Introducción a los Betunes Modificados con Polímeros (BM´s)

Presentación del tema: "Introducción a los Betunes Modificados con Polímeros (BM´s)"— Transcripción de la presentación:

1 Introducción a los Betunes Modificados con Polímeros (BM´s)

2 Introducción a los BMs Historia. ¿Por qué hacen falta los BMs?
¿Qué es un Polímero? ¿Para qué se usan los polímeros? ¿Cómo actúan? Efectos de los polímeros sobre el betún. Compatibilidad. Principales Aplicaciones.

3 Historia de los Betunes Modificados
iNo son nuevos! En 1873 se registró la primera patente de asfalto modificado con caucho. 1902 : En Francia se extiende por primera vez asfalto modificado con caucho. Durante los 50 y los 60 se analizan en el Reino Unido diversos tipos de modficadores. As early as 1873 a patent was granted for an asphalt paving mixture containing rubber latex and in 1902 rubber-modified asphalt was being laid in France. Today, polymers are playing an increasingly important role in the asphalt and bituminous surfacings industry.

4 ¿Por qué hacen falta los Betunes Modificados?
En determinadas zonas o para ciertas aplicaciones, pueden necesitarse pavimentos de alto rendimiento, debido a: Incremento de tráfico Cargas por eje más pesadas Mayores presiones de neumáticos Mayores esfuerzos en capas superficiales Reducidos costes de construcción de carreteras Menor mantenimiento Capas más delgadas Larga duración Además, y debido a sus mejores características, los Betunes Modificados pueden añadir oportunidades para la realización de superficies más respetuosas con el medio ambiente. Como consecuencia, los polímeros están jugando un papel de importancia creciente en la industria del asfalto y constituyen los modificadores de betún más avanzados In the majority of applications, normal paving grade bitumens are fully adequate in terms of performance. Polymeric modifiers for bitumen are becoming increasingly used world-wide in applications where enhanced performance of the binder is required to counteract adverse conditions of climate and/or traffic

5 ¿Qué es un polímero? Polímero - “hecho de muchas partes”
Largas cadenas químicas de elementos más pequeños (monómeros) Unidos extremo a extremo Copolímero 2 modos diferentes de replicar unidades moleculares Bloques de copolímeros Unidades moleculares repetidas siguiendo un modelo sistemático de bloque S S S B

6 ¿Para qué se usan los polímeros?
Generalmente, se aplican a la industria del betún estas familias de polímeros: Elastómeros Elástico, flexible Recuperan la deformación P.e. Gomas sintéticas (estireno-butadieno, SBR) o gomas termoplásticas (estireno-butadieno-estireno, SBS). Plastómeros Rígido, áspero, mas puede ser frágil Resistente a la deformación P.e. Acetato de etileno vinilo (EVA), Polietileno (PE), Cloruro de polivinilo (PVC). Whilst there is a variety of polymers currently being used world-wide in the asphalt paving industry they generally fall in one of two major polymer families : thermoplastic (crystalline) polymers and thermoplastic rubbers. Crystalline polymers, often termed 'plastomers', include such materials as polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene, ethylene vinyl acetate (EVA) and ethylene methyl acrylate (EMA). The group of thermoplastic rubbers, often called 'elastomers', consists of polymers such as natural rubber, styrene-butadiene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), polybutadiene (PBD) and polyisoprene.

7 Mecanismo modificador
La modificación se consigue formando una “red” de polímeros distribuída en el betún, otorgándole a éste las propiedades del polímero. Es de común conocimiento por los fabricantes de betunes modificados, por los de polímeros y por los suministradores de equipos que la modificación queda caracterizada por :- La elección del polímero y del betún - Elastómero/plastómero, composición del betún y aditivos Formación de la red de polímero - Diseño de la planta, condiciones del proceso, aditivos, condiciones de maduración Almacenamiento del producto - las propiedades cambian con el tiempo y la temperatura

