## 3 Results  
Investigation of the Influence of the Amount of Added RSS instead of CA on the Strength-Strain Features of Concrete  
The consequences of the influence of local replacement of CA with RT seed shells on the strength of concrete are indicated in Figures 4-7. Figure 4: The influence of local replacement of CA with RT seed shells on CS \(R_{b,cub}\). Figure 5: Results of investigational studies of the influence of local replacement of CA with RT seed shells on axial CS \(R_{b}\). Figure 4 demonstrates that when coarse filler is replaced with RSS in the quantity of 2% and 4%, a gradual increase in CS from 49.4 MPa to 51.7 MPa is observed. However, when replacing bulk filler, starting from 6% and up to 16%, the reverse trend of change in CS is observed. The CS values were 46.3 MPa when replaced with RSS in the amount of 6% and 44.8 MPa, 40.9 MPa, 39.7 MPa, 38.1 MPa and 37.6 MPa when replaced in the amount of 8%, 10%, 12%, 14% and 16%, respectively. This can be explained by the denser packing created by the battered sandstone and the shells of the RT seeds. The obtained experimental data have good convergence. The deviation of approximated and experimental data does not exceed 6%. The residual sum of squares is 6.87314. The coefficient of determination is R\({}^{2}\) = 0.968. The dependence of cubic strength on RSS is well approximated by the formula  
\[R_{b,cub} = 48.6+0.74x^{1.03}\sin(0.18x+2.22),\,R^{2}=0.968 \tag{7}\]  
Figure 6: Consequences of investigational studies of the influence of local replacement of CA with RT seed shells on TS in twisting \(R_{btb}\). Figure 7: Results of investigational studies of the influence of local replacement of CA with RT seed shells on axial TS \(R_{bt}\). where \(x\) is RSS, % and \(R^{2}\) is the coefficient of determination. The results of the experimental studies of CS (Figure 5), TS in twisting (Figure 6) and axial TS (Figure 7) with regard to the amount of RT seed shells are approximated by Equations (8)-(10):  
\[R_{b} =\ 36.1\ +\ 0.97\ x^{0.88}\ \sin(0.23x+1.66),\ R^{2} =\ 0.935 \tag{8}\] \[R_{btb} =5.8+0.177\ x^{0.80}\ \sin(0.23x+1.51),\ R^{2} =\ 0.963\] (9) \[R_{bt} =3.4+0.048\ x^{1.155}\ \sin(0.225x+1.81),\ R^{2} =\ 0.962 \tag{10}\]  
A large coefficient of determination indicates good agreement between the experimental data and the approximating theoretical function. The trend in axial compressive strength, flexural TS and axial TS (Figures 5-7) is similar in nature to that of compressive strength. So, the maximum values of strengths in all cases are fixed at the amount of RSS 4%. With a further increase in the replacement of coarse filler with the shell of the seeds of the RT, a drop in strength features is observed. Photos of the process of testing concrete samples for axial compression are shown in Figure 8.  
Figures 9-11 show the study results of the influence of the ratio of replacement of CA with RT seed shells on the deformation features of concrete. Figures 9 and 10 show that the nature of the change in ultimate strain is similar under axial compression and tension. Thus, when replacing coarse filler with the shells of seeds of an RT in the amount of 2% and 4%, a decrease in the values of limiting deformation is observed, and starting from 6%, an increase is noticeable. As for the modulus of elasticity, its maximum value was fixed at an amount of RSS of 4%, while when replacing coarse filler with RSS in an amount of 6% or more, a drop in the modulus of elasticity was observed. Changes in the strength-strain features of concrete samples depending on the ratio of local replacement of CA with RT seed shells are presented in Table 2 and are denoted as a ratio associated with the control composition (without RSS). Figure 8: Axial compressive testing of concrete specimens: (**a**) initial phase of loading: (**b**) collapse phase.