Getting better performance from bituminous materials - from waste to sustainability by Rob Vos

Abstract

From the late 19th century bitumen has moved up the chain from being a waste product to finding ways to expend its performance and durability. Bituminous products from seals, asphalt to microsurfacings and foam stabilised granular material have expanded their scope and the value they provide to the road user. The recent focus on the excess materials included in the waste stream and decreasing their placement in land fill has provided the bituminous product sector to get recognition for the decades of reuse of high value waste. This includes recycled asphalt products which has required upgrades and investment in new equipment and processing routes to extract the value out of the bitumen and the milled aggregates. Crumb rubber has been used in Australia since the 1970’s as a valuable bitumen enhancer both in flexibility, adhesion and durability. The carbon black in the tyres reduces the impact of the sunlight and extends the performance of the binder. The expansion of its use into asphalt further benefits aged concrete pavements which can be cracked in place and overlayed with a Crumb Rubber Modified Gap Graded Asphalt at half the normal thickness for the same performance. Glass can be consumed as a sand replacement in asphalt at 5% in the structural layers and 2.5% in the wearing course. Higher percentages are possible with more careful assessment of the glass properties. Glass is a waste that requires removal, whilst more expensive than the sand it replaces, it preserves the depletion of ever shrinking sources of high value engineering sand. The crushing and reuse of building infrastructure waste and improvement of granular materials through the addition of foamed bitumen is long proven as a sound value and performance addition. Increasing use is being made of locally available equipment to crush and fam stabilise local waste building material in towns and cities. Asset managers can now ensure their contruction waste is turned back into high value local used building material.