Sulfate-induced expansion of cement treated road base: Deterioration law of performance and air-void structure change under water-heat-salt coupling effect

The expansion and deterioration (E&D) of cement treated road base has become one of the common road problems in northwest and northern China, which seriously affected driving safety and increased road mainte-nance costs. In order to explore the influencing laws and mechanism of external salt on the expansion of cement treated road base in desert Gobi area with large temperature difference, based on the climate in Xinjiang and cement stabilized macadam (CSM) mixture, a laboratory accelerated simulation test under the coupling effect of water-heat-salt was designed to restore the working condition of the base course in Xinjiang. The expansion deformation and deterioration laws of CSM specimens under different gradation types, temperature, humidity and temperature-humidity cycle change were studied. Combined with MIP and computed tomography (CT), the air-void structure change, micro-pore morphology and accumulation of expansion products in the mixture were studied. The results showed that after 360-days' coupling effect, the damage height of the specimen was SD (suspension-dense structure) > FP (frame-pore structure) > FD (frame-dense structure). The mass of the partially-immersed specimens increased first, and the mass loss began to appear at about day 120. After 360 -days' temperature and humidity cycle change, the mass loss rate of SD, FD and FP were 4.15 %, 2.4 % and 4.9 %, respectively, which were 2.75, 2.53 and 2.62 times of that at 25 degrees C. Moreover, the expansion rate increased by about 20 %, and the performance deterioration decreased by 24.9 %-30 %. Additionally, the MIP and CT test results indicated that the aggregate proportion had a significant effect on the spatial distribution of the air-voids and the change of pore structure with coupling ages. This study provides reference for the design of cement-based composites and the acknowledgement of cement-treated base expansion in desert Gobi area.