Study of the interaction between bitumen and rubber

Dissertação de mestrado em Engenharia Civil (área de especialização em Engenharia Rodoviária)Approximately 9 to 10 kg of rubber from tyres per inhabitant and year are currently discarded in the industrialized societies. It is a waste material with a highly valuable constituent: vulcanized natural and synthetic rubber. Thus, the introduction of crumb rubber in the production of asphalt rubber (AR) mixes for road pavements should be considered as a sustainable technology which transforms an unwanted residue into a new bituminous mixture highly resistant to fatigue and fracture. However, the increasing demands in relation to the quality and durability of pavements lead to the need of a profound knowledge in the physicochemical changes of the materials which constitute the AR binders. Thus, the main objective of this research project is to characterize the influence of bitumen and rubber properties and their interaction in the AR binder performance, namely by (i) evaluating the influence of the rubber morphology and physical properties of base bitumen in the physical and rheological properties of AR binder, (ii) assessing the changes that occur, at a molecular scale, in the base bitumen and in the rubber during their mutual interaction, and (iii) analyzing the aging effects during the pavement construction. In this work several base bitumens interacted with crumb rubber in order to produce AR binders, which were subsequently separated by using a modified “Basket drainage method” to recover the residual bitumen and rubber. The aging effect was studied by using the RTFOT method. Additionally, a new method, the “Sphere AR production simulator”, was developed to reproduce the AR production without the contribution of rubber. CEN standard tests and the dynamic shear rheometer were used to evaluate the changes in the properties of the binders during the production of AR. The rubber changes were studied through microscopic observation, swelling and depolymerization tests. The laboratory tests demonstrated that the aging of bitumen make it harder due to oxidation and restructuration. Likewise the AR production also contributes to its hardening because of the diffusion of light fractions of bitumen (mainly non volatile molecules) in the rubber particles. The rubber particles swelled 250 to 300% their weight, but the equivalent diameter only increased 2.5%. It was found that the 150/200 bitumen is an excellent alternative to produce AR binders. Minor changes in the loss of weight and in the rheological and physical properties of the AR binder can be observed after aging if compared with the aging effect in the other studied materials (base and residual bitumen). The physical and rheological properties of all tested materials can be related through known mathematical equations.Nas sociedades industrializadas actuais são rejeitados aproximadamente 9 a 10 kg de pneus, por habitante por ano, sendo que os materiais desaproveitados do pneu têm um elevado valor intrínseco, nomeadamente o seu constituinte principal: borracha natural e sintética vulcanizada. Assim, a introdução de granulado de borracha na produção de misturas betuminosas com betume de borracha (BB) para pavimentos rodoviários deve ser considerada uma tecnologia sustentável, que transforma um resíduo indesejado numa nova mistura betuminosa com elevada resistência à fadiga e à fractura. No entanto, a crescente exigência de qualidade e durabilidade dos pavimentos obriga a um conhecimento profundo das alterações físico-químicas que ocorrem nos materiais constituintes do BB. Assim, o principal objectivo deste trabalho é determinar a influência das propriedades do betume e da borracha, e da sua interacção, no desempenho do BB, nomeadamente através da avaliação (i) da influência da morfologia da borracha e das propriedades físicas e reológicas do betume nas características do BB, (ii) das alterações no betume e na borracha, à escala molecular, durante a sua interacção mútua, e (iii) dos efeitos do envelhecimento durante a construção do pavimento. Neste trabalho, um conjunto de betumes interagiu com granulado de borracha para produzir BB, sendo subsequentemente utilizando um “método do cesto drenante” modificado para separar e recuperar o betume e a borracha residuais. O envelhecimento dos ligantes durante a construção do pavimento foi estudado através do método RTFOT. Foi desenvolvido um “simulador de produção do BB com esferas” para reproduzir o envelhecimento na produção do BB sem a contribuição da borracha. As alterações nas propriedades dos ligantes durante a produção de BB foram avaliadas através de normas CEN e do reómetro dinâmico de corte. As alterações na borracha foram estudadas através de observação microscópica e de ensaios para avaliação da densidade e do grau de inchamento e despolimerização. Os ensaios laboratoriais demonstraram que o envelhecimento e a produção de BB causam o endurecimento do betume, respectivamente devido à oxidação, crescimento e reestruturação molecular e devido à difusão das fracções leves do betume (principalmente moléculas não voláteis) através da borracha. As partículas de borracha incham cerca de 250 a 300% (em peso), mas o seu diâmetro equivalente aumenta apenas 2.5%. Concluiu-se que o betume 150/200 é uma boa alternativa para produção de BB. As alterações na perda de peso e nas propriedades físicas e reológicas do BB após envelhecimento são inferiores às observadas nos outros ligantes estudados. As propriedades físicas e reológicas dos materiais estudados relacionam-se através de equações matemáticas conhecidas

