# High-Durability Concrete Using Eco-Friendly Slag-Pozzolanic Cements and Recycled Aggregate
## 2 Slag-Pozzolanic CEM V Characteristics
### Cement Mortars Properties  
To evaluate fresh and hardened cement paste properties, fresh mortar and the derived test specimens according to [50] were produced, cf. [47; 49]. Therefore, test sand was mixed with cement at a ratio 3 to 1 and the corresponding amount of water to reach a water/cement ratio of 0.5 [49]. The fresh mortar properties slump, density, and air content, as well as setting time and soundness according to [51], are illustrated in Table 4, providing information about performance and workability of the tested cement types. Figure 3: XRD diagrams displaying angle 2\(\Theta\)-intensities of (**a**) CEM V/A types and reference cement CEM I and (**b**) CEM V/B types and reference cement CEM Iafter 365 days curing at 20 \({}^{\circ}\)C under water, whereby: CH—portlandite Ca(OH)\({}_{2}\); Cc—calcite, Q—quartz SiO\({}_{2}\), An—anorthite (CaAl\({}_{2}\)Si\({}_{2}\)O\({}_{8}\)). Cement types (3) and (4) show comparatively low slump values, indicating the need of super-plasticizers to reach a reasonable workability of the fresh mortar. By using a super-plasticizer with a dosage of approximately 0.5 wt% of the cement weight, the slump values were increased to the same level compared to (1) and (2). The fresh mortar density of CEM V/B types is lower than that of the CEM V/A types due to the lower density of the cementitious constituents compared to Portland cement clinker. The density of cement type (4) is noticeably low, due to the porous tectosilicate structure of zeolite that is probably also responsible for the comparably high air content. Setting time of the CEM V mortars is naturally delayed due to the posterior pozzolanic and latent hydraulic reactions of the additives. Soundness of all cement types falls significantly below the limit value of 10 mm according to [51], showing satisfactory volume consistency. The compressive and bending tensile strength of hardened mortar specimens were determined for a basic mechanical characterization according to [50] with due regard to strength development with time; see Figure 4 for the concrete compressive strength and Figure 5 for the bending tensile strength. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Cement Type**} & **Slump Value** & **Density** & **Air Content** & **Init. Setting** & **Final Setting** & **Soundness** \\  & **[mm]** & **[kg/m\({}^{3}\)]** & **[\%]** & **Time [min]** & **Time [min]** & **[mm]** \\ \hline CEM I 32.5 R & 155 & 2230 & 4.5 & 210 & 265 & 0.5 \\ (1) CEM V/A & 175 & 2220 & 4.1 & 265 & 320 & 0.5 \\ (S-V) 32.5 R & 166 & 2220 & 3.7 & 350 & 420 & 1.0 \\ (3) CEM V/A & 135 & 2150 & 4.4 & 270 & 340 & 0.5 \\ (5-V) 32.5 R & 106 & 2060 & 5.3 & 230 & 330 & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Fresh mortar properties of different CEM V cements. Figure 4: Compressive strength development of standard mortar specimens according to [51] (each value as a mean value of 3 individual tests), after 2, 7, 28, 56, and 90 days. The strength development of the considered cement types delivered the expected behavior: Standard cement CEM I 32.5 R reaches high early strength, though the CEM V/A cement types reach an equal strength level between 7 and 56 days of curing time. CEM V/B types lag behind but still show an increase in strength even after 56 days in contrast to CEM I and CEM V/A types. Considering bending flexural strength (Figure 5), all cement types reach a similar strength level after 28 days of water curing. Subsequently, cement type (2) CEM V/B (S-V) is the only cement type still exhibiting a significant increase in flexural bending strength. By using a super-plasticizer with a dosage of 0.5 wt% of the cement weight to improve the fresh mortar slump value of individual mixtures (cf. Table 4), the 28 day compressive strength for cement type (3) and (4) could be increased by approximately 10%, reaching a compressive strength of 52.1 and 40.3 N/mm\({}^{2}\), respectively. Figure 6: Development of total porosity (**a**) and percentage of macro-porosity (**b**) for a curing time of 28 and 365 days.