Modified Asphalt By Coffee Cup Fibres: An Optimum Mix Design Using Response Surface Method

Stone Mastic Asphalt uses fibres to stabilise high binder contents. The fibres are typically made from natural cellulose, and prevent binder draindown. This study investigates the use of post-consumer coffee cups (liquid paperboard) as a recycled fibre alternative. Coffee cups (CC) use laminated polyethylene as a liquid barrier, making them challenging to recycle in existing paper and plastic recycling systems; approximately one billion coffee cups are landfilled annually in Australia. In this research, coffee cup fibres are used up to 0.6% by total weight of the asphalt mixture across fourteen mix designs. The mixes are optimised by the response surface methodology using the Design-Expert software. Models are created based on Marshall and draindown test results. This study finds that shredded coffee cups effectively reduce the draindown, reduce flow of the asphalt mixture, increase stability, and increase the air voids. The LDPE content slightly increased the viscosity and the softening point of the asphalt binder and dropped its penetration value. Overall, the asphalt mixture containing 0.4% coffee cups (by total weight of the mixture) met all specifications in Australian Standards and performed similarly to the commercial cellulose fibre. This paper also provides practical insights from field trials conducted in Western Sydney using the optimised parameters identified. The pavements will continue to be monitored to develop long term performance comparison between CC and traditional fibres in SMA applications.