## 3 Result Analysis
### Mercury Intrusion Porosimetry
#### 3.3.1 Results of Mercury Intrusion Porosimetry
Therefore, based on the grey relation theory, this section takes the change rate of harmful pores, more harmful pores and total porosity after freezing and thawing tests in the MIP test of the 20% geopolymer content sample as the parent sequence and the corresponding UCS, ITS and CRM loss of the sample as the sub-sequence to analyze the correlation between the macro-mechanical performances and micro-indicators of geopolymer-cement-stabilized crushed stone mixture after freeze-thaw cycles. The formula of grey relation analysis is as follows: Formulas (1)-(3), where Formula (1) is the dimensionless processing formula of elements, Formula (2) is the expression of the grey correlation coefficient and Formula  
Figure 11: The porosity of mixture with different geopolymer contents after freeze–thaw cycles. Figure 12: The pore size distribution of the mixture with a content of 20% geopolymer changed after freeze–thaw cycles. (3) is the solution of the grey correlation index. The results of grey correlation analysis are listed in Table 13.  
\[x^{\prime}=\frac{x-\min(x)}{\max(x)-\min(x)/} \tag{1}\]  
\[\xi_{i}(j)=\frac{\min(\left|x_{i}^{\prime}-x_{0}^{\prime}\right|)+\rho\cdot\max( \left|x_{i}^{\prime}-x_{0}^{\prime}\right|)}{\left|x_{i}^{\prime}-x_{0}^{\prime }\right|+\rho\cdot\max(\left|x_{i}^{\prime}-x_{0}^{\prime}\right|)} \tag{2}\]  
\[r_{i}=\frac{1}{n}\sum_{j=1}^{n}\xi_{i}(j) \tag{3}\]  
In the formula, \(\xi_{i}(j)\) represents the correlation coefficient; \(r_{i}\) represents the correlation degree; and \(\rho\) represents the resolution coefficient. Based on the grey relation analysis, we can see that the correlation between the UCS loss and the total porosity growth of the mixture with 20% geopolymer content after freeze-thaw cycles is 0.75, which indicates that there is a distinct positive correlation between the two. Comparing the results for pore sizes 20-50 nm and greater than 50 nm, the increase in overall porosity has the greatest impact on the loss of UCS. For the loss of ITS, the increase in more harmful pores and total porosity leads to damage, and the correlation degree is above 0.70. Specifically, the correlation between more harmful pores and ITS loss is 0.91, and the correlation between total porosity and ITS loss is 0.74. Compared with UCS and ITS, the correlation between the loss of CRM and several pore size changes is low, which does not exceed 0.70. This means that the CRM loss of the mixture after freezing and thawing cycles is basically not influenced by these pore size changes. In summary, the UCS loss of the mixture after freezing and thawing cycles is mainly affected by increased total porosity, and the ITS loss is mainly affected by the increase in more harmful pores and total porosity, while the CRM is basically not affected by these pore size changes. After many freeze-thaw cycles, the mixture mechanical properties with different geopolymer contents were all damaged. Through the microscopic test, the theory of action is as follows: In the process of cycles, due to water's frost-heightening effect, frost heaving cracks appear in the mixture. At the same time, a part of the cementitious material is taken out during the cycles, leading to a change in the pore size distribution of the mixture. For the mixture with 20% geopolymer, after cycles, the harmful pores, more harmful pores and total porosity increased by 1.63%, 3.58% and 5.50%, respectively, and the UCS decreased by 2.43 MPa. According to the grey relation analysis, we found that the increase in total porosity from 10.68% to 16.18% is the main factor leading to the loss of UCS. In addition, the increase in harmful pores (3.58%) and the increase in total porosity (5.50%) are also the main reasons for the loss of ITS.