Development of Non-Petroleum-Based Binders for Use in Flexible Pavements – Phase II

Bio-binders can be utilized as asphalt modifiers, extenders, and replacements for conventional asphalt in bituminous binders. From the rheology results of Phase I of this project, it was found that the bio-binders tested had good performance, similar to conventional asphalt, except at low temperatures. Phase II of this project addresses this shortcoming and evaluates the Superpave performance of laboratory mixes produced with the enhanced bio-binders. The main objective of this research was to develop a bio-binder capable of replacing conventional asphalt in flexible pavements by incorporating ground tire rubber (GTR) into bio-oil derived from fast pyrolysis of agriculture and forestry residues. The chemical compatibility of the new bio-binder with GTR was assessed, and the low-temperature performance of the bio-binders was enhanced by the use of GTR. The newly developed binder, which consisted of 80 percent conventional binder and 20 percent rubber-modified bio-oil (85 percent bio-oil with 15 percent GTR), was used to produce mixes at two different air void contents, 4 and 7 percent. The laboratory performance test results showed that the performance of the newly developed bio-binder mixes is as good as or better than conventional asphalt mixes for fatigue cracking, rutting resistance, moisture sensitivity, and low-temperature cracking. These results need to be validated in field projects in order to demonstrate adequate performance for this innovative and sustainable technology for flexible pavements

Evaluation of the rheological behaviour of Warm Mix Asphalt (WMA) modified binders

Several processes and products are available to produce warm mix asphalt (WMA). The use of those may reduce the mixing and compaction temperatures in relation to hot mix asphalt (HMA), ensuring a good performance of the pavement. Lower plant mixing temperatures mean reduction in fuel consumption and lower emissions, what may contribute to diminish odours and health problems. A laboratory study on the properties of the modified binders (using two commercial WMA additives—Sasobit® and Cecabase®) was carried out through conventional (penetration, softening point), dynamic viscosity and rheology (DSR) tests, in order to establish the optimum additive content. Stripping of binder from the aggregates is a reported problem in WMA. Thus, the affinity of the modified binders was assessed without encountering significant problems. It was also observed that only Sasobit® alters the viscosity of the binder. A maximum temperature reduction of 15°C was achieved using 4% of Sasobit® with a softer binder

Rheological and functional evaluation of the interactions between bitumen and rubber

It is estimated that about ten kilograms of tires are discarded per inhabitant annually. The negative impact of this residue can be reduced, since rubber can be reused as a constituent of asphalt rubber (AR) binder in road pavements. However, the materials which constitute the AR binders and their interaction are not sufficiently characterized. In this work several base bitumens interacted with crumb rubber, in order to produce AR binders, which were subsequently separated, by using a modified “Basket drainage method” to recover the residual bitumen and rubber. EN 12591 or 14023 standards tests and the Dynamic Shear Rheometer (DSR) were used to evaluate the changes in the properties of the binders during AR production. The swelling and depolymerisation changes in the rubber were evaluated through microscopic tests. It was observed that the characteristics of the base bitumen significantly affect the rubber and the AR binder properties (mainly for interactions with softer bitumens)

Analysis of physicochemical interaction between the components of asphalt mixtures with rubber

