## 4 Performance Enhancement Tests on Fluid-Cured Soil  
### Analysis of Results of Polycarboxylic Acid Water-Reducing Agent Doping  
According to the related research [20], additives can effectively improve the performance of fluid-cured soil and increase its flow, strength, and durability. Admixtures can be categorized into many types depending on the conditions of use. Under the condition of a 140% water content (compressive strength met the requirement, and fluidity did not), the polycarboxylic acid water-reducing agent was selected to test the fluidity and compressive strength of the fluid-cured soil. We fixed the curing agent Ratios I and II and a mixing amount of 35%. Through the pre-tests, whose results are shown in Table 7, it was found that 6% was the critical value of the polycarboxylic acid water-reducing agent dosage acting on the fluidity of the cured soil for Ratios I and II before the flow value slowly increased. When the dosage of the polycarboxylic acid water-reducing agent exceeded the critical value of 6%, its effect on the flowability of the fluid-cured soil was very significant. From 6% to 7%, the flow value of the two ratios of the soil increased by 37.2% and 38.8%, respectively. When the water-reducing agent dosage was more than 6.2%, the fluidity of the soil met the specification requirements of Technical Standard for Filling of Ready-mixed Fluidized Cured Soil T/CECS 1 037-2022. \begin{table}
\begin{tabular}{l l l l} \hline
**Dosage of Water Reducer/\%** & **Combination I** & **Combination II** & **Water Content/\%** \\ \hline
1 & 130.1 & 129.1 & \\
2 & 131.7 & 131.2 & \\
3 & 133.4 & 133.1 & \\
4 & 134.1 & 132.8 & \\
5 & 136.6 & 135.2 & \\
6 & 139.4 & 136.4 & \\
7 & 191.3 & 189.3 & \\ \hline \end{tabular}
\end{table} 
Table 7: The influence of the polycarboxylate superplasticizer on fluidity. Figure 5: Unconfined compressive strength and flowability of flowable solidified soil with different moisture contents. Based on the pre-tests of the agents, detailed tests were carried out on polycarboxylic acid water-reducing agent dosages in the interval of 6% to 7%, with a gradient of 0.2%. We analyzed the change rules of the fluidity and unconfined compressive strength of the fluid-cured soil with different amounts of admixtures (6.0%, 6.2%, 6.4%, 6.6%, 6.8%) and with different maintenance ages (3d, 7d, and 28d). As shown in Figure 6, the 7d and 28d unconfined compressive strengths of Ratios I and II decreased slowly from 6.0% to 6.8%. The 3d compressive strength showed a slight increase and then a decrease, but compared with the unadulterated polycarboxylic acid water-reducing agent, there was a significant decrease in the 3d strength. The strength of cured soil was reduced by 9% and 10% for Ratios I and II, respectively. The compressive strength of the cured soil at 7d and 28d did not change significantly compared with that of the unadulterated water-reducing agent. This is because the molecular structure of the polycarboxylic acid water-reducing agent comprises a hydroxyl group, a carboxyl group, a sulfonic acid group, and other functional groups, promoting adsorption, complexation, electrostatic repulsion, and spatial site resistance. It effectively inhibits initial C\({}_{3}\)A and C\({}_{3}\)S hydration and delays the formation of cured soil structures but has little effect on the development of later structures [21]. At the same time, in the polycarboxylic acid molecule, the main chain is negatively charged and adsorbs cement particles and positively charged hydration products. The adsorbed particles form a double-layer structure and generate the same electrostatic repulsion between the particles. It is these two effects that allow polycarboxylic acid molecules to inhibit and disrupt the formation of flocculated structures at the microscopic level, resulting in the release of free water encapsulated in cement particles and a dramatic improvement in the flow properties of the cured soil at the macroscopic level [22].