# Unlocking the Potential of RFA and Stabilizers in High Moisture Geotechnical Applications
## 1 Introduction  
During rapid urbanization over the past few decades, extensive foundation excavations and construction activities have generated a large volume of discarded soft soil [1]. Due to its high compressibility, high water content, poor permeability, and low bearing capacity, soft soil is challenging to use directly in engineering projects, often causing settlement, deformation, and stability issues [2, 3, 4, 5]. Traditional disposal methods, suchas landfilling or open-air stacking, not only occupy vast land resources but also lead to environmental pollution, including dust emissions, soil erosion, and damage to soil structures, sometimes even causing land subsidence [6; 7; 8]. Thus, improving the mechanical properties of soft soil and reducing its reuse difficulty have become critical problems in construction engineering. At the same time, urbanization has also generated a significant amount of construction waste [9]. To enhance the utilization efficiency of construction waste, various management strategies and policies have been implemented worldwide [10; 11; 12]. Recycled fine aggregate (RFA) is one of the primary reuse forms of construction waste, typically produced by crushing and grading discarded concrete, stones, and bricks in specific proportions. This sustainable material offers notable environmental and economic benefits [13]. However, compared to natural aggregates, RFA generally has a higher water absorption rate, lower density, and certain limitations in mechanical performance and stability [14; 15; 16]. Enhancing the application effectiveness of RFA has become a research focus. Currently, RFA is widely used in fields such as recycled aggregate concrete (RAC), road pavements, and foundation reinforcement [17; 18; 19; 20; 21]. With the increasing accumulation of construction waste and discarded soft soil, there is an urgent need for an environmentally friendly, low-carbon, and cost-effective treatment method. Some studies have shown that RFA can be used not only as conventional building material but also for soft soil stabilization to achieve the required mechanical properties for engineering. For example, research on RFA-based granular piles for soft soil treatment demonstrated that RFA could effectively replace natural aggregates, enhancing the bearing capacity and settlement resistance of soft soil. The addition of binders such as cement and fly ash further improved the performance [22]. Furthermore, studies have indicated that combining soil stabilizers with RFA achieves peak strength when the RFA content reaches 30%. Microstructural analysis revealed that RFA promotes the formation of hydration products and provides effective mechanical support, but excessive content may lead to large pores in the matrix [23]. These findings suggest that RFA holds significant potential for soft soil reinforcement. However, most current methods for soft soil stabilization rely mainly on stabilizers such as silicates, lime, and cement [24; 25; 26; 27] which are limited in practical applications due to high energy consumption, pollution, and cost [28; 29; 30]. Therefore, the synergistic use of RFA and soil stabilizers for treatment is a promising direction worth exploring. This study introduces an innovative approach that combines the use of recycled fine aggregates (RFA) and soil stabilizers to improve the mechanical properties of soft soils, particularly red clay, which is characterized by high plasticity, low strength, and high moisture content. While previous studies have primarily focused on either recycled aggregates or soil stabilizers individually, the synergistic effects of combining these two materials have not been extensively explored. This research aims to address this gap by investigating the combined influence of RFA and stabilizers on soil strength and structural stability, providing a sustainable solution for soft soil stabilization.