Influence of ageing and moisture damage on the Illinois flexibility index value of polymer modified asphalt mixture

Abstract

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.