Microstructure And Mechanism Research On Cement Stabilized Salt-rich Clay

Cement Mixing Method (CMM) is frequently used to treat soft soils in highway construction nowadays with its advantages such as convenient installation and low expense. Nevertheless, researchers and engineers have found that the CMM doesn't work well in some marine area with high concentrations of soluble ions in the soil. Some lab researches also proved that the strength of such kind of cemented soil is much lower than the ordinary soils. The mechanism of this phenomenon is not clear at present.Marine clay collected from suburb of Lianyungang city is used in this research. Resulted by sea water invasion, the concentrations of soluble ions in this clay is very high, especially those of Mg²⁺, Cl^- and SO₄^2- compared with typical clay Shanghai. In situ tests indicated that the strengths of deep mixing piles here with ordinary cement ratio developed much slower with time. Even increasing the cement ratio by a considerable amount doesn't bring ideal effects. It has been inferred that high concentration of soluble ions may have restrained the hydration and pozzolanic reactions, thus the strength development of cemented soil.A special method in sample preparation has been adopted to remove the disturbing factors: The air-dried clay was carefully crushed, sieved, and "washed" 3 times. The "wash" procedure can effectively reduce the salt ions' concentration to ordinary level. Salts were mixed into the "washed" soil at different levels when making cemented clay samples (70.7×70.7×70.7mm). Meanwhile, samples with slag cement were also prepared. The curing dates are 7d, 28d, and 60d. Unconfined compression test, X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) test are performed. As for SEM, Two imaging methods are used: secondary electron (SE) and backscattered electron (BE) respectively. In order to strengthen the microscopic test results, qualitative andsemi-quatitative processing methods are adopted.The lab tests indicated that high concentration soluble ions can indeed harm the cemented clay, but the time and extent of the harm differ apparently with the ion type. Mg2+ can decrease mainly the mid and long term strength at a certain extent, Cl" affects the strength significantly in all periods, while SO42" has a great adverse effect on the long term strength of cemented clay. However, the slag cemented clay showed a strong ability to resist the infection of soluble ions.Finally, based on the microscopic tests, the mechanism of the salt ions' effects and the resistance ability of slag cemented clay are discussed. Advices to future research and applications of CMM in salt-rich clay are also proposed.