Effect of Freeze-Thaw cycles on the pavement performance of SBS modified and composite crumb rubber modified asphalt mixtures

The effect of freeze-thaw cycles on the pavement performance of SBS modified asphalt mixture (SBSMA) and SBS/crumb rubber composite modified asphalt mixture (CCRMA) was studied using a triaxial repeated creep test, semicircular bending fatigue test based on digital image correlation (DIC), and thermal stress restrained specimen test. The mechanical model of the residual strain (RS) of the asphalt mixtures is established, and the residual viscous flow strain (epsilon(Rvf,N)) and residual viscoelastic strain (epsilon(Rve,N)) are separated. Based on the horizontal strain (Exx) of DIC, a new mesofatigue damage variable (D) is proposed. According to the characteristic curve of D, the antifatigue damage parameter (AFDP) is established and the correlation between AFDP and fatigue life (N-f) is analyzed. Simultaneously, a calculation model of the relaxation temperature stress (sigma(Rts)(T)) of the asphalt mixture at different cooling rates (v) is established based on the finite element method. Results showed that the growth rates of RS, epsilon(Rvf,N), and D of both asphalt mixtures accelerate, AFDP decreases, and freeze-break temperature (T-D) rises with increasing freeze-thaw cycles. However, the growth rates of RS, epsilon(Rvf,N), and D of CCRMA are always slower than SBSMA, the AFDP is larger than SBSMA, T-D is lower than SBSMA, epsilon(Rve,N) is a fixed value under specific conditions, and a good correlation exists between the AFDP and N-f. The pavement performance of the asphalt mixtures worsens after the freeze-thaw cycles, and the influence of a salt freeze-thaw cycles is greater than that of a water freeze-thaw cycles. Moreover, CCRMA has better high-temperature deformation resistance, fatigue damage resistance, and low-temperature cracking resistance than SBSMA. The conversion point temperature (T-Z) increases with the acceleration of v, and the sigma(Rts)(T) calculation model can accurately reflect the sigma(Rts)(T) of the asphalt mixture at different v.