8 Efectos de los polímeros en las propiedades del betún
Disminución de la susceptibilidad térmica, produciendo : Incremento de la rigidez a elevadas temperaturas en la carretera (reduciendo la deformación permanente) Disminución de rigidez a bajas temperaturas del pavimento (disminuyen fisuración) Betún sin modificar Rigidez PMB An important effect of both types of polymer modifiers is on the temperature susceptibility of the stiffness of bitumen. Compared with many materials, bitumen viscosity or stiffness is highly dependent on temperature. Indeed, it is this characteristic which makes bitumen an ideal binder for many applications. However, where extreme conditions of high (eg 45-60°C) or low (eg below -10°C) pavement temperatures are encountered, the viscosity or stiffness of bitumen can lead to premature failure of a surfacing by rutting or cracking, particularly if traffic demands are also unusually high. In contrast to bitumen, organic polymers are generally far less susceptible to changes in temperature in terms of stiffness. Providing both the type of base bitumen and polymer modifier are carefully chosen to ensure compatibility, incorporating the polymer modifier into bitumen can significantly reduce the temperature susceptibility of the binder in the service temperature range. In order to obtain maximum benefit from the use of polymer modifiers and to ensure ease of application, it is essential to ensure that the polymer modifier systems used do not result in unduly high viscosities at elevated temperatures. Baja (fisuración) Alta (deformación) Temperatura

9 Efectos de los polímeros en las propiedades del betún
Disminución de la deformación de las losas de asfalto al paso de las ruedas : Betún sin modificar Profundidad de rodera The improvement in deformation resistance obtained by the use of a PMB in asphalt can be illustrated in a laboratory wheel tracking test. In the test, which is typically carried out at high pavement service temperatures eg 45-60°C, the depth of the rut developed is determined as a function of the number of passes of a standard loaded wheel over the asphalt specimen. The slide shows results obtained in the test which show the much slower development of the rut for an asphalt containing the PMB. BM Número de ejes

10 Efectos de los polímeros en las propiedades del betún
Mejora las propiedades a bajas temperaturas Esfuerzo Temperatura Contracción térmica de fractura Esfuerzo Reserva de de Tensión Fuerza Cambios de temperatura Longitud constante Esfuerzo Térmico Temperatura Esfuerzo de tracción The benefit of lower stiffness of PMBs at low pavement service temperatures can be demonstrated in the laboratory using tensile tests on asphalt. In one type of test, an asphalt specimen is cooled but not allowed to thermally contract, thus causing a thermally-induced stress to build up as the temperature is reduced. In a separate experiment, the tensile strength of the asphalt is determined as a function of temperature. The difference between the tensile strength at any temperature and the tensile stress at that temperature is known as the 'strength reserve', and is a measure of the load bearing capacity of the asphalt. At some temperature, the thermal stress in the asphalt will equal the tensile strength and the asphalt will fail due to cracking. This temperature is known as the 'fracture temperature'. Both strength reserve and fracture temperature are important performance characteristics of asphalts at low pavement temperatures. The diagram shows typical curves of strength reserve as a function of temperature for an unmodified bitumen and a PMB. It can be seen that the modified binder not only increases the strength reserve relative to the unmodified bitumen but also reduces the fracture temperature. BM Fuerza de reserva Temperatura constante Cambio de longitud Betún sin modificar Temperatura

11 Temperatura creciente
Efectos de los polímeros en las propiedades del betún Mejora de la cohesión (1) : Péndulo de impacto Árido o Bloques metálicos Betún Energía de fractura BM Better adhesion to aggregates, increased tensile strength and better cohesion of PMBs have been found to result in significant improvements in the performance of surface dressings and thin layers. The enhanced performance of PMBs in surface dressings may be demonstrated in the laboratory using the Vialit pendulum impact test. In this test a thin film of the binder is sandwiched between two blocks of metal or aggregate and the energy to remove the upper block using a standard sideways impact is measured. This energy is plotted as a function of temperature. The benefits of increased cohesion and adhesion of the PMB over unmodified bitumen can clearly be seen, the modified binder requiring higher impact energies to remove the aggregate block. Betún sin modificar Temperatura creciente

