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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

Long-term field ageing of asphalt pavement plays a vital role in limiting the pavements’ service life. Models have been established to represent the multiple physics that contribute to the ageing of asphalt pavement, including: (1) heat transfer to determine pavement temperature profile, (2) diffusion of oxygen from the air into the connected air voids of the asphalt pavement, (3) diffusion of oxygen from the air void channels to the inside of the asphalt mastic coating films, and (4) the growth of oxidation products in the asphalt binders. These four ageing-related physics were mathematically modelled individually in the literature; however, they were not effectively integrated and coupled into a comprehensive computational model. The challenge lies in that the ageing-related physics are circularly dependent and time-dependent. Another challenge results from the complexity in numerical modelling of the high nonlinearity caused by the circular dependency between the four physics. This study uses weak-form partial differential equation (PDE)-based finite element (FE) program to efficiently couple the physics into one integrated model. The model inputs include the available site-specific hourly weather data, binder oxidation kinetics, mixture design properties, and thermal characteristics of pavement materials. The model was validated using the field measurements of the oxidation products (carbonyl) from The Federal Highway Administration (FHWA) reports. Results show that the model can effectively address the circular dependency between the ageing-related multiphysics and reliably predict the oxidation products along pavement depth for asphalt pavement road section.

The aim of this study was to investigate the effects of different anti-ageing compounds (AACs) on the oxidative stability, rheological and mechanical properties of bitumen. Modified bitumen samples containing six different AAC combinations, with five samples containing Irganox acid (3,5-di-tert-butyl-4-hydoxyphenylpropionic acid), a hindered phenol polymer-based antioxidant, were fabricated and aged under different conditions using a Rolling Thin Film Oven (RTFO) as well as a Pressure Aging Vessel (PAV). The oxidative stabilising performance (anti-ageing) of the AACs was examined using Fourier Transform Infrared (FTIR) Spectroscopy. The effect of the AAC-modified bitumen on different rheological and mechanical properties was investigated - complex viscosity, linear viscoelastic (LVE) properties, fatigue and rutting - using a Dynamic Shear Rheometer (DSR). The results illustrated that all the AAC-combinations examined afforded good oxidative stability to the base bitumen, with outstanding anti-ageing performance achieved by formulations C, D, E and F (Irganox acid:NaMMT, Irganox acid:furfural without or with DLTDP or NaMMT). The rheological results showed that the AAC-modified bitumen samples displayed non-Newtonian characteristics associated with simple thermo-rheological materials. The AAC formulations A (DLTDP:furfural), D (Irganox acid:furfural) and F (DLTDP:Irganox acid:furfural) were shown to significantly strengthen the resistance of the bitumen samples to fatigue cracking. In contrast to Irganox acid:furfural combination, the addition of the NaMMT nanofiller to this mixture was found to enhance the rutting resistance of the aged bitumen samples.

Long-term oxidative ageing occurs in asphalt pavements when they are exposed to the ambient environment for extended periods. This ageing phenomenon is dependent on multiple physical fields, including heat transfer, oxygen diffusion from air into interconnected air voids of asphalt pavement, oxygen diffusion from air void channels to asphalt mastic inside, and growth of oxidation products in bitumen. Most existing oxidative ageing models were established via coupling of limited physical fields. However, to accurately determine the oxidative ageing effect on pavement performance, there is a need to develop a multiphysics model that integrates all ageing-related physical fields comprehensively. The challenge lies in that the ageing-related physics are circularly dependent, time-dependent and highly nonlinear. This study developed a multiphysics and time-dependent finite element model that successfully addressed the issues of high nonlinearity and circular dependency of oxidative ageing in the asphalt pavements. Specifically, a differential equation-based approach was employed to efficiently couple the multiple physical fields into one integrated model. The multiphysics framework included a pavement temperature prediction model and an integrated ageing model. The model involved a variety of inputs such as site-specific hourly climate data, parameters for oxidation kinetics of bituminous binder, volumetric properties of asphalt mixture, thermal and diffusive properties of pavement materials, and pavement structure. The pavement temperature model was validated using the pavement temperature profiles for different climate regions in the Long-Term Pavement Performance (LTPP) database. The integrated ageing model was validated using the Fourier-transform infrared spectroscopy (FTIR) data of field-aged asphalt cores in the literature. Results showed that the model can accurately predict the change in pavement temperature profile on an hourly basis and reliably predict the degree of oxidative ageing across pavement depth for different climate zones.

