The effect of freeze-thaw cycles on durability properties of SBS-modified bitumen

To study the high-temperature characteristics of bitumen under the influence of freeze-thaw cycles, the results of DSR tests of bitumen and SBS-modified bitumen after 0, 3, 6, 9, 12, 15, and 18 freeze-thaw cycles were investigated. First, based on the simplified model for the DSR tests, the relation between the rheological parameters of the bitumen was analyzed. Then, in combination with the MSCR tests of the SBS-modified bitumen after freeze-thaw cycles, the relation between %R and Jnr was discussed. Finally, FTIR was used to analyze the changes in the chemical composition of the bitumen under freeze-thaw cycles. The results showed that the incorporation of SBS modifiers can increase the elasticity of the bitumen significantly and slow the tendency of the bitumen's complex shear modulus to increase with the freeze-thaw cycles to a certain extent. The SBS modifiers also can reduce the bitumen's temperature sensitivity and improve its rutting resistance. After the freeze-thaw cycles, G∗/sinδ decreased as temperature increased, and G∗sinδ showed an exponential decay with increasing temperature. With an increase in the number of freeze-thaw cycles, G∗sinδ of the bitumen and SBS-modified bitumen increased gradually, which indicated that the bitumen's fatigue resistance weakens gradually after freeze-thaw cycles. The %R0.1 and %R3.2 of SBS-modified bitumen showed a decreasing trend under different stress levels, and the %R3.2-%R0.1 increased, which indicates that bitumen's high temperature characteristics and temperature fatigue performance show an attenuating trend. The difference between the FTIR spectra of the SBS-modified bitumen fingerprint area after a freeze-thaw cycle was reflected largely in the significant increase in the 1700 cm−1 carbonyl group and 1031 cm−1 sulfoxide group peaks, while the two peaks at 967 cm−1 and 700 cm−1 were relatively stable. These results provide a theoretical basis and technical support for the design, material selection, popularization, and application of an SBS-modified bitumen mixture in roads in regions with seasonal freezing.