## 4 Discussion  
### Workability and Mechanical Properties  
The mechanical properties of the nine studied BFRPC are presented in Table 5.  
The fluidity properties of the nine studied mixes are shown in Figure 4. The experimental results show, as expected, the W/B ratio is the most significant factor affecting the workability of BFRPC. The content of free water in the mixture increased with the growth of water-binder ratio, which improved the fluidity of concrete by 10-12%. However, as shown in Figure 4, the increase of mineral admixtures (SF and QS) content carried a 7-14% fluidity penalty. Due to the large specific surface area, the tiny silica fume particles would absorb the free water in the slurry, which led to a decrease in the fluidity of the mixture. On the other hand, the addition of QS played a stable supporting role in the mixture, enhancing the adhesive property of cementitious materials, and increasing the friction force between the fibers and the aggregate particles, which worsened the workability. However, it is evident from Figure 4 that, in the case of RPC, the presence of basalt fiber did not significantly worsen the fluidity performance. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Mix** & **BF1** & **BF2** & **BF3** & **BF4** & **BF5** & **BF6** & **BF7** & **BF8** & **BF9** \\ \hline Fluidity (mm) & 124 & 139 & 154 & 161 & 150 & 139 & 166 & 152 & 155 \\ Compressive strength (MPa) & 129.6 & 109.5 & 86.4 & 121.1 & 131.8 & 98.8 & 120.1 & 136.6 & 129.4 \\ Flexural strength (MPa) & 13.6 & 11.6 & 10.8 & 9.9 & 13.1 & 12.2 & 11.7 & 12.6 & 11.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mechanical properties of the studied BFRPC. Figure 3: Flexural test and sensor layout. BFRPC, Basalt fiber reactive powder concrete. The values of the compressive and flexural strength for nine groups of mixes are shown in Figures 5 and 6. With the increase of W/B ratio, the compressive and flexural strength values of BFRPC gradually declined. The high W/B ratio led to the increase of porosity, resulting in the generation of interface weaknesses and the decrease of strength. The highest compressive and flexural strength values of 131.8 MPa and 13.1 MPa were obtained when SF/C was 0.4. The hydration reaction of cement generated Ca(OH)\({}_{2}\), which generated C-S-H gel through the pozzolanic effect with SiO\({}_{2}\) contained in silica fume, filled the internal micro-pores of BFRPC, improved the compactness of the mixture and thus improved the compressive and flexural strength. However, excessive amount of silica fume would limit the immigration of free water in the mixture, which could lead to the occurrence of dry shrinkage. [PERSON] [29] proposed a similar effect in strength vanishes when the silica fume content is too high. Initial cracks would be formed inside the matrix, which could damage the integrity of BFRPC materials, resulting in a decrease in the strength. Figure 4: Fluidity of the BFRPC. Figure 5: Compressive strength of the BFRPC. Figure 6: Flexural strength of the BFRPC. It can be seen that the most favorable QS/C ratio for BFRPC strength was 1.3. Under this condition, the compressive strength of the material was 136.6 MPa and the flexural strength was 12.8 MPa. As a hard mineral particle, quartz sand could form a stable supporting framework when mixed into the mixture. The uniform filling of cementitious materials in it made good interfacial adhesion between aggregates and cement paste, which improved the density of the concrete matrix. Nevertheless, when too much quartz sand was mixed, the bonding performance between the cementitious materials and aggregates became worse. The resulting weak interfacial transition zone led to the decrease of strength. For the addition of basalt fiber, the compressive strength was observed to be highest for specimens with fiber content of 10 kg/m\({}^{3}\).