# Influence of Alternating Temperature on the Effectiveness of EICP in Consolidating Aeolian Sand
## 4 Discussion
### Influence of Alternating Temperature on the Calcium Carbonate Precipitation Rate  
The final calcium carbonate precipitation rate was highest in T2, followed by T3, and lowest in T1. Since the survival duration of urease directly affects the final calcium carbonate production, the process of T2 was able to keep urease alive for a longer period of time, which led to the highest final calcium carbonate production. The 15 samples had the same proportions of material mass, and theoretically, the calcium carbonate production of each sample would be the same. The highest final calcium carbonate content was found in the process of T2, which corresponded to the highest rate of calcium carbonate precipitation.  
As the mixing method is not subsequently supplemented with cementing solution, the initial cementing solution was used at a high concentration. The initial concentration of CaCl\({}_{2}\) is 3 mol/L, and the concentration of the cementing solution increases further under the influence of evaporation. However, the final calcium carbonate precipitation rate reached 81.43% in the process of T2. The average calcium carbonate precipitation rate in the three experimental groups (T1, T2, and T3) also reached approximately 75%. The literature found that the final calcium carbonate precipitation rate could be more than 80% or even 100% based on the multiple injection method and using a low concentration of cementing solution to consolidate aeolian sand [33; 38]. Reducing the concentration of the cementing solution has been confirmed as one of the methods to improve the calcium carbonate precipitation rate [39; 40].  
However, for the mixing method, a low concentration of the cementing solution cannot provide sufficient calcium ions to ensure the continuing production of calcium carbonate. For injection and grout methods, the high concentration of calcium carbonate can lead to the blockage of pore channels due to the high rate of calcium carbonate production in the initial period, which results in a low calcium carbonate precipitation rate [41; 42; 43]. In this study, the aeolian sand and the cementing material were mixed well before the reaction, there is no risk of the injection or grout channels being blocked, and a higher concentration of cementing solution could be used to ensure the continuous production of calcium carbonate. The literature found the inhibitory effect of a high calcium ion concentration will be weakened in the highly active urease solution, and the production rates of calcium carbonate can be maintained at a high level [44]. Of course, a commercial urease with high urease activity was used in this experiment, which was extracted from giant beans and exhibited a specific activity of 200 U/mg at room temperature. The initial concentration of urease activity and CaCl\({}_{2}\) in the cementing solution is approximately 17,000 U/L and 3 mol/L, respectively. The final calcium carbonate precipitation rate can be up to 81.43%. This suggests that the use of high calcium ion concentration and highly active urease solution is feasible based on the mixing method for sand consolidation by EICP.