## 3 Experimental Results  
Figure 10 illustrates the changes in flow values for OPC and VG mixtures immediately after mixing and 30 min later. The initial flow values for VG10 and VG20 were slightly higher than those of OPC, likely due to the ball-bearing effect of VG. Additionally, the flow values for VG10 and VG20 exhibited a smaller decrease 30 min after mixing compared to OPC. This is attributed to the partial replacement of OPC with VG, which reduces the aluminate phase content in the mortar and consequently slows the initial hydration reaction compared to pure OPC. In contrast, VG50 showed a significant reduction in its initial flow value. Fine particles, such as SF, with large specific surface areas, tend to agglomerate due to van der Waals forces. When a substantial amount of powder is mixed without sufficient shear force, these agglomerates reportedly absorb mixing water [33; 34]. A similar phenomenon is believed to occur with VG. Furthermore, the initial flow values of SF10 and SF20 were slightly higher than those of VG. This difference is attributed to particle shape: VG particles are angular [24], whereas SF particles are more spherical and lack edges [35; 36]. The variation in particle shape influences flow values immediately after mixing. However, these differences are minimal, and VG can achieve flow performance comparable to that of SF. Figures 11 and 12 illustrate the relationship between the admixture replacement ratio, curing temperature, and the compressive strength of mortar at 1 d (demolding age) and 7 d (shipping age). The compressive strength values represent the average of three specimens, with the standard deviation (SD) shown as error bars (average value \(\pm\) SD). Steam curing significantly enhanced compressive strength at 1 d compared to curing at 20 \({}^{\circ}\)C without steam. For VG, the highest compressive strength was observed at a 20% replacement ratio, whereas for SF, the peak strength occurred at a 10% replacement ratio, both surpassing the strength of OPC. The differences in optimal replacement ratios between VG and SF are attributed to variations in glass content, Si component content, and specific surface area. Previous studies have reported that compressive strength variations in SF-containing specimens are closely linked to Si content [37], suggesting that Si content is a key factor for other admixtures as well. The Si contents of VG and SF were 73.7% and 95.4%, respectively, indicating a significant influence on the optimal replacement ratio. Figure 10: Change in the mortar flow values. At 7 d of age, mortar with VG achieved a compressive strength of 123 MPa for VG10 and VG20 under curing conditions with a maximum temperature of 60 \({}^{\circ}\)C or higher. In contrast, for SF20, poor hardening was observed in some specimens. A decrease in compressive strength was noted at a maximum curing temperature of 80 \({}^{\circ}\)C. This reduction in strength is hypothesized to result from steam curing conditions, where air within the mortar can move easily--particularly in cases with high flow values--leading to bubble expansion and partial porosity on the mortar surface, which in turn reduces strength (Figure 13). This phenomenon did not occur in VG10, VG20, or SF10, likely due to their mortar flow values. As shown in Figure 10, the difference between the top of the bar graph and the shaded area represents flow loss, with SF20 exhibiting the smallest flow loss. In other words, SF20 had high fluidity, and its flow value remained highest until the steam-curing stage, suggesting that this phenomenon may have occurred due to excessive fluidity. A potential solution to this issue is adjusting the admixture content to lower the flow value or extending the pre-curing time [38]. Additionally, since the SP used in this study does not have an air-entraining effect, it is believed that the reduction in strength was solely due to entrapped air. Figure 11: Relationship between mortar compressive strength at different curing temperatures (curing age 1 d).