2 ASFALTO DRENANTE ASFALTO DRENANTE QUÉ ES Y CÓMO FUNCIONA DrenajeCapa de baseCapa intermedia(Impermeable)ASFALTO DRENANTEQUÉ ES Y CÓMO FUNCIONAPorous Asphalt is a development from the airfield friction course material, which has been used for many years to counteract aqua-planing. The UK began trialling porous asphalts in the late 1970s and in 1984, the first national trials were laid in Staffordshire. The pereived benefits were originally seen as reduction in spray and thus, road safety to the use. The trials utilised a design method which ensured the material had interconnecting voids (20-25 per cent) and optimised the binder content to maximise durability without causing binder drainage.The principle of operation is quite simple: rainwater passes through the porous surfacing (normally, 50mm thick) to the impermeable layer beneath and flows outwards to the edge of the carriageway. Designs can use a number of different aggregate sizes; typically, in the UK it is a 20mm grading; elsewhere in Europe there use 10 or 14mm aggregates. Specifications have been introduced in a number of countries. Whilst the surafcing was originally developed as a spray-reducing surface, its major benefit today is seen more in noise reduction. Its primary use is in urban situations, where noise is regarded as an environmental issue.The introduction of PMBs has greatly improved the overall performance (durability) of porous asphalts, as they allow a greater binder content to be held within the mixture. Its life is determined by the ability of the surfacing to resist fretting (ravelling); life is typically about 10 years. The voids also close up over time, reducing its capacity for spray reduction but it still maintains some of its noise reducing qualities.
3 ASFALTO DRENANTE Curva típica de escurrimiento de ligante Ligante en mezcla(%)Ligante retenido (%)Curva típica de escurrimiento de liganteLínea de igualdadBetúnModif.ConvencionalPorous asphalt mixtures rely on a heavily gap-graded aggregate grading, which is bound with filler and bitumen. The coarse aggregate content is high to ensure aggregate interlock in the compacted material; as a result, these materials are extremely rut resistant. However, there is a tendency for the binder to drain off the aggregates during the mixing and transporting operations. Therefore, it is necessary to optimise the binder for the chosen aggrgate and its grading.The binder drainage test was developed to optimise the binder content and basically involves increasing the binder content until binder drainage is observed. The mixed test samples (in perforated baskets) are held for 3 hours at the nominal mixing temperature and any binder (and filler) drained off the mixture determined. the point at which draindown occurs is used in the calculations to determine the design binder content.In a typical UK porous asphalt using a 20mm aggregate, the mixture can only hold about 3.8 per cent using unmodified binders; if PMBs are used the binder contents can be nearer to 5.0 per cent. The UK specification recommends either PMBs or fibres (also capable of increasing the overall binder content) should be used for heavily trafficked applications.
4 ASFALTO POROSO REQUERIMIENTOS DE LA MEZCLA Una matriz de áridos estable que resista compactación adicional una vez extendida.Alto contenido en huecos, interconectados para proporcionar canales de drenaje y reducción acústica.Un recubrimiento importante de ligante en el árido, para reducir la susceptibilidad al que implica fragilidad.The net result is a mixture which, when laid and compacted, resists further compaction (sometimes known as secondary compaction) when in-service. The aggregate grading is such that, once laid, there are at least 20 per cent of interconnecting voids. These voids provide the drainage channels for the removal of surface water and, additionally, absorb the generation of noise. Porous asphalt surfaces are approximately 2-5dBA quieter than conventional surface courses, which equates (roughly) to a halving of the traffic volume. This reduces the requirement for noise barriers and costly double-glazing schemes.Recommendations are avialable concerning where porous asphalt can (and cannot) be laid. Generally, in high stress locations, porous asphalt should not be laid because of the likelihood of shearing stresses. BP Bitumen is the largest supplier of PMBs for porous asphalt applications, including the M4, M5, M40 and M25.The thicker film of binder which can be achieved through using a PMB reduces the susceptibility to premature ageing and incresaes durability. The failure criterion for porous materials is determined by the rate of binder ageing and its ability to withstand the strains induced by traffic and/or tempearture. Once the binder cannot accommodate these traffic-induced strains, ravelling of the surface aggregate occurs leading to eventual failure.
5 ASFALTO POROSO VENTAJAS DE LOS BETUNES MODIFICADOS Mejoran la durabilidadAumentan la cohesión de la mezcla, reduciendo las pérdidas de materialIncrementan el grosor de la película de liganteIncrementan la resistencia a rotura frágilThe advantage of using PMBs in porous asphalt is principally one of improving the durability of the material. This is achieved through achieving a thicker binder film, a more elastic binder to accommodate traffic-induced strains, a more adhesive binder to resist the likelihood of ravelling and a more flexible binder to improve the low temperature properties (reduction in cracking susceptibility). This has greatly aided porous materials being considered as viable new construction and maintenance options.Further, there are many developments within Europe within the porous market; for example, making them thinner, or with an even higher voids content (up to 30 per cent). These newer developments have only been made more attractive by using PMB technology. These innovations in design have led to an increasing choice being made available to the highway engineer to select the most appropriate and cost-effective porous application for the site requirements.
6 ASFALTO POROSO VENTAJAS REDUCCIÓN DE RUÍDOS REDUCCIÓN DE SALPICADURAS ELEVADA MACROTEXTURA, QUE FAVORECE LA ADHERENCIA NEUMÁTICO-PAVIMENTOADECUADO COMPORTAMIENTO MECÁNICOCONDUCCIÓN MÁS SEGURAThe benefits are fairly obvious to the road user, particularly in terms of noise, spray and glare reduction. Further safety characteristics such as texture and skidding resistance are provided by voids present at the surface (negative texture) and through the use of high polish-resistant aggregates. The benefits noted by the general public are that porous surfacings are considered to be more environmental, the greatest benefit being the reduction in noise levels.The negative texture results in the surfacing offering a better rolling resistance for vehicular traffic. This benefit results in a lower fuel consumption and a corresponding better energy efficiency. All in all, porous asphalts provide for a safer driving environment.Two worthy publications which are available and cover porous asphalt in detail are:Porous Aspalt (PIARC, 1993): ISBN: XEuropean Conference on Porous Asphalt (Madrid, 1997): ISBN:
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