Bitumen and Asphalt Products

The results of another study that looked into the effects of modifying bitumen with a range of recycled polymers have been published by Shakhnazarli and co-workers [53]. The waste rubber that was used was SBR, and the other polymers included polyamide fibres and recycled PE. A range of properties were evaluated, including extensibility, softening point and adhesion. 

At the 4th Rubber Modified Asphalt Conference held in Akron, OH, USA in 2009, a wide-ranging paper was presented by Baumgartner [54] that addressed topics such as modified asphalt formulations, optimisation of the process temperature, and the ground tyre rubber loadings and particle size optimisation. The paper showed that rubber crumb produced from whole tyres contains around 30% reactive material for asphalt modification and that the asphalt source and chemistry directly influence the rubber loading and the final properties of the product. The processing time and temperature are also very important, as is the particle size of the crumb, which affects the efficiency of modification and the long-term performance. 

In March 2008 WRAP published the results of a review carried out to investigate the worldwide use of crumb-modified asphalt over the previous 25 years [2]. The work was conducted for WRAP by Scott Wilson and involved a desk study of published information from 1983 to 2008 on the use of rubberised asphalt (RA) worldwide and the results of communications with relevant industrial experts on the practical issues associated with the use of RA in their countries. There are two main processes for using rubber in asphalt (Le., the dry and wet processes) and this review concentrated on the use of the wet process, as this is the method to produce rubberised bitumen. Rubberised bitumen can be used in four different areas of application  

Some of the other salient findings of the review, which tended to focus on the asphalt mixture applications where rubber had been added at levels of at least 15 % by weight, are summarised as follows  

Overall the review s findings suggested that RA enhances the performance of asphalt pavements and that the target level of performance could be delivered if good-quality production control is applied throughout the process of mixing and constructing the RA layer. 

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PAHs, more correctly known as polyaromatic compounds (PACs) are common in the human environment, e.g, the exhaust of diesel engines, bitumen and asphalt production. Some of the PAHs are genotoxic and carcinogenic (e.g benz(a)pyrene). 

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