Traditionally, various forms of shift factors such as Arrhenius, Williams–Landel–Ferry (WLF), and polynomials have been used with asphalt materials. Shift factors have also been estimated with binder ...viscosity parameters. Successful extrapolation of viscoelastic functions requires a robust form of shift factor–temperature relationship. This form is important for performing calculations at the extremes of temperature found in practice. A preliminary analysis of complex modulus E* data of mixtures obtained from the Mechanistic–Empirical Pavement Design Guide (MEPDG) database demonstrated that the Kaelble form of shift factor could describe the functional form of the shift factor more accurately than the Arrhenius, WLF, or polynomial-fitting functions. However, the Kaelble shift function as originally described uses the same temperature as a reference temperature and as an inflection temperature. This factor creates a problem when attempts are made to implement the function in a design method or when materials are compared at a given temperature. Since 2008, additional work has investigated the use of this shift function to describe the properties of asphalt materials, particularly mixes and materials that require a wide range of property description (both above and below the glass transition or some other defining point). A modified form of the Kaelble function has been implemented in analysis software and thus makes multiple calculations more rapid. Additional analysis working with MEPDG E* database materials has shown that shifting works best with the Kaelble modification of the WLF equation. The same method has been applied to other asphalt materials.
The development of the well-known Christensen-Anderson (CA) rheological model grew out of attempts to model the relaxation spectra of asphalt binders using a skewed logistic distribution function. ...For this reason, there exist very strong relationships between the CA model parameters and the characteristics of relaxation spectra for asphalt binders. This paper presents a recently developed equation that allows direct and accurate calculation of the relaxation spectra from CA model parameters, demonstrating the nature of this relationship. Of the CA model/spectrum parameters, the most important in terms of describing overall behaviour and potential performance is the R-value, which describes the shape and skewness of the spectrum. This parameter and other similar rheological parameters have been linked to various important aspects of asphalt binder behaviour, including fatigue resistance, chemical composition and degree of oxidative ageing. This makes the parameter R a potentially useful parameter for inclusion in asphalt binder specifications, although care must be taken in how it is determined to ensure that it is accurate, repeatable and reflects the performance characteristics of interest.
Low-temperature cracking is a critical distress form and is heavily influenced by the relaxation and strength capabilities of the material. These properties are related to the stiffness through ...principles of viscoelasticity. Recently, there is elevated pressure on decisions made by pavement and materials engineers to produce the longest lasting, most resourceful pavement systems possible to optimise monetary and non-renewable resource usage. The primary objectives of this study are to: (1) assess the value of a parameter which can describe low-temperature cracking resistance by using dynamic modulus (|E*|) and phase angle (δ) of the mixture and laboratory-measured performance; (2) present shape parameters of a mixture master curve that are directly related to the relaxation spectra, which is expected to play a pivotal role in low-temperature distress resistance with ageing; (3) define failure lines in Black Space which correspond with laboratory-measured performance and operate under a well-understood basis reinforced by the literature; and (4) provide agencies with a tool to aid in the movement towards a performance-based mixture design, acceptance, or rehabilitation decision-making system. An analysis of the mixture master curve is done to establish parameters which describe the relaxation spectra and ageing potential of materials. A mixture-based Black Space parameter is presented based on results from the |E*| master curve construction and the thermal stress restrained specimen test. This approach holds promise, but must be calibrated with a robust database before serious implementation considerations are made. Future work will look to determine a common stiffness condition to better define the failure threshold and to identify possible alternatives to the modified Glover-Rowe function used in this study. Further evaluation is also needed to optimise the temperature-frequency combination of the Black Space parameter itself and ensure a condition is specified that can be captured by test equipment an owner agency or contractor may possess as part of a performance-based specification framework.
