Professor, School of Civil Engineering, Universiti Sains Malaysia, Malaysia

Speech Title: Superiority of the Two-Layer Porous Asphalt Mixtures to Resist Clogging Based on Laboratory Permeability Studies
Abstract: Porous asphalt is an open material used for highway surfacing. In the developed world, it is popularly used to mitigate traffic noise. Its aggregate gradation comprises largely of coarse aggregate, giving rise to an open material with continuous air voids that permits passage of water. Apart from its noise reduction potential, porous asphalt road surfacing can largely eliminates splash and spray, aquaplaning potential, glare and offers good riding quality. However, the service life of porous asphalt is limited due to clogging. Clogging disrupts air voids continuity. When the material becomes clogged, it looses all of its benefits associated with a porous mixture. Typical clogging agents includes any fine particles such as mud, debris, detritus, clays, fine sands and rubber particles. In the field, porous asphalt is cleansed twice annually by water spraying and vacuuming. The severity of clogging is measured in terms of the discharge time or hydraulic conductivity measured using a falling head permeameter. This paper describes a laboratory method developed at the Universiti Sains Malaysia to simulate the resistance to clogging of single layer and two-layer porous asphalt. It began by preparing a clogging agent made up of a known concentration of fine-grained soils that were used to progressively clogged the porous materials until the terminal permeability (equivalent to a discharge time 240 s ) was attained, beyond which specimen was flushed or cleansed and then vacuumed to simulate the cleansing method used in the field. The procedure was then repeated for several cycles on mixtures prepared at various binder contents, layer thickness and tested at different temperatures. The clogging and cleansing patterns enables researcher to quantify mixture susceptibility to clogging and to formulate a clog-recovery index. The results proved the superiority of the two-layer porous asphalt mixture to resist clogging compared to the single layer porous asphalt. It was also found that mixtures prepared at higher binder contents and conditioned at higher temperatures are more susceptible to clogging.