# Ultimate Compressive Strains and Reserves of Bearing Capacity of Short RC Columns with Basalt Fiber
## 2 Materials and Methods  
Two series of experiments were carried out to study the features of the operation of compressed basalt fiber steel reinforced (BFRC) elements, and to obtain the necessary data on their strength and deformability. During the first series of tests, the strength and strain of the fiber concrete (FC) of cubic and prism specimens in compression were studied. The variable factors were the type of concrete--heavy ([PERSON], 1971) and light. In the second series of experiments, the purpose of which was to study the ultimate compressive strains in reinforcement and concrete, the samples were made in the form of short columns. The variable factors, in this case, were: type of concrete, class of longitudinal reinforcement (A400 and A1000), percentage of fiber reinforcement, and eccentricity of longitudinal force \(e_{0}/h\) = 0; 0.15; 0.6 (\(e_{0}\) is the initial eccentricity of the application of the compressive force; \(h\) is the height of the column section). Ten samples were tested with a size of 120 mm \(\times\) 120 mm \(\times\) 600 mm and 130 mm \(\times\) 200 mm \(\times\) 600 mm. Control cubes and prisms were made simultaneously with the tested samples. For the manufacturing of laboratory samples from FRC, in the form of cubes, prisms, and columns, Portland cement of the 500 D 20 grade was used as a binder, according to GOST 10180-2012 (Russian standard). As aggregates for the preparation of fine-grained heavy concrete, crushed stone sifting with a fraction of up to 10 mm was used, and light-sifted expanded clay gravel (GOST 9759-83) with a bulk density of 650 kg/m\({}^{3}\), fractions 2.5-10 mm. The porous filler's compressive strength in the cylinder was 5.8 MPa, and the water absorption was 14.2%. The main properties of the screening out of crushed stone and expanded clay gravel are presented in Tables 1 and 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Diameter, mm** & **10.0** & **\textgreater{}10.0** & **5.0** & **2.5** & **Resolute** & **Total Weight** \\ \hline Fraction weight, kg & 0.08 & 0.98 & 3.02 & 0.79 & 0.12 & 5 \\ \hline \% & 1.4 & 20.3 & 59.0 & 18.8 & 1.5 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Granulometric composition of expanded clay gravel. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Size, mm** & **Humidity, \%** & **Strength, MPa** & **Volume Weight, kg/m\({}^{3}\)** \\ \hline
2.5–10 & 1.0 & 140 & 1420 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of heavy aggregate from crushed stone screenings. Quartz sand (GOST 8736-77) with a size modulus of 1.8 and an average bulk density of 1450 kg/m\({}^{3}\) was used as a fine aggregate to prepare heavy and light concrete. The prototype columns were reinforced with hot-rolled bar steel of class A400, with a diameter of 8.0 mm and high-strength steel, class A1000, with a diameter of 10.0 mm. To determine the actual mechanical properties of steel reinforcement, tensile tests were performed on samples, 5 pieces from each class. The tests were carried out on a GRM-20 universal tensile testing machine no. 1837 (Armavir, Russia), in accordance with GOST 12004-81. A strain gauge station measured longitudinal deformations, based on 100 mm, with a scale division of the indicators equal to 0. Cement and sand were first poured into an operating mixer with a capacity of 0.085 m\({}^{3}\) and a rotor speed of 500 rpm, which were mixed for 1.5 min with the simultaneous supply of fiber. Only then was the water and coarse aggregate fed. Uniform supply of fiber was provided by a special vibrating chute, through which pre-dosed coarse basalt fiber was fed into the concrete mixer. The total mixing time of the FC mixture with heavy crushed stone did not exceed 3.5 min, and with expanded clay gravel, 4 min. Compaction of the concrete mixture was carried out on a laboratory-vibrating platform, providing vertical-directional vibrations (up to 300 vibrations/min) with an amplitude of 0.5 mm.