## 3 Research Results and Analysis  
Composition No. 1 was elaborated on the basis of previous studies [31; 34] and was applied as a starting point for further modification. For this composition, as can be seen from Table 3, the \(W/C=0.318\), the compressive strength at the age of 2 days was \(f_{ck,cube}=46.5\) MPa, the compressive strength at the age of 28 days was \(f_{ck,cube}=85.5\) MPa, the flexural strength at the age of 2 days was \(f_{ctk2}=5.6\) MPa and the flexural strength at the age of 28 days was \(f_{ctk}=9.0\) MPa. In the rest of the mixtures, the cement content was kept the same as for the control mixture No. 1 (400 kg/m\({}^{3}\)) in order to be able to correctly determine the effect of the fiber and the hardening accelerator. All concrete mixtures had equal workability (slump 5-8 cm), determined according to the BS EN 12350-2:2019 [35] and the \(W/C\) ratio depended on the composition. Such workability was taken as typical for full depth repair mixtures. With a fixed \(W/C\) ratio, it would be impossible to ensure the equal workability of the mixture, which is important during repairs, or it would be necessary to change the amount of plasticizer and would not allow us to provide its optimal amount. The amount of water changed in the mixture, and the amount of sand and gravel was selected depending on the amount of water, fiber and hardening accelerator. The fiber was introduced into the mixer after the supply of crushed breakstone and sand but before the supply of cement and water with admixtures. This ensured the homogenous distribution of the fibers. According to the data in Table 3, to determine the influence effect of the steel fiber and the hardening accelerator dosages on the concrete's properties, an experimental statistical model (ES-model) was accepted (1). In the ES-model (1), the experimental error is 0.0013. The coefficients of all ES-models were calculated taking into account the accepted experimental error at 10% two-sided risk. For a given risk level, after each calculation, the hypothesis was tested about the difference between the estimates of the ES-model coefficients from zero, i.e., the significance of the coefficients. To test the hypothesis about the equality of the coefficients to zero, the Gaussian accuracy criterion was used. The coefficients which, according to the results of the check, did not differ from zero were excluded from the ES-model. After eliminating insignificant coefficients, the model was recalculated,  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{ \begin{tabular}{c} **No. of** \\ **Misture** \\ \end{tabular}  } & \multirow{3}{*}{\ \begin{tabular}{c} **X\({}_{1}\)** \\ **Hardening** \\ **Accelerator** \\ \end{tabular}  } & \multirow{3}{*}{ \begin{tabular}{c} **X\({}_{2}\)** \\ **Suel** \\ **Fiber** \\ \end{tabular}  } & \multicolumn{6}{c}{**Concrete and Fibrous Concrete Mixtures**} & \multicolumn{6}{c}{**Sixa**} & \multicolumn{6}{c}{**Steel**} & \multirow{6}{*}{**Water. **} & \multirow{6}{*}{**(MPa)**} & \multirow{6}{*  
and the test was repeated. The ES-model with all significant coefficient estimates was tested for adequacy using the Fisher criterion [33]. Recording the polynomials of the ES-models in place of the reduced insignificant elements, a coefficient equal to zero was written, that is, the value \(\pm 0\) was indicated:  
\[W/C=0.328-0.005x_{1}\pm 0{x_{1}}^{2}\pm 0x_{1}x_{2}+0.012x_{2}-0.003{x_{2}}^{2} \pm 0x_{1}x_{2}, \tag{1}\]  
According to (1), a diagram was drawn, shown in Figure 1.  
An analysis of the diagram in Figure 1 reflects that even with the maximum dosage of fiber (100 kg/m\({}^{3}\)), the \(W/C\) of mixtures are in the range of 0.332 to 0.344. It is at such values of the \(W/C\) ratio that it is possible to achieve a high-early strength of steel-fiber-reinforced concrete, which is especially important for road repair.