## 1 Introduction
### Interaction of CO\({}_{2}\) and Conventional Hydrated Cements  
Carbonation (i.e., formation of CaCO\({}_{3}\)) in hydrated cements causes a decrease of the pH-value from approximately 13 to approximately 8. The calcium carbonate (\(\overline{C}\)C) mostly appears in form of calcite but also as vaterite and aragonite [3; 4]. Carbonation is responsible for volume changes and formation of carbonates, hemicarbonates and monocarbonates, which leads to changes in porosity and permeability, and the formation of a fracture network. Dissolution of phases also may occur [3; 4]. \begin{table}
\begin{tabular}{c c c} \hline
**Phase** & **g of CO\({}_{2}\) per g Phase** & **Raw Materials** \\ \hline C\({}_{3}\)S Alite & 0.58 & 3 CaCO\({}_{3}\)/SiO\({}_{2}\)–OPC \\ C\({}_{2}\)S Belite & 0.51 & 2 CaCO\({}_{3}\)/SiO\({}_{2}\) \\ CS Wollastonite & 0.38 & CaCO\({}_{3}\)/SiO\({}_{2}\) \\ C\({}_{3}\)A & 0.49 & CaCO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) \\ CA & 0.28 & CaCO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) \\ CA\({}_{2}\) & 0.17 & CaCO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) \\ C\({}_{2}\)F & 0.32 & CaCO\({}_{3}\)/Fe\({}_{2}\)O\({}_{3}\) \\ C\({}_{2}\)A & 0.41 & CaCO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) \\ C\({}_{4}\)AF & 0.36 & CaCO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\)/Fe\({}_{2}\)O\({}_{3}\) \\ C\({}_{3}\)A\({}_{3}\)Cs SulfoALUinate & 0.22 & CaCO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\)/CaSO\({}_{4}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Raw meal CO\({}_{2}\)-output of selected cement clinker phases. [5]. Considering the chemical and mechanical stability for construction due to changes of the porosity, this process is very critical [3; 4]. Therefore, extensive research on the influence of CO\({}_{2}\) on OPC and wellbore cement was performed. [PERSON] et al. [14] investigated the carbonation of white portland cement (wPc, CEM 1 52,5 N) from Aalborg Portland A/S, Denmark, metakaolin (MK) and limestone (LS) mortars. Their mortars were hydrated for 91 days and exposed to a controlled atmosphere with one percent CO\({}_{2}\) at 293 K and 57% relative humidity (RH) for 280 days. They found that the Portland cement had the highest CO\({}_{2}\) binding capacity followed by limestone and metakaolin. [PERSON] et al. [15] and [PERSON] et al. [16] performed flow-through experiments with CO\({}_{2}\) and brine on fractured Portland cement. Their experiments were carried out at 333 K and 10 MPa for more than 100 h. They found that the leakage potential is controlled by the aperture of the fracture. [PERSON] and [PERSON] [17] investigated the effect of CO\({}_{2}\) rich brine (two percent salt solution) on artificially fractured well-cement (class H) in a flow-through experiment over 30 and 100 days. After 100 days, a secondary fracture network was developed which was not present after 30 days. The secondary fractures caused higher leaching rates. The obtained data by [PERSON] and [PERSON] [17] indicates a negative effect on porosity of cement under dynamic conditions which can be dependent on time. [PERSON] et al. [18], performed an experimental study on the dynamic alteration process of class-H wellbore cement caused by acidic brine. Their experiments confirmed leaching of Ca\({}^{2+}\) from the reacted cement. [PERSON] et al. [19] investigated the wellbore integrity and CO\({}_{2}\)-brine flow along the casing-cement. They performed flow-through experiments at 313 K and 14 MPa pore pressure for 394 h. The brine was a 50:50 mixture of scCO\({}_{2}\) and 30,000 ppm NaCl-rich brine. They were able to confirm that degradation of Portland cement is slow. [PERSON] et al. [20] compared the behavior of a Portland cement with a Schlumberger CO\({}_{2}\) resistant cement (SCRC) with expanding agent under CO\({}_{2}\) geological storage environment (363 K, 28 MPa). They used brine containing 220 g/L NaCl. They focused on the expansion of the cement because fractures caused by the expansion are one possible occurrence of leakages. The simulated injection scenario presented by [PERSON] et al.