## 3 Results and Discussion
### Level Analysis of Influencing Factors of SSCFC's Fluidity and Compressive Strength
#### 3.4.2 Effect of SS Substitution Rate on Fluidity and Compressive Strength of SSCFC  
Figure 8a systematically characterizes the influence of the SS substitution rate on SSCFC slurry's rheological behavior. The experimental results reveal nonlinear fluidity decay with SS substitution: 15.7% reduction at 10\(\rightarrow\)15% SS, decreasing to 7.1% at 15\(\rightarrow\)20%. This contradicts previous findings [61], where fine SS particles act as ball bearings to reduce cohesion/shear stress and enhance fluidity. [PERSON] et al. [62] demonstrated that FC fluidity is governed by shear stress and gravity, with high-foam systems showing shear-dominated flow, where the amount of solid content inversely correlates with the foam volume. SS shares chemical similarity with Portland cement, containing cementitious phases like tricalcium silicate and dicalcium silicate with comparable hydration kinetics [12]. Dislocations and defects in SS lattice create water-soluble amorphous structures, enhancing its hydration activity. Thus, both cement and SS particles undergo concurrent hydration in SSCFC. This dual hydration consumes free water, significantly increasing internal shear stress. Numerous studies confirm that bubble coalescence due to pressure gradients critically destabilizes foam systems [63]. The Laplace equation (Equation (15)) governs interfacial mechanics:  
\[\Delta P=\frac{2\sigma}{r} \tag{15}\]  
where \(\Delta P\) signifies the interfacial pressure difference between the gas phase and liquid environment (unit: Pa); \(\sigma\) corresponds to the liquid's surface tension (unit: mN/m); and \(r\) defines the bubble's radius (unit: m). Figure 9: Diagram of force analysis of foam and foam wall structure analysis. The equation indicates that a reduced curvature radius (\(r\)) causes a significant increase in interfacial pressure differential (\(\Delta P\)). In dynamic foam systems, smaller bubbles with reduced radii generate higher internal pressures, driving migration towards larger low-pressure bubbles and triggering coalescence (Figures 10 and 11). This coalescence creates macroporous defects in SSCFC, degrading pore uniformity and inducing stress concentration, which compromises the compressive strength. Experimental observations reveal that SS addition induces mechanical shearing during mixing, fragmenting bubbles into uniformly distributed finer foam (Figures 10 and 11). Although increasing shear stress reduces fluidity, this process eliminates macrovoids, decreases the overall porosity, and enhances the mechanical performance. Figure 8b-d systematically reveal the evolution of compressive strength in SSCFC specimens with SS replacement rates across the 7d/14d/28d curing ages. The experimental data demonstrate strong correlation in strength trends across curing stages, leading to the 28d compressive strength being selected as the primary analytical target for final performance characterization. The compressive strength exhibits a V-shaped variation with the SS substitution ratio (10-20%): a 8.9% decrease at 10-15% SS, followed by 6.5% recovery at 15-20%, indicating a distinct threshold effect. This unique strength pattern arises because at 10-15% SS, latent reactive components (e.g., CaO, SiO\({}_{2}\)) engage in secondary reactions with cement  
Figure 11: Cross-section pore distribution of FC and SSCFC. Figure 10: The process of foam coalescence and fragmentation. hydrates, theoretically generating supplementary cementitious materials. However, SS's lower early-age reactivity compared to cement [64] limits the short-term strength contribution. Concurrently, SS's limited cementitious content [12] dilutes the effective binder concentration, impairing matrix densification and stress transfer efficiency. The interplay of these competing effects creates a strength reduction inflection point. Studies suggest that calcite coatings on SS surfaces may weaken binder-aggregate bonding [65; 66]. These glass-like interfacial layers reduce adhesion between cement paste and aggregates.