## 3 Results and Discussion  
### Reactivity of Matrices  
#### 3.1.1 Influence of Solution Silica Modulus on Reactivity at Room Temperature  
The effect of the silica modulus of the potassium silicate solution on the reaction time was studied with isothermal calorimetry on Koranel (Figure 4). For potassium silicate solutions having a silica-to-potassium molar ratio (R) below 1.75, the reaction started earlier than the measurement (i.e., \(<\)45 min after mixing) and with a high rate. For R = 2.00, an induction period of 2 h was observed, and while increasing R, the induction time becomes 60 h (2.5 days) for R = 2.25 and 350 h (about 2 weeks) for R = 2.5 (Figure 4a). The peak of reaction also becomes broader and lower while increasing R from 2 to 2.5. For R = 2.25, even a double exothermic peak is observed, i.e., one main peak at 3 days and the second smaller bump with maximum at 5.5 days. Such a smaller bump is not observed for R = 2, likely due to the fast reaction and overlap, and is neither observed for R = 2.5, likely because it is small and could occur at an even later time than the measurement of 24 days. R = 2.25 thus gives the unique insight into the complex reaction mechanism of potassium silicate-activated Koranel. Two exotherms for certain non-ferrous slags were also observed by others [17] who performed sodium silicate activation. The main peak observed is corresponding to the polymerization reactions [29; 30], while the second, smaller and broader exotherm, seems to be depending on the silica content of the activator and is due to a secondary reaction or reorganization of the polymer network [17]. For none of the samples a split in decomposition, polymerization and stabilization was observed, as was described for metakaloinite [31]. The decomposition and polymerization seem to occur in  
Figure 3: Sketch of the experimental design. the same exotherm. More recently, [PERSON] [32] defined the steps in alkali activation more precisely as being first a nucleation and growth process, followed by volume contraction due to the polymerization, an induction period, a second nucleation and growth process corresponding to the second exotherm, new volume contraction process, and finally, slow diffusion controls further curing. According to our own insight, the first nucleation has not to be seen as a nucleation for crystals, but occurs as a result of polymerization and densification, comparable to the polymerization of an organic thermoset. An important difference is that no phase boundary, as between crystal and liquid, needs to be formed. The diffusion control occurs because of the formation of a dense layer around and in between the remaining slag particles, rendering the diffusion of ions more difficult than in the initial liquid activator. Although Koranel is an iron silicate (containing a high proportion of iron and silica), and thus chemically different from the slags and metakaolinite for which the mechanisms were described, one can assume that the general steps remain the same but that the products formed are different. Figure 4: Effect of the silica-to-potassium molar ratio (R = SiO\({}_{2}\)/K\({}_{2}\)O) of the activating solution on (**a**) the normalized heat flow, and (**b**) the cumulative heat released per gram of solid of alkali-activated Koranel. For a matrix to be used for textile, sufficient time before setting is needed if we consider a continuous production of several hours from prepared batches of matrix; the low reactivity will then prevent unwanted matrix setting during the production. The normalized cumulative heat released from the different compositions (Figure 4b) shows that the reaction heat increases with the reduction of R due to the higher concentration of OH\({}^{-}\) in the alkaline solution; this favors Koranel dissolution and polymerization reactions. However, a higher degree of dissolution is also associated with a faster reaction at room temperature.