Thermoreversible Aging Characteristics of Crumb Rubber–Modified Bitumen Based on Rheological and Fracture Mechanics Theories

Abstract

In cold regions, bitumen exposed to low temperatures for an extended period undergoes thermoreversible aging, which can cause premature cracking of the bitumen pavement. The rheological properties and fracture characteristics of natural bitumen and crumb rubber–modified bitumen (CRMB) were examined using the extended bending beam rheometer (EBBR) test and single-edge notch bending (SENB) test, while under the influence of thermoreversible aging. The results show that thermoreversible aging can diminish the anticracking properties of bitumen, while CRMB exhibits superior low-temperature properties and resistance to thermoreversible aging. To accurately characterize the thermoreversible aging effect on the anticracking properties of CRMB using the EBBR and SENB tests, it is essential to maintain constant temperature test conditions for at least 48 h. Furthermore, under prolonged low-temperature conditions, the hardening crystallization rate of CRMB follows a normal distribution with decreasing temperature, with the fastest rate of hardening crystallization observed at −18℃. The hardening rate and thermal stress constitutive model provide a convenient calculation method for studying the change in stiffness modulus and thermal stress of CRMB under the thermoreversible aging condition. It also serves to lay a theoretical and technical foundation for the development, design, and application of road bitumen in cold regions. In cold regions, prolonged periods of low temperatures can cause thermoreversible aging of bitumen, resulting in significant deterioration of the bitumen's resistance to cracking and significantly reducing the life of the bitumen pavement. Under thermoreversible aging, the level of hardening crystallization of bitumen is normally distributed with decreasing temperature, and it gradually decreases and becomes saturated with increasing constant temperature time. In comparison to conventional tests, the extended bending beam rheometer and single-edge notch bending tests are more precise in characterizing the low-temperature cracking resistance of bitumen following thermoreversible aging. However, it is essential to ensure that the test conditions maintain a constant temperature for 48 h to ensure accurate results. Concurrently, crumb rubber has been demonstrated to enhance the low-temperature cracking resistance and thermoreversible aging resistance of bitumen, rendering it a more optimal choice for pavement projects in regions with cold climates. The findings of the research study offer theoretical and technical support for the practical implementation of crumb rubber–modified bitumen in bitumen pavement engineering in cold regions, thereby facilitating improvements in the quality of bitumen road construction in cold regions.