A novel framework for determining optimum fibre content in high-performance asphalt concrete mixes for low temperature applications

ABSTRACT
The use of fibres in asphalt concrete mixes has become popular for many applications including inhibiting premature distresses in asphalt pavements, enhancing fatigue and rutting resistance, and lowering life cycle costs. Specific to cold temperatures and increasing vehicular loads, thermal failure is a widespread phenomenon that manifests as a series of transverse cracks extending across the pavement surface. Hence, using high-strength fibres (such as steel fibres and elastomeric polymers) to increase tensile strength has become a viable solution. The traditional approach for determining the optimum dosage of any type of fibre for use in asphalt mixes includes trial and error, previous testing literature or tapping into existing agency knowledge and best practice. This study adopts a framework for determining optimum fibre content that employs asphalt volumetrics and performance tests. This framework is represented in an accept-reject criteria-based flow chart to reach the optimum fibre content for use in high performance asphalt concrete (HPAC) applications in cold regions such as Canada. In this study, we add different percentages (0.05%, 0.10%, 0.15%, 0.20% and 0.30%) of one length (6mm) of polyethylene terephthalate (PET) to prepare samples with asphaltenes-modified binders for use as a base course in cold climates. In order to determine which PET percentage gives the optimum result, different criteria are analyzed, including compactibility, dynamic modulus, as well as indirect tensile strength. In this work, the criterion for a sample’s compactibility is considered as a maximum of 6% of air voids for the compacted specimens using 80 gyrations by a Superpave gyratory compactor. In addition, considering that this study aims to enhance HPAC for cold climate applications, dynamic modulus of HPAC mixes should be greater than 14 GPa at a temperature of 15˚C and a loading frequency of 10 Hz. Finally, to increase the pavement's lifespan, the mixture with optimum dosage must be prone to minimal thermal cracking at low temperatures by exhibiting the highest tensile strength and fracture energy compared with the control samples. Results show that the compactibility is not affected by the addition of PET, and that a fibre dosage of 0.15% gives the greatest increase (3.3%) in the mix stiffness and the best combined improvement effect of fracture energy (32% at 0°C) and tensile strength (13% at 0°C). This framework can be adjusted to add or omit other performance tests that are most suitable for the project location and climate in question.

Keywords: framework for optimum fibre content, high performance asphalt concrete, polyethylene terephthalate fibres, thermal cracking.