HIND FADHIL ABBAS AMARH

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.

Laboratory determination of fatigue characteristics of asphalt mixtures is a vital step in evaluating and designing asphalt pavement. This study aims to provide a comprehensive analysis of the fatigue resistance of the modified asphalt mixtures containing plastic waste and crumb rubber. These dry process-modified mixtures have been presented in the road construction on the basis of the basic understanding of the mechanical properties and lack of intensive studies on fracture mechanics. In this study, a controlled-stress, repeated load semi-circular bending test under two load levels with the effect of ageing and moisture condition was used to characterise the three stages of fatigue life of asphalt mixtures. The fatigue life was characterised on the basis of the crack mouth opening distance assessment and image analyses of the crack patterns on the sample surface. Digital image correlation was used to capture the strain field that forms the plastic zone of mixtures under consideration. Results show that rubberised asphalt mixture promotes crack propagation and failure stages by increasing the plastic zone, whilst plastic waste-modified asphalt mixtures function to increase the bonding properties. Consequently, the cracking initiation and propagation stages increase. The digital image analysis of the sample surface of modified asphalt mixtures indicates higher values of crack tortuosity, crack density and fractal dimension due to the increase in the cracking resistance of asphalt mixtures. The extracted strain field has successfully captured the effect of modifiers on the size of plastic zones under the fatigue test

Asphalt mixtures behave as linear viscoelastic materials when subjected to loading conditions that are similar to pavement operating conditions. Thus, this study proposed a novel method for extracting the linear viscoelastic properties of asphalt mixture at 25 °C using digital image correlation and repeated-load semi-circular bending (SCB) test. Digital image correlation was utilised successfully for extracting creep compliance using semi-circular samples under repeated loading conditions. A fractional time-dependent viscoelastic element converted the creep compliance data into relaxation modulus. The extracted relaxation modulus data were verified by simulating the viscoelastic response of control and modified asphalt mixtures using the extended finite element model (XFEM). The findings presented in this paper showed that digital image correlation has a high potential for bridging the gap between experimental and simulation work. The strain map provided by the prediction model was compatible with the DIC strain.

Asphalt pavements undergo ageing and moisture damage over the service life. The ageing and moisture process resulted in more cracking susceptibility and lowered pavement serviceability. Recently, the semi-circular bending (SCB) test has been widely utilised to characterise the fracture resistance of asphalt mixtures. In this study, the Illinois Flexibility Index Test (I-FIT) were utilised to investigate the impact of long-term ageing and moisture damage on the cracking resistance of asphalt mixtures modified by crumb rubber and plastic waste. This test is currently being adopted as a routine test in Illinois and has shown good correlations with the field cracking performance of asphalt mixture. For the Semi-Circular Bending (SCB) test, a sample width of 50 mm and a notch length of 15 mm was used for conducting the fracture test using a constant loading rate of 50 mm/min and a test temperature of 25 °C. The fracture energy-based crack mouth opening displacement of the control and modified mixtures was also evaluated using Digital Image Correlation (DIC). The results showed that the flexibility index (FI) values from the I-FIT are sensitive to the modifier type (elastomers or plastomers) and long-term ageing while underestimating the impact of moisture conditioning on the fracture performance of asphalt. Fracture energy results were higher for the rubberised mixture compared to the control and plastic waste modified asphalt mixture. Ageing condition has noticeably decreased the flexibility index (FI) of the rubberised mixture and consequently reduced the fracture performance.

The utilisation of plastic waste as a modifier in asphalt mixtures has inflicted significant impacts on the cracking resistance of the produced mixtures. Whilst many studies have evaluated the cracking resistance of asphalt mixtures incorporating plastic waste using wet method, limited studies have used the dry method are available. The current study aims to evaluate the effect of plastic waste incorporation on the fracture properties of conventional asphalt mixture. In addition, the impact of ageing and moisture damage on the fracture properties of modified asphalt was also investigated. Indirect tensile strength test was carried out to assess the CT-index, tensile strength, and fracture energy of the asphalt mixtures before and after exposure to ageing and moisture conditioning. The finding revealed that the asphalt mixture incorporating plastic waste demonstrated superior resistance to thermal and fatigue cracking compared to the control mixture, thus proving the capability of plastic waste in increasing the resistance of asphalt against ageing and moisture damage.