Multiscale Modelling of Bonding Performance of Bituminous Materials

Abstract

Bonding performance of bituminous materials fundamentally determines the resistance of asphalt to fatigue cracking which is one of the major distresses in asphalt pavements. Running laboratory fatigue tests of bitumen or asphalt is costly and time consuming, resulting in empirical-based fatigue life prediction models. To reveal the debonding mechanism of fatigue damage in bitumen, a hierarchical multiscale modelling framework was developed in this thesis to understand and model the bonding performance of bitumen in order to accurately and reliably predict fatigue crack initiation and propagation in bitumen. At the nanoscale, the bonding performance of bitumen was characterised by bond energy using molecular dynamics (MD) simulations, which was validated by contact angle measurements. The MD modelling and simulations were performed to understand the effects of minerals and oxidative ageing on the bonding performance of bitumen at the molecular level. At the microscale, cohesive debonding performance of bitumen under a rotational shear fatigue load was first quantified by a DSR-C model to predict fatigue crack length. Then, based on the quantification of cohesive debonding behaviour at the nanoscale, an energy-based fatigue crack initiation criterion was developed for bitumen using a viscoelastic Griffith’s theory. At the macroscale, the cohesive debonding behaviour in bitumen was modelled for fatigue crack propagation by a pseudo J-integral based Paris’ law. Dynamic shear rheometer (DSR) tests were conducted to validate the developed models at different environmental and loading conditions. Results indicated that the cohesive bond energy predicted at the nanoscale can be used as a fundamental material property and scale-independent input for the cohesive debonding modelling for fatigue cracking of bitumen at the microscale. Adhesive bonding performance of bitumen with minerals is attributed to non-bond energy including van der Waals and electrostatic interactions. Bitumen oxidative ageing trends to strengthen interfacial electrostatic interaction since the introduction of oxygen atoms makes bitumen polarity stronger. The developed DSR-C model is capable of accurately predicting the fatigue crack length in bitumen. The energy-based crack initiation criterion along with the DSR fatigue tests can act as a substitute for surface energy tests. The crack propagation model based on the pseudo J-integral Paris’ law is able to characterise the fatigue crack evolution in bitumen. The Paris’ law coefficients A and n are temperature dependent fundamental material property, which are demonstrated to be independent of loading frequency or loading amplitude.