## 2 Materials and Methods  
During the experimental investigations, Portland cement of the CEM I 42.5N brand (Novorosement, Novorossiysk, Russia) was used without additives. The main components and features of cement were as indicated in ref. [51]. Battered sandstone (\"Repnyanskoye quarry management\", Chistoozerny village, Russia) was employed as a thick aggregate with the following physical and mechanical features: fraction size 5-20 mm; bulk density 1428 kg/m\({}^{3}\); true density 2560 kg/m\({}^{3}\); crushability 13.8% by weight; content of lamellar and needle-shaped grains 7.2 wt.%; voidness 43%. Quartz sand (Arkhipovskay quarry, Arkhipovskoye village, Russia) was employed as a fine aggregate with the properties as specified in ref. [51]. As a natural CA for local replacement of battered stone, the shell of the seeds of an RT from Malaysia was employed. The shell was dried in a ShS-80-01 SPU oven (Smolenskoye SKTB SPU, Smolensk, Russia) and battered in a ShD-6 lab jaw crusher (Vibrotechnik, St. Petersburg, Russia) to a fraction size of 5-20 mm. The method for obtaining ready-made CA based on the shell of the seeds of the RT is indicated in Figure 2.  
The proportion of the mixture was as follows. Portland cement:waters:sand:crushed stone--1:0.57:2.25:3.21. The workability of the mixture corresponded to the draft of a standard cone with a height of 300 mm, a large diameter of 200 mm and a small diameter of 100 mm, equal to 5-9 cm. The preparation of concrete mixtures was performed in a lab BL-10 (\"ZZBO\", Zlatoust, Russia). To compress the mixture during the molding of the samples, a regular lab vibrating stage SMZh-539-220A (IMASH, Armavir, Russia) was chosen; the time was 60 s for vibration. The sample preparation procedure included the following main technological steps (Table 1). After curing for 28 days in a normal hardening chamber, the samples were tested on an IP-1000 hydraulic press and a R-50 tensile experiment machine. Concrete strength control and evaluation were performed in accordance with GOST 18105 [55]. A study of the structure of hardened concrete samples with local replacement of CA with RT seed shells was performed using a ZEISS CrossBeam 340 electron microscope. In total, 1 series of samples of the control composition and 8 series of samples with different amounts of RT seed shells were made and tested. The experimental research program is indicated in Figure 3. \begin{table}
\begin{tabular}{c c} \hline \hline
**Technological Operation** & **Description** \\ \hline \multirow{4}{*}{Dosing} & At the dosing stage, the concrete components were measured; the components were weighed on a \\  & VLTE-2100 balance (NPP Gosmert, St. Petersburg, \\  & Russia). The accuracy is 0.05 g. \\ \hline \multirow{4}{*}{Loading concrete mix components} & The components were loaded into the concrete mixer \\  & in the following order: water, cement, additive, sand, \\  & CA (battered stone and RT seed shell). \\ \hline \multirow{2}{*}{Mixing} & The components were mixed in the concrete mixer \\  & until a homogeneous mass was obtained. \\ \hline \multirow{4}{*}{Molding} & The mixture was poured into sample molds, then \\  & formed on the laboratory vibratory platform and \\  & compressed to the desired state. \\ \hline \multirow{4}{*}{Storage} & The samples were placed in a normal hardening \\  & chamber, where they were kept for 1 day; then, they \\ \cline{1-1}  & were removed from the molds and hardened for \\ \cline{1-1}  & another 27 days. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Sample preparation procedure. Figure 2: Method for obtaining CA based on the shell of the seeds of the RT. Flexural compressive and TS experiments were performed in accordance with GOST 10180 [56]. Prismatic strength was determined according to the standard GOST 24452 [57]. Also in this investigation study, measuring \"devices were employed: metal measuring ruler was selected as 500 mm; device for gauging deviations from the plane NPL-1; device for gauging deviations from perpendicularity NPR-1\" [58; 59; 60].