Microstructural and mechanical effect of salt crystallization on remolded loess

Areas of high salinity are increasing especially in the loess-covered areas in China mainly due to extensive irrigation and arid or semi-arid climate. It is anticipated that evaporation of free water would lead to formation of salt crystals which would modify the microstructure of loess soils. The disturbance brought by salinization to the shear strength behavior of loess soils has been commonly investigated, while few studies mentioned the microstructural and mechanical effect of salt crystallization. This study aims to examine the influence of salt crystallization on the microstructure, pore-size distribution specifically, and mechanical behavior of remolded loess. The results indicated that the modification induced by salt crystallization to the microstructure of remolded loess was mainly dependent on the initial (or molding) water content and soil density. Corresponding to two molding water contents, two modes for describing the microstructural modification due to salt crystallization were proposed from the views of inter-aggregate pores and intra-aggregate pores. At a low initial water content (less than the optimum water content, 10%), salt crystallization occurs mainly in the “body” of constricted pores as well as small intra-aggregate pores. While at a high initial water content (the optimum water content, 18%), salt crystallization would take place in both the “body” and “neck” of constricted pores. Furthermore, intra-aggregate pores with a wide range of diameter could be affected due to large volume of salt crystals and small volume of inter-aggregate pores. The collapsibility of remolded loess was closely related to the volume of salt crystals and salt type. The type of salt crystals has limited influence on the compressibility of remolded loess.