Thesis (M.A.)--Youngstown State University, 2008. / Includes bibliographical references (leaves 113-117). Also available via the World Wide Web in PDF format.

abstract: Crumb rubber use in asphalt mixtures using wet process technology has been in practice for years in the United States with good performance history; however, it has some drawbacks that include the need for special blending equipment, high rubber-binder temperatures, and longer waiting time at mixing plants. Pre-treated crumb rubber technologies are emerging as a new method to produce asphalt rubber mixtures in the field. A new crumb rubber modifier known as Reacted and Activated Rubber (RAR) is one such technology. RAR (industrially known as “RARX”) acts like an Enhanced Elastomeric Asphalt Extender to improve the engineering properties of the binder and mixtures. It is intended to be used in a dry mixing process with the purpose of simplifying mixing at the asphalt plant. The objective of this research study was first to perform a Superpave mix design for determination of optimum asphalt content with 35% RAR by weight of binder; and secondly, analyse the performance of RAR modified mixtures prepared using the dry process against Crumb Rubber Modified (CRM) mixtures prepared using the wet process by conducting various laboratory tests. Performance Grade (PG) 64-22 binder was used to fabricate RAR and CRM mixtures and Performance Grade (PG) 70-10 was used to fabricate Control mixtures for this study. Laboratory tests included: Dynamic Modulus Test, Flow Number Test, Tensile Strength Ratio, Axial Cyclic Fatigue Test and C* Fracture Test. Observations from test results indicated that RAR mixes prepared through the dry process had excellent fatigue life, moisture resistance and cracking resistance compared to the other mixtures. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2018

In recent years, the interest in the design, construction and utilization of rubber tracks for agriculture and earth moving machinery has increased considerably. The development of such types of tracks was initiated by the efforts to invent a more environmentally friendly vehicle-terrain system. These tracks are also the result of the continuous effort to develop more cost-effective traction systems. A rubber-surfaced and friction-based prototype track was developed and mounted on the patented modification of a new Allis Chalmers four wheel drive tractor. The track is propelled by smooth pneumatic tyres by means of rubber-rubber friction and the tractive effort of the track is mainly generated by soil-rubber friction between the rubber surface of the track elements and terrain. The experimental track layer tractor, based on an Allis Chalmers 8070 tractor (141 kW) was tested on concrete and on cultivated sandy loam soil at 7.8%; 13% and 21% soil water content. The contact pressure and the tangential force on an instrumented track element, as well as the total torque input to one track, was simultaneously recorded during the drawbar pull-slip tests. Soil characteristics for pressure-sinkage and friction-displacement were obtained from the field tests by using an instrumented linear shear and soil sinkage device. By applying the approach based on the classical bevameter technique, analytical methods were implemented for modelling the traction performance of the prototype track system. Different possible pressure distribution profiles under the tracks were considered and compared to the recorded data. Two possible traction models were proposed, one constant pressure model, for minimal inward track deflection and the other a flexible track model with inward deflection and a higher contact pressure at both the front free-wheeling and rear driving tyres. For both models, the traction force was mainly generated by rubber-soil friction and adhesion with limited influence by soil shear. For individual track elements, close agreement between the measured and predicted contact pressure and traction force was observed based on the flexible track model. The recorded and calculated values of the coefficient of traction based on the summation of the traction force for the series of track elements were comparable to the values predicted from modelling. However, the measured values of drawbar pull coefficient were considerably lower than the predicted values, largely caused by internal track friction in addition to energy dissipated by soil compaction. The tractive efficiency for soft surface was also unacceptably low, probably due to the high internal track friction and the low travel speeds applied for the tests. The research undertaken identified and confirmed a model to be used to predict contact pressure and tangential stresses for a single track element. It was capable of predicting the tractive performance for different possible contact pressure values. / Thesis (PhD (Argricultural Engineering))--University of Pretoria, 2007. / Civil Engineering / Unrestricted

