## 7 Conclusions  
This study evaluated the fresh and mechanical performance of ultra-high-performance concrete (UHPC) mixtures incorporating varying replacement levels of silica fume (SF), sodium naphthalene formaldehyde (SNF) as a second-generation superplasticizer, and different water-to-binder (w/b) ratios. The key findings are summarized as follows:  
**Fresh Properties**  
Increasing SF content from 15% to 25% led to reduced slump flow and shorter setting times, mainly due to reduced free water and accelerated hydration. Conversely, increasing the w/b ratio improved slump flow and extended setting time by enhancing particle mobility. A higher SNF dosage (from 0.7% to 0.9%) significantly improved both slump flow and setting time, demonstrating effective dispersion of cement particles and reduced agglomeration. Squeeze flow testing revealed three distinct paste behaviors:  
Low workability mixes with high stiffness and rapid transition to strain hardening;  
Highly flowable mixes exhibiting extended plastic phases and higher dilatancy;  
Transitional mixes highly sensitive to variables like flow rate and composition, affecting displacement trends. **Mechanical characteristics**  
Increasing the SF dose led to the closure of capillary paths and enhanced density, resulting in higher electrical resistance. The rise in the w/b ratio provided a conducive substrate for ion movement, leading to reduced electrical resistance. Higher SNF substitution enhanced cement particle packing density and raised electrical resistance. Increasing SF dosage from 15% to 25% reduced compressive and flexural strength due to uneven cement particle distribution, hydration disruption, and ITZ weakening. A higher w/b ratio also decreased strength by limiting the material for C-S-H gel formation. However, raising the SNF dosage from 0.7% to 0.9% improved UHPC strength by promoting complete hydration and reducing internal friction. The ANN model with 4-10-2 architecture presented an acceptable performance, according to the regression coefficient of >0.98. Also, the good performance of the FL model should not be overlooked. The error rate of the fuzzy logic model resulted in a range of 3.18-4.36%, while the error rate recorded for the ANN model was much lower (0.74-1.03%). **Benefits and Limitations of Second-Generation Superplasticizers**  
Naphthalene-based superplasticizers have the potential to improve workability without compromising strength while also improving particle dispersion for a denser, more homogeneous microstructure. However, their limitations include potential slump loss over time due to rapid adsorption on cement particles, reduced effectiveness in low-temperature conditions, and incompatibility with some cement types, which can lead to delayed setting or strength gain issues. Additionally, they may not provide the same level of flow retention as newer polycarbonate ether (PCE)-based alternatives, making them less ideal for highly complex UHPC applications requiring prolonged workability. Nevertheless, using this type of economic superplasticizer for relatively expensive concrete mixtures like UHPC may present a partial solution for further industrial application of this material. **Recommended Mix Design**  
Among the tested mixes, the most balanced performance was observed for:SF20 WB20N09: 20% SF, w/b = 0.20, SNF = 0.9%. This mixture exhibited high flexural and compressive strength, suitable setting time, and adequate slump flow, making it the recommended formulation for UHPC in practical applications. **Industrial perspective**  
* The study focused exclusively on second-generation SNF-based superplasticizers, and the conclusions remain within this scope. The results demonstrate that optimized SNF dosages (0.9%) can produce UHPC mixes with satisfactory fresh behavior and mechanical strength, suggesting the continued viability of SNF in cost-sensitive or prefabrication settings where flowability and early strength are critical.