## 2 Materials and Methods  
### Fabrication of one Dimensional (1D) and Two Dimensional (2D)-FCS  
Figure 1 depicts the experimental concept of embedding the FCS in concrete for its SHM, as evaluated in the work presented herewith.  
The fabrication of the FCS has already been reported [26; 27]. The fabrication technique was developed at the Saxon Textile Research Institute (STFI) in Chemnitz, Germany and is based on embroidering carbon fibers and optical glass fibers simultaneously in a grid-like format on a polyvinyl alcohol (PVA) nonwoven substrate. PVA was chosen for this purpose since it can be easily dissolved in hot water as well as it protects the FCS. The advantage of this fabrication technique is that depending on the application, tailored FCS can be produced with various forms of lattice structures, multiple layers of carbon filaments as well as with different configuration of the optical glass fibers inside the FCS. The latter is, in particular, interesting to optimize the bond between the textile carbon structure and the optical glass fiber and thus to optimize the sensor response.  
In order to explore the sensor response and the resistance to highly alkaline concrete environment of the FCS, one dimensional (1D) and two dimensional (2D) FCSs have been fabricated. The 1D-FCSs have been fabricated, in particular, to investigate the sensitivity of the FCS to the highly alkaline concrete environment. To do this, a single strand of carbon filaments of 400, 800 or 1600 tex have been simultaneously embroidered with SM fiber Corning ClearCurve (CC) on the PVA nonwoven substrate. After dissolving the PVA, the length of each 1D-FCS was measured to be 300 mm.  
The 2D-FCSs have been fabricated in order to evaluate whether the shape of the optical glass fiber inside the FCS has an impact on the sensor response. To explore this, FCSs have been fabricated with different configurations of the optical glass fiber, as shown in Figure 2. In total, the fiber is integrated into the FCS in three different configurations. In the first case, (a) the fiber is straight; in the second case, (b) the fiber is placed with a slight offset; and in the third case, (c) the fiber meanders along the material. The purpose of the second and third configurations is to explore spatial variation of the optical fiber inside the FCS and whether this results in a stronger bond between the optical glass fiber and the FCS and thus facilitates an optimized sensor response. The FCS fabricated for the investigation had a dimension of \(500\times 110\) mm\({}^{2}\) and a grid size of \(10\) mm \(\times\)\(10\) mm. These were fabricated using 1600 tex carbon filaments and optical glass fibers of type Corning CC with acrylate coating. For the second configuration, the offset of the optical glass fiber was introduced at half length of the FCS with an offset of one grid element. In case of the third configuration, the size of each meander was \(2\times 3\) grid elements. In case of the offset and meander configuration, no significant attenuation of the light propagating the optical fiber of the FCS could be measured.  
Figure 1: Schematic of the application of functionalized carbon structures (FCS) for the reinforcement and structural health monitoring (SHM) of concrete structures.