Interfacial bonding property and microscopic damage mechanism of bitumen-aggregate in salt-freeze-thawing environment

Deicing salt or snow-melting agent has a corrosive effect on the pavement, which reduces the durability of asphalt pavement. The interfacial bonding properties of bitumen-aggregate is one of the main factors affecting the durability of asphalt mixture. To evaluate the interfacial bonding properties of bitumen-aggregate and reveal the damage mechanism under salt-freeze-thaw coupling effect, the bitumen-aggregate samples with the same film thickness were formed by controlling the applied load. The corrosion of deicing salt on bitumen-aggregate and bitumen film samples was simulated by freeze-thaw cycles in 1 %, 3 % and 5 % NaCl solution. The pull-off test of SBS modified bitumen-aggregate after salt-freeze-thaw cycles was conducted. The Fourier transform infrared spectrometer (FTIR) test was carried out to qualitatively and quantitatively analyze the impact of salt-freeze-thaw coupling effect on bitumen functional groups. The surface morphology of bitumen samples treated in salt-freeze-thawing environment was also scanned by atomic force microscopy (AFM) in tapping mode. The results illustrate that the pull-off strength of bitumen-aggregate decreases sharply first and then the decrease rate slows down with the rise of salt-freeze-thaw coupling cycles. The carbonyl index and sulfoxide index of SBS modified bitumen increases, and the butadiene index decreases after freeze-thaw cycles in NaCl solution. The environment of salt erosion and freeze-thaw cycle accelerates the deterioration of SBS modifier and reduces the distinction of various phases in bitumen binder. Then the Ra and Rq of SBS modified bitumen decreases significantly in salt-freeze-thawing environment. The decrease of butadiene index and root mean square roughness leads to the weakening of adsorption between SBS modified bitumen and aggregate, which is the main reason for the damage of interfacial bonding performance of bitumen-aggregate. In summary, the salt-freeze-thawing environment damages the bonding performance of bitumen-aggregate. The damage law and deterioration mechanism of bonding properties of bitumen-aggregate presented in this paper provides some references for the optimal design of asphalt mixture in salt-freeze-thawing environment.