# High-Durability Concrete Using Eco-Friendly Slag-Pozzolanic Cements and Recycled Aggregate
## 5 Summary and Conclusions  
Cement production has a major contribution to global CO\({}_{2}\) emission. Composite cements with a partial substitution of CO\({}_{2}\)-intensive clinker by additives, like slag, fly ash, or pozzolana, are a promising approach to make cement manufacture more environmentally friendly, reducing the CO\({}_{2}\)-impact by up to two-thirds. In this research, slag-pozzolanic cements (CEM V) were produced and evaluated regarding their composition and characteristics. To evaluate their performance as binder, various concrete admixtures were produced and tested, whereby the mechanical properties regarding strength and durability were of central importance. In order to further increase the life cycle assessment of concrete using CEM V cements with slag-pozzolanic additives, conventional aggregate was partly exchanged by recycled rock aggregate originating from tunnel driving of the Brenner Base Tunnel. The results obtained in this research could encourage both the national standardization and the cement/construction industry for future applications because of its environmental, economic, and durability characteristics. In the course of this work, the following conclusions could be drawn:  
* Cementitious constituents were compared, whereby natural pozzolana zeolite (P) showed the highest SiO\({}_{2}\) content, and natural pozzolana zeolite (P) also demonstrated the highest pozzolanic activity compared to fly ash (FA) and blast furnace slag (S). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fresh Concrete Density** & **Flow Spread** & **Air Content** & **Hardened Concrete** & **Compressive** & **Bending Flexual** & **Fracture Energy** \\
[kg/m\({}^{3}\)] & [cm] & [Vol.\%] & **Density [kg/m\({}^{3}\)]** & **Strength \(\Gamma_{x}\)** & **Strength \(\Gamma_{x}\)** & **G\({}_{x}\) [N/m]** \\ \hline
2411 & 55 (74) & 2.5 & 2376 & 54.7 & 4.6 & 2.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Concrete properties of (1) CEM V/A (S-V) 32.5 R cement type and calcareous schist aggregate. Figure 14: Concrete cube test specimen after compressive strength testing according to Table 7.  
The CaO content (crucial with regard to ECO\({}_{2}\)-generation) of the manufactured CEM V cement types was considerably smaller compared to CEM I Portland cement. Individual CEM V types showed low slump values, indicating the need of superplasticizer to obtain good workability. Natural pozzolanaeolite (P) indicated a low fresh mortar density due to the porous tectosilicate structure, also containing a higher amount of air  
Compressive strength development was naturally behind CEM I cement types, whereby CEM V/B cement types with a higher proportion of additives showed lower strength (approximately 20 to 30%) after 90 days of curing time, at which there were no major differences considering bending tensile strength. Slag-pozzolanic cement types indicated high durability because of their lower porosity and permeability compared to Portland cement. Considering concrete production, different CEM V cement types showed a higher demand for superplasticizer to reach a good workability of fresh concrete; CEM V with natural pozzolanae zeolite (P) again showed a high air content and low fresh concrete density. Concrete compressive strength and bending tensile strength development corresponded to the cement strength development. Water penetration of CEM V concrete admixtures was considerably smaller compared to Portland cement. Frost resistance of CEM V concretes via reduction in the bending tensile strength after freezing could not be verified in the laboratory, but could be verified at large scale using 400 kg of CEM V cement per m\({}^{3}\) fresh concrete and increasing the air content to 5%. Additional aggregate recycling was tested using different processed rock types from tunneling: Mechanical characteristics, especially water permeability, are promising for the usability of such concrete types.