Effect of salt content on freezing temperature and unconfined compression strength of lime-treated subgrade clay

Salt content can have an effect on the freezing temperature (FT) and unconfined compressive strength (UCS) of lime-treated subgrade clay. However, very limited investigations have been carried out to reveal the effect of salt content on the engineering properties of lime-treated subgrade clay. Moreover, reported results in literature are not consistent. The influence of salt content on the FT and UCS of lime-treated subgrade clay of the Xi-Bao Expressway, Shaanxi, China, was investigated in this study. Lime-treated clay with various salt contents (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5%) and moisture contents (10, 13, 16, 19 and 22%) was prepared artificially. A series of FT and UCS tests of lime-treated clay specimens after 7-d curing periods were conducted. The analysis of experimental results indicated that FT and UCS were related parabolically to the salt content under different moisture contents. The results demonstrated that a high salt content had a detrimental effect on the UCS of lime-treated clay, the UCS loss increased greatly when the salt content exceeded 1.0%. Lime-treated clay mixed with salt content of 0.8-1.1%, reduced the FT from to −2.06 °C to −3.98 °C, which were more resistant to the negative freezing-thawing damage, and simultaneously the UCS meet engineering requirements. Based on the experimental results, empirical prediction equations of FT and UCS were established to describe the relationship with the salt content under different moisture contents, verified by a number of data for the He-Huai, He-An, Xi-Xian and G307 Expressways. The findings of this study can provide a rational basis to understand the effect of salt content on engineering properties of lime-treated clay.