12 Efectos de los polímeros sobre las propiedades del betún
Mejora de la cohesión (2) : El incremento de la superficie bajo la curva fuerza/distancia para los BM indica la mayor cohesión del ligante Fuerza BM Improved cohesion of the PMB may also be demonstrated by the ‘Toughness-tenacity’ or Benson test. In this test a hemispherical ball is pulled from the bitumen at a constant rate and force required to do this is continually recorded. The total area under the force-displacement curve is the total amount of energy reuired to remove the ball. For unmodified bitumens, there is an initial force or resistance but this soon drops to almost zero as the ball is pulled further. For PMBs under the same conditions, the force does not completely drop to a very low value but is maintained for much longer over a larger distance. As a result, the energy required to remove the ball from the PMB is much greater and clearly demonstrates the improved cohesion of PMBs compared to unmodified bitumens and hence their greater ability to retain chippings. Betún sin modificar Distancia

13 Efectos de los polímeros sobre las propiedades del betún
Mejora de la cohesión y adhesividad usando el Ensayo Cántabro de abrasión : Pérdida por abrasión (%peso) Después de la inmersión Antes de la inmersión Después de la inmersión In some European countries (eg France, Austria and Spain) the Cantabro abrasion test is used to design porous asphalts since it is believed that the test reflects the mechanism of deterioration on the road. In this test, a 100mm diameter cylindrical specimen (eg Marshall) of asphalt is tumbled in a rotating steel drum for 5 minutes and the loss in weight due to abrasion is measured. The test is often carried out before and after a period of immersion in water to try to estimate the tendency of the binder to strip from the aggregate. The slide shows typical results using unmodified bitumen and PMB where the improved performance of the latter is evident. Antes Betún sin modificar BM

14 Compatibilidad Betún/Polímero
La compatibilidad betún/polímero puede variar ampliamente, dependiendo de la composición química del betún y del polímero en particular. La compatibilidad de un polímero con un betún no implica que el betún sea compatible con otros tipos de polímero. The use of PMBs does not necessarily guarantee satisfactory performance in all situations. Due to its complex chemical nature and the interactions between different chemical species in bitumen, there is almost invariably a delicate balance in terms of compatibility between any polymer modifier and bitumen. Achieving this balance depends not only on the accurate selection of grade and chemical composition of base bitumen and polymer modifier but also in the processing conditions used for the production of the PMB. If the correct chemical balance is not accurately achieved, the performance of the PMB will not only be impaired but could actually be inferior to that of an unmodified bitumen. Bitumen can be processed from a variety of different crude oils and its broad chemical composition can be determined by analytical techniques such as thin layer chromatography (Iatroscan). The four main components are referred to as saturates, aromatics, resins A and resins B. The relative ratios of these components have a major influence on the way a polymer is solubilised or can swell in the bitumen. Additionally, in a particular bitumen different polymers will behave in different ways. This is illustrated in the following slides.

15 Compatibilidad Betún/Polímero
Sensibilidad del EVA a la composición química del betún - 3 betunes diferentes de penetración aproximada 70 Formulación Penetración a 25°C, Anillo yBola, °C mm/10 Betún 1 68 52 Betún 1 + 5% EVA 48 62.2 Betún 2 69 49 In the table, three 70 penetration grade bitumens were modified with 5% EVA (ethylene vinyl acetate) under standard mixing conditions. EVA is used as a bitumen modifier particularly to improve deformation resistance. Bitumen 1, when modified, showed a decrease in penetration and significant increase in softening point. When bitumen 2 was modified, however, there was no indication that the bitumen’s properties were significantly changed and the influence of the EVA is “lost”. With bitumen 3, the EVA appeared to have a detrimental effect in that the penetration increased whilst the softening point was virtually unchanged. These effects were attributed to the different chemistries of the three bitumens, which increased in aromatics and decreased in resins B contents from bitumen 1 to 3. Without extensive knowledge of the effect of the bitumen chemistry it would not be possible to predict the type of modification that would occur. Betún 2 + 5% EVA 67 51.8 Betún 3 72 48 Betún 3 + 5% EVA 79 49.2

