Abstract
ABSTRACT Oxidative ageing in field asphalt pavements is a complex process with coupled multiple physics. This parametric study uses Multiphysics modelling approaches to evaluate the effects of material thermal properties, air voids content and distribution, mastic coating thickness, oxygen accessibility and binder oxidative kinetics on the spatial and temporal evolution of the oxidative ageing in the asphalt pavements. Results suggest that increasing the thermal conductivity of asphalt layers leads to a lower ageing gradient. The variations of base and subgrade layers’ thermal properties cause little to no effects on the oxidative ageing. A high activation energy of the asphalt binder (e.g. by adding anti-ageing additives) reduces the oxidative ageing significantly. Asphalt layers built on unbound granular base will experience greater overall ageing with a C-shaped ageing gradient compared to that built on treated base. Air voids content of <5% yields limited oxidative ageing. Five to nine percent air voids generate a gradually increased oxidative ageing with an obvious gradient across pavement depth. Air voids content beyond 9% leads to a consistently high oxidative ageing due to a full access to the oxygen. Finally, the findings were validated using available literature results and field data from 14 European road sections.
Highlights
Non-uniform temperature distribution within pavement depth causes oxidative ageing and pavement modulus gradients to exist (Hall et al 2012, Yin et al 2017)
According to Lu et al (2009), the performance of asphalt pavements is closely related to the temperature profile, and the influence of temperature on pavement performance can be more significant than that of loading level and duration (Lu et al 2009)
The maximum daily surface temperature can be reduced by a maximum of 5°C, which according to previous literature, can extend the service life by five years when considering all distress factors, not that caused by oxidative ageing alone
Summary
Non-uniform temperature distribution within pavement depth causes oxidative ageing and pavement modulus gradients to exist (Hall et al 2012, Yin et al 2017). The scale of this alteration in the activation energy on the field ageing of asphalt pavements is still ambiguous, under a complex environmental condition including coupled temperature and oxygen distribution in the pavement structure. Another main physics affecting the oxidative ageing process is oxygen diffusion. The surface of asphalt concrete commonly experiences a higher degree of oxidative ageing than that for asphalt at deeper layers (Han 2011, Glover et al 2014, Yin et al 2017) This is a result of higher temperatures and easy access to oxygen from atmospheric air. The current parametric study is looking into the effect of mastic film thickness on the oxidative ageing propagation
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