Abstract: In order to simulate and study the effect process and mechanism of cemented soil by different sodium sulfate contents, a series of tests are conducted on the cemented soil samples, such as compression strength test, X-ray diffraction (XRD) phase test and scanning electron microscope (SEM) test, SEM pictures processed by Image-ProPlus6.0（IPP）software; the distribution of pore average diameter of SEM pictures at 200 magnified times is calculated. The test results show that the compressive strength of cemented soil increases with the increase of sodium sulfate content; and the value reaches its peak when the content is 9 g/kg. The distribution of cemented soil pore changes owe to sodium sulfate, and the porosity of SEM photo at 200 times decreases. From the SEM photos analyses show that the microscopic structure of cemented soil by sodium sulfate exhibits the granularity-inlay-cement. Chemical products are analyzed by means of XRD test. The testing results show that the chemical products become more such as Ca(OH)2, CaSO4, CaCO3 and C-A-S-H, after the sodium sulfate participated in chemical reactions. Those chemical products mainly play the role of crystallization action in the chemical reaction process, which is good for cemented soil strength when the chemical products in the sample with sodium sulfate content lower than 9 g/kg. With the sodium sulfate content increasing, the gel around soil particles is broken down, which make the strength of cement soil decrease.

Key words: microscopic structure, pore, cemented soil, sodium sulfate, average diameter