## 1 Introduction  
The construction industry is projected to experience steady growth until 2026, as it undergoes restructuring following the gradual relaxation of global lockdown measures implemented in response to the COVID-19 pandemic. However, the construction of the majority of buildings currently relies heavily on traditional methods that involve onsite concrete pouring. The drawbacks of these conventional methods include difficulties in sourcing construction materials, increased construction costs, inadequate quality control due to the demand for shortened construction periods, and a shortage of skilled workers [1; 2; 3; 4]. Measures are necessary to address these issues and improve construction management. The introduction of factory production methods for concrete structures (offsetic construction) can offer advantages such as low cost, fast delivery, and high performance [5; 6; 7; 8; 9]. Continuous efforts are being made to increase the production efficiency compared to traditional methods. In this regard, modular construction methods minimize onsite construction and simplify process management, utilizing advantages such as reduced construction time and streamlined processes [10; 11; 12]. Furthermore, factory-controlled production of building components enables comprehensive quality control in terms of concrete mixing, pouring, curing, and precise production due to the accuracy of the mold dimensions [13; 14]. Currently, modular industries such as assembly and multiunit housing construction are expected to demonstrate a steady growth rate of 7.0% annually, particularly dominating the modular construction market in the Asia-Pacific region [5; 15; 16; 17; 18; 19; 20; 21]. Consequently, the continuous development of modular technology is essential for sustaining growth in the construction market. As the modular industry expands, various building materials are being utilized. The most widely used construction materials are concrete, steel, and wood. Steel modular construction is the most common form and is characterized by ease of transportation and shortened production times. However, considering the properties of steel, completely avoiding issues such as corrosion is difficult, and demonstrating advantages in terms of price is challenging [22]. In particular, steel structures are vulnerable to noise and vibration due to the nature of the material, limiting the use of these structures as modules in multi-story buildings [23; 24]. Modular construction with wood can be environmentally friendly and offer aesthetic benefits. However, there are concerns about decay over prolonged use, and the creation of an environment suitable for insects such as ants and termites limits the use of wood as a construction material. In contrast, concrete is used for various structural components and offers superior durability compared to structures built with steel or wood. Concrete has better durability than steel or wood, thus requiring less effort and maintenance costs and maintaining quality for a longer period. For modular concrete structures, achieving lightweight structures with sufficient durability and structural performance is important. The self-weight of modular structural components must be minimized to achieve this goal. The use of lightweight, high-strength, and high-performance concrete is deemed feasible for lightweighting. Various types of natural and artificial lightweight aggregates are used in lightweight aggregate concrete [25; 26; 27; 28]. This trend is gradually increasing due to sustainable development efforts to reduce energy consumption and CO\({}_{2}\) emissions [29; 30]. The utilization of lightweight concrete in multi-story buildings is predicted to reduce the weight, resulting in flexibility and significant cost savings [31]. However, lightweight aggregate concrete is primarily used for nonstructural purposes [32; 33] because air trapped within the aggregates or cement matrix, although it reduces the weight and improves the thermal insulation, lowers the strength.