# Research on Solidification Methods and Stabilization Mechanisms of Sulfate Saline Soils
###### Abstract  
In cold regions, saline soils can cause dissolution, settlement, and salt expansion of the roadbed under the influence of freeze-thaw cycles, so they need to be stabilized during road construction. In this study, lime, fly ash (FA), and polyacrylamide (PAM) were used to stabilize sulfate saline soils, and the stabilized saline soils were subjected to the unconfined compressive strength test (UCS), splitting test, and freeze-thaw cycle tests (FTs). The stabilization mechanism of the three materials on saline soils was also studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and X-ray photoelectron spectroscopy (XPS). The test results showed that the addition of lime, FA, and PAM to saline soils can improve the mechanical properties and frost resistance of saline soils. After 28 d of curing, the UCS of FA-, PAM-, and lime-stabilized saline soils increased by at least 55%, 23%, and 1068%, respectively, and the splitting strength increased by at least 161%, 75%, and 2720%, respectively. After five freeze-thaw cycles, the residual strength ratios (BDRs) of the UCS of L2 (time 8%), F2 (FA 11%), and P2 (PAM 1%) stabilized soils and saline soils were 71.78%, 56.42%, 39.05%, and 17.95%, respectively, and the decreasing trend tended to be stable. The saline soils stabilized by lime and FA were chemically stabilized, and their mechanical properties and frost resistance were better than the physical stabilization of PAM. saline soils; stabilized soil; unconfined compressive strength; splitting strength; freeze-thaw cycles; lime; fly ash +
Footnote †: journal: Applied  
0000-0002-0002-3330]J. Sun  
0000-0002-3330-3300]J. Sun  
0000-0002-33300-3300]J. Sun  
0000-0002-33300-3300-3300-3300-3300-33000-3300-3300-33000-33000-33000-33000-33000-33000-33  
causing soil settlement. This is due to the fact that the salt in saline soils reduces the bonding of soil particles through softening or crystalline expansion, resulting in a loose soil structure [8]. The Xinjiang region of China has a dry climate with low precipitation, high temperature variability, and high evaporation rates [9]. Sulfate saline soils are widely distributed in Xinjiang [10]. If sulfate saline soils are used directly as a roadbed material, salt expansion and collapse may result in damage to the roadbed, affecting the normal service life of the road [11]. In addition, sulfate saline soils are highly sensitive to moisture, and the compressive strength of the soil decreases significantly upon water saturation. Moreover, Xinjiang is located in the middle and high latitudes, and the freeze-thaw cycles is frequent in late winter and early spring. When water freezes, it expands by about 9% in volume, generating high pressure [12] and forming ice crystals that separate and break the bonds of soil particles [13]. Therefore, in order to improve the frost resistance and stability of saline soils as roadbed materials, they need to be stabilized. In road engineering, inorganic binding materials such as lime, fly ash, and cement are usually used to stabilize the soil [14]. FA is a byproduct of coal's combustion in power plants [15] and is widely used in the road construction industry [16]. FA contains large amounts of reactive SiO and Al2O3, which can be used as binding materials for stabilizing saline soil geopolymers. In the Xinjiang region, there are many thermal power plants that generate large amounts of FA [15; 17]. FA-stabilized saline soils can not only solve the problems of environmental pollution and massive waste accumulation occupying land but also reduce the cost of road construction [18; 19]. Some researchers conducted mechanical tests on FA-stabilized saline soils and found that the strength of the stabilized soils increased significantly, and the chemical composition of the stabilized soils was evaluated using XRD [20].