regression methods, namely, genetic programming (GP), artificial bee colony programming (ABCP) and biogeography-based programming (BBP) were used for estimating the elastic modulus of RAC. Performances of the different automatic regression models were compared with each other. Moreover, the sensitivity analysis was performed to assess the trend of the elastic modulus as a function of effective input parameters used for developing the different automatic regression models. Overall, the results show that GP, ABCP, and BBP can be used as reliable algorithms for prediction of the elastic modulus of RAC. In addition, the water absorption of the mixed coarse aggregate and the ratio of the fine aggregate to the total aggregate were found as two of the most effective parameters affecting the elastic modulus of RAC.

Analysis of the Multiple Stress Creep Recovery Asphalt Binder Test and Specifications for Use in Indiana

The Superpave specifications and equipment, introduced in 1993, represented a major advancement with respect to offering a better understanding of the behavior and characteristics of asphalt binders based on their rheological properties. However, the Superpave high-temperature test protocol has been shown to be inadequate for characterizing the high-temperature behavior (rutting resistance) of asphalt binders, particularly polymer modified ones. Recently, a specification based on the Multiple Stress Creep Recovery (MSCR) test has been proposed to address the shortcomings of the Superpave high-temperature binder specifications. This study aims to investigate the merits of implementing the MSCR test and specification as a replacement for the conventional high-temperature testing in the Performance Graded (PG) system. A statistical analysis was conducted on a dataset from Indiana Department of Transportation (INDOT) to see how MSCR and PG procedures differ in grading different binders used in the state. In addition, an experimental study was conducted using seventeen different modified and unmodified binders. In addition to binder tests, seven of the binders were selected to conduct asphalt mixture tests such as dynamic modulus and flow number. The results confirm that the MSCR test is a suitable replacement for the current PG high temperature test since it provides a better tool to rank modified asphalt binders as well as unmodified ones. That is, creep compliance from the MSCR test more fundamentally represents binder behavior at high temperatures compared to the PG rutting parameter. In addition, the very simplified approach, known as grade-bumping, used in the current PG system to account for high traffic levels and low speed limits can be eliminated when using the MSCR test. The MSCR test also provides a better coefficient of correlation (at both stress levels) with flow number test results than the PG rutting parameter, again indicating that it more accurately reflects binder performance at high temperatures.