## 2 Proportioning of Alkali-Activated Composites' Cementitious Materials
### Test Results and Analysis  
#### 2.3.1 The Influence of the Slag-to-Fly Ash Ratio on the Strength of Alkali-Activated Composites  
Figure 2 shows the impact of varying slag-to-fly ash ratios on the UCS of alkali-activated composites at different ages. Under standard curing conditions, with a constant water glass modulus and alkalinity, an initial increase followed by a decrease in the UCS was observed as the slag content increased and the fly ash content decreased. This trend in strength variation over different ages was generally consistent. The maximum UCS values observed at a slag-to-fly ash ratio of 7:3 across all curing periods were 45.25 MPa, 49.85 MPa, and 62.33 MPa. When the age of maintenance is 28 days, it is 133% and 712% of the strength of pure slag and pure fly ash alkali-activated composites, respectively. These findings indicate that the optimum ratio of slag and fly ash in alkali-activated composites is 7:3, and the effect of compound mixing is much better than that of the single mixing of slag or fly ash. When comparing curing periods of 3 days and 7 days, the average strength of specimens increased by 30.1%. For slag-to-fly ash ratios of 10:0 and 9:1, the strength increments were minimal, at 0.04% and 0.77%, respectively. However, with a 5:5 ratio, the strength increased most significantly by 88.13%. Extending the curing period from 7 days to 28 days resulted in an average strength increase of 67.93%. Figure 2 shows that alkali-activated composites cured for 3 days achieve 51.5% of their 28-day strength, while those cured for 7 days reach 65.0%. Between 3 and 7 days, strength growth is low with a higher slag content, but increases as the fly ash content rises. From 7 to 28 days, the strength growth rate initially decreases, and then increases with a higher slag content and lower fly ash content. This indicates that slag contributes most to early strength, while fly ash enhances strength at later stages. The smaller particle size and larger specific surface area of slag enable a more complete reaction with the alkali activator. Thus, a higher slag content is generally preferred, but adding some fly ash can also improve the strength due to its ongoing reaction. However, higher fly ash proportions result in less complete alkali activation reactions, making reduced additions of fly ash beneficial for enhancing strength. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Number** & **Slag:Fly Ash** & **Modulus** & **Alkalinity** & **Water-to-Solid Ratio** \\ \hline A-1 & 10:0 & 1.3 & 10\% & 0.38 \\ A-2 & 9:1 & 1.3 & 10\% & 0.38 \\ A-3 & 8:2 & 1.3 & 10\% & 0.38 \\ A-4 & 7:3 & 1.3 & 10\% & 0.38 \\ A-5 & 6:4 & 1.3 & 10\% & 0.38 \\ A-6 & 5:5 & 1.3 & 10\% & 0.38 \\ A-7 & 4:6 & 1.3 & 10\% & 0.38 \\ A-8 & 3:7 & 1.3 & 10\% & 0.38 \\ A-9 & 2:8 & 1.3 & 10\% & 0.38 \\ A-10 & 1:9 & 1.3 & 10\% & 0.38 \\ A-11 & 0:10 & 1.3 & 10\% & 0.38 \\ B-1 & 6:4 & 1.3 & 5.0\% & 0.38 \\ B-2 & 6:4 & 1.3 & 7.5\% & 0.38 \\ B-3 & 6:4 & 1.3 & 10.0\% & 0.38 \\ B-4 & 6:4 & 1.3 & 12.5\% & 0.38 \\ C-1 & 6:4 & 0.9 & 10\% & 0.38 \\ C-2 & 6:4 & 1.1 & 10\% & 0.38 \\ C-3 & 6:4 & 1.3 & 10\% & 0.38 \\ C-4 & 6:4 & 1.5 & 10\% & 0.38 \\ \hline \hline \end{tabular} Note: slagfly ash in the table for the mass ratio of the two (later collectively referred to as slag:fly ash); water does not participate in the alkali activation reaction, taking into account the fluidity of the alkali-activated composites’ cementitious materials and the results of the previous pre-experimentation; the water-solid ratio is fixed at 0.38.  
\end{table} 
Table 4: Investigation test on the ratio of slag to fly ash. .3.2 The Influence of Alkali Activator Alkalinity on the UCS Behavior of Alkali-Activated Composites  
Figure 3 illustrates the effect of varying alkalinity on the unconfined compressive strength (UCS) of alkali-activated composites at different ages.