## 2 Materials and Methods
### Methods
Vibration was carried out for 60 s. Samples were tested by the following test equipment:  
* Hydraulic press IP-1000 (TEKHIMASH, Neftekamsk, Russia);
* R-50 tensile testing machine (IMash, Armavir, Russia);
* Metal measuring ruler 500 mm (Stavropol Tool Plant, Stavropol, Russia);
* Laboratory scales HT-5000 (Gosmett, St. Petersburg, Russia);
* Caliper ShTs-I-250-0.05 (Chelyabinsk Tool Plant, Chelyabinsk, Russia);
* A device for measuring deviations from the plane NPL-1 and a device for measuring deviations from perpendicularity NPR-1 (\"RNPO \"RusPribor\", St. Petersburg, Russia). Sample manufacture consisted of the following steps:  
* Dosing of the initial components of concrete using VLTE-2100 scales (NPP Gosmett, St. Petersburg, Russia) with an accuracy of 0.05 g;
* Loading of the components into a concrete mixer in the following sequence: water, cement, sand, crushed stone, coconut fibers;
* Mixing of the components until a mixture of a homogeneous consistency was obtained;
* Molding of FRC samples--The homogenized mixture was poured into molds, compacted by vibration, and then its surface was leveled in the molds;
* Hardening of the samples--The samples were in the molds for 1 day in a hardening chamber (RNPO RusPribor, St. Petersburg, Russia), then demolding was carried out. The samples were removed from the molds, and then they were again placed in the chamber and hardened there again for 27 days;
* Testing of samples: for compression, for flexural strength by GOST 10180 \"Concretes. Methods for strength determination using reference specimens\" [62], for axial com \begin{table}
\begin{tabular}{c c c c c c} \hline
**Name** & **Cement (kg/m3)** & **Water (L/m3)** & **Crushed Stone (kg/m3)** & **Sand (kg/m3)** & **\(\rho_{\text{cm}}\) (kg/m3)** \\ \hline Value & 375 & 210 & 1028 & 701 & 2314 \\ \hline \end{tabular} The composition of the concrete mixture is the following ratio of components: C:W:S:CS = 1.0.56:1.87:2.74.  
\end{table} 
Table 4: Composition of the concrete mixture. pression according to GOST 24452 \"Concretes. Methods of prismatic, compressive strength, modulus of elasticity, and Poisson's ratio determination\" [63]. * Concrete strength estimating following GOST 18105-2018 \"Concretes. Rules for control and assessment of strength\" [64] Detailed test procedures from these standards are described in [59]. Electron microscopy was used to study the dispersity and morphology of the samples. \"The structure of samples with coconut fiber was studied using a ZEISS CrossBeam 340 electron microscope (Carl Zeiss Microscopy GmbH (Factory), Jena, Germany)\" [58]. The experimental program scheme is presented in Figure 5. A photo of test samples is shown in Figure 6.  
Figure 5: The scheme of the experiment for the effect of dispersed reinforcement with coconut fibers on the strength and deformation properties of concrete. Figure 6: Test specimens: (**a**) cubes; (**b**) prisms. Figure 5 shows that at a dosage of coconut fibers from 0.25% to 1%, a gradual increase in compressive strength from 43.8 MPa to 51.6 MPa was observed, in the range from 1% to 1.5%, and the increase in compressive strength was already less intense, namely, from 51.5 MPa up to 53.6 MPa. At a dosage of coconut fibers of 1.75% by weight of cement, a peak was observed--the maximum value of compressive strength, equal to 55.1 MPa. However, with a further increase in the percentage of fibers from 2% to 2.5%, the strength began to decrease up to a value approximately equal to the strength of the control composition (without fibers). Figure 8 shows the most intense increase in axial compressive strength at a dosage of coconut fibers from 0% to 0.75% and then continues slightly less intensively with a peak  
Figure 10: Dependence of the axial tensile strength (\(R_{bt}\)) of prism concrete samples with dimensions of 100 \(\times\) 100 \(\times\) 400 (mm) on the percentage of dispersed reinforcement with coconut fibers.