## 3 Results and Discussion
### Properties of Composite Portland Cements (CPCs) Manufactured by 20% Slag
#### 3.2.1 Compressive Strength
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline
**Phase** & \multicolumn{4}{c}{**C\({}_{2}\)S**} & \multicolumn{4}{c}{**MW**} & \multicolumn{4}{c}{**C\({}_{4}\)AF**} & \multicolumn{4}{c}{**C\({}_{3}\)S**} & \multicolumn{4}{c}{**C\({}_{3}\)MS\({}_{2}\)**} & \multicolumn{4}{c}{**C\({}_{3}\)A**} & \multicolumn{4}{c}{**C\({}_{2}\)A\({}_{7}\)**} & \multicolumn{4}{c}{**C\({}_{2}\)AS**} \\ \hline
**Sample No/(wt.\%)** & **4-1a** & **4-1a** & **4-2a** & **4-2a** & **3-1b** & **3-1a** & **3-1b** & **4-2a** & **5a** & **5a** & **5a** & **3-1a** & **4-2b** & **4-2b** & **3-1a** \\ \hline SiO\({}_{2}\) & 35.99 & 39.70 & 35.83 & 33.34 & 36.17 & – & 2.22 & – & 0.75 & 1.98 & 26.57 & 37.18 & – & – & 19.75 \\ Al\({}_{2}\)O\({}_{3}\) & – & 1.87 & – & 1.08 & – & 1.46 & – & 0.89 & 22.59 & – & – & 41.18 & 51.97 & 24.59 \\ FeO\({}_{3}\) & – & 1.27 & – & – & 1.49 & 60.87 & 15.99 & 11.63 & 62.82 & 31.53 & – & 3.04 & – & – & 9.00 \\ MnO & – & – & – & – & 0.68 & 14.02 & 3.39 & 11.24 & 6.44 & – & – & 1.14 & – & – & 2.10 \\ MgO & 1.27 & 1.26 & 0.89 & – & 2.84 & 25.09 & 69.49 & 75.17 & 22.57 & – & – & 10.35 & – & – & 0.90 \\ CaO & 62.74 & 57.77 & 61.40 & 66.66 & 57.74 & – & 3.31 & – & 4.98 & 43.88 & 73.43 & 48.29 & 58.82 & 48.03 & 43.65 \\ Cr\({}_{3}\) & – & – & – & – & – & 4.15 & 1.96 & 1.55 & – & – & – & – & – & – \\ \hline Nr of ions in & & & 4 & O & & & 1 O & 10 O & 5 O & 8 O & 6 O & 33 O & 7 O \\ \hline Si & 1.020 & 1.100 & 1.008 & 0.964 & 1.016 & – & 0.016 & – & 0.007 & 0.170 & 1.010 & 2.048 & – & – & 0.987 \\ Al & – & – & 0.064 & – & 0.036 & – & 0.013 & – & 0.010 & 2.230 & – & 2.142 & 14.091 & 1.442 \\ Fe & – & 0.028 & – & – & 0.036 & 0.508 & 0.099 & 0.073 & 0.516 & 2.070 & – & 0.144 & – & – & 0.378 \\ Mn & – & – & – & 0.016 & 0.119 & 0.021 & 0.071 & 0.054 & – & – & 0.056 & – & – & 0.091 \\ Mg & 0.052 & 0.052 & 0.036 & – & 0.12 & 0.373 & 0.766 & 0.839 & 0.330 & – & – & 0.848 & – & – & 0.070 \\ Ca & 1.904 & 1.716 & 1.852 & 2.068 & 1.740 & – & 0.026 & – & 0.052 & 4.100 & 2.985 & 2.856 & 2.784 & 11.847 & 2.331 \\ Cr & – & – & – & – & – & – & 0.024 & 0.012 & 0.012 & – & – & – & – & – & – \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Representative semiquantitative analysis SEM/EDS of identified mineralogical phases in the slags; delacium silicate (C\({}_{3}\)S), magnesiovotstite (MW) solid solution phases, brownmillerite (C\({}_{4}\)AF), tricalcium silicate (C\({}_{3}\)S), merrwite (C\({}_{3}\)M\({}_{2}\)) and calcium aluminates (C\({}_{3}\)A, C\({}_{12}\)A\({}_{7}\), C\({}_{2}\)A\(S\)).—below detection limit. The beneficial effect of slag basicity on the 28-days of curing achieved compressive strengths of the CPCs for the air and water-cooled slags is presented in Figure 7. In general, the higher the slag basicity in the range of 0.9-2.7, the higher are the latent hydraulic properties of the slag expected to be, since slag's basicity is directly related to the formation of the hydraulic calcium silicate phases [19; 38; 39]. Deviation from absolute linearity in the obtained results is related to the fact that strength development does not solely depend on calcium silicates, thus on the CaO/SiO\({}_{2}\) ratio, but also on the other slag's constituents, which are not at the same levels in the slags. In example, the concentration of alumina, which participates in the formation of cementitious phases, also has an effect. As illustrated in Figure 8, the means of cooling, given the way it was employed, did not result in significant differences upon the obtained strength results. The slightly higher long term values in case of water-cooled slags may be possibly correlated to some amorphous content, as well as the presence of more active C\({}_{2}\)S polymorphs [40]. Probably, cooling with high pressure water jets and formation of vitreous slags of these compositions could favor even higher strengths.