## 1 Introduction  
Copper production is associated with high slag rates; on average, 2.2-3.0 tons of slag are generated per ton of produced copper [1; 2]. Based on these figures combined with data on copper production [3], the worldwide annual generation of copper slag is between 47 and 64 million tons. Undoubtedly, the slag must be utilized to ensure sustainable copper production from a resource-efficiency standpoint. Several external applications for copper slag have been reported, e.g., various construction applications excluding cement and concrete [1; 2; 4; 5], blasting abrasive media [2; 4; 5; 6], auxiliary sand in concrete [1; 2], and for its pozzolanic properties, i.e., as supplementary cementitious material (SCM) [1; 2]. Since the cement industry accounts for 5-8% of global anthropogenic carbon dioxide emissions [7; 8], utilizing copper slag in cementitious applications is an attractive alternative. Using the slag as an SCM would improve resource efficiency while lowering carbon dioxide emissions per ton of cementitious material. The former effect is obvious, i.e., the lower requirements for the generation of virgin material, while the latter relates to the fact that the SCM requires neither calcination nor clinkering [9]. A study on the possibility of using copper slag as an SCM was performed by [PERSON] et al. [10] in 1997. The results showed that the incorporation of the slag improved the compressive strength of mortars after curing beyond seven days [10]. Since 1997, several studies have been published explicitly addressing iron silicate copper slags for SCM applications [6; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Furthermore, an additional study has incorporated the slag in a comparison of different SCMs [21]. The slag compositions included in these studies are presented in Table 1. The primary methodologies employed for these slags include mortar testing [6; 11; 12; 13; 14; 16; 18; 21], cement composite testing [17; 19; 20], isothermal calorimetry on Portland cement blends [12; 14; 19; 20], isothermal calorimetry using the R\({}^{3}\) test [21], as well as the Chapelle and Frattini tests [14]. The studies have concluded that iron silicate copper slags exhibit pozzolanic properties [12; 14; 15; 16; 21]. However, the inherent reactivity is lower than, e.g., ground granulated blast furnace slag [21; 22], which is reflected when reviewing data on mortars and cement composites. More specifically, the data presented after the study by [PERSON] et al. [10] is ambiguous in terms of the contribution to the strength development. Several studies have shown that partial replacement of Portland cement with copper slag improves strength [11; 13], whereas other studies have shown negative effects [6; 12; 14; 16]. Nonetheless, accounting for the replacement ratio used in the different studies, the overall conclusion is that iron silicate copper slags contribute to the strength of both mortars [11; 12; 13; 14; 16] and composites [17; 19]. The reactivity of SCMs depends on such parameters as the degree of crystallinity, glass structure, thermal history, granulometric properties, and chemical composition [23; 24; 25; 26; 27; 28; 29; 30], which, naturally, have not been constant between the different studies discussed in relation to Table 1. In addition, the summary of the methodologies utilized in the different studies highlights the fact that different means to assess the reactivity of the copper slags have been employed. Therefore, the previously published data cannot be used across different papers to offer insight into how variations in chemical composition affect the reactivity of copper slags. However, two studies have subjected slags of different compositions to testing at the same laboratory [18; 19]. The study by [PERSON] et al. [18], comparing ten different copper slags, did not focus on the compositional aspect, which provides challenges in assessing their data in this manner. On the other hand, [PERSON] et al.