Study On Mechanism Of Cement Stabilizing Soil Polluted By Sodium Sulfate Or Magnesium Sulfate

Cement-soil method is widely used in underground engineering. But the structure of cement-soil is easy to be damaged, strength properties decreased, which eventually leads to the reduction of durability in poor environments due to the pollution of the ground water and the development of coastal and inland saline areas. Therefore, it is very necessary to study sodium sulfate and magnesium sulfate to improve reinforcement properties of cement soil in order to analyze how to increase the strength of cement soil in these saline and polluted areas.Soil samples with different content of sodium sulfate and magnesium sulfate are used for the research. Samples are prepared by adding sodium sulfate and magnesium sulfate into dry soil. Unconfined Compressive Strength test, Scanning Electron Microscopy test, X-ray diffraction test and Energy Dispersive Spectrometer test are used to study on the impact of the reinforced cement soil with magnesium sulfate and sodium sulfate and explain the strengthening mechanism of cement soil in the aspects of mechanical properties and microstructure analysis. The main results of this paper are listed as follows:1. UCS tests are carried to analyze the influence on soil strength of stabilized soil by sodium sulfate and magnesium sulfate and obtained the role between media content and the strength of the stabilized soil. It claimed that the strength of solidified soil both increase at first and then decrease with the increasing content of sodium sulfate and magnesium sulfate.2. SEM tests and EDS tests are carried out to study the influence of stabilized soil on the aspects of microstructure and analyze the microstructure rule of cement soil by IPP software quantitatively. It shows that rate of pore area decreased with the increasing content of sodium sulfate. The product filled the pore of soil particles which resulted in the decreasing of ratio of pore. But the ratio of pore area of magnesium sulfate performed conversely. The large pores and middle pores are important to the area of cemented soil pores in the side of pore distribution. Media content made no difference to the microporous, small and middle pores instead of the large pores in the side of pore shape.3. XRD tests are used to study the hydration process. The diffraction peaks of various minerals in XRD images are used to judge the materials and deduce the hydration process of cementitious material and the consolidation theory. Na+ and Ca2+ produced an equivalent exchange adsorption and made the soil transform into soil aggregate structure. This improved the strength of cemented soil. The increasing of SO42-made the strength increase at first and then decrease. Because the new product called gypsum in the reaction produced an expansive force to fill the pore of soil leaded to the strength improve at first. If the products are redundant, it could produce a force to destroy the soil structure which decreased the strength conversely. The increasing of Mg2+ decreased the strength of soil. Because there is a reaction between Mg2+ and C-S-H, C-A-H, which run out the cementitious materials and produced M-S-H and M-A-H with unsteady and low strength characteristics.