## 2 Materials and Methods
#### 3.1.2 Determination of Compressive Strength  
Based on the above, a selection of compositions with the best packing indices at a low content of fractions F3 < 15% was made, for which compressive strength studies were conducted: 15/80/5, 15/75/10, and 15/70/15. Additionally, to assess the effect of changes in the polyfractional composition of the cement on the strength of the SCC, the boundary compositions were selected: 100/0/0, 0/100/0, and 0/0/100. Furthermore, for comparison and to understand the dynamics of strength changes, two-component compositions with variable contents of F1 and F2 or F2 and F3 were selected. The results of the strength measurements are presented in Table 9.  
According to the results, the best compressive strength indicators were found in samples with a three-component composition and variable content of F1, F2, and F3, where the strength increases by 25-29% relative to the reference sample. In two-component composition samples with variable contents of F1 and F2, the strengths ranged from 17% to 25%, compared to the reference sample. It should also be noted that the rate of strength gain increases with the content of fine fraction particles. Strength gains at 7 days of age, relative to 28 days, range from 67% for the 100/0/0 composition to 77% for the 0/0/100 composition. For the reference sample, this figure is 72%, and for fractions with a 15% content of F3, it varies from 74% to 75%. Based on the dynamics of strength change, one can observe the influence of particle packing on strength, as the strength of the 0/0/100 composition (51.0 MPa), which should demonstrate the best cement activity due to the larger surface area of the particles, is less than the strength of the 15/70/15 composition (53.3 MPa). For further studies on the effect of polyfractional cement on the physical and mechanical characteristics of concrete, boundary samples (No. 2-4) were excluded, along with samples of two-component composition that had a negative or minimal effect on strength (No. 5-7).  
Thus, the sample compositions presented in Table 10 were selected for the main research.  
Samples of type 2-4 are made based on a two-component binder (hereinafter referred to as a two-component composition), and samples of type 5-7 are made based on a three-component binder (hereinafter referred to as a three-component composition).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**No**} & \multicolumn{2}{c}{**Composition (Components Content), \%**} & \multicolumn{2}{c}{**Compression Strength, MPa**} \\ \cline{2-6}  & **F1** & **F2** & **F3** & **7 Days** & **28 Days** \\ \hline
1 & & Reference sample & & 29.78 & 41.18 \\
2 & 100 & 0 & 0 & 20.17 & 29.81 \\
3 & 0 & 100 & 0 & 30.58 & 42.02 \\
4 & 0 & 0 & 100 & 39.14 & 51.00 \\
5 & 20 & 80 & 0 & 30.03 & 41.97 \\
6 & 25 & 75 & 0 & 28.73 & 40.75 \\
7 & 30 & 70 & 0 & 27.31 & 38.78 \\
8 & 0 & 80 & 20 & 36.06 & 48.16 \\
9 & 0 & 75 & 25 & 37.41 & 50.03 \\
10 & 0 & 70 & 30 & 38.09 & 51.60 \\
11 & 15 & 80 & 5 & 38.32 & 51.94 \\
12 & 15 & 75 & 10 & 39.14 & 52.61 \\
13 & 15 & 70 & 15 & 39.90 & 53.26 \\ \hline \end{tabular}
\end{table}
Table 9: Preliminary assessment of sample strength.