Apeagyei A.K.,Virginia Transportation Research Council
Construction and Building Materials | Year: 2011
A laboratory study was carried to investigate whether certain antioxidants could be used to reduce age-hardening in asphalt binders. Several additives including: Vitamin E, Irganox 1010, Irgafos P-EPQ, carbon black, hydrated lime, and DLTDP/furfural, were evaluated. The modified asphalt binders were subjected to two accelerated oxidative aging regimes in the laboratory. Short-term oxidative aging of the binders was simulated using a rolling thin film oven while long-term aging was performed using a pressure aging vessel. The effects of aging on the binders were evaluated based on changes in rheological properties of asphalt binders undergoing oxidative aging. Binders modified with a combination of furfural and DLTDP was found to posses the lowest aging index. The antioxidant-treated binders exhibited improved performance at both high and low pavement temperatures. © 2010 Elsevier Ltd. All rights reserved.
Diefenderfer S.D.,Virginia Transportation Research Council
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2011
The Virginia Department of Transportation (VDOT) is expecting to transition to using the methodology described in the Guide for the MechanisticEmpirical Design of New & Rehabilitated Pavement Structures (MEPDG) in the near future, and decisions must be made regarding the hierarchical level of desired asphalt material inputs and the extent to which asphalt mixture characterization must be performed. Thus a study was undertaken to investigate the effects of these variables using input values measured from 11 typical plant mixtures (i.e., three surface, four intermediate, and four base mixtures). The predicted fatigue and rutting distresses were used to evaluate the response of the MEPDG to differences in the mixture properties and to assess the future needs for implementation. Two example pavement sections were modeled: a primary and an interstate roadway section. Pavement distress data were compiled for an interstate and primary route corresponding to the modeled sections and were compared to the MEPDG-predicted distresses. Predicted distress quantities for fatigue cracking and rutting were compared to the calculated distress model predictive errors to determine if the material property input levels were statistically different. There were differences between all rutting and fatigue predictions using level 1, 2, and 3 asphalt material inputs, but they were not statistically significant. Various combinations of level 3 inputs showed expected trends in rutting predictions when increased binder grades were used, but the differences were not statistically significant when the calibration model error was considered. Fatigue distress predictions were approximately comparable to the pavement distress data, but the model predictive errors were greater than the distress predictions. Although this study was limited, it indicated several steps VDOT should take prior to implementing the MEPDG. Additional work to identify the source of predictive insensitivity to changes in both asphalt mixture properties and the level of input values is necessary. The comparisons of predicted fatigue and rutting distresses to pavement distress data for the primary and interstate pavement indicate the need to consider local calibration and verification of the predictive models.
Kweon Y.-J.,Virginia Transportation Research Council |
Lee J.,University of Virginia
Accident Analysis and Prevention | Year: 2010
Beneficial effects of bicycle helmet use have been reported mostly based on medical or survey data collected from hospitals. This study was to examine the validity of the United States General Estimates System (GES) database familiar to many transportation professionals for a beneficial effect of helmet use in reducing the severity of injury to bicyclists and found potential risk of erroneous conclusions that can be drawn by a narrowly focused study when the GES database is used. Although the focus of the study was on bicycle helmet use, its findings regarding potential risk might be true for any type of traffic safety study using the GES data. A partial proportional odds model reflecting intrinsic ordering of injury severity was mainly used. About 16,000 bicycle-involved traffic crash records occurring in 2003 through 2008 in the United States were extracted from the GES database. Using the 2003-2008 GES data, a beneficial effect of helmet use was found in 2007, yet a detrimental effect in 2004 and no effect in 2003, 2005, 2006, and 2008, which are contrary to the past findings from medical or hospital survey data. It was speculated that these mixed results might be attributable to a possible lack of representation of the GES data for bicycle-involved traffic crashes, which may be supported by the findings, such as the average helmet use rates at the time of the crashes varying from 12% in 2004 to 38% in 2008. This suggests that the GES data may not be a reliable source for studying narrowly focused issues such as the effect of helmet use. A considerable fluctuation over years in basic statistical values (e.g., average) of variables of interest (e.g., helmet use) may be an indication of a possible lack of representation of the GES data. In such a case, caution should be exercised in interpreting and generalizing analysis results.
Apeagyei A.K.,Virginia Transportation Research Council
Proceedings of the Institution of Civil Engineers: Transport | Year: 2011
The correlation between dynamic modulus of asphalt concrete and rutting was investigated in the laboratory. Five asphalt concrete mixtures of different stiffnesses produced according to Virginia specifications were tested using dynamic modulus and flow number tests. The dynamic modulus (E*) tests were conducted at a single temperature. (38°C) and six loading frequencies (25, 10, 5, 1, 0 5, 0.1 Hz) and flow number (FN) tests, designed to evaluate rutting, were conducted at a temperature of 54°C. An asphalt mixture performance tester was used to perform both the dynamic modulus and flow number tests. The results were used to develop correlations between E* and FN at each of the testing frequencies used. Very good correlation (R2= 94) was found between E* at 0.1 Hz loading frequency and FN at 54°C. Additionally, the correlation between FN and the slope of the graph of E* plotted against frequency. was also found to be equally good (R2 = 95). The results suggest rutting susceptibility could be evaluated using E* testing performed at 38°C. The results of this study may be useful to agencies with field or district laboratories looking for an epigrammatic test to valuate rutting susceptibility during mix designs and field quality control and quality assurance (QC/QA).
Ozyildirim C.,Virginia Transportation Research Council
Transportation Research Record | Year: 2010
A study described the development of the Virginia Department of Transportation's (VDOT) end-result specifications (ERSs) for hydraulic cement concrete. The work had two phases. In Phase 1, a special provision was developed and applied to two pilot projects. In Phase 2, the special provision was applied to more pilot projects from districts across Virginia. Pay adjustments were not applied for the pilot projects; VDOT's current specifications were applied for acceptance and rejection. The ERSs have three parts. The first part introduces process control measures. The contractor is responsible for the concrete design and is required to provide a quality control plan. The plan addresses all elements that affect quality, including mixture designs, aggregate sources, ingredients, tests and testing frequency, fresh and hardened concrete properties, and control charts. The second part covers the mixture design approval by VDOT. The third part covers project acceptance, which includes pay adjustments depending on test results. The pilot projects are continuing. However, some of the features of the ERS are already included in the supplemental specifications, such as using combined cementitious material and using curing boxes with continuously recording thermometers. Or they are permitted if requested by the contractor and approved by the project engineer, such as using combined aggregates, mixing gravel and crushed stone, combining retarding admixtures and water-reducing admixtures, and exceeding the 300 revolution limit or the time limit of 1.5 h from the addition of water.