Abstract: The Central Plains are located in an area that experiences seasonal freeze-thaw cycles, which can have significant effects on the soil structure of soil relics. To determine if lime-metakaolin (L-MK) is a feasible alternative to natural hydraulic lime (NHL) for earth site restoration work, tests were conducted using lime, metakaolin and silty sand from the site as main raw materials. Mass loss, unconfined compressive strength and splitting tensile strength tests were carried out on L-MK improved silty sand soil undergoing different numbers of freeze-thaw cycles to study its strength characteristics in depth. X-ray diffraction (XRD) thermogravimetry (TG), and scanning electron microscope (SEM) microscopic tests were also performed on some samples to reveal the internal mechanism of strength deterioration law of L-MK improved soil. Results indicate that L-MK improved soil has better freeze-thaw cycle resistance than NHL improved soil under the experimental mix ratio. Increasing the content of metakaolin improves the strength of L-MK improved soil. As the number of freeze-thaw cycles increases, the strain softening characteristics of L-MK improved soil show a weakening trend, and unconfined compressive strength and tensile strength decrease monotonically. After 30 freeze-thaw cycles, the unconfined compressive strength and splitting tensile strength of L-MK improved soil are about 3.79 and 1.16 times higher than that of NHL improved soil, respectively. The variation of strength is consistent with hydration products such as CSH and C₄AH13 generated by hydration reaction under the influence of freeze-thaw cycle for L-MK and NHL improved soil.

Key words: earthen sites, freeze-thaw cycle, lime-metakaolin, hydraulic lime, microstructure