When exposed to the ambient environment for an extended period, bitumen ages and causes the failure of asphalt pavement, the addition of anti-ageing compounds (AACs) to bitumen binders can prolong the service life of the pavement. This study investigates the effects of anti-ageing compounds on the fatigue performance of bitumen when subjected to different ageing conditions. The AAC-modified bitumen binders were tested by dynamic shear rheometer (DSR) and Fourier transform infrared spectroscopy test (FTIR) at different ageing conditions including unaged, short-term ageing by thin film oven test (TFOT) and long-term ageing by pressure ageing vessel (PAV). The fatigue performance of the AAC-modified bitumen was characterised by the dissipated energy ratio (DER), SHRP fatigue parameter and the DSR-cracking (DSR-C) approach developed by the authors. Linear amplitude sweep (LAS) tests were firstly run at 20 °C, 10 Hz and 0.1–15% controlled shear strain conditions, to obtain the phase angles and shear moduli at the undamaged conditions. Time sweep (TS) tests were then conducted at 5% shear strain, also at 20 °C and 10 Hz, and up to 24,000 loading cycles to obtain phase angles, shear moduli and DER at damaged conditions. The crack lengths in the TS tests were calculated by DSR-C model and then validated by the image analysis method. The results suggest that, compared to the DER or SHRP fatigue parameter, DSR-C predicted crack lengths show a more consistent and reliable agreement with laboratory measurements. DSR-C test can differentiate fatigue cracking performance among binders modified with AACs, and the normalised carbonyl index may be a reliable parameter to reflect the impact of ageing products on the fatigue resistance of AAC-modified binders. Bitumen samples modified with 12% (1 furfural: 5 Irganox 1076), 15% Irganox 1076 and 3.5% (3 DLTDP: 4 furfural) demonstrated the best anti-ageing behaviour by retarding carbonyl content growth and decreasing the fatigue damage among selected AACs without sacrificing the stiffness of binder. However, rutting susceptibility at earlier stages of service life needs further investigations.

This paper investigates the effect of different anti-ageing compounds (AACs) on the oxidation kinetics of bitumen using Fourier Transformation Infrared (FTIR) spectroscopy. Twenty different AACs were examined, including new and existing AACs for bitumen and polymer products. The AACs were mixed with bitumen to fabricate thin film samples of AAC-modified bitumen which were subjected to laboratory oven ageing at 100 °C with different ageing periods up to 504 h. A Normalized Carbonyl Index (NCI) was proposed based on a selected reference peak (1377 cm−1) to eliminate the impact of the inherent carbonyl content from the bitumen or AACs and manifest the carbonyl growth rate for evaluating the AACs’ anti-ageing performance. It was found the activation energy of fast-term oxidation can be utilized to quantitatively screen the anti-ageing compounds and evaluate their anti-ageing effectiveness in terms of decreasing the formation of carbonyl groups in bitumen. AACs that exhibited high anti-ageing performance were those contained furfural, Irganox acid with sodium montmorillonite, furfural with DLTDP, and high concentrations (e.g., 15%) of Irganox acid. The proposed protocol should be followed by further laboratory rheological and mechanical tests on the AAC-modified bitumen with different binder sources.

This work presents a study on intermediate pyrolysis of the organic fraction of municipal solid waste (OFMSW) and characterisation of organic liquid product (pyrolysis oils) with particular focus on aging and rheological characteristics. The feedstock was a real municipal waste sample received from a local waste treatment plant. Shredded into small particles, it contained a high amount of moisture (51.2%) and ash (17.4%). A pilot-scale intermediate pyrolysis system was used to process the material. The process mass balance showed that the yield pyrolysis oil was 10.6%. GC-MS and FTIR experiments showed that the accelerated aging (80 °C for 24 h) did not cause an obvious change in the liquid chemical composition, but led to a significant reduction in the solids and moisture contents. The dynamic viscosity tests demonstrated that the intermediate pyrolysis oil derived from OFMSW is a non-Newtonian fluid. The dynamic viscosity of the pyrolysis oil reduced with the increase of temperature or shear rate, which can be modelled by WLF function and the Carreau model, respectively. A shear rate-temperature superposition method was proposed to construct the viscosity master curve at a wide range of shear rate, where WLF function was employed to model the shear rate-temperature shift factor. The accelerated aging caused an obvious reduction in dynamic viscosity, resulting from the decomposition of the semisolid organic agglomerates in the solids content during the aging of the OFMSW intermediate pyrolysis oil. The relatively high viscosity and reduced viscosity after aging of the OFMSW pyrolysis oil has indicated its potential for application as a substitute of the light fraction in the bitumen for road construction.