Presentación del tema: "Los Betunes Modificados y sus aplicaciones en las capas de rodadura de convencionales y de tipo SMA (Stone Mastic Asphalt) This presentation will cover."— Transcripción de la presentación:
1 Los Betunes Modificados y sus aplicaciones en las capas de rodadura de convencionales y de tipo SMA (Stone Mastic Asphalt)This presentation will cover the role of PMBs used in asphalt surfacing applications with particular emphasis on Stone Mastic Asphalt (SMA). However, PMB usage in the the most common wearing course material, asphaltic concrete (AC) will also be covered in some detail.With increasing traffic volumes and loading, together with more congestion and high summer temperatures, the demands placed on the road layers, in particular the wearing, or surface, course, are increasing. Road users increasingly want less traffic delays caused by roadworks and thus, more durable highways.All sides of the road industry have been involved in the development of a new generation of surfacing materials which will meet the performance requirements expected. BP Bitumen has been actively involved in this process, developing new speciality binders to perform in these surfacing materials.
2 Requirimientos Resistencia a las roderas Resistencia a la fatiga Resistencia a la fisuraciónDurabilidadFlexibilidadFacilidad de fabricación y extendidoRentabilidad coste/beneficioAssuming the lower layers of the road pavement are sound and provides sufficient structural strength, then the surface course provides the surface characteristics which allow for safety and ride comfort.Therefore, the surface course should be fatigue resistant, rut resistant, crack resistant, provide adequate texture and skidding resistance, resist ravelling and provide for an even ride. These desirable performance characteristics could be viewed as being in conflict with each other. The road engineer must often balance these properties and arrive at a cost-effective compromise solution, suited to the particular site requirements.In addition, it is desirable that the surfacing can be either re-laid (recycled) or overlaid once maintenance becomes necessary.
3 Mezclas de rodadura convencionales Uso extendido en todo el mundoAceptables en la mayor parte de las situacionesGranulometría continua de áridosDiversos tipos de mezclas (de densas a abiertas)Mezclas establesDiseñadas de acuerdo al ensayo Marshall (normalmente)By far the most common material used as a surface course In the world is asphaltic concrete (AC). For virtually all low volume roads, AC has been used in many recipe type mixes. The aggregate gradings are such that the mixture can vary from dense to medium to open. Even in higher volume roads, recipe type mixtures have been common, although it is more usual to design the mixture to optimise the binder content to give certain desirable performance properties.Generally, an AC mixture relies on the aggregate interlock to provide performance requirements. Mixes may be designed; the most common is the Marshall design method, where the properties of Mix density, compacted aggregate density, Stability (60°C) and flow are optimised. However, new design procedures are being specified, particularly in the United States, where the SUPERPAVE design system has recently been introduced.
4 Comportamiento de las mezclas densas Fisuración a bajas temperaturasFisuración por fatigaRoderasRuttingMezcla/extendidoTo understand the performance requirements of surface mixtures, one needs to consider the mixture at different in-service temperatures. Asphaltic (bitumen bound) mixtures are very susceptible to temperature, yet the material is expected to perform over the whole range of expected temperatures.At high in-service temperatures the material must be rut resistantAt mid in-service temperatures the material must be fatigue resistantAt low in-service temperatures the material must be crack resistant/thermal resistantThe degree to which a material will perform will primarily depend upon the mix gradation and the binder used.
5 Papel del ligante Contenido de ligante Tipo de ligante Adhesividad del liganteViscosidad del liganteElasticidad del liganteEstabilidad del liganteTODOS estos factores contribuyen al comportamiento de la mezclaThe binder used in surfacing mixtures, both the type and the amount, plays a crucial role in the overall performance of the mix.The contribution of the binder is effectively seen in its ability to:resist flow,resist fatigue,adhere, and remain adhered, to the aggregateaccommodate thermally and traffic induced strainsresist cracking at low temperaturesmaintain its properties over time.There are many tests which can be carried out to measure the binder properties ranging from empirically-based tests through to fundamentally-based tests and specifications either exist, or performance tests are being developed, which it is hoped will predict the likely asphalt performance from such tests.
6 Comportamiento del ligante (1) Mayor punto de reblandecimiento y menor punto de Fraass=Mayor rango de plasticidad (rango de eficacia del betún)One such performance measure, empirically-based, is a so-called flexible (or working) range of the binder - defined as the difference in temperature between the Fraass Breaking Point (low temperature) and the Ring and Ball Softening Point (high temperature). The larger the temperature difference, the better the performance range of the binder. The most effective way of increasing this working range of the binder is to modify the bitumen with polymer.More recently, in terms of fundamental measurements, the range can be alternatively defined as the temperature difference between the temperature at which the binder has a stiffness of 1kPa (fresh binder) and a stiffness of 300MPa after an accelerated ageing test.
