**4. Discussion**

On the basis of the conducted research, it can be concluded that individual strength results depend on the reinforcing fibers used. Samples with the addition of glass fibers are the most advantageous in the strength tests carried out, which are shown in Figures 16–19.

**Figure 16.** Results of the compressive strength test.

**Figure 18.** Results of the elastic modulus test.

**Figure 19.** Stresses in the track plate depending on the fibers used in the block supports.

In the case of compression (Figure 16), the next in terms of strength are samples with the addition of polypropylene fibers, which in relation to glass fibers are characterized by a strength lower by about 4 MPa. On the other hand, steel fibers have a strength lower by about 5 MPa than glass fibers. The lowest compressive strength of about 68 MPa is characterized by concrete without reinforcing fibers.

In the case of frost resistance of cement concrete (Figure 17), samples with the addition of steel fibers, whose strength drop is 1.8 MPa, are the most advantageous. Glass fibers with the most favorable compressive strength are also characterized by the highest strength

of samples subjected to frost, but their strength drop is greater than that of steel fibers and amounts to almost 2 MPa. Next are samples with the addition of polypropylene fibers, which are characterized by a decrease in strength equal to 2.3 MPa. The least favorable are samples without the addition of fibers, whose strength drop is over 3.2 MPa.

Analyzing the modulus of elasticity of concrete samples (Figure 18), it can be concluded that, as in the case of compressive strength, the highest module is characterized by samples with the addition of glass and polypropylene fibers. The difference between the obtained results for both fibers is within the limit of statistical error. Steel fibers are characterized by a modulus of elasticity lower by about 1000 MPa, while samples without the addition of fibers are characterized by a module lower by about 2000 MPa.

Taking into account the influence of reinforcing fibers on the work of the concrete slab supporting the block supports, it should be noted that the most advantageous variant is the use of glass fibers in block supports, thanks to which the concrete slab is characterized by the highest tensile strength in both longitudinal and transverse systems. In the case of steel fibers, the tensile strength of the concrete slab at bending is reduced by about 0.4 MPa. For polypropylene fibers, the strength is lower by about 1 MPa. The least favorable effect on the strength of the concrete slab is the use of block supports without the addition of fibers, which is shown in Figure 19.

The analyses carried out above show that the most advantageous in terms of strength and proper work of the surface is the use of glass fibers in block supports, which at the same time increase the strength of concrete intended for block supports and increase tensile strength when bending the concrete slab constituting support for block supports.

Having in mind the above discussion one may conclude what follows.

Tables 1–4 present the properties and compositions of concrete mixtures accepted for the production of samples without the addition of fibers (Z1 and Z5) and with the addition of fibers (Z2–Z4). All samples (Z1–Z5) were subjected to strength tests. Some of the tests concerned the samples themselves. The concrete mixes (Z1–Z5) were then used for elements of the railway surface, made on a laboratory scale. After that, additional tests were made for properly made aggregated railway track elements. The values of the tested physical quantities differed, and, moreover, their distribution was not the same in each individual test. The sequences of positions of individual material samples or elements made of them are different in different Tables 1–4 and different diagrams (Figures 16–19). Hence, the resulting material with various additives has different properties. This applies both to the compressive strength of the material samples themselves and to the bending strength of the fixed elements of the railway track, which are made of various materials with additives. The study of the influence of low temperatures on the change in the technical parameters of individual materials and elements made of them, as it was presented, is also very important. This factor in engineering practice must be taken into account, especially in climatic conditions, in which specific structures will be exposed to sub-zero temperatures or to cyclical temperature changes.

Finally, it should be stated that when changing the rail support in the transition railway sections, in order to eliminate the threshold effect, it is necessary to use a proper sequence of various reinforcing fibers in the set of railway concrete elements, which will properly affect the total rigidity of the track system in the transition zone.
