# Effect of Coupled Mechanical-Chemical Activation on Hydration Activity of Copper Slag Powder
## 3 Results and Discussion
### Hydration Products  
It can be seen from Figure 6 that the hydration products of the pure cement paste samples were mainly fiber flocculent spherical hydrated calcium silicate gel, which was interspersed with a large amount of hexagonal flake calcium hydroxide, and needle-like ettringite could be observed in the large pores [32,33]. The hydration products interlaced with each other to form a continuous network structure, and the unhydrated particles were connected to form a loose system skeleton, which promoted the development of the early strength of the hardened paste. The morphology of the hydration products of hardened pastes with different copper slag powder contents was similar, but the hydration products of the copper slag powder-based composite cementitious system were more abundant. In the ESEM spectrum, the flake calcium hydroxide, needle-like ettringite, fiber flocculent spherical hydrated calcium silicate gel, and granular unhydrated cement particles could be observed. A large amount of needle-like ettringite was observed in the samples with a copper slag powder content of 30% and 40%, indicating that with the increase in copper slag powder content, the number of pores in the hardened paste of composite cement increased  
Figure 5: The (**a**) hydration rate and (**b**) hydration heat of the copper slag powder-cement composite systems at 20 \({}^{\circ}\)C.  
and the compactness of the structure deteriorated. This also reduced the compressive strength of the samples, which is consistent with the mechanical properties test results. It can be seen from Figure 7 that the hydration products of the pure cement samples at 28 d were similar to those at 3 d of age, but the structure was denser and the needle-like ettrinigite was not easy to observe. A large amount of needle-like ettrinigite could still be observed in the microscopic morphology of the CA40-90 sample mixed with copper slag powder. This indicates that the incorporation of copper slag powder led to the loose microstructure of hardened paste in the early stage, and the pores provided the growth space for the ettrinigite [34,35]. By comparing Figures 6 and 7, it can be seen that with the development of the hydration age, the microstructure of each sample became denser, and the content of hexagonal flake calcium hydroxide increased. This indicates that the hydration degree of the hardened paste increased with the development of the hydration age, which again confirms the conclusion of the mechanical property measurement. The XRD patterns of pure cement paste and CA40-90 mixed with 40% copper slag powder at 3 and 28 d of age are shown in Figure 8.  
Figure 6: ESEM map of 3 d of age. (**a**) Cement; (**b**) CA20-90; (**c**) CA30-90; (**d**) CA40-90. The XRD patterns show that the hydration products of the pure cement samples were mainly Ca(OH)\({}_{2}\), CaCO\({}_{3}\), ettrinigite, and unhydrated tricalcium silicate (C\({}_{3}\)S). With the extension of age, the diffraction peak of Ca(OH)\({}_{2}\) increased, and the diffraction peak of reactant C\({}_{3}\)S gradually weakened, indicating that the hydration degree of the pure cement samples gradually increased with the increase in age. This is consistent with the ESEM test results. The types of hydration products generated by the hydration of the pure cement samples are shown in Fig. 7. The 2-Calcium carbonate 3-Tricanium silicate 6-Dicalcium silicate 7-Calcium iron oxide  
the composite cement after mixing copper slag powder were essentially unchanged, as shown in Figure 8b. In addition to Ca(OH)2, CaCO3, ettringite, and unhydrated tricalcium silicate, a new hydration product, calcium iron oxide, was also generated. The characteristic main peak intensity of Ca(OH)2 was weaker than that of the pure cement sample, and the diffraction peak intensity of ettringite was stronger than that of the pure cement paste sample. Figure 8a,b shows that as hydration age increased, the diffraction peak of ettringite in each sample decreased, whereas the diffraction peak of Ca(OH)2 increased.