Browsing by Author "White, G"

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item: Conference-Full-text
Challenges for the compaction and proving of granular fills and layers in airport pavements
(Springer, 2021) White, G; Anstee, H; Pasindu, HR; Bandara, S; Mampearachchi, WK; Fwa, TF
The compaction and proving of granular materials during construction is fundamentally import to airport pavement design practice. This is particularly so in countries that make significant use of granular base courses with relatively thin asphalt surfaces, such as Australia. The compaction of dredged sand fills, up to 1500 mm deep is also important where airport pavements are constructed over low bearing capacity marine clays, primarily in areas of reclaimed land. The large 180 tonne Supercompactor for compacting sand fills is no longer available in Australia and the 50 tonne Macro rollers for proving granular pavement layers were downgraded from 1400 to 1000 kPa tyre pressure. Meanwhile, large commercial aircraft have ever-increasing tyre pressures and wheel loads. This has created a challenge in the form of a gap between roller capability and aircraft demand. The gap is relatively minor for the compaction of deep sand fills, but the inability to theoretically compare the effect of static rollers with that of vibrating and impact rollers makes this difficult to quantify. The alternate is an expensive field trial to demonstrate acceptable sand density at depths to 1500 mm. In contrast, a significant gap exists for the proving of fine crushed rock layers used in upper base courses under thin (60–100 mm) asphalt surfaces. This challenge requires rollers with higher tyre pressure or significantly thicker asphalt surface courses to be adopted, both of which are expensive.
item: Conference-Full-text
The volumetric challenge of crumbed rubber modified asphalt mixtures
(Springer, 2021) White, G; Kidd, A; Pasindu, HR; Bandara, S; Mampearachchi, WK; Fwa, TF
Significant research has demonstrated the potential benefits associated with crumb rubber modification of bituminous binders for asphalt road surface production. Most of this previous research has focused on higher (20–30%) dosages of crumbed rubber and there is now an increased interest in lower (5–15%) dosages for improved binder and asphalt ageing to extend the time between periodic local road surfacing. For Marshall designed asphalt mixtures, the volumetric composition of the mixture is important and isolating the effect of the crumb rubber modification from the effect of an increased modified binder content is critical to understanding the economic viability of low dosage crumb rubber as an anti-ageing additive. Testing of a typical 10 mm dense graded asphalt mixture showed that the rubber is partially dissolved into the bitumen and both complete dissolution (100%) or no dissolution (0%) based calculations have a significant effect on Marshall volumetric properties such as binder film thickness, air voids and voids in the aggregate. Further work is required to determine a reliable method for determining the degree of crumb rubber dissolution on a case-by-case basis.