The use of crumb rubber modified bitumen in the Australia road network

Description

The use of crumb rubber modified bitumen in the Australia road network

Trevor Distin, John Esnouf

ABSTRACT: The modification of bitumen with rubber particles extracted from used vehicle tyres has been used extensively in spray sealing by some of the State Road Authorities in Australia since the early 1970’s. The early practices started with and continue to do so in Victoria by blending rubber (generally 5 – 18% by mass of binder) into the bitumen in the field, in existing bitumen sprayers. Some higher percentages were used on occasions but these were not suited to blending in the relatively simple bitumen sprayers of the time.

In the 1990’s the industry developed plant based blending which allowed preblended crumb rubber binder (>13% by mass of binder) to be transported to work sites over longer distances and sprayed successfully.

Crumb rubber in asphalt has been used in specialist asphalt mixes via a dry mixing process incorporating in the range of 2 – 3% crumb rubber by mass of the mix. These mixes are generally used to withstand high crack reflections in pavements over expansive clays and/or weak subgrades.

This paper will share the latest best practices employed to field blend recycled tyre rubber into bitumen for spray sealing using conventional spray equipment.

The modification of bitumen incorporating crumb rubber provides construction and performance benefits when compared to using unmodified bitumen in spray sealing and compares favourably with the performance improvements achieved using synthetic polymers. This has resulted in some States using crumb rubber modified bitumen as the preferred binder in sprayed seals on cracked surfaces, high stressed seals and stress inter layer membranes.

In asphalt applications there have been some concerns with fumes and odours effecting workers and neighbours of asphalt plants. To overcome this the recent focus has been on reducing the mixing and paving temperatures using warm mix technologies and additives.

There is currently considerable effort being placed on developing crumbed rubber modified binders that improves the performance properties of the bitumen used in asphalt mixes and that can be used in lieu of synthetic polymers.

Investigations into its use in open graded asphalt and semi gap graded mixes (as is the case in California and Arizona) are currently being undertaken.

The use of crumbed rubber modified bitumen in asphalts is anticipated to achieve longer lasting asphalt surfaces that require less maintenance during their service life.

In Australia there is keen support for the continued development of crumb rubber bitumen technology as a sustainable practice for both spray sealing and asphalt mixes to improve long term pavement performance, and ensure that worker health and safety is not compromised.

This should result in a win for sustainability, the environment, worker health and safety, whilst at the same time delivering higher performing and longer lasting pavement surfaces for road agencies and the travelling public.

KEYWORDS: crumb rubber binder field blending, crumb rubber binder spray sealing, dry rubber asphalt mixing, warm mix rubber asphalt.