## 3 Results and Discussion
Significant change of the IR spectrum of the sample, modified with the complex additive can be observed compared to spectrum of the reference sample and the spectra of the samples, modified with carbon black in the amount of 0.01% by the cement weight and chrysotile fibers in the amount of 0.05% by the cement weight. In the spectra of the samples, the intensity of the absorption line corresponding to calcium silicate hydrates decreases in the frequency range of 1008.7 cm\({}^{-1}\) and a shift of the absorption lines is noted from 1089.78 cm\({}^{-1}\) to 1080.14 cm\({}^{-1}\) as well as from 1008.77 cm\({}^{-1}\) to 993.34 cm\({}^{-1}\). A change in the character of a doublet with a shift of the maximum peak to a lower frequency region can be caused by a change in the basicity of calcium silicate hydrates predetermining the increase of cement matrix strength. In addition, the IR analysis of the reference sample (Figure 4a) showed the presence of OH' hydroxyl group (3421.72 cm\({}^{-1}\)) and chemically bound water (1662.24 cm\({}^{-1}\)) that in the case of composite modification with the complex additive were taken over by multiple peaks in the frequency range 3400-3900 cm\({}^{-1}\). Here, the decrease of the amount of free water (3800-3400 cm\({}^{-1}\) and 1653.00 cm\({}^{-1}\)) can be explained by a different degree of OH-hydroxyl group bonding in calcium silicate hydrates as well as a decrease in the total amount of free calcium hydroxide due to its replacement by calcium silicate hydrates. It can be noted that the maximum change in the IR spectra curve is observed when the additives are added into the composition together, which evidences their synergetic effect. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Compressive Strength, MPa**} & \multicolumn{4}{c}{**Flexural Strength, MPa**} \\ \cline{2-13}
**Chrysotile** & \multicolumn{4}{c}{**Carbon Black Amount, \%**} & \multicolumn{4}{c}{**Carbon Black Amount, \%**} \\ \cline{2-13}
**Amount, \%** & **0** & **0.005** & **0.01** & **0.02** & **0.05** & **0.1** & **0** & **0.005** & **0.01** & **0.02** & **0.05** & **0.1** \\ \hline
0 & 27.6 & 30.7 & 29.9 & 30.3 & 27.8 & 27.4 & 4.39 & 4.45 & 4.76 & 4.82 & 4.42 & 4.51 \\
0.01 & 28.2 & 31.0 & 30.7 & 30.8 & 31.5 & 30.1 & 4.84 & 4.73 & 4.72 & 4.90 & 4.87 & 4.79 \\
0.025 & 29.7 & 31.3 & 31.4 & 32.8 & 31.5 & 30.2 & 4.79 & 4.98 & 4.87 & 5.22 & 4.98 & 4.80 \\
0.05 & 32.3 & 34.2 & 36.4 & 35.4 & 33.2 & 30.0 & 4.58 & 5.12 & 5.56 & 5.48 & 5.29 & 4.77 \\
0.075 & 30.9 & 34.6 & 33.9 & 33.1 & 32.3 & 28.7 & 4.57 & 4.91 & 5.17 & 5.11 & 4.84 & 4.56 \\
0.1 & 29.7 & 30.9 & 30.2 & 29.9 & 28.3 & 28.2 & 4.51 & 4.60 & 4.42 & 4.58 & 4.42 & 4.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Compressive and flexural strength of samples at various ratios of components in complex additive. Thermal analysis of the reference sample and the sample modified with the complex additive based on carbon black and chrysotile fibers were carried out on a TGA/DSC1 Star system derivatograph. The results of the study are presented in Figure 5a,b. Figure 4: IR spectra of: (**a**) reference sample, (**b**) sample modified with the carbon black in the amount of 0.01% by cement mass, (**c**) sample modified with chrysotile dispersion in the amount of 0.05% by cement mass, (**d**) sample modified with the complex additive. Figure 5: DSC and TGA spectrum of samples: (**a**) reference sample, (**b**) modified sample. The TGA curves show a change in the intensity of mass loss of the sample modified with the complex additive. When the samples were heated from 90 to 200 \({}^{\circ}\)C, the mass loss was equal to 4.64% for the control sample and 3.26% for the sample modified with the complex additive. With further heating up to 465 \({}^{\circ}\)C, the control sample lost 1.74% of its original weight, whereas the modified sample lost only 1.15%.