## 1 Introduction  
Concrete structures form an essential foundation for modern society, serving as the backbone of various infrastructural developments, including buildings, bridges, highways, and dams. As these structures are subjected to numerous environmental and operational factors, their durability and safety become critical concerns. The early detection of structural degradation and performance issues is imperative to prevent catastrophic failures, ensure public safety, and optimize maintenance efforts. In this context, structural health monitoring (SHM) has emerged as an indispensable tool to assess the integrity and performance of concrete structures [1, 2, 3]. To monitor concrete structures effectively, a range of monitoring systems have been developed and employed in various engineering applications, focusing, among others, on monitoring cracking [4, 5, 6], corrosion of reinforcing steel [7, 8, 9], and excessive deflections [10, 11]. Another very important aspect in monitoring concrete structures is strength development, especially at early ages. Depending on the concrete type, strength development after 3 days can already amount to 40 to 70% of the 28-day strength, which could enable, for example, a faster removal of formworks or advancements in the construction stage. However, real-time monitoring of concrete strength using non-destructive methods is still a big challenge and a major source of uncertainty. In this context, maturity methods for in situ estimation of concrete strength, based solely on temperature, have been widely used [12; 13; 14; 15] and many commercial solutions have been developed. But these might not always be the most accurate, as the maturity and related compressive strength are also influenced by concrete mixture and the weather (as reported by [PERSON] et al. [12], differences of up to 30% between estimated and real strength could be obtained when using maturity methods for certain types of cement and curing conditions). In terms of data collection and transmission during the monitoring of concrete structures, traditional wired monitoring systems have been in use for decades and rely on physical cables to connect sensors to data acquisition units. These wired systems often involve significant installation efforts, especially in existing structures, which can be both time-consuming and expensive [16]. Moreover, the presence of cables may introduce potential damage to the structure and hinder the aesthetic aspects. In recent years, wireless monitoring systems have gained considerable attention in the field of structural health monitoring [17; 18; 19; 20]. Unlike their wired counterparts, wireless systems do not require physical cables, offering numerous advantages that significantly enhance monitoring efficiency and overall system performance; among these are flexibility and easy installation, scalability, enhanced data accessibility, and reduced structural impact. However, when working with wireless systems, sufficient attention should be given to in-to-out data transmission and communication. Wireless communication of antennas within concrete structures poses a unique set of challenges due to the high attenuation and signal loss caused by the dense and absorbent nature of concrete [21]. The propagation of radio waves through concrete is affected by its composition and thickness, resulting in significant path loss. To address these challenges, researchers have explored techniques such as the utilization of innovative antenna designs to enhance the penetration of signals into concrete structures [22]. As wireless communication continues to be crucial for various applications within and beyond concrete structures, ongoing research efforts are vital to optimize signal propagation and coverage in this challenging context. Regarding monitoring techniques, the utilization of electrical resistivity (ER) measurements within concrete emerged in several studies as an indicative measure of moisture content and durability [23; 24].