# Influence of Sulphate Attack on Properties of Modified Cement Composites
## 3 Results and Discussion
The differential thermal spectrum of the control sample (Figure 3)after exposure to aggressive media for 28 days is characterized by an endothermic peak at 136.5 \({}^{\circ}\)C (this peak is characteristic of decomposition of free water, calcium hydrosilicates, and ettringrite) and the peak of 492.5 \({}^{\circ}\)C (this peak is characteristic of the decomposition of portlandite). The uncharacteristically low intensity of the portlandite decomposition peak and the significantly lower mass loss of the sample at this stage should be noted. This effect is associated with a significant amount of portlandite dissolved as a result of aging in the aggressive environment. The endothermic effect at the temperature of 575.95 \({}^{\circ}\)C is associated with the partial dissociation of chemically bound water from calcium hydrosilicates. The endothermic peak of 794.30 \({}^{\circ}\)C is caused by the process of decomposition of calcium carbonate and dehydration of the CSH phase. Figure 2: Effect of sulphate attack on the electrical resistivity of samples. When comparing the spectra of the control and electrically conducting compositions, it was found that the endothermic peak of 146.5 \({}^{\circ}\)C corresponding to the dehydration of calcium hydrosilicates, free water, and ettrinigite appears in the electrically conducting composition in the temperature range from 90 to 400 \({}^{\circ}\)C on the DTA curve. In addition, the mass loss of the sample in this stage is higher, which may indicate a larger volume of formed ettrinite. The endothermic peak of 451.3 \({}^{\circ}\)C corresponds to the beginning of the thermal decomposition of calcium hydroxide and calcium hydrosilicates. Free calcium oxide is formed during the endothermic reaction. In the air environment, free calcium oxide reacts actively with carbon dioxide, leading to the process of secondary carbonation. The  
Figure 4: The spectrum of differential scanning calorimetry of the sample with the addition of an electrically conductive component of 7% and calcium nitrate of 3% after 28 days in the aggressive environment. 1 stage–mass of sample 83 mg, masse loss 4.49 mg; 2 stage–mass of sample–82.13 mg, mass loss 0.86 mg; 3 stage–mass of sample 80.1 mg, mass loss 2.03 mg.  
Figure 3: Spectrum of differential scanning calorimetry of the control sample after exposure for 28 days in the aggressive environment. burning of organic products in the material composition, which leads to the intensification of the process described above, should also be noted. An intense exothermic effect with the temperature peak of 528.0 \({}^{\circ}\)C corresponds to the oxidation reaction of carbon black, whereas the formation of gaseous products leads to the appearance of a local curvature on the thermogravimetric curve. The endothermic effect in the temperature range of 600-1000 \({}^{\circ}\)C (including the peak of 778.6 \({}^{\circ}\)C) with the loss of 2.7% of the sample mass corresponds to the decomposition of calcium carbonate, and the removal of chemically bound water from calcium hydrosilicates and ettrinigite. The increase in mass loss can also be due to the secondary carbonation of cement matrix. Repeated thermal analysis in an inert gas environment is necessary to clarify the features of the process. The temperature peaks corresponding to the decomposition of ettrinigite and thaumasite due to their crystal-chemical similarity coincide on the thermograms [49]. Based on this, the IR analysis method was used to obtain additional information, as shown in Figure 5. The results of scanning electron microscopy are shown in Figure 6.  
Analysis of the IR spectra of the control and electro-conducting composites showed the presence of -Si-O- groups in the composition of calcium hydrosilicates, and characteristic peaks of the absorption of duplets in the range from 1083.99 to 1010 cm\({}^{-1}\) were observed in the structure of materials after exposure to aggressive environment.