# Influence of Variotropy on the Change in Concrete Strength under the Impact of Wet-Dry Cycles
## 2 Materials and Methods
### Methods
Prior to being loaded into the concrete mixer, each component of the concrete mixture was weighed on a VK-3000.1 scale (MASSA-K, St. Petersburg, Russia) to ensure the required dosage. The mixing of the components in the concrete mixer was carried out until a homogeneous consistency was obtained. Then, the mixture was poured into metal cube molds 2 FK-50 and prism molds FB-50/200 (NPO Priborinform, Rostov-on-Don, Russia). Next, the mixture was compacted in molds on a laboratory vibration platform SMZh-739M (RNPO RusPribor, St. Petersburg, Russia) for 50 s. Next, the surface of the mixture was smoothed, leveled with the edges of the molds, and placed in a KNT-1 normal curing chamber (RNPO RusPribor, St. Petersburg, Russia). After 1 day, the samples were removed from the molds and placed back in the curing chamber for the remaining 27 days. Thus, the hardening of the samples was carried out until they reached the age of 28 days. The concrete mixture was prepared in the following proportions of components: PC:W:S:CrS = 1:0.52:1.38:3.03. The preparation of the concrete mix according to the technologies of centrifugation and vibrocentrifugation was carried out in a laboratory vibrocentrifuge, the design and parameters of which are described in detail in [51]. The composition of the concrete mix corresponded to the following proportions of its components: PC:W:S:CrS = 1:0.44:1.67:2.89. The centrifugation parameters were set as follows: rotation speed--156 rad/s, molding time--12 min; vibration parameters: height of clamp projections--5 mm, projection length--20 mm, pitch between projections--30 mm. In general, the technology for manufacturing concrete elements of an annular section using centrifugation and vibrocentrifugation technologies included the following main technological operations: batching of concrete mixture components, mixing of the concrete mixture, determining the characteristics of the workability of the resulting mixture, loading the concrete mixture into a mold, the centrifugation process, draining the sludge, holding for 24 h in the mold, and removing the element of the annular section from the mold [52]. The concrete mixing ratios in 1 m\({}^{3}\) are presented in Table 4.  
In total, 13 centrifuged and 13 vibrocentrifuged annular elements were manufactured, having an outer diameter of 210 mm, an inner diameter of 70 mm, and a height of 630 mm (Figure 1). Samples from the elements of the annular section were sawn according to the scheme shown in Figure 2.  
A total of 117 cubes and 117 prisms were sawn from 13 centrifuged samples; the same number was obtained from 13 vibrocentrifuged samples. Thus, a total of 117 cubes and 117 prisms were made for each technology--vibrating, centrifuging, and vibrocentrifuging. For each technology, nine cubes and nine control prisms were made; the rest were the main samples. The samples were cut on a Cedima CTS-175 high-precision stone-cutting machine (CEDIMA GmbH, Celle, Germany) (Figure 3). In the process of cyclic moistening and drying, the characteristics of the change in the strength of vibrated concrete were studied on cubes and prisms with dimensions, respectively, of 50 \(\times\) 50 \(\times\) 50 (mm) and 50 \(\times\) 50 \(\times\) 200 (mm); on centrifuged and vibrocentrifuged concrete--on cubes and prisms with dimensions, respectively, 50 \(\times\) 50 \(\times\) 50 (mm) and 50 \(\times\) 50 \(\times\) 200 (mm), sawn from elements of an annular section. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Technology** & **PC (kg/m\({}^{3}\))** & **W (L/m\({}^{3}\))** & **S (kg/m\({}^{3}\))** & **CrS (kg/m\({}^{3}\))** \\ \hline Vibration & 383 & 199 & 529 & 1160 \\ \hline Centrifugation and vibrocentrifugation & 409 & 180 & 683 & 1182 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Concrete mixing ratios in 1 m\({}^{3}\). The samples were tested for the effects of alternating wetting and drying with an intensity of about 60 cycles per month.