## 1 Introduction
Many scholars have studied cement-based materials' physical and chemical properties under different curing conditions by adding slag, fly ash, metakaolin waste, nanomaterials, and other materials and used SEM/EDX, XRD, TGA/DTG, resistivity, and other test methods to verify and analyze the unconfined compressive strength, viscosity value, yield strength, and other macromechanical properties of the enforcement [14; 15; 16; 17]. In this experiment, the particle size distribution in the composite curing agent was improved by adding UFC. A higher Blaine area and smaller particle diameter of cement accelerated cement's hydration rate and strength development [18]. Improving cement particle fineness and optimizing the particle size distribution, type, and content of compound curing agents improved cement soil's mechanical properties. At the same time, the external admixture of UFC abandons the idea of traditional peat soil treatment with high organic matter content. In the context of global energy conservation and emission reduction, increasing the amount of cement or changing the type of cement to improve its strength is contradictory. In this study, the partial replacement of OPC with UFC increases the strength of cement soil and reduces the amount of cement. It is of great practical importance for China to achieve its carbon peaking and neutrality goals. Also, it can provide some ideas for the future treatment of different types of soft foundations. [PERSON] et al. [19] have shown that increasing the fineness of cement reduced the plastic viscosity of cement paste to a certain extent, significantly improved the early strength of cement paste, increased the hydration heat, advanced the peak of hydration heat, and shortened the induction period. The porosity of cement paste decreased with the increase in cement fineness. [PERSON] et al. [20] investigated the impact of cement fineness on the physicochemical properties and microscopic structure of cement. The results indicated that fineness greatly influenced the early compressive strength. After 24 hours of hydration, the finer UFC's compressive strength was approximately three times that of OPC. The UFC showed a more compacted microstructure at the initial curing stage. At 28 days, macropores were partially filled with hydration products. After 28 days of hydration, the larger pores were in the 30-100 nm range, and the pore range of ordinary cement was in the 100-200 nm range. [PERSON] et al. [21] investigated the relationship between cement particle size distribution and cement properties. The results demonstrated that a narrow particle size distribution improved the hydration rate. The more extensive distribution index accelerated the hydration rate. Narrow distribution was advantageous in reducing the porosity of cement stone in the same water-cement ratio. [PERSON] et al. [22] investigated that UFC was an effective cementitious material to improve the performance of cement. The bulk density of cement and the fluidity, rheology, and strength of cement paste increased when the UFC was 10-20%. [PERSON] et al. [23] introduced that UFC's incorporation improved cement particle distribution, optimized bulk density, and reduced porosity. The strength of the mortar is significantly improved when the UFC is 30-40%. [PERSON] et al. [24] used lime, gypsum, slag powder, UFC, and other parts to replace cement to form curing agents with different proportions and studied the early curing effect and failure characteristics of different proportions of curing agents on high water content soft soil. The results indicated that UFC greatly influenced the solidified soil strength, as the curing agent ratio was 20%. The solidified soil strength of 50% moisture was enhanced slowly as the UFC increased. There was a UFC threshold value. The mechanical properties of cement soil fundamentally depend on its pore structure [25].