## 3 Result and Discussion  
Through rigorous testing, the efficacy of the epoxy resin in enhancing the structural integrity, durability, and chemical resistance of treated cementitious materials was assessed. Table 10 lists the density results. The observed increase in density with a higher silica content is attributed to the inherent density of the silica particles (approximately 2.7 g/cm\({}^{3}\)), which is significantly higher than that of the epoxy resin (1.3 g/cm\({}^{3}\)). This relationship highlights the direct impact of the filler content on the physical properties of composite materials, demonstrating how incorporating sand can modify and enhance the final product's characteristics. Figure 8 shows the stress-strain diagrams for the mixtures. The tensile tests revealed that the addition of silica sand improved the tensile strength and Young's modulus of the epoxy resin composites. All mixtures exhibit an elastic behavior and a brittle response. Table 11 summarizes their tensile mechanical properties. The tensile strength increased from 29.47 MPa in Mixture 1 to 35.52 MPa in Mixture 3. Similarly, the elastic modulus ranges from 4.38 GPa to 5.83 GPa, indicating a substantial enhancement in the material's stiffness. Conversely, the elastic deformation decreases by 38%. The increase in the tensile strength and elastic modulus can be attributed to the improved interfacial bonding between the filler and the epoxy matrix. The angular and rough surface texture of the silica particles contributed to better interlocking and load transfer within the composite. This output complies with previous studies on the mechanical performance of mineral fillers in polymer matrices (RIF). The optimal performance was observed at a 10% silica sand content and beyond the tensile strength slightly decreased (Mixture 4). This reduction may be due to the increased brittleness and reduced elongation at the break (from 8.87% to 5.5%), which indicates a transition from a ductile to a more brittle failure mode. Therefore, only Mixture 1 and Mixture 3 have been investigated in the resin-reinforcement adhesion tests. Table 12 lists the results of the Resin-Reinforcement adhesion tests. The  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & **Density (g/cm\({}^{3}\))** & **Average (g/cm\({}^{3}\))** & **S.D (g/cm\({}^{3}\))** & **C.V (\%)** \\ \hline Mixture 1 & 1.397 & 1.507 & 1.551 & 1.485 & 0.079 &  
adhesion strength between the CFRP and the resin was significantly improved with the inclusion of silica sand. As shown in Table 12, the average maximum pull-out force increased from 6.37 kN in the unfilled resin (Mixture 1) to 8.97 kN in Mixture 3. Figure 9 demonstrates the failure mode of the resin-CFRP bond, which is abrupt at the bonded surface. Notably, the resin retains traces of carbon fibers, indicating chemical solid adhesion. Cleaning the carbon reinforcements with acetone enhances the adhesion process, ensuring optimal bonding [6]. Two concrete blocks were cast and subjected to direct pull-out tests to investigate the effect of a sand addition to the resin. Table 13 lists the direct pull-out tests. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Mix**} & \(\sigma_{\text{max}}\) & **S.D** & \multirow{2}{*}{**C.V (\%)**} & \multirow{2}{*}{**\(\varepsilon_{\text{rup}}\) (\%)**} & \multirow{2}{*}{**S.D (\%)**} & \multirow{2}{*}{**C.V(\%)**} & \multirow{2}{*}{**E (GPa)**} & \multirow{2}{*}{**S.D (GPa)**} & \multirow{2}{*}{**C.V (\%)**} \\  & **(MPa)** & & & & & & & \\ \hline Mixture 1 & 29.47 & 0.60 & 2.04 & 8.87 & 0.13 & 1.47 & 4.38 & 0.16 & 3.65 \\ Mixture 2 & 32.82 & 1.00 & 3.05 & 7.93 & 0.07 & 0.88 & 4.92 & 0.08 & 1.63 \\ Mixture 3 & 35.52 & 0.48 & 1.35 & 6.50 & 0.20 & 3.08 & 5.83 & 0.07 & 1.20 \\ Mixture 4 & 31.28 & 1.48 & 4.17 & 5.50 & 0.20 & 3.64 & 5.82 & 0.18 & 3.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: The tensile mechanical properties of mixtures. Figure 8: The tensile curve of mixtures. The blocks have a comparable behavior of the slip-adhesion curve (Figure 10).