## 3 Results and Discussion  
### The Compressive Strength of AN-LAC  
As shown in Figure 4a, the compressive strength of AN-LAC at 3 d, 7 d, and 28 d showed an increasing trend when the average particle size decreased. In single-particle size gradation groups, the compressive strength of AN-LAC-1 and AN-LAC-2 at 28 d was 19.1% and 10.5% higher than that of AN-LAC-3, respectively. In combined-particle size gradation groups, it should be noted that AN-LAC-6, the average particle size of which was the highest, exhibited a relatively low compressive strength. The reason for the above-mentioned phenomenon was that the particle size of NSLA affected the homogeneity of the concrete [33; 34]. Coarse aggregate with a larger particle size is more likely to cause internal defects in concrete, resulting in reduced homogeneity and lower compressive strength. For instance, the compressive strength of AN-LAC-4, AN-LAC-5, and AN-LAC-7 at 28 d was 17.3%, 6.6%, and 10.3% higher than that of AN-LAC-6, respectively. Among all the groups, it is obvious that the compressive strength of AN-LAC-4 and AN-LAC-3 at 28 days reached the maximum value of 56.7 MPa and minimum value of 43.7 MPa, respectively. The incorporation of NSLA with a small particle size could improve the structure of the ITZ and enhance the inner skeleton of the concrete, resulting in better compressive strength. In addition, Figure 4b shows the increase in the compressive strength of AN-LAC with increasing curing age. The compressive strength of specimens at 3 d and 7 d reached  
Figure 4: The test results of the compression test: **(a)** the compressive strength of AN-LAC; **(b)** variation of the compressive strength of AN-LAC vs. curing age. 70.7-76.1% and 84.6-87.4% of the compressive strength of concrete at 28 d, respectively, indicating that AN-LAC had high early strength. To clearly observe the change in compressive strength, the relative compressive strength of AN-LAC at different curing ages is listed in Table 5. It is obvious that there was a change in law between the compressive strength development of concrete and the curing age. [PERSON] et al. [35] predicted the compressive strength of sintered ceramics concrete at different curing ages through Equation (2) and the fitting curve showed an excellent correlation. Then, Equation (3) can be obtained by modifying Equation (2) based on a large amount of test data to predict the compressive strength of AN-LAC. However, the correlation coefficient \(R^{2}\) was only 0.6636, indicating that the correlation was weak, as shown in Figure 5a. Therefore, the change law of the compressive strength of sintered ceramics concrete with the increase in curing age was not applicable to AN-LAC:  
\[f_{\text{cu, n}}=34.65e^{-\frac{1.4672}{\text{n}}} \tag{2}\]  
\[f_{\text{cu, n}}=51.57e^{-\frac{1038}{\text{n}}} \tag{3}\]  
To solve this problem, Equation (4) was proposed to predict the compressive strength of AN-LAC in this study according to previous research [35; 36; 37]. The relationship between relative compressive strength and curing age is shown in Figure 5b. It is clear that the correlation coefficient \(R^{2}\) was 0.9686, in which case the accuracy of the predicted results for the compressive strength of AN-LAC at different curing ages could be guaranteed:  
\[\frac{f_{\text{cu, n}}}{f_{\text{cu, 28}}}=1.024e^{-\frac{1.02}{\text{n}}} \tag{4}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Group** & **Relative Compressive Strength** & **3 d** & **7 d** & **28 d** \\ \hline AN-LAC-1 & & 0.761 & 0.874 & 1.000 \\ AN-LAC-2 & & 0.739 & 0.862 & 1.000 \\ AN-LAC-3 & & 0.707 & 0.846 & 1.000 \\ AN-LAC-4 & \(f_{\text{cu, n}}/f_{\text{cu, 28}}\)* & 0.728 & 0.857 & 1.000 \\ AN-LAC-5 & & 0.741 & 0.856 & 1.000 \\ AN-LAC-6 & & 0.729 & 0.857 & 1.000 \\ AN-LAC-7 & & 0.730 & 0.858 & 1.000 \\ \hline \hline \end{tabular}  
* \(f_{\text{cu, n}}\) and \(f_{\text{cu, 28}}\) are the compressive strength of concrete at \(n\) and 28 days, respectively.  
\end{table} 
Table 5: Relative compressive strength of AN-LAC at different curing ages.