Volvo Car Corporation (Volvo Cars) develops powertrain mounting systems that uses components made up largely of filled rubber materials. The development of such components is today relying on external suppliers to design components based on requirements set by Volvo. To reduce costs and lead-time in the development process the possibility of in-house design of such components at Volvo Cars is being investigated. For this to be possible, knowledge must be built concerning modelling the mechanical properties of rubber materials. As part of this a parameter extraction method for modelling of filled rubber materials intended for finite element use has been developed in this project. Both a simple static model fitting procedure and a more complex dynamic model fitting procedure are detailed. Mechanical testing of four filled natural rubber materials with varying hardnesswas carried out at the facilities of Volvo Cars and recommendations have been made regarding the limits of the equipment and the specific test body geometry used. It was found that the lower limit for dynamic testing in regards to displacement amplitude is 0.02 mm. The highest frequency recommended is dependent on the material hardness but a higher limit of 200 Hz is recommended for the softest material investigated. The upper limit was found to be necessary due to inertia effects in the material. The models used to describe the static behaviour were hyperelastic phenomenological models independent on the second invariant such as the Yeoh and the linear neo-Hookean models. The dynamic model used the overlay method to capture therate and amplitude dependent properties of filled rubber. A generalized viscoelastic-elastoplastic rheological model using Maxwell and friction elements in parallel with alinear elastic element was presented and used. These were limited to having maximumfive of each element and no attempts at minimizing this number was made in this work.The dynamic model was fitted to experimental data using a minimization procedure focusing on dynamic modulus and damping at a range of frequencies and strain amplitudes.The proposed fitting procedure is a three segment loop in which FE simulationsof the experimental data is used as both a correction and a validation tool.Model validation showed good correlation of the fitted model to measured databefore correction was attempted. The correction step did not improve the model qualityand the reason for this was identified as poor post-processing. The proposed method together with lessons learned during the course of the project will be of importance for the future in-house development of rubber components at Volvo Cars.

The popularity of natural rubber as an important raw material was distorted in the post-World War Two period. It received heavy competition from synthetic rubber. The main purpose of this paper is to determine and to study supply elasticity and demand elasticity of natural rubber in the case of Malaysia. The main aim of analyzing the period since 1971 is that both price and quality competitiveness of Malaysian natural rubber have drastically improved. Therefore, in order for Malaysia to maintain her position as the leading producer and exporter of natural rubber in the world, supportive policies and incentives from the government would further enhance the prospects for improvements in this industry.

