# High-Performance Concrete Nanomodified with Recycled Rice Straw Biochar
## 2 Materials and Methods  
In the experiments, Portland cement of the CEM I 42.5N brand produced by JSC Novorosement (Novorossiysk, Russia) was used. Table 1 presents the main physical and mechanical properties of Portland cement, and Table 2 shows its mineralogical and chemical composition. Granite crushed stone produced by Pavlovsk Nerud JSC (Pavlovsk, Russia) was used as a large dense aggregate, with the following physical and mechanical characteristics: fraction size--5-20 mm; bulk density--1503 kg/m\({}^{3}\); true density--2620 kg/m\({}^{3}\); crushability--11.4% by weight; the content of lamellar (flaky) and acicular grains is 8.1% by weight; voidness--43%. Quartz sand produced by OAO Arkhipovsky Quarry (village Arkhipovskoye, Belorechensky District, Krasnodar Territory, Russia) with the following physical characteristics was used as a fine aggregate: fineness modulus--1.66; the content of dust and clay particles is 1.2%; bulk density--1438 kg/m\({}^{3}\); true density--2650 kg/m\({}^{3}\). Recycled rice straw biochar modified by the electromagnetic method was used as a modifying additive. The method for obtaining rice straw carbonization (rice husk) is shown in Figure 1. \begin{table}
\begin{tabular}{c c} \hline \hline
**Indicator** & **Value** \\ \hline Residue on a 45 \(\upmu\)m sieve, \% & 3.5 \\ Blaine specific surface area, cm\({}^{2}\)/g & 3635 \\ Normal density of cement paste, \% & 27.7 \\ Beginning of setting, min & 138 \\ End of setting, min & 187 \\ Compressive strength at the age of 28 days, MPa & 52.2 \\ Flexural strength at the age of 28 days, MPa & 8.5 \\ Uniformity of volume change, mm & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical and mechanical characteristics of Portland cement. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{4}{c}{**Mineralogical Composition, \%**} & \multicolumn{4}{c}{**Chemical Composition, \%**} \\ \hline
**C\({}_{3}\)S** & **C\({}_{2}\)S** & **C\({}_{3}\)A** & **C\({}_{4}\)AF** & **MgO** & **SO\({}_{3}\)** & **Na\({}_{2}\)O + K\({}_{2}\)O** & **CaO** & **SiO\({}_{2}\)** & **LOI** \\ \hline
68.8 & 10.3 & 8.9 & 11.3 & 0.9 & 2.34 & 0.75 & 50.1 & 14.0 & 3.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mineralogical and chemical composition of Portland cement. Potassium hydroxide (KOH) produced by Soda-chlorat LLC (Berezniki, Russia) was used to activate rice straw. The alkali solution concentration was 20 g per 1 L of water (2% KOH solution). For drying at a temperature of 105 \({}^{\circ}\)C to obtain rice straw carbonization, an ShS-80-01 SPU drying oven (Smolensk SKTB SPU, Smolensk, Russia) was used. Carbonization of rice straw was carried out in a laboratory electric furnace SNOL 6.7/1300 (AB UMEGA GROUP, Utena, Lithuania). Electron microscopy and simultaneous thermal analysis were also performed for the obtained sample of rice straw biochar modified by the electromagnetic method. The microstructure was studied using a ZEISS CrossBeam 340 (Carl Zeiss Microscopy GmbH (Factory), Jena, Germany). Synchronous thermal analysis was performed on a STA 449 F1 Jupiter instrument (NETZSCH-Geratebau GmbH, Selb, Germany). Thermal analysis was carried out in the air. Electromagnetic treatment was carried out on a process activation unit (UAP) manufactured by DSTU (Rostov-on-Don, Russia). With small equipment sizes and low unit energy costs, UAP allows changing the structure and properties of processed materials. The scheme of the process activation installation is shown in Figure 2, and the general view of the UAP (Figure 3a), the working body (Figure 3b), and the control cabinet (Figure 3c), as well as the side view of the loading opening (Figure 3d) are shown in Figure 3.  
Figure 1: Method for obtaining carbonized rice straw (rice husk). Figure 2: Scheme of the process activation installation: 1—incoming liquid flow for processing; 2—cooling jacket housing; 3—working area; 4—replaceable insert; 5—working bodies—ferromagnets (needles); 6—induction coils; 7—processed stream.