The need for a viscoelastic characterisation of hot mix asphalt is increasing as advanced testing and modelling is incorporated through mechanistic-empirical pavement design and performance-based ...specifications. Viscoelastic characterisation includes measurement of the mixture stiffness and relative proportion of elastic and viscous response. The most common method is to measure the complex modulus, where dynamic modulus represents the stiffness and the phase angle represents the relative extent of elastic and viscous response. Determination of phase angle from temperature and frequency sweep tests has been challenging, unreliable and prone to error due to a high degree of variability and sensitivity to signal noise. There are also large amounts of historical dynamic modulus data that are either missing phase angle measurements or have poorly measured phase angle data that inhibit their use in further evaluation. This paper evaluates the robustness of phase angle estimation from stiffness data for asphalt mixtures. The objectives of the study are to: (1) evaluate the procedure of estimating phase angle from the slope of log-log stiffness master curve fitted with a generalised logistic sigmoidal curve and compare it with lab measurements and the Hirsch model; (2) assess the effect of measured and predicted phase angles on a mixture Black Space diagram; (3) evaluate the effect of using predicted phase angles on SVECD fatigue analysis particularly regarding damage characteristics curves and fatigue coefficients and (4) evaluate the impact on layered viscoelastic pavement analysis for critical distresses (LVECD) pavement fatigue performance evaluation due to the use of predicted phase angles. Three sets of independent mixtures were evaluated in this study comprising a wide range of mixture conditions. The results indicate good agreement between measured and predicted phase angle values in terms of shape and peak master curve values. In terms of magnitude, the values from both matched very well for certain sets of mixtures and subsequently manifested in similar performance predictions. However, for other sets of mixtures, a considerable difference was observed between measured and predicted phase angle values as well as SVECD and LVECD results. The differences may be attributed to the use of different types of linear variable displacement transducers (loose core versus spring loaded). Another possible explanation for the difference could be the contribution of plastic strain, which may create a difference in phase angles of 1-2°.
Recently, researchers have made effective use of Black Space diagrams to model stiffness and relaxation changes relating to non-load-associated cracking. A Black Space-based approach to detecting ...cracking susceptibility is the Glover-Rowe (G-R) parameter, which requires complex modulus and phase angle at a particular temperature-frequency combination. This parameter is being evaluated as a replacement for low-temperature Superpave binder criteria. Primary objectives are to validate the G-R approach for binders with laboratory and field performance measurements; develop an indicator parameter for low-temperature cracking of mixtures using a combination of material properties; and develop alternate approaches to study mixture performance in Black Space. The G-R intermediate-temperature parameter shows mixed results with Black Space location for sections with thermal cracking. The G-R low-temperature parameter is used to determine a critical cracking temperature that agrees with Superpave binder specification. A preliminary evaluation of a mixture-based Black Space parameter is included.
The evaluation of emergency department (ED) quality of care is hampered by the absence of consensus on appropriate measures. We sought to develop a consensus on a prioritized and parsimonious set of ...evidence-based quality of care indicators for EDs.
The process was led by a nationally representative steering committee and expert panel (representatives from hospital administration, emergency medicine, health information, government, and provincial quality councils). A comprehensive review of the scientific literature was conducted to identify candidate indicators. The expert panel reviewed candidate indicators in a modified Delphi panel process using electronic surveys; final decisions on inclusion of indicators were made by the steering committee in a guided nominal group process with facilitated discussion. Indicators in the final set were ranked based on their priority for measurement. A gap analysis identified areas where future indicator development is needed. A feasibility study of measuring the final set of indicators using current Canadian administrative databases was conducted.
A total of 170 candidate indicators were generated from the literature; these were assessed based on scientific soundness and their relevance or importance. Using predefined scoring criteria in two rounds of surveys, indicators were coded as "retained" (53), "discarded" (78), or "borderline" (39). A final set of 48 retained indicators was selected and grouped in nine categories (patient satisfaction, ED operations, patient safety, pain management, pediatrics, cardiac conditions, respiratory conditions, stroke, and sepsis or infection). Gap analysis suggested the need for new indicators in patient satisfaction, a healthy workplace, mental health and addiction, elder care, and community-hospital integration. Feasibility analysis found that 13 of 48 indicators (27%) can be measured using existing national administrative databases.
