# Experimental Study and Modelling on the Structural Response of Fiber Reinforced Concrete Beams
## 3 Experimental Results and Discussion  
The resultant segregation value for all three groups of fibre concrete mixtures was zero. The slump cone test results for the concrete matrix Group CSf are as follows: slump height equal to 24 cm with a settling time of 8 s (see Figure 3a). Based these results, it can be concluded that this concrete matrix has very low workability. For Group CPPfS, slump height was 4 cm with a settling time of 5 s (Figure 3b). It indicates that the workability of concrete in this group is very good. For Group CPPfD, the slump height was 23 cm with a settling time of 7 s (see Figure 3c). These indicators imply that this group is characterised by very poor workability. Compressive strength of 6 specimens were found out, materials compressive test (concrete cube test) was used in accordance with EN 12390-3 [58]. According to standard LVS 156-1 [59], the correction factor 0.95 was implemented, thus, the obtained concrete corresponds to class C70/85. The results of tests under the impact of bending forces were presented in the form of Excel values. All values were taken for all three groups, strength-deflection average values were plotted using MATLAB software for 4 PBT test and the average graphs were drawn based on the results thereof. During the experiment, a large amount of data was obtained, and the values along the deflection axis often did not coincide with each other. Therefore, using the code in MATLAB software, a selection of experimental data values with the given deflection step was obtained. The resulting database was used to obtain the average strength-deflection values. The graphs in Figure 4 represent the three groups  
Figure 3: Slump cone test: (a) Group CSf; (b) Group CPPfS; (c) Group CPPfD. respectively, and all three groups are drawn in a single frame to plot the differences in their behaviour. The above plotted curves consist of the following phases:  
Group Csf:  
1. The phase of linearly elastic deformation of concrete matrix, indicating the linear deformation from 0.02 mm to 0.25 mm with no formation of visible cracks and without significant load in the fibres. 2. The phase of critical load, showing the linear deformation of concrete matrix from 0.25 mm to 0.5 mm. 3. The phase of fibre pull-out, indicating the formation of macro-cracks with the opening width from 0.1 mm to 0.35 mm. The tension force transfer resulted in the resistance to crack propagation, imparting the strength, i.e., the fibres were bridging the cracks, collecting tension forces at the edges of the cracks. The results obtained correlate with the data from the related research [60, 61]. The comparison of experimental data of the steel fibre pull-out test and numerical simulation results was carried out. The third phase corresponds to the growth of delamination along the fibre and matrix interface until full debonding of the fibres (crossing micro-cracks), followed by fibre sliding out of the matrix with friction, and partial plastic deformation of the fibres [62, 63]. Group CPPfS and Group CPPfD:  
1. The phase of linearly elastic deformation indicating the linear deformation from 0.01 mm to 0.15 mm with no formation of visible cracks and without significant load in the fibres. 2. The phase of critical load showing the linear deformation from 0.15 mm to 0.2 mm. 3. The phase of elastic deformation provided by the PP fibres, increasing the load bearing capacity of the members and resisting the loads. The change in the deformation from 0.2 mm to 2 mm during the fibre pull-out or change indicating the formation of cracks with the opening width from 0.1 mm to 0.35 mm was recorded. The tension force transfer resulted in the increased resistance to crack propagation, imparting the strength to the prism members. Steel fibres demonstrate good performance in the elastic deformation, as it is demonstrated in Figure 4. Mechanical (not chemical) adhesion between steel fibres and concrete is higher compared to the adhesion between PP and concrete.