ABSTRACT
The durability of porous asphalt is affected by clogging, over-compaction and rapid aging of the binder. The open nature of the mix significantly exposes the surface of binder to the atmosphere. This caused bitumen to undergo weathering, which leads to embrittlement and eventually disintegrate with age. The durability of porous asphalt wearing course is adversely affected mainly due to raveling. Raveling or loss of aggregate from the wearing course layer is a form of fatigue that occurs in the top layer of the pavement structure (Khedoe et al. 2006). In temperate countries, serious raveling problem will be occurred during the cold season. Aging of bitumen is one of the factors that contribute to the reduction of adhesion and cohesion property, and raveling of porous asphalt (Whiteoak et al. 2003, Nielsen 2007, Mo et al. 2009). When the asphalt binder aged to a certain extent, the mixture began to deteriorate and failed rapidly during cool weather. Sometimes the entire pavement layers will ravel in a few weeks (Huber 2000). Commonly, Cantabro test was used as a gauge to evaluate the durability of porous asphalt and as a control parameter to determine the design binder content
1 INTRODUCTION
Asphalt generally consists of aggregate bound together with asphalt binder, where the aggregate can constitute between 60 to 90% or more of the mixture’s volume. Asphalt binder is a visco-elastic material which deforms and flows at high temperature but becomes brittle at low temperature. Porous asphalt is a type of open mix with more than 75% coarse aggregate, resulting in high air voids and air voids continuity. The mix is widely used in developed nations due to its ability to mitigate traffic noise. Hamzah et al. (2010) stated that the good sound reduction potential has led to the application of porous asphalt on the expressway passing close to residential areas. Huber (2000) reported that the application of porous asphalt could reduce the noise level by approximately 3 dB(A) for passenger cars travelling at 80 km/hr compared to the corresponding noise level from a reference dense asphalt wearing course. Bendtsen (1996) indicated that the noise level measurements achieved reductions of up to 6 dB(A) with the two-layer porous asphalt surfacing. Newcomb & Scofield (2004) stated that porous asphalt is 2.5 to 4.5 times more effective when comparing the noise
of porous asphalt mix. Nowadays, most agencies in Japan proposed this test as a compulsory (Asshi & Kawamura 2003, AAPA 2004) or as an optional (FAA 2005) in porous asphalt mix design. Australia, South Africa and some European countries used the Cantabro test to design porous asphalt mixtures (Alvarez et al. 2006). While, Poulikakos et al. (2004) reported that the test is commonly used in Japan to evaluate particle loss resistance of porous asphalt under winter conditions.
