# Influence of Sulphate Attack on Properties of Modified Cement Composites
## 1 Introduction
However, studies of the corrosion resistance of cement composites with electrical properties are insufficient. Analysis and evaluation of changes in the electrical resistivity under the influence of a complex of external factors [22] is a priority in research, and considers promising practical applications of the modified cement-based composites, such as resistive self-heating of road surfaces [23], grounding, elimination of static electricity, and lightning protection [24; 25]. Studies have shown [26; 27] that the analysis and assessment of the degree of influence of external factors on the solid phase of cement-based composites is possible due to laboratory modeling of the hydrosulphate corrosion process, which consists of holding samples in solution with a sodium sulphate amount of 1 to 10%. The use of the solution of sodium sulphate [28; 29] is preferred. This solution, unlike, for example, magnesium sulphate [30], allows the ettrintigte-thaumasite system to be fully synthesized due to the absorption of SO\({}_{4}\)\({}^{2}\)- ions by samples from a Na\({}_{2}\)SO\({}_{4}\) solution. This process intensifies the crystallization of salt in a moist environment, and leads to the salt crystallization in samples and the further formation of cracks [23]. Studies of the mechanism of electrical conductivity of the solid phase of composite based on Portland cement show that the hydrated concrete is a combination of hydration products with non-hydrated clinker minerals [1; 23], with thermodynamically unstable compounds having imperfectly ordered crystal structures. It is shown [31] that the total calculated change of the entropy in the reactions of the formation of calcium silicates, aluminates, and aluminofferites is significantly less than the entropy of the clinker materials themselves. In turn, these data confirm that the solid phase of concrete is not a regular crystal lattice with the presence of vacancies in the nodes and a variety of ions in the internodes. The bonds of these ions are significantly weaker than those in regular crystals, which affects all the physical and chemical properties of cement-based composites, including their electrical conductivity [1]. As a result, the combined action of thermal motion and the electric field can lead to the creation of certain conditions under which a particular ion can become a current carrier. Thus, the electrical conductivity of clinker minerals can be attributed to the ionic type that is characterized by a strong dependence of the electrical conductivity of concrete on the order of ions in its structure [23]. The quantitative values of the electrical conductivity of hydrated clinker minerals are discussed in detail in paper [32]. The crystalline hydration products permeating the cement gel contain water molecules in a chemically bound form. During the independent synthesis of crystal hydration products and their subsequent study [23], it was found that the nature of the electrical conductivity of these new formations is similar to the nature of the electrical conductivity of clinker minerals. In the works of many authors, it has been stated that the specific electrical resistances of the crystal hydration products of the concrete are in the range from \(10^{6}\) to \(9\times 10^{9}\)\(\Omega\)/cm. It can be stated that the mineral components of Portland cement, crystal hydrates, and cement matrix, overall, have an ionic character of electrical conductivity that depends on the value of the positive entropy of crystals (crystals in the structure in which there are violations in the arrangement and movement of particles), the degree of crystallization, and the amount of adsorption-bound water. The use of electrolytic additives effects the structure formation, and changes the dispersion, quantity, and shape of hydrates [33; 34; 35].