Mechanical Properties and Microstructure Changes of Steel Slag–Fly Ash-Solidified Soil under Freeze–Thaw Cycles

Abstract

In recent years, the application of green, low-carbon geopolymer cementitious materials in engineering construction has increased. However, the winter freezes and spring thaws in northwest China often result in structural deterioration. To investigate the freeze–thaw (F-T) resistance and microstructure change of the solidified soil with steel slag–fly ash geopolymer (SF-GP), a series of mechanical and microscopic tests were conducted under the condition of F-T cycle. The objective of these tests was to systematically analyze the F-T resistance and disintegration changes of geopolymer-solidified loess after undergoing F-T cycles. The results indicated that the deterioration degree of the solidified soil would increase as the number of F-T cycles increased; yet, the addition of SF-GP could effectively reduce the deterioration degree of the solidified soil. After seven F-T cycles, the unconfined compressive strength and cohesion value of samples with geopolymer additions of 0%, 10%, and 20% decreased by 23.4%, 16.5%, and 12.0%, respectively, and 51.0%, 42.6%, and 42.1%, respectively. After 15 cycles, the reductions were 34.0%, 21.7%, and 25.3%, respectively, and 83.4%, 67.3%, and 67.1%, respectively. The incorporation of SF-GP effectively reduced both the disintegration rate and the total amount of disintegration, which increased with the number of F-T cycles. The mechanical properties of the solidified soil were analyzed from a microscopic perspective and the change of physical image, allowing a deterioration prediction model between the mechanical properties of the solidified soil, number of F-T cycles, and amount of SF-GP to be established. Overall, the study findings can serve as a foundation and theoretical guideline for studies on the deterioration of geopolymer-solidified soil in cold regions as well as practical engineering applications.