For the development of intelligent vehicle tires, especially for future self-driving cars, suitable strain sensors are mandatory. The design of such a strain sensor must fulfill several criteria and most important of them all, it must be easily mounted or implanted into the tire and the elastic nature of the sensors must synchronize with the deformation of the tire. This work is therefore focused on understanding the piezoresistive characteristics of a composite developed from tire rubber. Thus, a commercially available grade of solution styrene butadiene rubber (SSBR) was primarily chosen as the matrix rubber along with butadiene rubber (BR) and natural rubber (NR). The initial focus was given to develop simple strain sensors by exploiting the concept of piezoresistivity with conductive rubber composites based on SSBR filled with carbon black and carbon nanotubes. As the internal structure of the filler particles was found to rearrange or alter during deformation, it was important to study the piezoresistive performance with respect to critical material parameters such as crosslink density, hardness, and stiffness of the composite in details. The developed sensors were able to be stretched to several hundred percents of their original length and strain sensitivity as much as ~1000 (gauge factor) was achieved. Quasi-static cyclic tests indicated the ability of the developed materials to respond and recover within the given time frame. This motivated to assess the suitability of these materials for dynamic sensing. As a consequence, the dynamic piezoresistive characteristics were studied for the conducting SSBR composites. The temporal changes in electrical resistance of the SSBR composites were monitored real-time during dynamic mechanical studies. The influence of critical parameters such as filler content, test frequency, test temperature, and matrix crosslink density was taken into consideration. The filler network was found to rearrange in the rubber matrix during dynamic loading, witnessed from the changes in electrical resistance over time. The findings offered a preliminary understanding of the filler network behavior inside the SSBR matrix. Situations that eased the filler mobility such as high temperature, low frequency, and low crosslink density resulted in the minimal effect on the filler network changes. For a given strain cycle, the samples responded with two distinct responses pertaining to the loading and unloading, reflecting as two signals. Filler network reconfiguration during unloading was found to be the reason for the second piezoresistive response. The behavior of the second peaks was analyzed in detail at different conditions. The stress relaxation, an inevitable process pertaining to viscoelastic materials, resembled the overall piezoresistance change of the material. The two properties were therefore correlated, and a relationship was deduced, offering the possibility to monitor the mechanical performance using electrical resistance data. Apart from evaluating the phase shifts between stress and strain (δσ-ε) during the dynamic tests, phase shifts were also evaluated between resistance and strain (δR-ε) as well as between stress and resistance (δσ-R). The piezoresistive phase shift values (δσ-R) were found to be larger than the mechanical phase shifts values (δσ-R > δσ-ε) It perceived information regarding the time taken by the filler network to respond for the applied strain. To realize the concept of dynamic piezoresistivity in commercial use, (i) SSBR filled with conventional carbon blacks N220, N330, and N660 and (ii) NR and BR (two more rubbers that are widely used in tire industry) filled with Printex carbon black were tested for their piezoresistive behavior under dynamic conditions. The experimental results were promising and guaranteed the applicability of the concept for all rubber - filler combinations that display piezoresistive characteristics. This basic scientific study would be the stepping stone to understand dynamic piezoresistivity in rubbers, which would help in developing rubber-based sensors that are capable of performing under dynamic conditions for the future. Moreover, the study offered a much deeper insight not only on the dynamic piezoresistivity but also on the behavior and changes in the filler network during dynamic deformation. / Für die Entwicklung von intelligenten Fahrzeugreifen, insbesondere für zukünftige selbstfahrende Autos, sind geeignete Dehnungssensoren notwendig. Die Konstruktion eines solches Sensors muss mehrere Kriterien erfüllen: am wichtigsten ist, dass er einfach in den Reifen eingebaut oder implantiert werden kann und dass die Verformung des Sensors mit der Verformung des Reifens synchronisiert ist. Daher konzentriert diese Arbeit sich auf das Verständnis der piezoresistive Eigenschaften eines bekannten Reifenkautschuks, gefüllt mit leitfähigen Füllstoffpartikeln. Eine kommerziell erhältliche Sorte von Lösungs-Styrol-Butadien-Kautschuk (SSBR), Butadien-Kautschuk (BR) und Naturkautschuk (NR), welche in der modernen Reifenindustrie weit verbreitet sind, wurden deshalb als Matrix-Kautschuk gewählt. Der Fokus lag zunächst auf der Entwicklung einfacher Dehnungssensoren unter Ausnutzung des Konzepts der Piezoresistivität mit leitfähigen Gummimischungen auf Basis von SSBR, welche mit leitfähigem Ruß und Kohlenstoff-Nanoröhrchen gefüllt sind. Da sich die innere Struktur der Füllstoffpartikel während der Verformung verändert, war es wichtig, das piezoresistive Verhalten in Bezug auf kritische Materialparameter wie Vernetzungsdichte, Härte und Steifigkeit des Komposits im Detail zu untersuchen. Die Sensoren konnten auf mehrere hundert Prozent ihrer ursprünglichen Länge gestreckt werden, wobei eine Empfindlichkeit bis zu ~1000 (Gauge Faktor) erreicht wurden. Quasistatische zyklische Tests zeigten die Fähigkeit der entwickelten Materialien, innerhalb des vorgegebenen Zeitrahmens zu reagieren und sich zu erholen. Dies motivierte dazu, die Eignung dieser Materialien für die dynamische Sensorik zu beurteilen. In der Folge wurden die dynamischen piezoresistiven Eigenschaften für die elektrisch leitfähigen SSBR-Verbundwerkstoffe untersucht. Die zeitlichen Veränderungen des elektrischen Widerstandes dieser SSBR-Verbundwerkstoffe wurden während dynamisch-mechanischer Studien in Echtzeit überwacht. Der Einfluss kritischer Parameter wie Füllstoffgehalt, Matrixvernetzungsdichte, Messfrequenz, und Messtemperatur wurde dabei berücksichtigt. Es wurde festgestellt, dass sich das Füllstoffnetzwerk während der dynamischen Belastung in der Elastomermatrix neu anordnet, wie die Veränderungen des elektrischen Widerstands im zeitlichen Verlauf zeigen. Diese Ergebnisse bieten ein vorläufiges Verständnis des Verhaltens des Füllstoffnetzwerks der SSBR-Matrix. Situationen, die die Füllstoffmobilität begünstigen, wie hohe Temperatur, niedrige Frequenz und niedrige Vernetzungsdichte, führten zu minimalen Auswirkungen auf das Füllstoffnetzwerk. Für einen gegebenen Dehnungszyklus reagierten die Proben mit zwei getrennten Signalen, welche dem Be- und Entlasten des Materials entsprechen und sich als zwei Peaks in der Widerstandsmessung widerspiegeln. Der Grund für das zweite piezoresistive Signal ist die Rekonfiguration des Füllstoffnetzwerks während der Entlastung. Das Verhalten dieser zweiten Peaks wurde unter verschiedenen Bedingungen detailliert analysiert. Die Spannungsrelaxation, ein unvermeidlicher Prozess bei viskoelastischen Materialien, ähnelte der gesamten Piezowiderstandsänderung des Materials. Diese beiden Eigenschaften wurden daher korreliert und ein Zusammenhang abgeleitet, der die Möglichkeit bietet, die mechanische Leistung anhand von elektrischen Widerstandsdaten zu überwachen. Neben der Auswertung der Phasenverschiebungen zwischen Spannung und Dehnung (δσ-ε) bei dynamischen Tests wurden auch die Phasenverschiebungen zwischen Widerstand und Dehnung (δR-ε) sowie zwischen Spannung und Widerstand (δσ-R) bewertet. Die piezoresistiven Phasenverschiebungswerte (δσ-R) erwiesen sich als größer als die mechanischen Phasenverschiebungswerte (δσ-R > δσ-ε). Dies bietet Informationen über die Zeit, die das Füllernetzwerk benötigt, um auf eine angelegte Belastung zu reagieren. Um das Konzept der dynamischen Piezoresistivität im kommerziellen Einsatz zu realisieren, wurden (i) SSBR gefüllt mit konventionellen Rußen N220, N330 und N660 und (ii) NR und BR (zwei weitere Kautschuke, die in der Reifenindustrie weit verbreitet sind) gefüllt mit leitfähigem Ruß auf ihr piezoresistives Verhalten unter dynamischen Bedingungen getestet. Die experimentellen Ergebnisse sind vielversprechend und garantieren die Anwendbarkeit des Konzepts für alle Gummi-Füllstoff-Kombinationen mit piezoresistiven Eigenschaften. Diese grundlegende wissenschaftliche Studie ist ein wichtiger Schritt, um die dynamische Piezoresistivität in Kautschuken zu verstehen, was bei der Entwicklung von zukünftigen, dynamisch arbeitenden Sensoren auf Kautschukbasis helfen kann. Darüber hinaus liefert diese Studie einen viel tieferen Einblick nicht nur in die dynamische Piezoresistivität, sondern auch in das Verhalten und die Veränderungen im Füllstoffnetzwerk während der dynamischen Verformung.

