# Effect of Coupled Mechanical-Chemical Activation on Hydration Activity of Copper Slag Powder
## 1 Introduction  
Copper slag is an industrial solid waste generated during the copper smelting process. About 2 to 3 tons of copper slag are discharged for every ton of copper produced [1, 2], mainly in the form of water-quenched copper slag. The accumulation and discharge of copper slag as solid waste slag not only occupies a large amount of land but also causes serious environmental pollution due to the heavy metal composition. Copper slag has been proven to have cementitious properties, and it can be applied as a concrete admixture instead of fly ash and slag to address admixture shortages in some areas [3]. Partial replacement of cement with copper slag not only reduces greenhouse gas emissions from cement production, but also reduces energy consumption in the cement industry. In addition, the application of copper slag in cement-based materials can also solidify the heavy metal components, reducing or eliminating the threat of copper slag to the environment [4, 5]. Copper slag as a novel mineral admixture applied in cement-based materials has important economic and social benefits, so it has been widely investigated by researchers [6, 7]. The main chemical composition of copper slag is SiO\({}_{2}\) and Fe\({}_{2}\)O\({}_{3}\), accompanied by a minor quantity of CaO and Al\({}_{2}\)O\({}_{3}\). The crystalline phase of copper slag is mainly fayalite (2 FeO-SiO\({}_{2}\)), mixed with some magnetite (FeO and Fe\({}_{2}\)O\({}_{3}\)) and quartz (SiO\({}_{2}\)) [8, 9]. When copper slag is exposed to the alkaline environment of cement-based materials, the silicate species released by its glassy network decomposition can combine with the calcium hydroxide of cement hydration product to form calcium silicate aluminate hydrate [10]. However, considerable research has revealed that the hydration activity of raw copper slag is poor [11; 12]. Numerous studies have been carried out to improve the hydration activity of copper slag [13; 14]. Studies have shown that the activity of volcanic ash materials is positively correlated with the specific surface area. Mechanical grinding destroys the vitreous body inside the copper slag and fully exposes active components such as silicate and aluminate to the alkaline environment of cement-based materials. Mechanical grinding can enhance the hydration activity and improve the early hydration reaction progress of copper slag [15; 16]. [PERSON] [17] grinded the copper slag for 4 h, then calcined it at 750 \({}^{\circ}\)C for 2 h. The results showed that the copper slag-based composite admixture had high hydration activity, and the generated hydration products could fully fill the internal pores of hardened paste. When the content of copper slag-based composite admixture was 10% and 15%, the 28 d compressive strength of cement-based materials increased by 12% and 14%, respectively. [PERSON] [18] prepared copper slag-based composite cement by partially replacing cement with copper slag. Experiments revealed that the incorporation of copper slag improved the mechanical properties, durability, and sulfate resistance of the composite cement. The porosity of the copper slag-based composite cement-hardened paste at each age was lower than that of the control sample. SEM images of the sample mixed with 30% copper slag showed that the C-S-H gel had a dense microstructure, which was one of the causes of the increased compressive strength. Most studies have demonstrated that copper slag powder reduces the early compressive strength of cement-based materials, whereas alkaline activators such as lime can alleviate the negative effects of copper slag on the early compressive strength of cement-based materials [19; 20]. [PERSON] developed a new low-strength filling material mixed with copper slag. The results revealed that the copper slag powder can fully hydrate only when it reaches a certain fineness, and that particles less than 10 \(\upmu\)m are beneficial to the early strength development. The copper slag powder grinding for 60 min was activated by CaO.