**3. Results**

### *3.1. Consistency of Concrete Mix*

The results of measuring the consistency of the concrete mix are presented in Table 6.


**Table 6.** Results of the measurement of cone fall.

The greatest cone fallout was observed in the case of concrete without the addition of fibers and with steel fibers. The smallest for concrete with the addition of glass fibers. The reason for this is the effect of fibers on the workability and consistency of the mixture. Fine

polymer and glass fibers propagated in the mixture, improving its stability. Steel fibers, due to their greater rigidity and larger size, did not provide this property. Concrete without the addition of fibers, as a reference result, confirms this thesis.

### *3.2. Compressive Strength*

The compressive strength test was carried out for concrete used for the production of block supports and concrete used to make a concrete slab. Below in Table 7 and Figure 15 are the results of tests of concrete with additives in the form of fibers and reference concrete.


**Table 7.** Results of the compressive strength test.

Based on the presented results, it can be concluded that the use of fibers slightly increased the compressive strength of concrete intended for block supports. The average strength of concrete without the addition of Z5 fibers is 68.5 MPa, while the strength of concrete with the addition of fibers is from 71.7 MPa for Z2 concrete, to 76.9 MPa for Z4 concrete, which is a strength increase of 4.7% to 12.3%. Although fibers have a greater impact on the increase in tensile strength than on compression, the conducted research shows that their use significantly increases the compressive strength and thus the class of concrete. In addition, it should be stated that the strength reserve is acceptable and allows us to assume that the concrete intended for the slab (Z1) and block supports (Z2–Z5) has been designed correctly.

### *3.3. Frost Resistance*

The frost resistance test was carried out for concrete intended for the production of block supports and concrete intended for making a concrete slab. Below in Table 8 are the results of tests of concrete with additives in the form of fibers and reference concrete.

Based on the analysis of the obtained results, it should be concluded that all concrete samples meet the standard requirements. The permissible maximum loss in weight of samples after the frost resistance test should not exceed 5%, and the decrease in strength in relation to comparative samples not exposed to frost should not exceed 20%. All designed concretes are characterized by a loss of mass below 0.5% and a decrease in strength below

4%, which significantly exceeds the standard requirements. The research also shows that the use of fibers improved the frost resistance parameters of concrete intended for block supports in relation to the reference concrete Z5. In the case of steel fibers, the Z2 sample, the average strength decrease is reduced by 45.2% compared to the average strength decrease of concrete without fibers, and the average loss weight is reduced by 26.5%. For concrete with polymer fibers, Z3 concrete, the average strength decrease is reduced by 27.5%, and the average loss weight is reduced by 17.6%. When it comes to concrete with glass fibers, Z4 samples, the average strength decrease is reduced by 39% compared to the average strength decrease of concrete without fibers, and the average loss weight is reduced by 5.6%. Both due to the compressive strength and loss of mass after the impact of negative temperatures, concrete with the use of steel fibers looks the most advantageous. In terms of the decrease in compressive strength, Z4 concrete with glass fibers is not much worse, but in the case of a loss of mass, it is characterized by slightly more favorable results than concrete without fibers.


**Table 8.** Results of the frost resistance test.

### *3.4. Modulus of Elasticity*

As in the case of previous tests, the test of the modulus of elasticity was carried out for concrete intended for a concrete slab and concrete block supports with fibers and reference concrete without the addition of fibers. In the non-destructive method, based on the frequency of vibrations propagating in the sample, the modulus of elasticity was determined by the method of propagation of the wave in the sample. In the classical method, the modulus of elasticity was calculated on the basis of the recorded deformation of the sample during loading according to Formula (2). The results of the elastic modulus for individual samples determined by method one are summarized in Table 9 and by the classical method in Table 10.

> *E*

$$\text{where:}$$

Δ *σ*—compressive stress increment (MPa);

<sup>Δ</sup>*ε*—sample deformation.

The results obtained by the resonant method are higher, but the difference between the results in relation to the classical method is about 2% to 4%. In both test methods used, the influence of the addition of fibers on the modulus of elasticity of cement concrete can be seen. The highest modulus of elasticity in both resonance and load tests is characterized by samples with glass fibers, whose modulus of elasticity is greater than concrete without fibers in the resonant method by 4.8% and in the classical method by 3.9%. Slightly worse are samples with polypropylene fibers, whose elastic modulus is higher by 4.2% in the resonance method and in the classical method by 3.8%. Steel fibers, whose elastic modulus is higher by 1.4% in the resonance method, and by 1.2% in the classical method, have the least positive effect.

$$
\varepsilon = \frac{\Delta \sigma}{\Delta \varepsilon} \tag{2}
$$


**Table 9.** Results of the resonance test of the modulus of elasticity.

**Table 10.** Results of the classical elastic modulus test.


### *3.5. Tensile Strength of the Cross-Section of the Ballastless Railway Surface*

In order to determine the influence of the strength parameters of block supports on the concrete slab, tensile strength tests at bending described in Section 2 of the laboratory model reflecting the actual track layout in the cross-section, with a scale factor of 0.3, were carried out. Z1 concrete was used as the material of the concrete slab and for block supports both concrete without Z5 fibers and with the addition of Z2 steel fibers, Z3 polypropylene and Z4 glass fibers. The results of the tensile strength at bending are shown in Table 11.

**Table 11.** Results of the tensile strength test at bending of the Z1 concrete beam depending on the reinforcing fibers used in the block supports.


Based on the analysis of the presented results, it should be concluded that the fibers used in the concrete of block supports affect the tensile strength when bending the concrete slab. The highest tensile strength during bending has a plate with supports in which glass fibers are used, and the smallest with supports in which concrete without the addition of fibers is used. Glass fibers in concrete intended for block supports increased the tensile strength of the plate at bending by 17.5% compared to block supports in which no fibers were used. Steel fibers increased the tensile strength of the plate at bending by 10.7%, and polypropylene fibers by only 1.2%. It should also be noted that the degree to which individual fibers affect does not depend either on the compressive strength of the cement concrete or on the modulus of elasticity. The key in this case is how the material of block supports cooperates with the concrete slab in the transfer of loads.

### *3.6. Tensile Strength of the Longitudinal Section of the Ballastless Railway Surface*

Another important study is to determine the influence of the material from which block supports were made on the tensile strength of the concrete slab in a longitudinal system. In this case, as before, the tests were performed on laboratory samples prepared on a scale of 0.3. The research was carried out for a concrete slab using block supports without fibers (Z5) and with the addition of fibers (Z2–Z4). The results of the study are presented in Table 12.

**Table 12.** Results of the tensile strength test at bending of the Z1 concrete beam depending on the reinforcing fibers used in the block supports.


In the case of the longitudinal system, one can also notice increased tensile strength when bending the concrete slab after using reinforcing fibers in block supports. However, in the longitudinal arrangement, the difference in the results is not as large as in the case of the transverse arrangement. In the longitudinal system, block supports with glass fibers also had the best effect on increasing the tensile strength when bending the concrete slab and increased it by 8.6%. For the transverse system, it was 17.5%. Polypropylene and steel fibers increased the strength of the concrete slab by 7.5% and 7.1%, respectively. In the case of the longitudinal system, you can see a much more favorable effect of polypropylene fibers on the tensile strength when bending the concrete slab than in the case of the transverse system, where this benefit was only 1.2%. In the case of the longitudinal system, you can see a slightly more correlation of the impact of the increase in tensile strength when bending the concrete slab with the compressive strength of the concrete block supports. However, it is not possible to talk about a full correlation due to the value of standard deviations of the obtained results, which indicate that each type of fibers used equally affects the tensile strength of the concrete slab.
