Abstract: Saline soil is widely distributed and highly salinized in the coastal areas of China,so it is difficult to be directly used in the construction of roadbed fillers. Using calcium carbide slag as composite geopolymer curing agent (CSG),the strength characteristics and enhanced curing mechanism of improved coastal saline soil were studied under the excitation of NaOH and sodium silicate alkali. Taking the unconfined compressive strength as the test index,the curing effect of modified saline soil and soil-cement was compared in freezing and salt environment. The results showed that the 28 d unconfined compressive strength of solidified saline soil is 3. 47 MPa,which is 8. 8% higher than that of solidified soil with the same amount of cement. After 10 freeze-thaw cycles,the strength of soil-cement is only 66. 7% of that of CSG soil,and CSG solidified soil has better freeze-resistance. The minimum strength of the solidified soil after salt solution erosion can reach 2. 21 MPa,and the strength decline is smaller than that of cement soil,and the effect of CSG on salt fixation is better. X-ray diffraction (XRD) and scanning electron microscopy ( SEM ) found that C - ( A ) - S - H gel, ettringite ( AFt ) and Friedel salt (3CaO·Al 2O3·CaCl 2·10H2O) were formed in the hydration process of CSG solidified saline soil,and a large amount of cementation materials were filled in the surface or gaps of soil particles. The hydration products interweave and bond to improve the strength of solidified soil. This study provides ideas for engineering construction and resource utilization of solid waste in coastal saline soil area. 

Key words: coastal saline soil,geopolymer,compressive strength,freezing and salt environment,microscopic mechanism