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Sousa J.,Consultores e Projectistas de Pavimentos Lda. | Vorobiev A.,Alltech Investments Ltd. | Rowe G.,Abatech Inc. | Ishai I.,Technion - Israel Institute of Technology
Transportation Research Record | Year: 2013

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.

Rowe G.M.,Abatech Inc. | King G.,15 Quick Stream Pl. | Anderson M.,Asphalt Institute
Journal of Testing and Evaluation | Year: 2014

It is well known that asphalt rheology affects the cracking performance of asphalt binders. For many years researchers have struggled to develop tests that adequately deal with this aspect of pavement performance in a manner that can be incorporated rapidly into a specification. The use of the fatigue parameter developed during the Strategic Highway Research Program (SHRP), G∗sin δ, has been shown to be a poor surrogate for cracking performance. Other tests, such as the direct tension test, used for cold-temperature cracking, also have been implemented poorly into specifications. However, use of the bending beam rheometer as an indicator of cold-temperature cracking has been widely adopted. As a result, a pavement stiffness of 300 MPa has been regarded as a reasonable parameter for cold-temperature cracking performance. The interrelationship between coldtemperature cracking parameters and those selected for fatigue cracking is not well understood. The onset of brittle behavior that occurs around 300 MPa stiffness and the selection of a fatigue parameter G∗sin δ at 5 MPa are not wildly divergent in concept. More recently, the Glover-Rowe parameter has been revealed as a good indicator of cracking performance. In this paper we explore those differences that have occurred and make suggestions for the use of alternate parameters to better define the rheology of the binder as it relates to cracking. © Copyright VC 2014 by ASTM International.

Mensching D.J.,University of New Hampshire | Rowe G.M.,Abatech Inc. | Daniel J.S.,University of New Hampshire | Bennert T.,Rutgers University
Road Materials and Pavement Design | Year: 2015

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. © 2015 Taylor&Francis

Rowe G.M.,Abatech Inc. | Blankenship P.,Asphalt Institute | Bennert T.,Rutgers University
Four-Point Bending - Proceedings of the 3rd Conference on Four-Point Bending | Year: 2012

During a fatigue test, damage is accumulating and the characteristic properties for the material are changing. Typically, this is expressed as a change in modulus, and when this has reached some critical value, the test is terminated. This has resulted in different definitions of failure for the two types of test, controlled stress and strain, and results in different definitions of failure and consequently different fatigue relationships. The use of dissipated energy concepts has been used as a method to bring the results of controlled stress and strain testing closer together. However, some of the analysis conducted with dissipated energy has not considered the way a specimen damages during a test. The flexural fatigue life of asphalt mixes is currently assessed by the AASHTO T321 procedure in the USA. Meanwhile, the ASTM D 7460 test method offers an alternate analysis procedure that does not rely upon a curve fit to determine the point of failure, but rather considers a maximum value in the nS curve as the definition of cracking. The nS curve is based upon an understanding of how energy is dissipated during the test. Recently, some mixtures with asphalt binders that contain approximately 10 to 15% polymer (defined as heavily modified in this paper) have been evaluated in these test devices. The data demonstrates that crack initiation occurs beyond the 50% stiffness reduction, which in AASHTO T321 is used as the value to terminate the test, with the assumption that all necessary data has been collected to determine the specimen's fatigue life. The origins of both methods are discussed and data is presented that demonstrates the fatigue process that occurs in different modes of testing. In addition, analysis is presented of heavily modified mixes and these are contrasted to those made with conventional binders. Recommendations are made with regard to the interpretation of data from the various two methods. © 2012 Taylor & Francis Group, London.