Tese de Doutoramento em Engenharia CivilEarth is full of resources; in reality there is no waste, what sometimes happens is a lack of knowledge and ability to transform that waste into valuable materials. The present work can be a good example of how waste can be transformed into a needed construction material. Asphalt is the most common binder material in road construction. However, the need for more durable and safer road pavements requires a better understanding of asphalt concerning its aging mechanisms, and how its characteristics can be improved by the addition of polymers. Despite asphalt modified with crumb rubber from used tires has been applied with great success all over the world since the sixties, the phenomena of interaction between the asphalt and rubber are not yet fully understood. The bio-oil produced by fast pyrolysis of organic materials is commercially available for over a decade. This material has been mainly used as fuel, in the same way as petroleum. However, its properties are similar to those of asphalt and it may prove to be an excellent substitute. In this thesis the mechanisms of aging of asphalt and its interaction with rubber were studied, so that this knowledge could be applied to produce an alternative binder comprising bio-oil and rubber. Thus, the work began with the study of the effects of asphalt aging in its rheological properties, in order to further understand and distinguish aging from changes in the asphalt caused by the interaction with rubber, and the effect of the asphalt on rubber particles. Processes developed for the production and investigation of various asphalt rubber components were applied in the production and study of the bio-binder (bio-oil rubber). This part of the work resulted in the production of a binder with appropriate characteristics, suggesting that it would be suitable for paving in a wide range of temperatures. Finally, this bio-binder was blended with conventional asphalt and two mixes were designed, compacted and their characteristics studied. The results showed that these mixes have excellent characteristics to be used in pavement construction.A terra está repleta de recursos; na realidade não há resíduos, o que por vezes falta é conhecimento e capacidade para transformar os desperdícios de uns em valiosos materiais para outros. O presente trabalho pode ser um bom exemplo desta realidade. O ligante mais comum em construção de estradas é o betume. No entanto, a necessidade de pavimentos rodoviários mais duráveis e seguros impõem um melhor conhecimento do betume no que diz respeito ao seu envelhecimento e à melhoria das suas características através da adição de polímeros. Apesar do betume modificado com granulado de borracha de pneus usados ser aplicado com grande sucesso em todo o mundo desde os anos sessenta, os fenómenos de interação entre o betume e a borracha ainda não se encontram totalmente clarificados. O bio-óleo resultante da pirólise rápida de materiais orgânicos está disponível no mercado há mais de uma década. Este material tem sido maioritariamente usado como combustível, tal como acontece com o petróleo. No entanto, este possui propriedades semelhantes ao betume e pode vir a ser um excelente substituto. Neste trabalho pretende-se estudar os mecanismos de envelhecimento do betume e a forma como este interage com a borracha de forma a poder aplicar estes conhecimentos à produção de um ligante alternativo constituído por bio-óleo e borracha. Assim, iniciou-se o trabalho pelo estudo dos efeitos do envelhecimento do betume nas suas propriedades reológicas, de forma a posteriormente compreender e distinguir o envelhecimento das alterações no betume provocadas pela interação com a borracha, assim como o efeito do betume sobre as partículas de borracha. Os processos desenvolvidos para a produção e estudo dos vários componentes do betume borracha foram aplicados na produção e estudo do bio-ligante (bio-óleo com borracha). Esta primeira parte do estudo resultou na produção de um ligante com características adequadas que sugeriam que este seria um ligante adequado para pavimentação numa larga gama de temperaturas. Por fim foi estudada a combinação deste ligante com o betume tradicional, e foram produzidas misturas que revelaram ter ótimas características para construção de pavimentos.PhD Thesis funded by the Portuguese Government and by the European Social Fund of the European Union (UE/FSE) through the Portuguese Foundation for Science and Technology ( FCT) with the grant SFRH/BD/72169/2010, and in the scope of the Operational Programme for Human Potential inscribed in the National Strategic Reference Framework (POPH/QREN) for the period 2007-2013

Avaliação da interacção entre o betume, a borracha e o filer em misturas betuminosas

A utilização de borracha de pneus usados em pavimentos rodoviários é uma tecnologia promissora, pois reduz o impacto ambiental e confere aos pavimentos características de desempenho melhoradas. No entanto, os estudos existentes sobre a melhoria do desempenho das misturas com betume borracha têm sido realizados com base em metodologias empírico-mecanicistas, e não conseguem explicar a razão intrínseca dos resultados obtidos. Neste trabalho faz-se uma primeira abordagem à forma como a borracha, o betume e o filer interagem, de forma a explicar as alterações provocadas nas propriedades do ligante pela introdução do granulado de borracha e do filer (origem petrográfica e concentração). Complementarmente, as propriedades moleculares do filer são analisadas através de ensaios espectroscópicos para compreender os resultados obtidos na caracterização dos mastiques

Development of Non-Petroleum-Based Binders for Use in Flexible Pavements – Phase II

