## 3 Material Preparation  
### Selection and Preparation of Modifiers  
MRP recycled concrete is a kind of special concrete modified by uniformly mixing waste rubber powder into ordinary concrete and adding appropriate modifiers. This kind of concrete not only has the advantages of good toughness, light weight, durability, and strong impact resistance, it can also utilize waste rubber in large quantities, which has good environmental significance. In the relevant literature at home and abroad, the modifiers of rubber powder are mainly categorized into two main groups, i.e., inorganic modifiers and organic modifiers. Inorganic modifiers are further subdivided into different types, such as water, acid, alkali, and salt. These modifiers can change the surface properties of rubber powder and make it bond more tightly with the cement matrix, thus improving the mechanical properties and durability of concrete [12; 13]. For example, water can make the rubber powder become wetter and promote its bonding with the cement matrix, while acids, alkalis, and salts can change the surface polarity and chemical properties of the rubber powder to make it more compatible with the cement matrix. In the experimental study, two modifiers that had good surface activity, low or non-toxicity, and were environmentally friendly were selected to modify the rubber powder: Sipan 40 and SDBS. By efficiently enhancing the bonding qualities between rubber powder and the cement matrix, both modifiers can increase the mechanical qualities and longevity of concrete. At the same time, they also have good environmental performance and will not cause harm to the environment or human body. Sipan 40, also known as sorbitan palmitate, is a creamy to light brown waxy solid with a slightly fatty odor. It has a freezing point of 45-47 \({}^{\circ}\)C. It can be dispersed in hot water and dissolved in hot oil. At room temperature, Sipan 40 is stable in different pH and electrolyte solutions. In addition, Sipan 40 has emulsifying and dispersing properties. The molecular formula is C\({}_{22}\)H\({}_{42}\)O\({}_{6}\), nonionic surfactant, HLB value 6.7, and its molecular formula is shown in Figure 1.  
There are numerous methods for the production of strychnine, most of which use direct esterification. First, the following starting materials need to be prepared: refined hexadecanoic acid (C\({}_{16}\)), chlorine, sodium hydroxide (NaOH) water, methanol (CH\({}_{3}\)OH), which serve as the basic ingredients for the synthesis of strychnine 40. In the second step, an oxidation reaction is conducted during which the prepared hexadecanoic acid is oxidized with chlorine gas in the presence of sodium hydroxide. The purpose of this step is to produce chlorine hexadecanoate. In the third step, a hydrolysis reaction is carried out in  
Figure 1: Molecular structure diagram of Sipan 40.  
which the generated chlorohexadecanoic acid is hydrolyzed with methanol in the presence of sodium hydroxide to produce sodium hexadecyl methanol. The fourth step is to carry out washing and decolorization, and the generated sodium cetyl methanol needs to be washed and decolorized to remove impurities and colored substances therein. The fifth step is to carry out a stananization reaction, wherein the washed and decolorized sodium cetyl methanol undergoes a stannization reaction with sulfuric acid to generate stannum 40. The sixth step is to carry out separation and purification, wherein the generated stannum 40 needs to undergo a separation and purification process to remove impurities and by-products therefrom. The seventh step is end-product testing; after the separation and purification process, the stannous 40 needs to be subjected to end-product testing to ensure that it meets quality standards. Finally, after the end-product inspection, the spiroplasma 40 needs to be packaged and stored for subsequent use and transportation. The preparation process is shown in Figure 2.  
One popular anionic surfactant is SDBS.