Using acoustic emission and X-ray CT to study the freeze–thaw damage mechanism of water-retaining asphalt mixture

Water-retaining asphalt mixture (WRAM) can mitigate the urban heat island effect by effectively lowering the pavement temperature through water evaporation. Understanding the characteristics of freeze–thaw damage is crucial for developing methods to prolong pavement life. This study first analyzed the effect of freeze–thaw cycles (F-TC) on the fracture modes of WRAM by monitoring acoustic emission (AE) signals during uniaxial compressive test. Furthermore, the distribution and evolution of WRAM's mesostructure during F-TC were investigated using X-ray computed tomography (X-ray CT). Finally, freeze–thaw damage parameters were proposed based on the observed pore characteristics. The results indicated that the percentage of tensile cracks during the entire damage process of WRAM increased from 77.5% to 88.9% as the number of F-TC increased from 0 to 30 cycles. F-TC contributed to a more concentrated areas of cracking. Moreover, F-TC increased the both quantity and volume of pores in WRAM, a process characterized by pore generation, expansion and coalescence. Indicative CT analysis revealed that the reduction in aggregate-grout contact length accounted for approximately 89.5% and 58.8% of the increase in aggregate-pore and grout-pore contact length, respectively. Freeze-thaw damage predominantly occurred at the aggregate-grout interface. Damage parameter (D_E) can more accurately characterize the damage state of WRAM.