Bio-binders can be utilized as asphalt modifiers, extenders, and replacements for conventional asphalt in bituminous binders. From the rheology results of Phase I of this project, it was found that the bio-binders tested had good performance, similar to conventional asphalt, except at low temperatures. Phase II of this project addresses this shortcoming and evaluates the Superpave performance of laboratory mixes produced with the enhanced bio-binders. The main objective of this research was to develop a bio-binder capable of replacing conventional asphalt in flexible pavements by incorporating ground tire rubber (GTR) into bio-oil derived from fast pyrolysis of agriculture and forestry residues. The chemical compatibility of the new bio-binder with GTR was assessed, and the low-temperature performance of the bio-binders was enhanced by the use of GTR. The newly developed binder, which consisted of 80 percent conventional binder and 20 percent rubber-modified bio-oil (85 percent bio-oil with 15 percent GTR), was used to produce mixes at two different air void contents, 4 and 7 percent. The laboratory performance test results showed that the performance of the newly developed bio-binder mixes is as good as or better than conventional asphalt mixes for fatigue cracking, rutting resistance, moisture sensitivity, and low-temperature cracking. These results need to be validated in field projects in order to demonstrate adequate performance for this innovative and sustainable technology for flexible pavements.</p

Identification of a fuel contamination problem in the production of warm mix asphalts

A number of new processes and products that have the capability of reducing the temperature at which hot mix asphalt (HMA) is mixed and compacted, apparently without compromising the performance of the pavement, has become available. These technologies, usually referred as warm mix asphalt (WMA), can reduce the production temperature of bituminous mixtures by as much as 40 °C. While there is a great deal of promise that comes along with lower temperatures, there are also concerns about some field performance characteristics of WMA mixtures. Thus, a thorough work was carried out in order to answer some questions that are still open about WMA performance in laboratory and in situ. Three bituminous mixtures were studied, namely a conventional HMA control mixture (AC 14 surf 50/70), and other two WMA mixtures with the same composition but using binders modified with different additives (a synthetic wax, Sasobit®, and a surfactant, Cecabase®). These mixtures were initially designed and characterized in the laboratory. Then, they were produced in an asphalt plant and laid down in a pavement trial in order to validate the good laboratory performance of the WMA mixtures in situ. The comparison between the laboratory and in trial performance showed that the rutting resistance of the studied mixtures was severely affected during their production in the asphalt plant. Some authors have referred that WMA mixtures have higher susceptibility to be contaminated with fuel, because it is difficult to adjust the burners with low production temperatures combined with low quantities produced, particularly in pavement trials. Therefore, additional tests were carried out with the studied mixtures and their binder (recovered with the rotary evaporator), thus being possible to conclude that the performance of the mixtures in situ was influenced by their contamination with fuel during the heating of the aggregates

Development of Non-Petroleum-Based Binders for Use in Flexible Pavements – Phase II

Bio-binders can be utilized as asphalt modifiers, extenders, and replacements for conventional asphalt in bituminous binders. From the rheology results of Phase I of this project, it was found that the bio-binders tested had good performance, similar to conventional asphalt, except at low temperatures. Phase II of this project addresses this shortcoming and evaluates the Superpave performance of laboratory mixes produced with the enhanced bio-binders. The main objective of this research was to develop a bio-binder capable of replacing conventional asphalt in flexible pavements by incorporating ground tire rubber (GTR) into bio-oil derived from fast pyrolysis of agriculture and forestry residues. The chemical compatibility of the new bio-binder with GTR was assessed, and the low-temperature performance of the bio-binders was enhanced by the use of GTR. The newly developed binder, which consisted of 80 percent conventional binder and 20 percent rubber-modified bio-oil (85 percent bio-oil with 15 percent GTR), was used to produce mixes at two different air void contents, 4 and 7 percent. The laboratory performance test results showed that the performance of the newly developed bio-binder mixes is as good as or better than conventional asphalt mixes for fatigue cracking, rutting resistance, moisture sensitivity, and low-temperature cracking. These results need to be validated in field projects in order to demonstrate adequate performance for this innovative and sustainable technology for flexible pavements.</p

Optimization of warm mix asphalts using different blends of binders and paraffin wax contents

In road construction, several processes and products are now available to produce environmentally friendlier warm mix asphalts, including the use of synthetic paraffin wax additives. These additives facilitate the production of energy efficient asphalt mixtures at reduced manufacturing and construction temperatures. However, their sustainability during the road life cycle can only be obtained by optimizing the mixture's performance. Thus, the objective of this work was to assess the properties of different blends of base bitumens (softer to harder ones) containing a range of synthetic wax contents, as well as the performance of the corresponding warm mix asphalts, that could ultimately lead to more sustainable mixtures. It was concluded that different blends should be selected to maximize the temperature reduction, the fatigue or the rut resistance, without compromising the other properties of the mixture. (C) 2010 Elsevier Ltd. All rights reserved