## 1 Introduction  
Optimizing long-term performance of road infrastructure is a crucial objective for civil engineering, particularly in light of the evolving global climate. In particular, designing and constructing durable pavement structures that balance economic viability and environmental sustainability in regions characterized by low temperatures constitutes a significant challenge. The phenomenon of differential frost heave and the increase in soil moisture content due to prolonged exposure of pavements in cold regions to extremely low temperatures during the winter months, as well as repeated freezing and thawing cycles in the spring, can have detrimental effects on the pavement structure. These effects include the premature development of cracks and a reduction in the bearing capacity of the pavement, leading to shorter service lives and higher maintenance costs [1; 2; 3; 4]. As a result, various research studies have been conducted to investigate alternative design and construction techniques, as well as the use of alternative materials. The selection of materials for pavement construction in cold regions should consider factors such as the material's response to changes in climatic conditions, cost, environmental impact, ease of use, and structural capacity. The implementation of innovative materials in the subbase layer of pavement structures has been proposed to address the subgrade weakness issue. Material compositions and functional capabilities of the subbase are deemed imperative to enhance the pavement system's overall structural integrity.  
In cold climates, insulation layers are commonly employed directly on the subgrade to mitigate frost penetration within pavements [5]. Various insulation materials have been utilized within the pavement structure to reduce frost penetration, including polystyrene, bottom ash, foamed glass aggregates, foamed concrete, wood residues, and tire chips [6; 7]. In addition to their insulating function, several of these materials also serve as a pavement subbase. In contrast, unbound granular layers are not typically regarded as insulating layers due to their thermal conductivity properties. Studies have also shown that these unbound granular material deformation and performance, in general, are influenced by material gradation (size), stress level and moisture content [8; 9]. Research has recently demonstrated that lightweight cellular concrete (LCC) possesses superior insulating properties compared to traditional flexible pavements [10; 11].  
An investigation by Ni [12] evaluated the mechanical properties and suitability of lightweight cellular concrete (LCC) as a subbase material for pavements in Canada. The study determined that LCC possessed greater stiffness than unbound granular materials but a lesser stiffness than chemically stabilized base materials. Additionally, the study identified that the density of LCC plays a crucial role in its properties, with densities of 475 kg/m\({}^{3}\) and 600 kg/m\({}^{3}\) displaying improved pore structure and durability after 180 cycles of freeze-thaw testing, in contrast to the 400 kg/m\({}^{3}\) density LCC. The research suggests that LCC could serve as a viable subbase material option, as it offers enhanced durability when compared to traditional materials [12]. At low densities, LCC can exhibit a high percentage of voids ranging from 80-90%, thus minimizing the requirement for raw materials and decreasing the generated waste. Due to the free-flowing nature of LCC, compaction is not required, thus reducing noise pollution and energy consumption associated with compaction [13]. Utilization of industrial by-products, such as slag and fly ash, can reduce waste disposal and increase sustainability [14; 15]. The replacement of Portland cement with fly ash, up to a maximum of 75%, in low-density lightweight concrete (LCC) can decrease embodied carbon dioxide (eCO\({}_{2}\)) while also improving properties such as lower thermal conductivity, reduced dry shrinkage, and diminished heat of hydration [16; 17; 18; 19].