## 3 Research Results and Analysis
The amount of fiber has a nonlinear effect on the water demand of the mixtures and with the addition of dispersed reinforcement in the amount of 50 kg/m\({}^{3}\)\(W/C\) ratio increases more visibly than with an increase in the fiber dosage from 50 to 100 kg/m\({}^{3}\). The volume of the hardening accelerator Sika Rapid 3 does not significantly affect the \(W/C\) ratio of mixtures of equal workability, while the introduction of this modifier does not significantly reduce the \(W/C\). In general, due to the use of the effective polycarbonate type superplasticizer MasterGlenium SKY 608, the \(W/C\) ratios of all investigated concrete and fiber-reinforced concrete mixtures were in the range of 0.307 to 0.344, which makes it achievable to provide high physical and mechanical properties and durability of concrete and fiber-reinforced concrete for the rigid pavements repair. For each concrete and fiber-reinforced concrete composition, compressive strength tests were performed for samples at the age of 2 and 28 days (cubes 10 cm \(\times\) 10 cm \(\times\) 10 cm) and flexural strength (prisms 10 cm \(\times\) 10 cm \(\times\) 40 cm). The size of the samples was taken based on the size of the aggregates and the length of the fibers in accordance with the building codes ASTM C78/C78M-16 [36], DSTU B V.2.7-214:2009 [37], BS EN 12390-5:2009 [38] and BS EN 12390-3:2009 [39]. The strength tests of the concrete and fiber-reinforced concrete were carried out according to the same standards. To determine the strength at each experimental point at the age of 2 and 28 days, 3 cubes and 3 prisms were tested. Figure 2 represents a scheme of the flexural strength tests of prism specimens, and Figures 3 and 4 represent steel-fiber-reinforced specimens after strength tests. Figure 1: Variation of concrete and fiber-reinforced concrete mixtures \(W/C\) depending on variable composition factors. An analysis of the diagram in Figure 5a shows that with a volume of the Sika Rapid hardening accelerator from 1.2% and with a steel fiber dosage from 60 kg/m\({}^{3}\) and higher, the early flexural strength of the repair concrete (2 days age) is at least 8.5 MPa. This level of concrete flexural strength allows the highway pavement to be operational. The values of the flexural strength of the investigated concretes and fiber-reinforced concretes at the age of 2 days are most influenced by the amount of steel anchor fiber. The highest\(f_{\text{cft2}}\) value reaches 8.7-9.3 MPa with a fiber dosage in the range of 85-90 kg/m\({}^{3}\), and a further increase in the amount of fibers already negatively effects on the early flexural strength. At the design age of 28 days, due to dispersed reinforcement with anchor steel fiber in the amount of 70-90 kg/m\({}^{3}\), the concrete flexural strength increases more than 2 times: from 7-8.5 MPa up to 15.5-17.5 MPa (Figure 5b). The high efficiency of fiber reinforcement at the age of 28 days is explained due to the increase in concrete strength over time and the growth of the fiber adhesion strength to a cement-sand matrix [40]. Using anchor steel fiber in a dosage of more than 60 kg/m\({}^{3}\), the flexural strength of the fiber-reinforced concrete is not less than 16 MPa, which ensures the high-quality function of the material as a road pavement under the highest loads. Nevertheless, at the design age, when a hardening accelerator is added to the concrete composition, the flexural strength decreases slightly. This reduction is limited to 10-12% of the composition's strength without hardening accelerator with the same amount of fiber. It is important to note that the positive effect of fiber on strength is achieved despite the increase in the \(W/C\) ratio required to maintain the workability of the mixture when dispersed reinforcement is introduced.