# Effect of Coupled Mechanical-Chemical Activation on Hydration Activity of Copper Slag Powder
## 3 Results and Discussion
### Mechanical Properties  
#### 3.2.1 The Effect of Mechanical Grinding on the Hydration Activity of Copper slag Powder  
Copper slag powder-based composite cement was prepared by mixing cement and copper slag powder with different grinding times in a certain proportion. Figure 3 shows the effect of mechanical grinding on the hydration activity of the copper slag powder. It can be seen from Figure 3 that the compressive strength of the specimen increased with the development of age, and showed an increasing trend with the extension of the copper slag grinding time. The compressive strength of the raw copper slag composite cement-hardened paste samples at each age was low, indicating that the hydration activity of the raw copper slag was relatively poor. When the grinding time was within 90 min, the compressive strength of each sample increased with the grinding time of the copper slag. This indicates that prolonging the grinding time was beneficial to stimulating the hydration activity of the copper slag powder, and that increasing the fineness and specific surface area of the copper slag powder promoted the development of the mechanical properties of the copper slag powder-based composite cement-hardened paste. This is because the incorporation of copper slag powder grinding for 90 min was beneficial to filling the gap between the particles of the composite cementitious system, so that the hardened paste samples obtained a higher degree of close packing, and the fine particle copper slag \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Ball-Milling Time/Min** & **Specific Surface Area/m\({}^{2}\cdot\)kg\({}^{-1}\)** & **d10/\(\upmu\)m** & **d25/\(\upmu\)m** & **d50/\(\upmu\)m** & **d75/\(\upmu\)m** & **d90/\(\upmu\)m** \\ \hline
0 & 178 & 9.840 & 10.741 & 32.676 & 66.596 & 107.749 \\
30 & 334 & 1.449 & 5.365 & 23.234 & 51.996 & 82.391 \\
60 & 427 & 0.850 & 3.113 & 11.967 & 32.679 & 54.272 \\
90 & 513 & 0.853 & 2.809 & 9.204 & 25.507 & 42.719 \\
120 & 569 & 0.682 & 2.229 & 8.178 & 23.474 & 40.128 \\ Cement & 416 & 1.539 & 4.642 & 12.853 & 29.746 & 49.653 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Particle characteristics of cement and copper slag powder at different grinding times. Figure 3: Effect of mechanical grinding on hydration activity of copper slag powder. (**a**) Compressive strength; (**b**) compressive strength activity index. powder had a physical filling effect on the hardened paste samples [26]. On the other hand, mechanical grinding destroyed the dense layer on the surface of the copper slag powder, which was conducive to the dissolution of active silicon, aluminum, and other components. The active component further underwent a hydration reaction in an alkaline environment of the cement-based material to generate hydration products with cementitious properties. The formation of hydration products further enhanced the compressive strength of the hardened paste sample. When the grinding time of the copper slag was extended from 90 min to 120 min, the compressive strength of the sample did not change significantly. This is due to the fact that the fineness and specific surface area of the copper slag powder changed little after the grinding time exceeded 90 min, resulting in the compressive strength of the copper slag powder-based composite cement-hardened paste sample not changing significantly and tending to be stable. Figure 3b shows the compressive strength activity index of the copper slag powder composite cement-hardened paste samples. Figure 3b shows that the compressive strength activity index of the sample is related to the copper slag powder content and curing age. When the copper slag grinding time was 0, 30, 60, 90, and 120 min, the 28 d compressive strength activity index of the samples was 78.95%, 83.69%, 86.57%, 89.75%, and 88.49%, respectively. It can be seen that except for the CS20-120 sample, the compressive strength activity index of the paste sample increased with the extension of copper slag grinding time when the copper slag powder content was the same.