Mohd Zul Hanif Mahmud

Air void characterisation in porous asphalt using x-ray computed tomography

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.

Use of Imaging Techniques for Viewing the Internal Structure of Rubberised Asphalt Mixtures

This paper presents the application of different imaging techniques for viewing the internal structure of rubberized asphalt mixture as road materials. Two imaging techniques were used to capture the internal structure images of its compacted samples i.e. X-ray Computed Tomography (non-destructive method) and Scanning Electron Microscope, SEM (destructive method). Since a lot of previous researchers have produced extensive works on the mechanical properties, therefore, this study is an attempt to introduce the microstructure of rubberized asphalt mixtures produced using dry process method. Two types of dry mixed rubberized asphalt mixture were prepared by modifying a Hot Rolled Asphalt Mixture (HRA 60/20) with different crumb rubber sizes. A mixture of conventional HRA 60/20 was also scanned for comparison. The illustrations are aimed to provide the researchers more information regarding their internal structure distribution.Keywords: Imaging techniques, X-ray Computed Tomography, Scanning Electron Microscope, Rubberised Asphalt Mixture

Influence of diatomite filler on rheological properties of porous asphalt mastic

ABSTRACT Mineral filler is usually added into asphalt mixture to stiffen the asphalt binder and improve mixture strength. This is particularly important for open gradations such as porous asphalt which is known to have poor strength and durability because of its open nature and large air voids. The interactions that occur between asphalt binder and filler results in certain mastic properties that affect the mixture strength. In this study, the effect of different types of filler on the rheological properties of asphalt–filler mastics for porous asphalt were evaluated using the frequency sweep and multiple stress creep recovery (MSCR) tests. Hydrated lime, cement and diatomite with 2% content were selected to produce asphalt–filler mastic. The influence of diatomite filler was investigated and compared to the hydrated lime and cement fillers. Results indicated that the use of filler increased the stiffness of mastics. The MSCR test showed that hydrated lime and diatomite mastics exhibited the lowest non-recoverable compliance and high recovery than the original PG 76 binder and cement mastic. Diatomite mastic exhibits the best resistance to rutting at high temperatures and stress levels, verifying that the use of diatomite filler is favourable because of its high temperature properties.