## 6 Results and Discussion
### Fresh Tests
#### 6.1.2 Vicat Needle Test (Setting Time)  
As illustrated in Figure 8, increasing the dosage of SF from 15% to 20% led to a corresponding decrease in setting time. This effect was quantified by reductions of 4.5% and 19% in the initial and final setting times, respectively. Furthermore, increasing the SF dosage from 15% to 25% resulted in a more pronounced reduction in setting time, ranging from 13% to 33%. This phenomenon can be attributed to the acceleration of the hydration process caused by the presence of SF due to its fineness, chemical reactivity, and ability to enhance microstructural densification, all of which contribute to the faster setting of UHPC.  
An increase in the w/b ratio from 0.18 to 0.22 demonstrably extended the setting times, as observed in the increased initial set time by 38% and fin  
Figure 8: Vicat needle test (setting time) results for series 1 mixtures.  
Figure 7: Slump flow test results for series 1, 2, and 3 mixtures.  
90% (Figure 8). This phenomenon can be attributed to the dilution effect of a higher water content. As the w/b ratio increases, the concentration of cement particles within the mix is reduced. This translates into a decrease in the probability of contact between particles, consequently slowing down the hydration reactions essential for setting. The hydration process is a chemical reaction between water and cement that forms the binding compounds responsible for concrete hardening. When the water content surpasses the binder content (including cement and supplementary cementitious materials like silica fume), the cement particles become more dispersed, hindering their interaction and subsequent hydration [79; 80; 81].  
As observed, increasing the SNF dosage from 0.7% to 0.9% resulted in corresponding extensions of setting time, with increases of 52% and 74% in the initial set time and final set time, respectively (Figure 8). This phenomenon can be ascribed to the multifaceted interplay between chemical and physical processes induced by the incorporation of superplasticizers within the concrete matrix. Compounding further, a higher dosage of superplasticizer promotes superior dispersion of cement particles, thereby enhancing the workability of the mix. However, this improved workability comes at the expense of a modified hydration process, ultimately leading to a prolonged setting time for the concrete [82]. Superplasticizers, particularly second-generation types like SNF, alter the hydration process by dispersing cement particles and delaying their interaction with water. This dispersion reduces the rate at which hydration products form, slowing the buildup of the initial structure needed for setting. Additionally, by improving workability without adding extra water, superplasticizers reduce early particle clustering, which further delays the formation of calcium silicate hydrate (C-S-H) gel, resulting in an extended setting time [83; 84].  
In contrast, increasing silica fume (SF) content significantly reduced both initial and final setting times. Raising the water-to-binder ratio (w/b) from 0.18 to 0.22 prolonged the setting time markedly by up to 90% for final setting. Additionally, higher superplasticizer (SNF) dosage also led to longer setting times, by up to 74%.