Strength Degradation and Prediction Model of Flowable Solidified Soil Under Coupled Salt Erosion and Freeze-Thaw Conditions

To investigate the strength degradation behavior of flowable solidified soil under the coupled effects of salt erosion and freeze-thaw cycles, flowable solidified soil specimens were prepared using cement blended with slag and phosphogypsum. Laboratory tests were conducted to simulate freeze-thaw cycles in fresh water, sodium chloride solution, and sodium sulfate solution. The strength evolution, mass variation, and deterioration characteristics of different solidification systems were analyzed. The results show that with increasing freeze-thaw cycles, the compressive strength of all specimens exhibits a three-stage degradation pattern, including slow reduction, rapid reduction, and gradual stabilization. The incorporation of slag significantly improves resistance to salt erosion and freeze-thaw damage. After ten freeze-thaw cycles, the strength retention rate of slag modified specimens ranges from 36% to 54%, while the mass change rate is between 0.25% and 0.60%, indicating the best durability performance. Under coupled salt erosion and freeze-thaw conditions, the cement slag system experiences greater strength loss in sodium sulfate solution than in sodium chloride solution, with an increase of 28% to 39%. In contrast, the cement phosphogypsum system shows better resistance in the sodium sulfate environment. Based on the experimental results, a strength degradation model suitable for coupled salt erosion and freeze-thaw conditions is established through regression analysis. The proposed model can be used to predict long term strength evolution of flowable solidified soil in harsh environments and provides reference for engineering applications in cold and saline regions.