Evolution Mechanism of Strength Characteristics of Sludge Soil Cured with Solid-Waste Cementitious Agent Under Drying-Wetting and Freezing-Thawing Cycles

Abstract

Cementitious agent can enhance soil properties and be used as subgrade filler, but its cementing effect and the strength characteristics of solidified soil are easily affected by external climatic conditions. This study measured the strength and durability of solidified sludge soil (PSCS) through unconfined compressive strength (UCS) tests, drying-wetting (D-W) cycles, and freezing-thawing (F-T) cycles, and optimized the cementitious agent dosage. MIP tests were used to analyze changes in microscopic pore structure and explore the balance between hydration reactions and the effects of D-W and F-T cycles. The results show that a cementitious agent dosage above 15% is more beneficial for the strength and durability of PSCS, with PSCS15 being more economically advantageous. MIP analysis also indicated that D-W and F-T cycles respectively increased the porosity of pores in the 5-30 μm and 1-10 μm ranges, supporting the macroscopic strength evolution mechanism. In the first stage, incomplete hydration and the dominant effects of D-W and F-T cycles damage internal pores, reducing strength. In the second stage, continuous hydration becomes dominant, with hydration products filling the pores and increasing strength. In the third stage, the drying phase of D-W cycles, accompanied by moisture evaporation, inhibits hydration, reducing hydration products and negatively affecting strength as pore sizes increase. Meanwhile, during F-T cycles, moisture remains in the soil, allowing hydration to continue, filling pores and increasing strength. Compared to F-T cycles, D-W cycles have a more significant negative impact on solidified soil.

Keywords: Solidified soil, Drying-wetting cycle, Freezing-thawing cycle, Strength characteristics, micro-pore structure