## 2 Materials and Methods
Determining the defects in the form of cracks, ribs, crusts and debris was limited to visual inspection in the experiment. Samples with cracks, rib holes with a depth of more than 10 mm, shells with a diameter of more than 10 mm and a depth of more than 5 mm, as well as traces of delamination and under compaction of the concrete mix were not subject to experiment. Reference surfaces were chosen as noticeable on the samples to which forces were operative through loading. The supportive surfaces of the molded cubes planned for the compression experiment were selected. Thus, throughout the test, the compressive force was activated. Before placing the sample on the press, the concrete elements enduring from the earlier test on the base plates of the experimental machine were removed. The specimens were loaded continuously at a constant rate of load rise until their failure. The load time until the sample was destroyed was at least 30 s. The highest force obtained during the test was determined as the breaking load. The destroyed sample was limited to visual inspection. The top plate of the test machine was aligned, for example, with the upper support face, and the planes were adjacent to one another. The sample was loaded at a constant load increase rate of (0.6 \(\pm\) 0.2) MPa/s [56]. For a tensile test in twisting, a prism sample was placed on a press and loaded at a constant load increase rate of (0.05 \(\pm\) 0.01) MPa/s. If the specimen did not fail in the middle third of the span, or if the fracture plane of the specimen was inclined to the vertical plane by more than 15\({}^{\circ}\), then this test result was not taken into consideration while defining the average strength of the concrete of a series of samples [56]. In the axial tensile test, the sample was fixed in a tensile experiment machine and loaded to failure at a continuous rate of load rise of (0.05 \(\pm\) 0.01) MPa/s. The examination results were not considered if the obliteration of the sample did not take place in the  
Figure 3: The program of investigations of the influence of local replacement of CA with RT seed shells on the strength–strain features of concrete. operational area or the flat surface of obliteration of the sample was disposed more than 15\({}^{\circ}\) to its horizontal axis [56]. The CS of concrete conflict of interest \(R_{b,cub}\) was determined with an exactitude of 0.1 MPa using Equation (1):  
\[R_{b,cub}=\alpha\frac{F}{A} \tag{1}\]  
The TS of concrete in twisting \(R_{btb}\) was determined with an accuracy of 0.01 MPa using Equation (2):  
\[R_{btb}=\delta\frac{Fl}{ab^{2}} \tag{2}\]  
The axial TS of concrete \(R_{bt}\) was calculated with an accuracy of 0.01 MPa using the following formula:  
\[R_{bt}=\beta\frac{F}{A} \tag{3}\]  
where \(\alpha\), \(\delta\), \(\beta\) are scale factors; \(F\) is the breaking load, N; \(A\) is the area of the working section of the sample, mm\({}^{2}\); \(l\) is the span size between the supports; \(a\) and \(b\) are characteristic dimensions of the prism. When determining the modulus of elasticity, the press force-meter scale was chosen, and the anticipated assessment of the breaking load \(P_{ult}\) was set as 70% to 80% of the maximum permitted by the nominated scale. When determining the prism strength, the scale of the force meter was chosen in accordance with the requirements of ref. [56]. Prior to experimentation, the alignment of the sample initial reading with the instruments was tested by dividing the instrument scale. As a result, the initial compression force, taken as the limiting zero in tests, could not be more than 2% of the breaking force. The value of the anticipated breaking load of the samples during the experiment was established according to the CS of cube samples made from one batch, determined in accordance with GOST 10180 [56]. The ratio for the same sections of cubes and prisms occupied 80 to 90% of the average refractive load of the cube samples [57].