## 1 Introduction  
The replacement of conventional techniques used for structural health monitoring (SHM) based on electrical means (i.e., strain gauges for strain measurement) [1, 2] with fiber optic sensors (FOSs) has seen increased popularity over the last decade due to the number of advantages they possess over conventional schemes. The glass (silica) construction of fiber optics renders them robust and capable of withstanding harsh and corrosive environments [3, 4, 5, 6, 7]. The low attenuation of optical glass fiber enables them to be interrogated over a long length (i.e., several 100 s of kilometers). The fact that a multitude of sensors can be multiplexed within a single strand of fiber together with the possibility of utilizing a wider bandwidth makes FOSs most suitable for applications that require extraction of data from a vast amount of sensing elements such as those required for SHM of large structures [8, 9, 10, 11, 12]. Moreover, the sensors, although multiplexed along one fiber, have the capability to monitor several parameters simultaneously and thus provide the opportunity to assess not only, for example, the strain levels but also other chemical parameters, such as humidity and pH. Thus, it is evident from the current literature that the utilization of FOSs for SHM has not yet reached its full potential and requires further investigations paired with advances in chemical and materials engineering. In fact, the recent merging between textile and sensor engineering has seen rapid developments in wearable technology, especially in the biomedical engineering field [13; 14; 15], which provides much motivation for adopting advances in chemical/textile engineering in other areas of sensing, i.e., SHM. Conventional FOSs used for SHM have been mainly grating-based and require adequate attachment of the sensor region to the structure. This had been mainly achieved using binding agents, such as epoxy [16; 17]. The installation of such a sensing scheme not only requires specialist trained personnel in fiber optics to carry out the installation, but also, the accuracy of the sensing mechanism relies heavily on the efficiency of the intermediate transfer agent, i.e., epoxy. In addition, the hassle of having to somehow attach the fiber on the structure makes it unattractive to civil engineers, who are not used to dealing with cables that are of micro-meter-diameter-level dimension [18]. An ideal solution would be to embed the sensors on to the strengthening element of the structure itself, which saves time and costs, increasing the efficiency of the overall scheme. Projects such as the Carbon Concrete Composite (C3) initiative in Germany aim to replace traditional steel reinforced concrete (SRC) as a building material with carbon reinforced concrete (CRC) [19]. The inherent characteristics of CRC possess a considerable number of advantages over conventional SRC, i.e., light weight, lifespan, thermal and electrical conductivity properties, flexibility of fabrication, efficiency and immunity to risk of corrosion. Further, CRC can be constructed in thin layers with high tensile strength, which makes it most suitable for intelligent building construction. The direct integration of FOSs into CRC forms an advanced field of research, which needs careful investigation into the durability of the said integration and thus its practicality in long-term use. To this end, it is of vital importance to evaluate whether the physical construction of the optical glass fiber (preferably single-mode fiber with acrylate, polyimide or carbon coating) is able to withstand its host environment, i.e., concrete. The combination of the high alkaline environment in concrete and the concrete mechanical stress adversely affects not only the integrity of the optical fiber but the strength of the bonding between the carbon fiber reinforcement and the optical fiber. In a worst-case scenario, the optical fiber can be damaged to a level of non-operation.