## 2 Materials and Methods
### Mechanical Property Evaluation Parameters  
The mechanical behavior of concrete is obviously dependent on FA content, cement type, cement grade, aggregate type, concrete placement, age, the porosity of cement stone, and field conditions [38]. Experimental evaluation is an important tool to understand the changes in mechanical properties of concrete with material design. The laboratory tests of the same concrete mix design under different FA content were performed in this study. According to the measured data, the mechanical property evaluation parameters can be reasonably determined. Through the above comprehensive analysis, the flexural strength can be calculated as shown in Equation (1). The flexural strength of concrete test specimens is key evaluation index of concrete in mechanical properties. \[f_{f}=\frac{FL}{bh^{2}}\cdot 1.5 \tag{1}\]  
where \(f_{f}\) is the flexural strength of concrete cube specimen (MPa); \(F\) is the failure load under flexure (N); \(L\) is the distance between two fulcrums (mm); \(b\) is the section width of the specimen (mm); \(h\) is the section height of the specimen (mm). In the flexural strength test, the specimen was installed according to Figure 2. The \(b\) and \(h\) of the sample are 40 mm, and the loading head is a rigid cylinder with a diameter of 25 mm and hinged support. The average of the three specimens in each group is taken as  
Figure 1: Concrete specimens in the preparation process: (**a**) test piece to be cured, (**b**) cured sample. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Serial** \\ **Number** \\ \end{tabular} & \begin{tabular}{c} **Water** \\ **Cement** \\ **Ratio** \\ \end{tabular} & \begin{tabular}{c} **Water Binder** \\ **Ratio** \\ \end{tabular} & \
\begin{tabular}{c} **Standard** \\ **Sand/g** \\ \end{tabular} &
\begin{tabular}{c} **Material of** \\ **Cementation/g** \\ \end{tabular} & **FA/\%** & **Cement/\%** \\ \hline B1 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 0 & 100 \\ B2 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 5 & 95 \\ B3 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 10 & 90 \\ B4 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 15 & 85 \\ B5 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 20 & 80 \\ B6 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 25 & 75 \\ B7 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 30 & 70 \\ B8 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 35 & 65 \\ B9 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 40 & 60 \\ B10 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 45 & 55 \\ B11 & 0.55 & 0.33 & 247.5 & 1350 & 450 & 50 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Experimental scheme of cement replaced by FA. the test result. After being removed from the curing place, the specimen should be tested in time and the surface of the specimen should be wiped clean. The application of loads should be uniform and continuous. The loading rate was 0.05-0.08 mm/s. After standard curing to the specified age, tested specimens were taken out for determination. The strength of the compression test is obtained by Equation (2). \[f_{cc}=\frac{F}{A} \tag{2}\]  
where: \(f_{cc}\) is the compressive strength (MPa); \(F\) is the failure load (N); \(A\) is the bearing area of the specimen (mm\({}^{2}\)). The compressive strength of each test group was treated as required by the Chinese standard for the evaluation of concrete compressive strength (GB/T 50107-2010). After removal from the curing site, the specimen shall be tested in time, and the surface of the specimen and the upper and lower bearing plates shall be wiped clean. In the test process, the load should be continuous and uniform, and the loading rate was 0.5-0.8 MPa/s. When the loading value was recorded after the failure, the testing data was obtained from three specimens. The X-ray diffraction (XRD) test was measured by a SHIMADZU (Kyoto, Japan) X-ray diffractometer, as shown in Figure 3. Mainly for the test of concrete ground into powder, the test range is \(-\)3-150\({}^{\circ}\), the full spectrum of \(<\)\(\pm\)0.02\({}^{\circ}\) deviation, and the concrete can withstand up to 120 kg.