7 Comportamiento del ligante (1) Rango de plasticidadThis effect can be seen in the Figure, where the addition of a polymer to the bitumen has increased the working range of the binder at both the low temperature and the high temperature end. Some PMBs will dramatically improve the ‘working’ range of a binder. There are limits though and they can be reduced to two:costnot having to unduly alter normal mixing and laying temperature practices.-20°CBM´sBetún convencional
8 Comportamiento del ligante (2) Viscosidad vs Temperatura1.00E+091.00E+081.00E+071.00E+06Betún modificadoViscosidad (Pa.s)As already stated, bituminous binders are very temperature susceptible (and shear susceptible). A binder’s viscosity can change from near fluid to near solid over a relatively narrow (100°C) temperature range. The use of polymers can greatly alter both the temperature and shear susceptibility of the binders.In performance terms, this means the binder is stiffer (more viscous) at higher temperatures (where rut resistance is important) and more flexible (less viscous) at lower temperatures (where crack resistance is important)The benefits of this are evident in high and low temperature service conditions. BUT, care needs to be exercised to ensure the binder is fluid enough at mixing temperatures to be able to coat the aggregates and to be compacted!!1.00E+051.00E+04Betún Convencional1.00E+031.00E+02-10102030405060Temperatura (°C)
9 El Problema Volumen de tráfico creciente Tráfico estacionario y en movimiento lentoIncremento de las cargas por ejeMayores expectativasBúsqueda de vida útil más largaiiiNecesitamos productos mejores!!!For the majority of the highway network, normal AC mixes have performed, and are performing, well in most situations (lightly trafficked and rural roads). However, for the strategic road network, which often carries a disproportionate amount of heavy traffic (both load and volume), there is an increasing demand for better and more durable roads. The introduction of the new ‘super-single’ tyres with their increased contact pressure has increased the damaging factor on the road layer.The reasons are fairly obvious:increasing traffic inevitably leads to congestion. Result is slower traffic, which equates to an increased loading time. At high road temperatures this increases the potential for rutting. Road works and contraflow situations exacerbate these effects.Using stiffer binders helps reduce the rutting potential, but often at the expense of lower temperature performance (i.e. the working range of the binder is effectively shifted in favour of the high temperature performance).It is for these reasons that there is an increased use of PMB - but we can also consider whether, in addition, we can determine change the type of mixture.
10 Historia de las SMA (1)Desde los años 60 – para reducir el desgaste originado por los neumáticos con clavosCaracterísticas:Alta cohesión de áridos formando un másticoAlto contenido en Filler y liganteAditivos estabilizantes para evitar la segregaciónThe question might reasonably be asked whether there is an acceptable alternative to AC.It was common in Germany in the 1960s (and earlier) for vehicles to be fitted with studded (spiked) tyres to maintain contact with the road surface during the winter months. The normal surfacing was AC and it was common that wear in the wheel-tracks was fairly excessive because of the high abrasive action of the studded tyres. Various in-fill materials were tried to reduce this wear and materials were initially developed to inlay the ruts caused by the tyre abrasion.It was found that highly stable, high mortar mixes were the best which resisted subsequent winter trafficking. The best materials were effectively a stone filled mastic and proprietary products (e.g. Mastimac) were found to be very successful.Eventually, the material became the subject of a National Specification and today is known as Splitt Mastic Asphalt (Splitt means gap-graded), or Stone Mastic Asphalt (SMA)
11 Alto grado de áridos de calidad Alto contenido en ligante Historia de las SMA (2)SMAAlto grado de áridos de calidadBetúnBMAlto contenido en liganteEstabilizadorThe success of SMA mixtures lies in the combination of the components used. High quality aggregates are used and the aggregate grading is such that a high coarse gap-graded skeleton is produced which results in a strong stone-on-stone contact. This skeleton is then filled with a mastic, comprising a high percentage of both filler and binder, which provides for a very dense low voids content mixture.The resultant mixture is very rut-resistant, from its stone skeleton, and very durable, from its low voids, high mortar volume.Stabilising additives (fibres) are often used to maximise the binder to be ‘carried’ in the mixture without associated draindown, although some PMB binders negate the use of these fibres.
12 Diseño de SMA (1) Fundamentalmente un solo tamaño (0/11, 0/8, 0/5) Contenido en huecos 3-5%Contenido en Filler (~9.0%)Contenido de ligante ( , , )Various grades of SMA have been incorporated and standardised into the German ZTV Asphalt specifications.In Germany, over 100 million sq.metres have been laid and in several states is the preferred wearing course material. SMA mixtures are also becoming more popular in other parts of the world, including Western Europe and the USA.The coarse aggregate size is related to the laid thickness and the high binder/filler is for durability. Crushed rock fines (CRF) are typically used as the fine aggregate.