Asphalt binder modification is a common method of improving Hot-mix Asphalt (HMA) performance by enhancing mix properties and reducing or delaying three general HMA distress types: deformation (rutting and shoving), cracking (from repeated loads and low temperatures) and general deterioration (raveling and stripping). Since the early 1960’s, a common modified asphalt alternative has employed reclaimed rubber as an economical and environmental friendly method of recycling waste tires while improving asphalt physical and mechanical properties. Pavement network deterioration combined with increasing material costs makes polymer modification of asphalt binder desirable, with reclaimed rubber from waste tires being an attractive alternative which addresses performance, economics and environmental issues. The primary objective of this dissertation is to demonstrate the importance of proper processing of all types of modified bituminous binders, whether they be virgin (e.g. styrene-butadiene-styrene (SBS) or styrene-butadiene rubber (SBR)), post-consumer polymers (e.g. ground tire rubber (GTR)) or a combination (GTR plus SBS). To achieve this four secondary objectives were identified: 1) characterize GTR using thermo-gravimetric analysis (TGA), 2) improve processing of GTR modified binders, 3) improve testing and specifications of GTR modified binders and 4) evaluate mixes containing GTR modified binders. A simple efficient instrumental, TGA, method to analyze polymers in binary rubber compounds was developed to quantify the functional polymer content available in GTR. TGA analysis provides a better understanding of the general chemical characteristics of GTR used in modification of asphalt binders for production of asphalt paving mixtures. Results are presented from efforts to optimize GTR modified binder formulations with respect to how GTR loading, GTR particle size, processing temperature and asphalt cement source affect modified binder properties and ability to meet performance graded binder specifications. These results are the basis to establish recommended processing parameters for formulation and preparation of GTR modified asphalt binders. GTR modified binders were used in: dense graded asphalt (DGA), stone matrix asphalt (SMA) and open graded friction courses (OGFC) and compared to conventional asphalt cement and styrene-butadiene-styrene (SBS) modified asphalt binders. Mixture performance evaluation with respect to binder effectiveness as it relates to the three general HMA distress types.

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