Modified asphalt by coffee cup Fibres: An optimum mix design using response surface method

Abstract

Asphalt mixtures with high binder content, such as Stone Mastic Asphalt (SMA), have difficulties retaining the binder in the mix. To prevent the draindown of the binder, natural cellulose fibres (made from wood) are usually added to these asphalt mixes. This study investigates the suitability of recycled coffee cups as an alternative source of natural cellulose fibres. Around 16 billion coffee cups are used worldwide every year, leading to the logging of approximately 6.5 million trees. Since coffee cups are hard to recycle due to the inner side of the cups being lined with plastic, around one billion coffee cups are landfilled annually in Australia. In this research, coffee cups of up to 0.6% of the total weight of the asphalt mixture are used in fourteen different 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. It has been found that shredded coffee cups effectively reduce the draindown and the flow of the asphalt mixture and increase the stability and the air voids. The optimum amount of shredded coffee cups are measured to be 0.4% by the total weight of the mixture. Also, the plastic liners in the coffee cups slightly increased the viscosity and the softening point of the asphalt binder and dropped its penetration value. Overall, the asphalt mixture containing 4% coffee cups (by total weight of the mixture) met all specifications in Australian Standards and performed similarly to the commercial cellulose fibre.