# Influence of Variotropy on the Change in Concrete Strength under the Impact of Wet-Dry Cycles
## 4 Discussion  
The considered features of the change in the mechanical properties of concrete in the process of alternate moistening and drying according to the adopted method should be explained by the fact that in the initial period favorable conditions are created for further hydration of non-hydrated cement grains. In addition, during cyclic moisture migration, neoplasms are transferred and deposited on the walls of pores and capillaries, which leads to their narrowing and, as a result, a decrease in the permeability of concrete, which favorably affects its durability. However, a further decrease in strength occurs due to a violation of the adhesion of the cement stone with the aggregate. As is known, the contact zone is the main way of penetration and migration of moisture in concrete [53; 57; 58; 59]. Subsequently, in accordance with [53; 57; 58; 59], there occurs a kind of dissolution of the bonds between the cement stone and aggregate and a decrease in the strength of their mutual adhesion. Thus, it can be considered that one of the main reasons for the decrease in the strength of concrete, both during freezing and thawing and in the process of cyclic moistening and drying, is a violation of the strong bond between the cement stone and the aggregate. At the same time, the development of micro- and macrocracks in the first case occurs when the moisture in the contact zone is frozen, and in the second case, when it tries. So, when heated concrete is moistened, the alternation of cycles is similar to an impact that causes stresses of a changing sign, leading to the appearance of microcracks and then their development. The accumulation of such disturbances is accompanied by an increase in the external volume and porosity, a decrease in strength, as well as a change in other physical and mechanical properties of the material. With alternating effects of moisture and drying, they can lead to a loss of operational properties of the material of structures or elements of engineering structures. In concrete, the negative effect of exposure to alternating cycles of moistening-drying is usually explained by a significant difference in changes in the volume of individual components of concrete with moisture fluctuations. The structure and properties of concrete in the process of cyclic influences of the environment change. In particular, with fluctuations in humidity, the strength and deformation properties of concrete change. For example, the continued hydration of cement particles leads to an increase in the strength of concrete, while intensive and uneven dehydration of the cement stone components causes brittleness due to a decrease in the volume content of the gel-like component of the cement stone and the formation of microcracks. These cracks, for example, during long cycles of moistening and drying, can self-heal, but in other cases, with alternating short-term cycles of moistening-drying, they can be centers of destruction. As the number of moistening and drying cycles increases, the formed cracks deepen and their surfaces carbonize. One of the reasons for the predominant development of destructive processes is the aging of the gel component of the cement stone. A decrease in the volume of the gel component during its aging leads to the emergence and development of internal tensile stresses sufficient to disrupt the structure of the material. This is facilitated by the decrease in the deformability of the gel component during its aging [53; 60; 61]. The results obtained in this work are in good agreement with the studies presented in [2; 20; 62]. In [20], the authors studied the effect of the action of \"dry-wet\" cycles on the mechanical and seismic characteristics of reinforced concrete columns. According to the results of the experiments, the fact of the negative impact of alternate moistening and drying on the studied characteristics was recorded.