# Influence of Sulphate Attack on Properties of Modified Cement Composites
## 1 Introduction  
The durability of cement composite is determined not only by its physical and mechanical properties, but also by its electrical characteristics, and can ensure the operational reliability of materials. Studies aiming to stabilize the dielectric properties and the resistance to sulphate attack of electrically insulating concrete have been successfully performed in recent decades [1; 2; 3]. However, the corrosion resistance to sulphate attack of electrically conducting composites has not been sufficiently studied. At present, the purpose of preserving the electrical properties and durability of cement concretes is primarily toprotect against aggressive influences. Waterproofing via surface penetration of the compositions or bulk thermocatalytic impregnations can be distinguished as the main methods of waterproofing building capillary-porous materials [4; 5; 6]. As the most widespread and hybrid type of destructive process, the degree of material resistance to sulphate corrosion is considered to be the main criterion for the effectiveness of waterproofing [7; 8; 9]. Hybridity relates to the fact that sulphates in water increase the solubility of the components of cement matrix, and also initiate the development of exchange reactions between the components of cement matrix and a sulphate-containing solution [2; 6; 7]. In addition, the action of sulphates can cause the crystallization and accumulation of secondary poorly soluble reaction products with an increase in the volume of the solid phase of the ettrintigte-taumasite system. This creates internal stress and leads to damage to the concrete structure [6; 7; 10]. The degree of material resistance to sulphate attack is the main criterion for the effectiveness of waterproofing measures [7; 8] because sulphate attack is the most common type of destructive processes in cement matrix. This process is accompanied by the formation of compounds with a high quantity of crystallization water and the formation of the ettrintigte-taumasite system [9; 10]. Studies of sulphate attack and the formation of crystallohydrates of calcium hydrosulphoaluminate (ettrintigte) and calcium hydrosulphocarbosilicate (taumasite) in the structure of solid phase of concrete are widely presented in the literature of recent years [11; 12; 13; 14; 15]. Analysis of the studies has shown [7; 16; 17] that the formation of ettrintigte-type crystal hydrates occurs due to the reaction of sulphates with hydro-aluminates, whereas thaumasite is formed due to the presence of sources of calcium silicates, sulphates, and carbonates at relatively low ambient temperatures less than 15 \({}^{\circ}\)C.  
Studies of synthesized pure samples of ettrintigte and thaumasite, and hydration products formed in the structure of cement matrices [2; 7], have shown that it is not possible to draw unambiguous conclusions about the volume of these minerals [2; 6; 7; 10]. Most researchers describe the effect of sulphate attack as a process in which the sulphate ions in water, when penetrating into concrete, significantly increase the solubility of the components of the solid phase of concrete, which accelerates the corrosion of the first type [2; 6]. Simultaneously, the development of exchange reactions occurs with the substitution of the cation in the sulphate for the calcium ion from the concrete, which initiates corrosion of the second type [2; 6]. Today, materials based on cement composites are increasingly used at the intersection of construction materials science and instrument engineering. Accordingly, the need arises for the development and research of new cement composites with a number of functional properties. In addition to the study of physical and mechanical properties, during the past ten years, active attention has been paid to the study of the electrical properties of the solid phase in concrete and, as a result, concrete compositions with specified electrical properties have been developed [18; 19; 20; 21].