## 4 Conclusions  
Copper slag is an industrial residue with a large unutilized fraction. The present study investigated the development of alkali-activated composites from copper slag named Koranel and carbon textile-woven fabric. In the first step, the matrix for the composites was developed. The reactivity of Koranel with potassium silicate solutions, with molar ratio R = SiO\({}_{2}\)/K\({}_{2}\)O varying from 1 to 2.75 at 0.25 intervals, was investigated using isothermal calorimetry. The results showed that the solution with R = 2.0 has an open pot life of only a few hours at room temperature, while the solution with R = 2.25 has an open pot life of several days at room temperature, but reacts quickly at 80 \({}^{\circ}\)C. Hence, the potassium silicate solution with the silica modulus of 2.25 is more suitable for a process in which the composite is impregnated, and in the following hours, would be used for making a laminated composite. The substitution of 5% and 10-20 wt.% Koranel, respectively, by OPC and metakaolinite, led to higher reaction heat. However, higher mechanical strength, especially in flexion, was only observed when 20 wt.% Koranel was substituted by metakaolinite. Meanwhile, OPC addition of only 5 wt.% induced a fast setting of the matrix,  
Figure 13: Elastic modulus vs. temperature of (**a**) the matrix and (**b**) composite 80K20 MK. which was not deemed suitable for composite preparation. The effect of the 2 surfactants, 2-methyl 2,4 pentanediol and polyethylene glycol on the workability is limited, but PEG further increased the flexural strength. Composites were made of four layers of carbon fabric and five layers of inorganic polymer matrix. Pure Koranel-based matrix presented a compressive and flexural strength of about 30-35 MPa and 1-5 MPa, respectively. An improvement in the bending strength was observed with a fiber addition in the prepared composites, with flexural strength values reaching 83 MPa. The addition of 2 wt.% polyethylene glycol/2-methyl 2,4 pentanediol was beneficial for the flexural strength of pure matrix, but the same was not observed in the mechanical properties of the composites. The microstructure of the cross section showed alternating layers of matrix and carbon fiber, even though the matrix was not perfectly adhering on the carbon fiber and little to no impregnation of the fiber bundles was observed. The E modulus of pure matrix dropped by 50% above 200 \({}^{\circ}\)C. The pure matrix healed from 300 \({}^{\circ}\)C onwards, and its E modulus reached a maximum at 630 \({}^{\circ}\)C, after which it decreases again. At 700 \({}^{\circ}\)C, the modulus was about 5 GPa, and remained almost constant upon cooling. The composites have a modulus about 3 times higher at room temperature and lose only 25% of it up to 250 \({}^{\circ}\)C. Above 300 \({}^{\circ}\)C however, the modulus of the composite gradually decreases. The composite prepared with 20 wt.% metakaolinite still retained 50% of its elastic modulus on heating until 400 \({}^{\circ}\)C. However, upon further heating, the modulus decreases to almost 0 at 640 \({}^{\circ}\)C.  
The results are interesting for the repurposing of Koranel copper slag in the development of alkali-activated composites for various engineering applications, including high strength lightweight panels and laminates. There are several aspects that need further investigation, such as the fiber-matrix interaction, the better impregnation of the fiber bundles, the thermal behavior of the matrix and composites, and the different processes responsible for deterioration and healing. All these aspects will be dealt with in future research. Conceptualization, P.N.L. and H.R. ; Methodology, P.N.L., G.M.H., N.D., J.G. and H.R. ; Formal analysis, G.M.H., F.K. and J.G. ; Investigation, G.M.H. and F.K. ; Data curation, G.M.H. and F.K. ; Writing--original draft, P.N.L., G.M.H. and N.D.; Writing--review & editing, P.N.L., G.M.H., N.D., J.G. and H.R. ; Supervision, H.R. ; Project administration, H.R. ; Funding acquisition, H.R.