Air Void Characterisation in Porous Asphalt Using X-Ray Computed Tomography

Abstract

This study presents the characterisation of the air voids distribution for porous asphalt mixtures compacted using gyratory compactor. The distribution of voids content and voids shape within the porous asphalt were characterised for different nominal maximum aggregate size (NMAS) and specimen height. This is to evaluate the effect of different aggregate size composition and lift thickness on the air voids characteristics of the compacted porous asphalt. Two types of gradations were adopted i.e. Grading A (with NMAS=10 mm) and Grading B (with NMAS=14 mm) and they were fabricated for two different heights (50 and 100 mm). The internal structure was captured using X-ray Computed Tomography and image analysis techniques were used to process and analyse the images. It was found that mixture with coarse aggregate gradation produced larger void size with an elongated shape, which indicates voids connectivity within the mixture compared to fine gradation with more circular and smaller void size.For lift thickness, itacts differentlyfor different aggregate gradations. The specimen produced greater voids connectivity when the fine and coarse gradations were compacted at 100 mm and 50 mm respectively. These show that NMAS and lift thickness influence the mobility of the aggregate particles during compaction which affect the voids formation and determine the effectiveness of the compaction.