## 3 Results and Discussion
### Pore Solution Chemistry  
Figure 3 shows the results of the major ionic concentrations of the pore solutions expressed in paste specimens of increasing slag content hydrated from 1 day up to 120 days. The main components of the pore solutions were Na\({}^{+}\), K\({}^{+}\), and OH\({}^{-}\). The content of minor components Ca\({}^{2+}\) and SO\({}_{4}\)\({}^{2-}\) were found to be obviously lower in the slag-blended binders than in the OPC binders. Their concentrations were below 0.01 mol/L for all slag-blended binders after 1 day. The data are not presented herein. It should be emphasized that logarithmic plots are presented in Figure 3c in order to observe more clearly the evolution of ions in the pore solution during the first few hours of mixing. Accordingly, very few changes in the OH\({}^{-}\) can be seen in the first 6 h. It is expected that the concentrations of alkalis Na\({}^{+}\) and K\({}^{+}\) did not differ significantly in the meantime, considering the charge balance in the pore solution. Another expectation can be reached that the slag did not react in the first 6 h.  
Figure 2: Differential thermogravimetric (DTG) curves of 28-day paste specimens incorporating different contents of slag: At—ettrinigite, Ht—hydrotalcite, CH—calcium hydroxide, CC—calcite.  
The addition of slag considerably changed the pore solution chemistry, particularly at later ages. A higher slag content normally results in lower concentrations of alkalis Na\({}^{+}\) and K\({}^{+}\). The dilution effect of slag can be the main reason for the reduction of such ionic concentrations. Between 65% slag and 85% slag binders, the Na\({}^{+}\) concentration exhibited merely a slight difference at 1 day. However, the difference was apparently larger for the K\({}^{+}\) concentration. This implies that the alkalis in the raw slag particles had already dissolved in part. The dissolution of alkalis Na\({}^{+}\) and K\({}^{+}\) proceeded rapidly in the first 14 days. The ionic concentrations changed slowly after 28 days and tended to reach a plateau in the long term. This is true for both alkalis Na\({}^{+}\) and K\({}^{+}\). On the other hand, a reduction in the ionic concentrations can be observed in some cases after 60 days, particularly for OH\({}^{-}\). This is related to the solubility of slag, which is limited at early ages and becomes pronounced at later ages. The continuous dissolution of slag leads to more hydration products (secondary C-S-H) to be precipitated in the capillary pores. These secondary C-S-H hydrates enable the adsorption of alkalis, subsequently reducing the alkali content in the pore solution.  
The concentration of K\({}^{+}\) was obviously higher than that of Na\({}^{+}\) at all ages. At 1 day, the OH\({}^{-}\) concentration decreased markedly from 0.30 mol/L of neat OPC binder to 0.13 mol/L of 85% slag binder. The difference in the OH\({}^{-}\) concentration was further enlarged at the age of 120 days: 0.67 mol/L (OPC) versus 0.24 mol/L (85% slag). For all binders under study, the pH value differed in the range of 13.13-13.48 at 1 day, compared to 13.38-13.83 at  
Figure 3: Concentrations of the main ions present in the pore solutions of OPC paste specimens with increasing slag contents: (a) Na\({}^{+}\); (b) K\({}^{+}\); (c) OH\({}^{-}\); (d) pH value calculated based on OH\({}^{-}\) concentration.  
120 days. It is expected that all these binders with or without slag will maintain high alkalinity and keep high pH values in the long term.