Study on Properties of Expansive Soil Improved by Steel Slag Powder and Cement under Freeze-Thaw Cycles

摘要

Expansive soil is considered to be an unfavorable soil due to its swelling-shrinking behavior. In order to improve the properties of expansive soil, the addition of steel slag powder (SSP) has been used to improve expansive soil that has been mixed with the cement. In this study, a series of cylindrical improved expansive soil specimens were prepared, which were improved either by the addition of cement, cement SSP, or cement SSP sodium hydroxide (NaOH). All of the specimens were prepared with an optimum water content and then subjected to a maximum of 12 closed-system freeze-thaw (F-T) cycles. The specimens were subjected to different curing times and temperatures (-5°C,-10°C and -15°C) during the tests. After each freeze-thaw (F-T) cycle, the volume of each specimen was measured and an unconfined compression strength (UCS) test was performed. The results have shown that as the temperature of the F-T cycle decreased, the volume expansion rate increased with the increase of the length of the F-T cycle. As the curing time increased, the effect of the F-T cycles on the volume change rate of the specimens reduced and the UCS increased. The first F-T cycle had the greatest influence on the volume of the specimen as well as the UCS of the improved expansive soil. After the improved expansive soils had undergone more than eight F-T cycles, the volume change rate of the specimen tended to stabilize. The maximum F-T volume change rate of the improved soil was 1.93%.When the curing age was 60d and 90d, the strength of the specimen with cement SSP sodium hydroxide was 377.3 kPa and 294.7 kPa higher than the specimen with cement only (ES specimen), and its strength degradation rate was 18.737% and 9.97% lower than the ES specimen. The results have shown that the addition of SSP and cement improved the expansive soil; moreover, NaOH inhibited the degradation of the soil during an F-T cycle.