## 3 Results and Discussion
Therefore, the effect of the maximum grain size of the aggregate on the tested values of modulus of elasticity should be treated as insignificant. This was also confirmed by the ANOVA \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Type of**} & \multicolumn{2}{c}{**Compressive**} & \multicolumn{2}{c}{**Splitting Tensile**} & \multicolumn{2}{c}{**Elastic**} & \multirow{2}{*}{**K**} \\
**Concrete/Descriptive** & \multicolumn{2}{c}{**Strength**} & \multicolumn{2}{c}{**Strength**} & \multicolumn{2}{c}{**Strength**} & \multicolumn{2}{c}{**EN 1992**} & \multicolumn{2}{c}{**Modulus**} & \multicolumn{2}{c}{**EN 1992**} \\
**Statistics** & \multicolumn{2}{c}{**f\({}_{\text{cm}}\)**, (MPa)**} & \multicolumn{2}{c}{**Class**} & \multicolumn{2}{c}{**f\({}_{\text{cm,sp}}\) (\(\mathbf{f_{cm,m}}\))**} & \multicolumn{2}{c}{**[33]**} & \multicolumn{2}{c}{**E\({}_{\text{cm}}\)**,**} & \multicolumn{2}{c}{**[33]**} \\  & & & & **(MPa)** & & **(GPa)** & & \\ \hline \multirow{3}{*}{GC2/8} & Mean & 54.0 & \multirow{3}{*}{C40/50} & 5.01 (4.51) & \multirow{3}{*}{33.5} & \multirow{3}{*}{35} & 0.09 \\  & CV & 2.8 & & & & & & 0.09 \\ \cline{1-1}  & SD & 1.52 & & & 0.36 & & 0.86 & & 0.006 \\ \cline{1-1}  & Mean & 54.7 & & & 3.69 (3.32) & & 33.1 & & 0.06 \\ \cline{1-1}  & CV & 4.8 & & & 3.5 & 3.5 & 1.8 & 35 & 5.0 \\ \cline{1-1}  & SD & 2.61 & & & 0.13 & & 0.58 & & 0.003 \\ \cline{1-1}  & Mean & 56.1 & & & 3.28 (2.95) & & 32.7 & & 0.05 \\ \cline{1-1}  & CV & 5.0 & & & 4.6 & 3.5 & 4.0 & 35 & 6.0 \\ \cline{1-1}  & SD & 2.81 & & & 0.15 & & 1.30 & & 0.003 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Mechanical properties of the concretes. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type of Concrete** & **Air Content (\%)** & **Slump Test (cm)** \\ \hline GC2/8 & 2.40 & 5.0 \\ GC2/16 & 2.60 & 4.0 \\ GC2/31.5 & 2.70 & 4.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Properties of gravel concrete. test, which shows that the differences between the values of concrete E\({}_{\rm cm}\) modules are statistically insignificant (\(p=0.43>p=0.05\)). By referring the results of the E\({}_{\rm cm}\) test to the values according to the EN 1992 standard [33], all the specified modules correspond to class C30/37, i.e., by two concrete strength classes below the specified C40/50. However, it should be noted that the modulus of elasticity of concrete is not only dependent on its compressive strength. The influence of the type of coarse aggregate on the value of modulus of elasticity is very strongly visible, which is reflected not only in the EN 1992 standard [33], and also in the literature [35; 36; 37; 38]. In particular, this effect may be difficult to assess in the case of gravel aggregates, which are polymerisations with a mineral composition often very different depending on the origin (location of the mine). The brittleness, i.e., the ratio of the splitting tensile strength to the compressive strength f\({}_{\rm cm}\)/f\({}_{\rm cm}\), of the tested concretes is also varied. A material is considered brittle when the f\({}_{\rm cm}\)/f\({}_{\rm cm}\) ratio is less than 1/8 (0.125) [39]. The lower the \(K\)-value, the more brittle the material is. The K value calculated on the basis of the EN 1992 standard [33] is 0.07 for all concretes. In the case of two types of aggregates, it was found that the brittleness of the concrete GC2/16 and GC2/31.5 is higher than the value calculated according to standard values (for a given concrete strength class). Only concrete GC2/8, with a brittleness index equal to 0.09, met the requirements calculated on the basis of the EN 1992 standard [33]--it turned out to be less brittle than other concretes (Table 6). In the case of concrete, the matrix, as well as aggregates, are brittle materials. The higher brittleness of concretes GC2/16 and GC2/31.5 may be caused by concrete defects, such as air voids, cracks, discontinuities in the crystal network that may have formed between aggregates of different sizes.