13 Diseño de SMA (2) Árido grueso Finos de machaqueo Filler Ligante 100% Air380%71Árido grueso6260%The mixture may be shown schematically as shown in the chart. In volume terms, the mortar, comprising the CRF, filler and binder accounts for about 35% of the total volumeFinos de machaqueo40%1113Filler20%8.3Ligante15.70%Por pesoPor volumen
14 Mezclas convencionales y SMA (esquema) MCSMAViewing the schematic figure, the essential differences between AC and SMA can be easily seen. The SMA is differentiated by its gap-graded nature.
15 MC SMA M. convencionales y SMA (Curvas granulométricas) % Pasa 100% 0% 0.075mm11mmTamaño del tamiz% PasaMCSMAThese grading differences can be seen clearly on the respective aggregate grading charts.
16 Comportamiento de las mezclas SMA (1) Resistencia a roderas: <1.0mm/hrResistencia a la fatiga: muy buenaRigidez (ITS): hasta 5 GPaDurabilidad: >15 añosResistencia aldesgaste/impacto: muy buenaResistencia al deslizam.: buenaEmisión acústica: 2-3 dB(A) menos que MCContribución estructural: buenaThe nature of SMA is that it provides for an excellent in-service performance. Various mixture tests can be carried out to verify the performance properties and typical results are shown in the ‘Performance’ tables
17 Comportamiento de las mezclas SMA (2) Con Betunes Modificados:Mejor resistencia a fisuraciónMejor comportamiento a bajas temperaturasIncremento de la resistencia a las roderasMejor flexibilidadMejores adhesividad y cohesiónBuen comportamiento frente al envejecimientoThe benefits to be gained from the use of pre-blended PMBs are given in the Table.
18 Aplicaciones de las mezclas SMA Amplio rango de grosores (20mm - 70mm)Puede usarse para regularización superficialZonas sometidas a altos esfuerzosCarreteras de tráfico elevadoCarreteras de nueva construcción y mantenimientoPuede usarse sobre hormigónTableros de puentesGiven that SMA is a premier material, it has application in a number of areas. It can be laid in a range of thickness, dependent on nominal aggregate size, and may be used as in the surface course or the binder course.It can also be used as a regulating material, although it is quite a difficult mixture to hand-lay. It is particularly suited to heavily-trafficked and high stress sites and there has even been experience of it being used as a bridge decking material.It can be used as an overlay over both existing bituminous or concrete roads and in new construction or maintenance contracts.
19 Fabricación y Compactación de SMA (1) Tiempo de mezcla ligeramente superior (aprox. 30 segundos)Mezclado a °C; Compactación a 140°CPlantas convencionalesAt the mixing stage, generally higher temperatures are needed, particularly when stabilising additives are used, although the temperatures are not excessively high. Where fibres are used, a slightly longer mixing time is required to ensure adequate dispersion of fibres and satisfactory coating of the aggregates by the binder.Mixing and compaction temperatures are generally on the high side (but not extreme) and the material is laid using conventional plant machinery. Steel rollers are usually specified and it should not be necessary to use vibration.In common with all bituminous materials, good construction practice must prevail if the surfacing is to perform over its intended design life.
20 Fabricación y Compactación de SMA (2) Si se usan Betunes Modificados:No existe segregación durante todo el procesoNo hay escurrimiento del ligante (mezcla homogénea)No hay necesidad de usar fibrasNo hay costes añadidos de elaboraciónAs stated earlier, a new generation of PMBs has allowed for the possibility of designing SMA mixtures without the necessity for using stabilising additives. Of course, one could use both PMBs and fibres to give a very stable and durable mix. However, cost considerations and availability will determine the choices.It is important that the PMB is a homogeneous blend and has the characteristics necessary to prevent draindown even at a relatively high binder volume.
21 Ejemplos de aplicación de SMA Alemania (uso extendido y multitud de ensayos)SueciaAustralia (Ensayos generales)Polonia (tableros de puentes)Reino Unido (ensayos de comportamiento)Turquía (ensayos)España (aplicaciones esporádicas y ensayos)SMA has either been trialled, or is used, quite extensively under a range of different conditions. The overall assessment of the material is highly favourable and it is likely to remain one of the premier bituminous materials for a long time to come.BP Bitumen has been actively involved in both supplying binder for, and designing, SMA mixtures. BP Bitumen has a wealth of experience in a number of countries having different climatic conditions.
22 CONCLUSIONES Rendimiento comprobado Años de experiencia Creciente interés internacionalUso de la tecnología de Betunes Modificados(Apoyo técnico de BP Bitumen)It is likely SMA materials will gain an increasing share of the market, particularly in surface courses and thin layers, because of documented proven performance.BP will continue to be active in SMA technology both in providing binders of proven performance and in offering specific designs to new and/or existing customers.
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