| Driven by “the Belt and Road” initiative,the construction of highways,bridges,tunnels and other engineering facilities in western China has increased significantly.However,the saline soil environment in the western region is widely distributed,and the environmental conditions are harsh.The effects of high and low temperature,freeze-thaw cycle and high salt corrosion coexist.The performance damage of ordinary concrete in this environment is serious and cannot meet the needs of some important projects.Ultrahigh performance cement-based composites(UHPC),as a new type of green highperformance cement-based composites,have much higher strength,toughness and durability than ordinary cement-based materials,and have broad application prospects in the western saline soil environment.However,there are few studies on the durability of UHPC and it is limited to the general atmospheric environment.The research on the durability of UHPC in the western saline soil environment has not been reported.In this study,a combination of theoretical analysis and rapid test in the laboratory was used,and the macroscopic performance test and microstructure characterization were complementary to each other.According to the environmental characteristics of saline soil in Baijiantan area of Xinjiang,a laboratory simulated erosion system in line with the erosion environment of saline soil in the west was established.The UHPC sulfate erosion test under the laboratory simulated erosion system was carried out.Considering the influencing factors such as raw materials(water-binder ratio,silica fume content and fiber type),curing system(90°C hot water curing and standard curing)and salt solution(sulfate solution and composite salt solution),the degradation law of UHPC macroscopic performance under this erosion system was studied.The performance degradation mechanism of UHPC was discussed by XRD、TGA-DTG、SEM-EDS and MIP.The main conclusions are as follows:(1)According to the annual temperature changes and the characteristics of saline soil in Baijiantan area of Xinjiang,the annual average duration of high temperature,low temperature,freeze-thaw cycle and normal temperature,as well as the type and concentration of salt were obtained.Based on the similarity relationship between the saline soil environment in Baijiantan area and the concrete salt erosion in the laboratory simulation environment,the laboratory simulation erosion system in line with the western saline soil erosion environment was established by using a reasonable equivalent acceleration method.(2)The degradation law of UHPC macroscopic performance under the simulated erosion system of western saline soil environment laboratory was studied.The results showed that the degradation degree of UHPC performance decreased first and then increased with the increase of water-binder ratio.The compressive strength of UHPC with0.18,0.20 and 0.22 water-binder ratio decreased by 3.36%,5.01% and 8.18% respectively,and the flexural strength decreased by 16.11%,14.24% and 18.22% respectively.The peak load decreases but the equivalent flexural toughness increases by 18.11% at 0.20water-binder ratio.The relative dynamic elastic modulus decreased to 98.56%,101.05%and 95.58%,respectively.With the increase of silica fume content,the deterioration degree of UHPC performance decreases gradually.After erosion,the compressive strength and flexural strength of PVA fiber UHPC decreased by 7.79% and 35.48%,respectively,the equivalent flexural toughness decreased by 42.01%,and the relative dynamic elastic modulus decreased to 97.29%.The degree of performance degradation is much greater than that of steel fiber UHPC;compared with 90°C hot water curing UHPC,the surface deterioration of standard curing UHPC is more serious after erosion,and its compressive strength and flexural strength are reduced by 5.57% and 17.96% respectively.The change of equivalent flexural toughness is the same as that of hot water curing UHPC.The relative dynamic elastic modulus is reduced to 98.96% and the reduction is greater than that of hot water curing UHPC;after the erosion of composite salt,mortar spalling appeared on the surface of UHPC.(3)Combined with the microscopic test method,the microstructure of UHPC under the simulated erosion system of the western saline soil environment laboratory was studied.The results show that The type of raw materials,curing system and salt type have no effect on the types of products produced by UHPC.After sulfate attack,ettringite and gypsum exist in the pores of UHPC.High temperature,wet-dry cycle,freeze-thaw cycle,low temperature and other temperature stresses,expansion internal stresses caused by erosion products,and crystallization stresses caused by salt precipitation can cause more voids and microcracks in UHPC,and the degree of its internal structure damage is consistent with the degradation law of macro physical properties. |
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