Plastic Derived Bitumen Modifiers (w-Binder) from Pyrolysis in Sustainable Road Construction

Abstract

There are current largescale efforts within the paving industry to move
towards the use of sustainable binder alternatives to bitumen, which is a nonrenewable and highly impacting resource. The use of waste plastics as binder
materials within asphalt concrete is considered as a practical and cost-effective
alternative, especially as the growth of new recycling capacities is becoming
more crucial. Furthermore, plastic-derived bitumen modifiers from the
thermochemical treatment of plastics could be a viable solution to the current
limitations associated with plastic bitumen modifiers (PMB), while producing
asphalt with enhanced rheological properties and failure resistances.

This study provides a novel contribution to outlining the potential of highdensity polyethylene (HDPE) thermal pyrolysis waxes in the modification of
bitumen (w-binder) and subsequent hot mix asphalt (HMA) mixtures (w-asphalt),
as well as in reclaimed asphalt (RAP) rejuvenation. In the interest of product and
process optimisation, it establishes key relationships between pyrolysis process
parameters, the chemical and thermal properties/ mechanisms of the wax
modifiers and the rheological and mechanical performance of the modified
binders/mixtures. Finally, dense graded asphalt concrete modified with an
optimal HDPE pyrolysis wax (6 wt% of the binder) and 20% RAP was produced
and its resistance to key pavement deterioration modes was determined.

The optimal wax was produced at higher pyrolysis temperatures and
nitrogen flowrates (having the lowest vapour residence times.) Such process
parameters had a crucial role in the resultant wax chemistry and thermal ageing
behaviours. Oxidation and polymerization reactions were key mechanisms
identified during wax thermal ageing and their effect on the resultant binder and
mixture properties were highlighted. The asphalt mixtures produced had
enhanced or unaffected resistance to the key failure modes studied, with the RAP
+ HDPE pyrolysis wax mixture showing superior performance. The HDPE
pyrolysis wax acted as a sufficient rejuvenating agent to mitigate the otherwise
adverse effects to fatigue resistance of high RAP content in HMA mixtures. This
application of plastic pyrolysis wax could help to reduce the amount of nonrenewable materials used for HMA production, increasing the usage of recyclable and secondary materials within flexible pavements in the effort to approach a circular economy.

Date of Award	2023
Original language	English
Supervisor	Yuqing Zhang (Supervisor) & Jiawei Wang (Supervisor)