Reclaimed asphalt pavement (RAP) has received much attention recently due to its increased use in hot mix asphalt (HMA) pavements to enhance pavement sustainability. The use of aged asphalt in RAP, which is highly oxidised and has lost its properties due to exposure to traffic loads and climatic conditions throughout its lifespan, can cause asphalt mixtures to stiffen and embrittle, thus negatively affecting the behaviour of asphalt mixtures. This issue may be resolved by including rejuvenating agents that can restore both physical and rheological properties of aged asphalt by increasing maltene fractions and decreasing asphaltene. However, the high restoration capacity of any kind of rejuvenating agent does not assure the durability of restored aged asphalt. This study explored the performance and durability of rejuvenated asphalt mixtures embedded with several types of rejuvenators identified from the extensive literature review. The study serves as a significant reference to predict future challenges in rejuvenating aged asphalt.

The wide application of reclaimed asphalt pavement (RAP) is hindered due to the highly brittle nature of the material, which contributes a major factor towards cracking-related distresses. While the utilisation of rejuvenating agents has been shown to enhance the flexibility of RAP, they also trigger certain negative effects on the performance of asphalt mixtures. In view of this, potential rejuvenators should be able to alter the rheological properties of asphalts to limit fatigue issues and enhance the potential of low-temperature cracking. Therefore, this study aimed to investigate the possibility of extraction and characterisation of maltene from virgin asphalt (VA) as a potential rejuvenating agent in RAP. Several physicochemical characteristics were examined, including density, viscosity, gas chromatography–mass spectrometry (GC–MS), Fourier-transform infrared (FTIR) spectroscopy, CHNS elemental analysis, and energy dispersive X-ray (EDX) analysis. Finally, the stiffness modulus characteristics of the different types of asphalt binders were evaluated at low and high temperatures. The results demonstrated that maltene was successfully extracted from VA using petroleum ether. In addition, the GC–MS showed that the extracted maltene contained polar and non-polar compounds with low molecular weights compared to VA. Furthermore, the spectra curve of maltene was very similar to that of asphalt, indicating its compatibility with asphalt binder and prospective use. Finally, adding maltene to aged asphalt decreased stiffness values to 0.0063, 0.0499, and 0.0108 MPa, which are equivalent to VA values (0.0061, 0.0481, and 0.0104 MPa) at loading times of 1.0, 0.1, and 0.55 s, respectively. Meanwhile, the stiffness modulus characteristics at low temperature were restored with the addition of maltene.

The semi-circular bend (SCB) test is widely used to characterize asphalt mixture cracking resistance. However, the practical usefulness of the test depends on the reliability of the measured fracture parameters. This study investigates SCB testing from a reliability perspective, with the aim of identifying the specimen number required for dependable interpretation and the testing conditions that provide the most stable response. The analysis considered nominal maximum aggregate size, notch depth, binder type, aging condition, test temperature, and loading rate. Fracture energy, peak load, and flexibility index, together with their cumulative coefficients of variation, were tracked from n = 3 to n = 6, while six-specimen raw datasets were used for Weibull reliability analysis. The results show that notch depth had the clearest effect on response stabilization, with the 15 mm notch providing the most reliable configuration and reaching the adopted variability limits earlier than the other notch depths. The descriptive Weibull analysis further indicated that the SBS-modified mixture exhibited the highest fracture-energy consistency within the tested dataset, whereas long-term aging, testing at 0 °C, and loading at 50 mm/min were associated with the lowest fracture-energy consistency within the tested dataset. Overall, SCB interpretation should be guided by response reliability, not mean fracture parameters alone. On this basis, a reliability-based SCB framework is proposed to support more dependable mixture comparison and more rational specimen planning.