# Reactivity Assessment of Modified Ferro Silicate Slag by R\({}^{3}\) Method  
[PERSON]  
1 Magnel-Vandepitte Laboratory for Structural Engineering and Building Materials, Ghent University, Technologiepark Zwijnaarde 60, BE-9052 Ghent, Belgium; [EMAIL_ADDRESS] (P:PS. ); [EMAIL_ADDRESS] (S.M. ); nele.debele  
widely used in abrasive tools, roofing granules, cutting tools, glass, and in the cement and concrete industry [3]. Global annual production of Portland Cement (PC), which contributes to 6-8% of the global CO\({}_{2}\) emissions, has reached over 4.5 billion tons, and is expected to increase to approximately 6 billion tons by end of 2030 [4; 5; 6]. This, together with the need for intensive energy in terms of electricity, explains the major environmental concerns and economic considerations related to the production of PC [7]. One of the possible solutions to decrease the environmental impact of the clinker production and to achieve a circular economy is the use of industrial by-products as a raw material source for replacement of cement. Many researchers have investigated the use of industrial by-products as SCM [8; 9; 10; 11]. Typical by-products used are materials possessing high content of amorphous phase (generally >90 wt%). Depending on the elemental composition of the amorphous phase, these by-products can be categorized as latent hydraulic (e.g., ground granulated blast-furnace slag (GGBFS)) or pozzolanic (e.g., fly ash (FA)) [12]. These compounds, if used in the concrete, can increase strength, improve durability behavior such as chloride ingress, and make concrete much 'greener' [13]. The term pozzolanic usually implies natural or artificial siliceous/aluminous material which reacts with H\({}_{2}\)O in presence of Ca(OH)\({}_{2}\)[12]. Since a wide range of Cu slags are siliceous rich and have an amorphous structure, they can also be termed as pozzolanic. However, when Cu slags are added as SCM with PC, their mechanism and interaction with the cement phase is still not well understood. Nevertheless, several publications have described the use of Cu slag as an alternative SCM and its influence on compressive strength [14; 15]. In the work of [PERSON] et al. [16], reactivity of the Cu slag was investigated by using PC and hydrated lime as activator. The final findings of [PERSON] stated that the use of Cu slag delayed the initial strength development of the mortar made with a 15% replacement level of PC (at 1 and 7 days) while increasing the strength after 28 and 90 days. [PERSON] et al. [17] examined the mechanical properties of concrete synthesized with Cu slag and PC. Concrete containing up to 15 wt% Cu slag as PC replacement with water to solid ratio of 0.4 was subjected to a compressive test. Compressive strength results showed a significant increase in the strength of the Cu slag incorporated concrete in comparison to the reference PC concrete after 160 days. Literature reveals that the usage of Cu slag as a SCM with PC increases the compressive strength at late ages (after 28 days). The contribution towards strength may generally be due to two reasons, those being: The pozzolanic behavior or the filler effect, although filler effect would be more pronounced at earlier ages. The filler effect is usually attributed to the fact that the surface of the SCMs grains acts as a nucleation site for the precipitation and growth of binder hydrates, which contribute to the increase in compressive strength [18; 19]. There has been a wide range of traditional experimental techniques carried out to understand the reaction mechanism of SCMs, such as isothermal calorimetry, Chapelle test, Frattini test, and Strength Activity Index (SAI) [20; 21; 22; 23; 24; 25]. For instance, [PERSON] et al. [22] studied the pozzolanic activity of calcined clay by direct pozzolanic methods such as Frattini and saturated lime test, and indirect methods such as SAI and electrical conductivity.