## 2 Materials and Methods  
Six polymer fiber-reinforced concrete prisms were tested under three-point bending conditions according to the EN14651 standard [19]. The prisms were designated with the names B23258/1-B23258/6. The bending tests were conducted at the Slovenian National Building and Civil Engineering Institute. The prisms had a length of 600 mm and a rectangular cross-section with a height (h) and width (b) of 150 mm. The prisms were notched at the midspan. The notched cross-section height (h\({}_{\text{sp}}\)) was 125 mm. The measurement of the notched cross-sections showed that the tolerance for the prism dimensions could be assumed to be less than 1 mm (Table 1). Each prism's notched cross-section width was measured four times, while the height was measured two times, and then the measurements were averaged. The three-point bending configuration can be seen in Figure 1. The span length was 500 mm. Instead of measuring the crack mouth opening displacement (CMOD), the vertical midspan displacement was measured (with a linear transducer). Although the test procedure of the EN14651 standard [19] was designed to determine the CMOD and residual tensile strength (understood as the tensile strength after crack formation), the standard gives the option to measure vertical midspan displacements instead. In order to determine the CMOD values, the EN14651 standard [19] gives a relation between the CMOD and vertical midspan displacement (\(\delta\)) values, equal to:  
\[\delta=0.85\text{-CMOD}+0.04\ (\text{CMOD and $\delta$ in mm}). \tag{1}\]  
According to Equation (1), the specified CMOD load rates were transformed into vertical displacement load rates. Up to a vertical displacement of 0.13 mm, the displacements were increased at a constant rate of 0.08 mm/min. After reaching the displacement of 0.13 mm, the displacements were increased at a constant rate of 0.21 mm/min. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **B23258/1** & **B23258/2** & **B23258/3** & **B23258/4** & **B23258/5** & **B23258/6** \\ \hline B [mm] & 150.33 & 149.57 & 149.62 & 149.21 & 149.87 & 150.96 \\ H\({}_{\text{n}}\) [mm] & 125.06 & 125.03 & 125.01 & 125 & 125.2 & 125.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Averaged notched cross-section dimensions. The concrete composition (mix design) can be found in Table 2. The concrete mix herein presented was designed to reach a characteristic compressive strength (on cylinders, according to the EN1992-1-1 standard [20]) of at least 25 MPa, respectively, the properties of strength class C25/30. After concrete pouring, the concrete prisms were wrapped in polyethylene foil and stored at room temperature, approximately 20 degrees Celsius. The bending tests were performed 49 days after concrete pouring. In addition to the regular concrete components, 5 kg of the Barchip 48 [21] polymer fibers were added per cubic meter of the concrete composition. The fibers were added by hand into the batching plant's concrete-mixing machine. The chosen polymer fibers were high-performance macro-synthetic polypropylene fibers designed for structural reinforcement in precast, paving, and flooring works [21]. They can be classified as Class-II fibers (according to the EN 14889-2 standard [22]), generally used where an increase in residual flexural strength is required. Table 3 summarizes the properties of BarChip 48 fibers. In order to disclose the potential impact of the relatively high fiber dosage on the compressive strength, compression tests following the EN12390-3 standard [23] were performed (Figure 2). The compression tests were performed on three cubes without fibers (designated with the names BV1-BV3) and three cubes with fibers (designated with the \begin{table}
\begin{tabular}{c c} \hline \hline
**Component** & **Dosage [kg/m3]** \\ \hline Aggregate (maximum grain size: 16 mm) & 711 \\ Cement (CEM II/A-S 52.5 N) & 135 \\ Total water & 71.4 \\ Plasticizer & 0.4 \\ Barchip 48 fibers & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Concrete composition.