# Effect of Coupled Mechanical-Chemical Activation on Hydration Activity of Copper Slag Powder
## 3 Results and Discussion
### Grinding Characteristics
#### 3.1.2 Particle Size Distribution  
The particle size distribution of the cement and copper slag at various grinding times is shown in Figure 2. The differential passing and cumulative passing curves of the copper slag powder gradually shifted to the left with the extension of the grinding time, indicating that the particle size distribution of the copper slag powder narrowed and the particle size became smaller, which confirmed the results of ESEM. The laser particle size test results show that most of the copper slag powder particles were less than 60 \(\upmu\)m after grinding for  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**OPC/\%**} & \multicolumn{2}{c}{**Copper slag**} & \multirow{2}{*}{**CaO/Extra-Mixing \%**} & \multirow{2}{*}{**Water–Binder Ratio**} \\ \cline{3-4}  & & & **Ball-Milling Time/Min** & & \\ \hline Cement & 100 & - & - & - & 0.35 \\ CS20-90 & 80 & 90 & 20 & - & 0.35 \\ CA20-90 & 80 & 90 & 20 & 2 & 0.35 \\ CS30-90 & 70 & 90 & 30 & - & 0.35 \\ CA30-90 & 70 & 90 & 30 & 3 & 0.35 \\ CS40-90 & 60 & 90 & 40 & - & 0.35 \\ CA40-90 & 60 & 90 & 40 & 4 & 0.35 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Mixing ratio of mechanical–chemical coupling-activated copper slag-based composite cement samples.  
60 min. The particle size distribution of the copper slag powder after grinding for 90 min and 120 min was superior to that of cement.  
The equivalent particle size (d10, d25, d50, d75, and d90) was applied to characterize the effect of grinding time on the particle distribution of the copper slag powder [24,25]. Table 4 shows the particle characteristics of the cement and copper slag with different grinding times. It can be seen that the specific surface area of the copper slag powder increased gradually with the increase in grinding time, but the increase rate gradually slowed down with the increase in grinding time. For example, the specific surface area of the raw copper slag was 178 m\({}^{2}\)/kg, the specific surface area of the copper slag powder was 334 m\({}^{2}\)/kg after 30 min of grinding, and the specific surface area of the copper slag powder increased by 87.64% after 30 min of grinding. The specific surface area of the copper slag powder increased by 27.84%, 20.14%, and 10.92%, respectively, when the grinding time increased from 30 min to 120 min. It can also be seen from Table 4 that with the extension of the grinding time, the equivalent particle size of the copper slag powder gradually decreased. When the grinding time was extended from 0 min to 90 min, the equivalent particle size of the copper slag powder decreased.  
Figure 1: Morphology of copper slag powder. (**a**) 0 min, (**b**) 30 min, (**c**) 60 min, (**d**) 90 min, and (**e**) 120 min.  
Figure 2: Particle size distribution of cement and copper slag with different grinding times. (**a**) Differential passing; (**b**) cumulative passing.  
particle size of the copper slag powder decreased rapidly. For example, the d50 of the copper slag powder decreased from 32.676 \(\upmu\)m to 9204 \(\upmu\)m, and the d90 decreased from 107.749 \(\upmu\)m to 42.719 \(\upmu\)m. When the grinding time was extended from 90 min to 120 min, the particle size distribution of the copper slag powder changed little. The d50 of the copper slag powder decreased from 9204 \(\upmu\)m to 8178 \(\upmu\)m, and the d90 decreased from 42.719 \(\upmu\)m to 40.128 \(\upmu\)m. This shows that the early grinding efficiency of the copper slag powder was high, and that the later grinding efficiency was low, which is consistent with the change in specific surface area.