## 3 Results and Discussions
### Tube Tests
#### 3.1.2 Effect of Cementation Solution Concentration on the Reaction  
Figure 3 shows the variation of the residual calcium ion concentration and calcium carbonate precipitation mass as a function of the reaction time. Considering the residual calcium ion concentration of the treatment solution being less than 0.01 M as the end standard of the reaction, the proportion of calcium ions that reacted in each group at different time periods can be plotted to illustrate the precipitation speed of the calcium carbonate (Figure 4). From the change in calcium ion concentration in the solution (Figure 3), the calcium ion concentration in each solution decreased continuously with the reaction of urease and the cementation solution in the aqueous solution. Finally, the reaction stopped. The curve can be roughly divided into three stages: a rapid reaction period, a weak period, and a stable stage. During the first stage, the calcium ion concentration decreased sharply with increasing time, the urease content was sufficient, its activity was the highest, and the calcium ions in solution were also sufficient. In the second stage, the rate of calcium ion concentration continued to decrease. During the third stage, the calcium ion concentration tended to be stable, and the reaction gradually stopped. The reduced reaction rate may be because the extraction of soybean urease required the lysis of the soybean intracellular cells. During the rapid reaction stage, the improved EICP with organic material added could provide a higher initial activity than MICP, but it could be easily inhibited due to the lack of cell structure protection. As the reaction progressed, the urease activity decreased continuously after being oxidized, and the effective calcium source in the solution also decreased gradually, weakening the precipitation efficiency. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Test Number** & **CaCl\({}_{2}\) (M)** & **Urea (M)** & **CaCl\({}_{2}\):Urea** & **Precipitation** & **Precipitation** & **Precipitation Mass (g),** & **Average** \\ \hline
1 & 0.5 & 0.375 & 1:0.75 & 0.8712 & 0.9392 & 0.9162 & 0.9089 \\
2 & 1 & 0.75 & 1:0.75 & 0.9421 & 0.9661 & 0.8972 & 0.9351 \\
3 & 1.5 & 1.125 & 1:0.75 & 0.4136 & 0.3895 & 0.3841 & 0.3957 \\
4 & 0.5 & 0.5 & 1:1 & 1.3108 & 1.3822 & 1.3529 & 1.3486 \\
5 & 1 & 1 & 1:1 & 1.4419 & 1.3842 & 1.3914 & 1.4058 \\
6 & 1.5 & 1.5 & 1:1 & 0.6636 & 0.6268 & 0.6721 & 0.6542 \\
7 & 0.5 & 0.625 & 1:1.25 & 1.421 & 1.4171 & 1.371 & 1.4030 \\
8 & 1 & 1.25 & 1:1.25 & 1.4588 & 1.4737 & 1.4695 & 1.4673 \\
9 & 1.5 & 1.875 & 1:1.25 & 0.7798 & 0.7652 & 0.7855 & 0.7768 \\
10 & 0.5 & 0.75 & 1:1.5 & 1.4611 & 1.4209 & 1.4768 & 1.4529 \\
11 & 1 & 1.5 & 1:1.5 & 1.5014 & 1.5423 & 1.5182 & 1.5206 \\
12 & 1.5 & 2.25 & 1:1.5 & 0.8463 & 0.8713 & 0.8898 & 0.8691 \\
13 & 0.5 & 0.875 & 1:1.75 & 1.46 & 1.4912 & 1.4321 & 1.4611 \\
14 & 1 & 1.75 & 1:1.75 & 1.5231 & 1.5407 & 1.5009 & 1.5216 \\
15 & 1.5 & 2.625 & 1:1.75 & 0.9183 & 0.9224 & 0.9017 & 0.9141 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Precipitation mass for different constituent concentrations and proportions. As the cementation solution concentration increased from 0.8 M to 2.4 M, the precipitation mass of calcium carbonate continued to increase, but the precipitation mass with a cementation solution concentration of 3.2 M was less than that of 2.4 M. The precipitation ratio of calcium carbonate at a concentration of 1.6 M remained the highest as a result of the relatively high concentration of urease in the low concentration cementation solution and the inhibition action on calcium carbonate precipitation. If the cementation solution concentration was appropriately increased, the calcium carbonate yield improved. When the optimal concentration was exceeded, the urease was inhibited by excessive calcium chloride concentration, which reduced the ability of the urease to hydrolyze the urea and decreased the calcium carbonate yield.