16 Compatibilidad Betún/Polímero
Sensibilidad del SBS a la composición química del betún - 2 tipos de SBS en 2 tipos de betún 60/70 Estabilidad al almac., 3 días Penetración Anillo y Ductilidad a Formulación at 180°C a 25°C, Bola 25°C, cm Pen AyB mm/10 °C mm/10 °C Betún A 58 51.2 86 1 0.8 SBS X Betún B 46 70.0 17 9 0.2 SBS X Betún A Two types of SBS with differing microstructures were used to modify two bitumens with different chemical compositions. Results using a proprietary additive were also included to illustrate how modification levels can be enhanced further by PMB producers. SBS is typically used to improve the elastic and deformation resistance properties of asphalt. When SBS “X” was added to the two, different 60/70 grade bitumens there were obvious differences in the degrees of modification. The Bitumen A formulation showed less decrease in penetration, increase in softening point but had good stability (low polymer separation) as determined in a storage test. The Bitumen B formulation appeared to be more modified in terms of penetration and softening point but had a considerably lower ductility and a tendency to separate in storage. When the Bitumen A formulation was modified using an additive system, the softening point and ductility of the resulting PMB was increased compared to the additive free PMB. With SBS “Y” both Bitumen A and B formulations had similar penetration values but there was still a difference in the level of softening point increase. Also, the separation of SBS ”Y” during storage was more severe with Bitumen B. 57 59.2 >100 0.2 SBS X + aditivo Betún A 43 56.2 98 2 1 SBS Y Betúnn B SBS Y 45 72.6 17 123 15

17 Aplicaciones de los Betunes Modificados
Tratamientos superficiales Mejor retención de áridos particularmente en puntos sometidos a fuertes esfuerzos. Reducción de exudaciones. Mejor control de fisuración. Betún sin modificar BM

18 Aplicaciones de los Betunes Modificados
Mezclas Densas Mejor resistencia a la deformación. Mejor resistencia a la fatiga. Mejor control de la fisuración a bajas temperaturas. Capas Delgadas Mayor retención de áridos. Mejor adhesividad entre capas.

19 Aplicaciones de los betunes modificados
Asfalto drenante/mezclas abiertas Disminuye la pérdida de betún durante la fabricación el transporte y extendido de asfalto BM Betún sin modificar Betún retenido (%) Trials have shown that the durability of Porous Asphalts is directly related to the thickness of the binder film coating the aggregate - a thicker film provides a more durable asphalt because embrittlement of the binder, due to oxidation, is delayed. With unmodified bitumens, it is difficult to increase the binder content of Porous sphalts, and thereby increase the binder film thickness, without drainage of the binder occurring from the hot asphalt during mixing, transportation and laying. Although a higher viscosity (harder) binder may be used to partially overcome this problem, the resulting harder binder in the asphalt on the road is then closer to a brittle state, which reduces the life of the asphalt. Because they can have higher viscosities and different flow characteristics at asphalt mixing temperatures, PMBs allow the use of higher binder contents and hence thicker films without the problem of binder drainage. Combining this with a lower stiffness than unmodified bitumens at pavement service temperatures provides a more durable surfacing than could be obtained with an unmodified bitumen. Ligante en mezcla (%)) Película de ligante más gruesa -> incremento de durabilidad. Mejora de la adhesividad -> Retención de los áridos

20 Betunes Modificados de Alto Rendimiento
BP Olexobit Betunes Modificados de Alto Rendimiento PMBs can offer significant performance advantages over conventional unmodified bitumens. BP has a strong core PMB technology which supports a range of high performance binders for all types of road applications.