## 3 Results and Discussion
### Reactivity of Matrices
#### 3.1.2 Influence of Additives and Koranel Replacement on Reactivity  
With the selected activator solution, the influence of surfactants and small amounts of other precursors was investigated. The isothermal calorimetry at 20 \({}^{\circ}\)C (Figure 5) of the different compositions (Table 3) shows that the start of the reaction at room temperature differs depending on the composition of the solid phase. The addition of 5 wt.% OPC (brown curve; Figure 5a) decreased the open pot life with a factor of about 3; a sharp exotherm is observed. Meanwhile, the addition of metakaolinite (gray curves; Figure 5a) induced a delay in the appearance of the first exotherm. For the Koranel-based system (black curves; Figure 5a), the addition of surfactants slightly speeds up (2,4 methyl pentanediol) or delays (polyethylene glycol) the reaction; however, with the addition of metakaolinite, the effect of the surfactant was less obvious, a slight broadening of the peak might be observed. The cumulative heat released (Figure 5b) of the different compositions clearly shows that the addition of OPC and metakaolinite leads to higher reaction heat, the latter being higher for the sample made of 20 wt.% metakaolinite in comparison to those made of 10 wt.% metakaolinite. The cumulative heat released per g of matrix varied from about 85 J/g for the composition made of Koranel to 140 J/g for the composition containing 20 wt.% metakaolinite. The increase from 85 J/g for Koranel to 115 J/g for 90K10 MK is rather large, and the replacement of 10 wt.% more of Koranel by MK does not give rise to the same step in heat released, but only to an extra amount of 15 J/g. The cumulative heat released lowers upon the addition of both surfactants to the Koranel system. This was not expected but it shows that they interact chemically during the reaction and this interaction has a more important effect than being pure catalytic. Two evident ways the surfactants can play a role in the reaction rate are: (i) interaction with the surface of the precursor which could lead to a reduced reaction rate due to a reduced effective surface area; and (ii) interaction with the ions in solution, comparable to a chelating effect, although none of the surfactants are ionic, as is usually the case for chelating agents. This effect could also explain a reduction in reaction rate. No explanation was found for the shorter induction period observed for 2,4 methyl pentanediol. The maximum heat flow, thus maximum reaction rate, is for both pastes with surfactants substantially lower, as expected, according to the explanation given. These mechanisms can however not explain the slightly earlier start of the reaction and no other explanation could be found so far. Upon replacement of Koranel with metakaolinite, both surfactants have a different effect. While \"p\" does not influence the reaction too much, \"m\" decreases the total heat released substantially, though both had a slightly accelerating effect on the start of the reaction. For an optimum dosage of alkali in alkali-activated materials from known precursors such as metakaolinite, the added alkali, M, should be enough to compensate the charge balancing of Al; hence, the M/Al molar ratio should be 1 [33]. Considering the chemical composition of Koranel and metakaolinite and the use of potassium silicate solution of R = 2.25 and a liquid-to-solid ratio of 0.7, the molar ratio K/Al in the alkali-activated mixture was 0.88 for matrix 80K20 MK (Table 3) made of 20 wt.% metakaolinite and 80 wt.% Koranel. This means the alkaline reagent in matrix 80K20 MK is theoretically not in excess for the alkali-activated reaction. Furthermore, for iron-rich slags, iron or iron-bearingphases in the slag also participate in the formation of the binding phase [14; 34]. However, the degree of reaction of most of non-synthetic aluminosilicates is usually not 100% and some relics of the precursors are often evidenced by SEM [35].