# Influence of Variotropy on the Change in Concrete Strength under the Impact of Wet-Dry Cycles
## 4 Discussion
In the study [2], concretes for lining tunnels with various mineral additives were considered, and their characteristics were evaluated under the influence of cycles of alternating wetting in an aggressive environment and drying, and according to the results of experimental measurements, the coefficient of resistance to the destruction of concrete during the first 20 cycles increased and then decreased. The work [62] studied the effect of wetting-drying cycles on reinforced concrete columns under eccentric loads. The results of the experiments showed that the ultimate bearing capacity of the columns first increased and then decreased with an increasing number of sulphate dry-wet cycles. Thus, the obtained dependences of the strength characteristics on the number of moistening and drying cycles and various moistening media in the current study are similar in nature to those in the studies [2; 20; 62] for vibrated concrete but completely differ from them by a visual comparison of the behavior of the strength of concrete made by vibration with the behavior of the strength of concrete made by centrifugal compaction methods--centrifugation and vibocentrifugation. Further, the mechanism for the formation of a higher resistance to alternating cycles of wetting and drying in concrete with a more perfect structure is given in detail. So, vibrated concretes, which have a simple structure and are uniform throughout the thickness of the structure, which works by resisting cycles of wetting and drying, are the least resistant. The fact is that the nature of the structure formation and porosity of such concrete, obtained by vibrating, is permeable to moisture from the outside, which thereby makes it possible to create susceptibility through the penetration of moisture and the creation of potential centers of internal stress. At the same time, centrifuged concrete, with the correct creation of a variotropic structure, has the ability to more effectively prevent the penetration of water into the concrete body. This is due to the nature of closed porosity in the outer layer of centrifuged concrete and structures made of it and the increased resistance to moisture penetration from the outside. That is, the improved variotropic structure, in comparison with the vibrated simple structure of concrete, creates a redistribution of porosity due to the escape of pores into the non-working inner layer, which, in fact, does not play a key role [63; 64; 65; 66]. At the same time, due to this donor-acceptor mechanism of pore migration, the outer layer becomes hardened and compacted. Thus, there is an effect of preventing the penetration of moisture into the body of the structure, and, thereby, the effect of greater security of the reinforcing cage and maintaining the durability and reliability of the structure for a long time is created. As for vibocentrifuged concrete, here we have the most effective type of structure due to an even greater redistribution of the nature of porosity, an improvement of the donor-acceptor mechanism for distributing pores in the body of concrete, the appearance of a densely protected shell, which actually prevents the penetration of unwanted water into the body of concrete, and a reinforced concrete structure. Thus, the mechanism of water migration in concretes made using different technologies has a completely different character, and thus, experimentally and theoretically proven higher resistance and efficiency of vibrocentrifuged and centrifuged concretes compared to vibrated concretes for use in structures subject to alternating moistening cycles and drying.