## 3 Results

Table 3: Concrete mixture compositions (per 1 dm\({}^{3}\)), compressive strength values at 28 days and density at different cement paste layer thicknesses (CPLTs). same time, an excess of cement paste is useless because it fills the voids between the grains and is essentially a ballast. In addition, it can lead to the stratification of the concrete mix. The experimental and calculated parameters of the aggregate (granite crushed stone, fraction 5-10 mm) are given in Table 4. The composition of the mixes at different CPLTs and different water/cement ratios, as well as the values of strength and density, are given in Table 5. The calculations were calculated in the same way as for the granite screenings of 2.5-5 mm fraction. As can be seen from the above data, when using a crushed stone fraction of 5-10 mm with a layer thickness of 150 microns, the highest strength is achieved at W/C = 0.45. At the same time, when the W/C decreases to 0.4 or increases to 0.5, the strength decreases slightly. At a W/C of 0.35, the strength decreases sharply (to 2.8 MPa) due to insufficient mix workability. Figure 3 shows the dependence of the porous concrete compressive strength on W/C at different CPLTs. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic (Index)** & **Value** & **Unit of Measurement** \\ \hline Grading & 5–10 & mm \\ \hline Specific surface area (\(S_{d}\)) & 0.918 & m\({}^{2}\)/kg \\ \hline Grain density & 2.7 & kg/dm\({}^{3}\) \\ \hline Bulk density & 1.53 & kg/dm\({}^{3}\) \\ \hline Void content & 43.3 & \% \\ \hline Conditional grain size (diameter) & 5 & mm \\ \hline Conditional grain radius (\(R\)) & 2.5 & mm \\ \hline Grain surface area (\(S\)) & 78.5 & mm\({}^{2}\) \\ \hline Cement paste layer thickness on grains (\(\delta\)) & 100 & 125 & 150 & \(\upmu\)m \\ \hline Volume of cement paste on grains (\(V_{c,p}\)) & 0.0918 & 0.1147 & 0.1376 & 1 (dm\({}^{3}\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Experimental and calculated characteristics of aggregate (granite crushed stone) for porous concrete. Figure 2: Dependence of porous concrete compressive strength on W/C and CPLT (aggregate: granite screenings). At a CPLT value of 125 \(\upmu\)m, the highest strength is achieved at a W/C of 0.4, but the difference between the strengths at a W/C of 0.4 and 0.45 is not significant. At a CPLT value of 100 \(\upmu\)m, the strength is lower than at thicknesses of 125 and 150 \(\upmu\)m.  
Comparing the results obtained for the two aggregates, the following can be noted. The compressive strength of porous concrete using screenings is higher than that using crushed stone at all layer thicknesses and different W/C ratios. Thus, at W/C = 0.45 and \(\delta\) = 150 \(\upmu\)m, the strength for the 2.5-5 mm fraction is 11.4 MPa (Figure 4), while for the 5-10 mm fraction, it is 7.6 MPa, which is almost 50% higher. This can be explained by the larger amount of contact between the grains of the finer fraction and, accordingly, by the higher strength. At the same time, the density is also higher for the 2.5-5 mm fraction (Figure 5), since the void content of such concrete is smaller. Considering the above, the better quality of the porous concrete with an aggregate fraction of 2.5-5 mm can be confirmed by the coefficient of structural quality (CSQ), which is determined by the ratio of compressive strength to the relative density of concrete. As can be seen in Figure 6, the CSQ for concrete at the 2.5-5 mm fraction is higher than for the 5-10 mm fraction. This means that despite the slightly higher density of such concrete, it has significantly higher strength, indicating a better quality of porous concrete at the 2.5-5 mm fraction. Figure 3: Dependence of porous concrete compressive strength on W/C and CPLT (aggregate–granite crushed stone).