# Ultimate Compressive Strains and Reserves of Bearing Capacity of Short RC Columns with Basalt Fiber
## 3 Results of Testing Cubes and Prisms from Heavy and Light Expanded Clay BFC
In heavy concrete, with an increase in stresses and the development of microcracks, the rate of growth of plastic strains increases sharply, the proportion of elastic strains decreases, while in lightweight concrete, this process is less intense. The coefficient of elastic-plastic strains \(\
u_{b}\) at a load level of 0.8-0.9 changed for expanded clay FRC within 0.88-0.79, significantly exceeding the value adopted in SNiP 2.03.01.84. To the greatest extent, the features of the elastoplastic properties of FRC manifested during crushing at \(\sigma/R_{b}\). The ultimate coefficient of elastic-plastic strains, values increased in heavy FRC by 6-8%, and in expanded clay FRC, ranged from 11 to 27%. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Indicator Name**} & \multicolumn{4}{c}{**Concrete Type**} \\ \cline{2-5}  & **Expanded Clay Concrete** & **Expanded Clay FRC** & **Heavy Concrete** & **Heavy BFRC** \\ \hline
1 & 2 & 3 & 4 & 5 \\ \hline Average density \(D\), kg/m\({}^{3}\) & 1600 & 1570 & 2420 & 2395 \\ Cubic strength \(R\), MPa & 21.3 & 23.4 & 24.1 & 25.6 \\ Prismatic strength \(R_{b}\), MPa & 18.5 & 21.8 & 18.3 & 21.3 \\  & 0.87 & 0.93 & 0.76 & 0.83 \\ Initial modulus of elasticity & 17.3 & 16.38 & 24.8 & 23.8 \\ \(E_{b}\cdot 10^{-3}\), MPa & & & & \\ Concrete strains: & & & & \\ ultimate \(\varepsilon_{\alpha\cdot}10^{-3}\) & 2.26 & 2.85 & 1.87 & 2.24 \\ peak \(\varepsilon_{\alpha\cdot}10^{-3}\) & 3.2 & 4.34 & 2.5 & 3.6 \\ The coefficient of transverse & 0.22 & 0.27 & 0.20 & 0.22 \\ strains at \(\sigma/R_{b}=1\) & & & & \\ Coefficient of elastic–plastic & 0.59 & 0.72 & 0.52 & 0.58 \\ deformations at \(\sigma/R_{b}=1\) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Results of short-term tests of prisms with a size of 10 \(\times\) 10 \(\times\) 40 cm from light and heavy BFRC for axial compression. Fiber reinforcement significantly affected the value \(\
u_{b}\). Thus, the coefficient of elasticity at a load level from \(0.75R_{b}\) to \(0.8R_{b}\) varied in elements made of structural expanded clay concrete within 0.83-0.7. To the greatest extent, the features of the elastoplastic properties of FRC were manifested during crushing; that is, at \(\sigma/R_{b}=1\). Therefore, the coefficient of elastic-plastic strains of samples with fiber was of greater importance than unreinforced (Table 7). In general, for FRC with a strength of 20-25 MPa, both on a conventional aggregate and on a lightweight expanded clay aggregate, higher values of the coefficient of elastic-plastic strains \(\
u_{b}\) are characteristic than for concrete without fiber. Figure 5 shows that the strain diagrams of heavy concrete and expanded clay concrete were different, although they had approximately the same strength. The curves are plotted in relative values for easy comparison of the deformability of the samples. Thus, in the calculation and design of expanded clay concrete elements, the increased deformability of the FRC should be taken into account. In particular, the ultimate compressibility of expanded clay FRC at \(\mu_{f}=10\%\) can be increased by 1.3 times; that is, it can be taken at short-term loading equal to \(2.6\times 10^{-3}\), and the limiting elongation can be taken equal to \(0.5\times 10^{-3}\); that is, 2 times more than for concrete without fibers. Figure 4: Dependence of the coefficient of elastic–plastic strains \(\
u_{b}\) on the growth of stresses in expanded clay concrete (1) and expanded clay FRC (2). \(\
u_{b}=\epsilon_{\rm e}/\epsilon_{\rm b}\)—coefficient of elastic–plastic strains of concrete, \(\epsilon_{\rm e}\)—elastic concrete strain; \(\epsilon_{\rm b}\)—total concrete strain.