A broadly representative modified Delphi panel process resulted in a consensus on a set of 48 evidence-based quality of care indicators for EDs. Future work is required to generate technical definitions to enable the uptake of these indicators to support benchmarking, quality improvement, and accountability efforts.
Reacted and Activated Rubber Sousa, Jorge B.; Vorobiev, Andrey; Rowe, Geoffrey M. ...
Transportation research record,
01/2013, Letnik:
2371, Številka:
1
Journal Article
Recenzirano
Traditionally, asphalt rubber (AR) mixtures have been difficult to produce. Their production requires specialized plants and equipment, which has resulted in their high cost to manufacture. In part ...this difficulty is due to the need to produce AR binder by blending it at high temperatures for a significant period of time (typically at about 190°C for 45 min to 1 h). The complexities in the process have caused AR mixes to be significantly more expensive to produce than conventional paving mixtures. A new technology that produces a reacted and activated rubber (RAR), which is an elastomeric asphalt extender, has been developed by hot blending and activation of a rubber granulate with a selected asphalt binder and activated mineral binder stabilizer. RAR achieves results comparable to those of other types of polymer modified binders (PMBs). However, a principal advantage of RAR is that it can be added easily to any hot-mix asphalt manufacturing facility with systems designed to feed particulate material into a batch plant (pugmill) or drum mix plant. This paper describes how RAR is produced from raw constituent materials. Various binder tests contrast performance with typical paving grades and PMBs used in the United States. The implementation of RAR in various types of asphalt mixtures is discussed, and demonstrative examples of test results are provided. Tests on mixtures in wheel tracking and fatigue demonstrate how the binder performance tests translate into mixture performance. In all cases evaluated, the RAR mixtures outperformed nonmodified and even conventional rubber modified equivalent materials.
A dynamic modulus master curve for asphalt concrete is a critical input for flexible pavement design in the Mechanistic–Empirical Pavement Design Guide developed in NCHRP Project 1-37A, which has ...drawn much attention among asphalt technologists. The objectives in this study were (a) to consider and compare different analysis techniques for construction of the master curve and (b) to measure and analyze the effect of permanent strain on samples that have been evaluated with one of the simple performance tests, dynamic modulus. It was found that differences existed in the calculated asymptote values and the shape of the master curve, depending upon which method was adopted. Recommendations are made for modifications to the testing protocol and for further work to determine the effect of permanent strain at higher test temperatures.
Background:
The evaluation of emergency department (ED) quality of care is hampered by the absence of consensus on appropriate measures. We sought to develop a consensus on a prioritized and ...parsimonious set of evidence-based quality of care indicators for EDs.
Methods:
The process was led by a nationally representative steering committee and expert panel (representatives from hospital administration, emergency medicine, health information, government, and provincial quality councils). A comprehensive review of the scientific literature was conducted to identify candidate indicators. The expert panel reviewed candidate indicators in a modified Delphi panel process using electronic surveys; final decisions on inclusion of indicators were made by the steering committee in a guided nominal group process with facilitated discussion. Indicators in the final set were ranked based on their priority for measurement. A gap analysis identified areas where future indicator development is needed. A feasibility study of measuring the final set of indicators using current Canadian administrative databases was conducted.
Results:
A total of 170 candidate indicators were generated from the literature; these were assessed based on scientific soundness and their relevance or importance. Using predefined scoring criteria in two rounds of surveys, indicators were coded as “retained” (53), “discarded” (78), or “borderline” (39). A final set of 48 retained indicators was selected and grouped in nine categories (patient satisfaction, ED operations, patient safety, pain management, pediatrics, cardiac conditions, respiratory conditions, stroke, and sepsis or infection). Gap analysis suggested the need for new indicators in patient satisfaction, a healthy workplace, mental health and addiction, elder care, and community-hospital integration. Feasibility analysis found that 13 of 48 indicators (27%) can be measured using existing national administrative databases.
Discussion:
A broadly representative modified Delphi panel process resulted in a consensus on a set of 48 evidencebased quality of care indicators for EDs. Future work is required to generate technical definitions to enable the uptake of these indicators to support benchmarking, quality improvement, and accountability efforts.