Healing characterisations of waste-derived bitumen based on crack length:Laboratory and modelling

Abstract

The accumulations of waste plastics and municipal solid wastes from the resident groups and industrial companies have been causing serious environmental issues in the UK, due to difficulties in logistics, sorting, and reuse. In this sense, this paper is stimulated to develop novel approaches to convert some wastes into eco-friendly infrastructural materials, which provides a new way of waste reduction and reuse and extending the service life of asphalt pavement. This study aims to characterise the healing performance of waste-derived bitumen before and after pressure ageing vessel (PAV) ageing based on the crack length. One waste-derived bitumen was fabricated by blending the bio-oil pyrolysed from the organic fraction of municipal solid waste (5 wt%) with a control bitumen (X70) using a high shear mixer at a speed of 150 revolutions per minute (RPM) for 30 min at 150 °C under nitrogen atmosphere. A second waste-derived bitumen was fabricated using the low-density polyethene (LDPE) and mixed with the control bitumen at a concentration of 6 wt% at a speed of 900RPM for 90 min at 180 °C under nitrogen atmosphere. Crack length-based healing index and Ramberg-Osgood model were employed to characterise the healing rate and healing capability of the bitumen, respectively. Material properties (e.g., relaxation modulus and surface energy) of the bitumen used in the healing models were calibrated by linear amplitude sweep test (10 Hz and 20 °C), frequency sweep test (10 Hz, 10–70 °C), and time sweep fatigue-healing test (10 Hz and 20 °C) at a controlled strain level of 5% with different rest durations. Advancing contact angles used in the healing models of the bitumen were measured by a sessile drop tensiometer based on the tilting cradle method. Results show that the bio-oil productively promotes the healing potential and capability of the unaged bitumen, and the LDPE slightly strengthens them. The PAV ageing process evaporates most of the modifier bio-oil; hence, the PAV-aged bio-oil modified bitumen does not show better healing performance than that of the PAV-aged control bitumen. The PAV-aged LDPE modified bitumen has much better healing performance than those of the PAV-aged control bitumen and the PAV-aged bio-oil modified bitumen. The short-term healing rate and healing potential dominate the healing behaviours of the bitumen. The unaged bio-oil modified bitumen heals the fastest (having the highest short-term healing rate) and most (having the highest healing potential), followed by the unaged LDPE modified bitumen, and the unaged control bitumen heals the least and slowest. The PAV-aged LDPE modified bitumen heals the fastest and most, followed by the PAV-aged bio-oil modified bitumen and the PAV-aged control bitumen. The fundamental reason for LDPE's enhancement to bitumen's healing is that the LDPE increased the deformation recovery ability of the bitumen, leading to a higher wetting rate of the cracked surfaces and thus a higher short-term healing rate. However, the LDPE in bitumen cannot accelerate the molecular diffusion to increase the intrinsic healing or the long-term healing rate.