## 4 Experimental Results and Their Analysis
### The Impact of Longitudinal Reinforcement
However, the increase in the wall's thickness causes an increase in the values of coefficients \(\alpha_{s2}\) and \(\alpha_{s1}\), though \(\alpha_{s2}\) is always larger than \(\alpha_{s1}\). Analysis of the experimental results demonstrate that with the increase in the thickness of the wall of reinforced concrete elements, the influence of the reinforcement amount on the strength \(f_{cs}\) of centrifuged concrete of annular cross section and the modulus of elasticity \(E_{cs}\) decreases. The graphs presented in Figure 5e,f show that when the wall's thickness exceeds 50 mm (i.e., when the ratio of the thickness of the external layer to the internal protective layer of longitudinal reinforcement \(\sim\)1.0) the difference between \(\alpha_{s1}\) and \(\alpha_{s2}\) is the same, regardless of the reinforcement amount. We conclude by arguing that the amount of longitudinal reinforcement for the elements with the wall thickness \(t\geq 50\) mm has no influence on the concrete strength because it depends on the technology of the concrete structure's formation. In other words, longitudinal reinforcement influences concrete strength not only in the process of its loading, but also during the concrete mixture formation. At this time, reinforcement has a negative effect on the cement stone structure and its cohesion with aggregates. Our experimental results have shown that longitudinal reinforcement has a different effect on the strength of the reinforced elements with the thickness \(t=35\)-\(45\) mm. In this case, longitudinal reinforcement often causes premature destruction of concrete in the elements with a thin wall. The effect of reinforcement on the strength of centrifuged concrete can evaluate by applying the coefficient \(\alpha_{s2}\) as follows:  
\[\alpha_{s2}\ =\ 1-\beta\mu_{s} \tag{17}\]here \(\beta=0\)-3 is the coefficient assessing the size of crushed granite. When crushed granite fraction varied from 5 to 20 mm, \(\beta=1.5\). In design practice it is recommended to use \(\alpha_{s2}\geq 0.8\), when \(\gamma\leq 1\) and \(\alpha_{s2}=0.8\) if \(\gamma>1\). The experimental results presented in Figure 5g show that for a wall with a thickness of more than 50 mm longitudinal strain of the compressed concrete element are \(\varepsilon_{c\text{s1}}\approx\varepsilon_{c1}\), while the coefficient is \(\alpha_{s3}\approx 1.0\). Thus, as presented in Figure 5c,g, the ratio of reinforcement increases the formation of longitudinal concrete strain \(\varepsilon_{c\text{s1}}\) from 5% to 10%. Generally, this increase depends on the wall thickness and the ratio of reinforcement. For the thin wall, the value of the coefficient \(\alpha_{s3}\) decreases even from 0.7 to 0.8 due to the premature failure caused by the peeling of the interior concrete layer and breaking of the reinforcement. Figure 5: _Cont._  
The experiments indicate that longitudinal strains \(\varepsilon_{cu}=\varepsilon_{\varsigma 2}\) of the compressed centrifuged concrete, matching the carrying capacity of the compressed reinforced concrete element, are larger than the longitudinal strain of the concrete element \(\varepsilon_{c1}\) under the maximum load. Moreover, when the ratio of reinforcement \(\mu_{s}\), is growing longitudinal strain, matching the carrying capacity \(\varepsilon_{\varsigma 2}\) of the compressed reinforced concrete element, is significantly increased (Figure 5d,h). In the considered case, with the ratio of reinforcement \(\mu_{s}\approx 4.0\%\), the strain of the reinforced concrete element reaches \(\varepsilon_{cu}\approx(2.8\)-\(3.5)\times 10^{-3}\), while the strains of the non-reinforced concrete element are much smaller, reaching \(\varepsilon_{c1}\approx(2.0\)-\(2.5)\times 10^{-3}\). A different type of deformability and failure of an element with a thin (from 35 mm to 45 mm) wall can be observed. In this case, longitudinal strains \(\varepsilon_{c2}\) are much smaller than those of the elements with a thicker wall, while the failure takes place when the inner concrete layer cracks and peels off.