## 3 Results and Discussion
### The Freeze-Thaw Resistance of HSC under Dry Conditions  
Figure 4 illustrates the freeze-thaw resistance of HSC cured under 50% RH and 30% RH conditions. The results indicate that when HSC is cured in a dry environment, insufficient hydration of cement occurs. This not only affects the growth of hydration products and the densification of pore structure at the microscopic level but also leads to the formation of internal microcracks due to the dry shrinkage of concrete, resulting in a reduction in the freeze-thaw resistance of the reference HSC. \begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline \multirow{2}{*}{**No.**} & **Fiber Density, g\(\cdot\)cm\({}^{-3}\)** & **Fiber Diameter, mm** & **Fiber Length, mm** & **Fiber Volume Fraction, \%** & **Fiber Fraction, \%** & **Fiber Type-Dimension Random Distribution** & **Three-Dimensional Random Distribution** & **Three-Number, Single m\({}^{-3}\)** \\ \hline HSC-3 & 7.8 & 0.650 & 20 & 2 & 5.10 & 5.75 & \(1.9\times 10^{4}\) \\ HSC-4 & 0.97 & 0.035 & 20 & 0.1 & 1.23 & 1.38 & \(5.344\times 10^{7}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Fiber Spacing and Fiber Quantity in Two Fiber-Reinforced Concretes. Figure 4 illustrates the freeze-thaw resistance of HSC cured under 50% RH and 30% RH conditions. The findings suggest that when HSC undergoes curing in a dry environment, there is insufficient cement hydration. This not only impacts the growth of hydration products and the microscopic densification of the pore structure but also leads to the formation of internal microcracks due to the dry shrinkage of concrete, ultimately resulting in reduced freeze-thaw resistance of the reference HSC. Figure 5 displays the mass loss and surface damage of HSC with varying mix ratios after undergoing freeze-thaw cycles under 50% RH. HSC-1 and HSC-2, which experienced the most significant mass loss, are used as examples. Figure 4 displays mortar spalling, exposing a large area of coarse aggregate and causing damage and detachment at the end. Figure 4 shows coarse aggregate shedding, resulting in obvious missing ends and severe damage. Figure 4: Freeze-Thaw Resistance of HSC cured under 50% RH and 30% RH Conditions. Figure 5: Mass variation and surface damage following freeze-thaw tests (RH 50%). Figure 6 illustrates the mass loss and surface damage of HSC after freeze-thaw cycles with varying mix ratios at 30% RH. The figure illustrates that HSC-1 and HSC-2 suffered significant freeze-thaw damage after 725 cycles, resulting in mortar flaking, large aggregate exposure, and broken ends. HSC-3 remained largely unaffected by the freeze-thaw process. HSC-4 exhibited frost-crisp ends, with mortar flaking on the surface and exposed aggregate and fiber. A detailed view of the aggregate and fiber exposure is shown in Figure 7. Both HSC-5 and HSC-6 displayed mortar flaking with a rough surface and HSC-5 also experienced corner loss. The study compared the damage caused by freeze-thaw cycles on HSC under different RH conditions. The results showed that the severity of freeze-thaw damage on concrete increased with higher RH levels. However, HSC-3 with steel fibers did not exhibit significant damage, regardless of the RH conditions. For the reference HSC-1 cured at 30% RH and 50% RH after 850 freeze-thaw cycles, there is a notable acceleration in the decrease of the relative dynamic elastic modulus and the rate of mass loss. Moreover, the drier the curing environment, the poorer the freeze-thaw resistance. This demonstrates the sensitivity of HSC's freeze-thaw resistance to the RH of the curing environment. In the case of HSC-2, with the addition of an AEA expansive agent, the degradation observed is more severe, attributed to the hydration process of cement and expansive agents in low RH environments. XRD analysis [20] reveals a 163% increase in the characteristic peak intensity of AFm in HSC-2 compared to HSC-1, while the characteristic peak intensity of AFt decreases by 19% when cured at 50% RH.