Grzybowski K.,PRI Asphalt Technologies Inc | Rowe G.M.,Abatech Inc. | Prince S.,PRI Asphalt Technologies Inc
RILEM Bookseries | Year: 2012

The development of reflective cracking mitigation techniques depends on the proper evaluation of different technologies from geo-synthetic inter-layers to highly modified thin lift overlays. A methodology has been developed to investigate these technologies using a novel Accelerated Pavement Weathering System (APWS) which exposes the pavement structure to the combination of temperature, moisture and UV radiation that a pavement will experience in service. This methodology is based on well documented and widely used accelerated weathering methods used by other industries to determine the durability of various materials and systems to environmental exposure. Currently, most pavement accelerated testing is based on load-associated stresses instead of temperature; no system has been developed to-date that accurately reproduces the effect of temperature, moisture, and UV radiation on a pavement structure. The APWS can be a powerful conditioning tool to evaluate different pavement materials, pavement systems, improve modelling and product performance. This conditioning methodology has been used in conjunction with a newly developed test method that can measure the resistance to reflective cracking using a modified Asphalt Pavement Analyzer test. The Reflective Cracking Resistance Test (RCRT) was developed to run both on laboratory-prepared samples, as well as cores taken from the field. The method is ideally suited to measure the crack propagation through an interlayer or overlay as function of loading cycles. This method was used to evaluate pavement systems before and after accelerated weathering in the APWS. This paper focuses on the results of this study and the practicality of this type of testing to understand different technologies to mitigate crack propagation. Specifically, several different pavement structures were prepared which consist of conventional overlays, overlays with geosynthetic membranes, and 4.75 mm thin lift overlay. An overview of the methodology and summary of the testing of these systems is presented in this paper. © RILEM 2012.

Rowe G.M.,Abatech Inc. | Baumgardner G.L.,Paragon Technical Services Inc.
Journal of ASTM International | Year: 2011

The increased understanding of material behavior with rheology has existed for approximately 80 years as a science and has been applied to roofing products for over 50 years. With asphalt binders, several techniques exist for understanding rheology via the use of models. One of the best recognized models for the evaluation of the rheology of unmodified asphalt binders is the Christensen-Anderson model, and various developments of that model have occurred, enabling its use with filled systems such as those used in roofing applications. In addition to this model, the Rowe-Baumgardner-Sharrock model (developed by the authors) is introduced as an alternate method for defining the properties of roofing products that exhibit visco-elastic solid properties. When rheological data are fitted to master curve functional forms, changes in the model parameters can be rapidly visualized. The performance of various products can be assessed using this technique and can be related to the rheological parameters developed from this model (for example, the rheological index, crossover frequency, etc.). An analysis of the data is presented that includes testing using various rheometers over a wide range of temperatures. These data have been combined into a single master curve and plotted in various formats. The data show how the rheological index and the crossover frequency of the materials change over time, particularly with aging. Performance products can then be assessed and evaluated from both the historical data and models that enable the prediction of cracking and deformation. A discussion of the key parameters and a trend analysis are shown. Furthermore, the analysis is applied toward understanding the effectiveness of polymer networks in the roofing materials. As materials age, their properties change, and this can be observed, allowing the study of the effects of polymer network degradation with aging. This paper offers some further understanding of how key rheological parameters change. Copyright © 2011 by ASTM International.

Baumgardner G.L.,Paragon Technical Services Inc. | Rowe G.M.,Abatech Inc. | Reinke G.H.,Mathy Technology Inc
RILEM Bookseries | Year: 2012

A simple Bending Beam Rheometer (BBR) test to determine binder low temperature properties from asphalt mixtures was recently developed by the University of Minnesota. The mixture BBR test was performed concurrent with binder BBR testing to evaluate the effect wax addition has on stiffness/physical hardening and potential for low temperature cracking in asphalt mixtures. Asphalt mixture and binder BBR tests were performed at low temperatures typical of binder grading, after equivalent low temperature conditioning in air for incremental extended periods up to 32 days. Results from temperature saturation are compared to conditioning corresponding to normal 20 hours of PAV aging and testing in accordance with parameters specified in AASHTO M320. Data produced by the BBR suggests that at temperatures close to or below the glass transition temperature mixture beams became less stiff with time when held at a constant temperature. This effect appears to be reversible if a heating/annealing cycle is applied to the beams. This paper reports further investigation of the observed phenomenon and the potential that observations may be indicative of low temperature micro-cracking and subsequent healing in asphalt mixture. © RILEM 2012.

Rowe G.M.,Abatech Inc. | Sharrock M.J.,Abatech Inc.
Transportation Research Record | Year: 2011

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.

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