# A Comprehensive Review on Clay Soil Stabilization Using Rice Husk Ash and Lime Sludge
## 1 Introduction
### Sustainable Stabilizers  
Byproduct materials, such as rice husk ash (RHA) and lime sludge (LS), can play a significant role in soil stabilization applications. These materials provide several benefits, including environmental sustainability, cost-effectiveness, and improved engineering properties of the stabilized soil [55]. RHA contains high amounts of amorphous silica (SiO\({}_{2}\)), contributing to its pozzolanic properties. RHA can be used in soil stabilization as an additive to improve soil properties, including strength, durability, and permeability. It reacts with calcium hydroxide, a byproduct of lime, to form additional calcium silicate hydrates (CSH) gel. This pozzolanic reaction improves cementitious properties, such as increased strength and reduced permeability [56]. Utilizing RHA as a sustainable utilization in soil stabilization provides an environmentally friendly solution by recycling agricultural waste material to reduce waste generation and promote sustainable practices [57]. Line sludge (LS), also known as lime waste or lime byproduct, possesses cementitious properties that make it suitable for soil stabilization. LS is rich in calcium hydroxide (Ca(OH)\({}_{2}\)), which is the main compound responsible for its cementitious properties [58]. Calcium hydroxide is an alkaline compound that reacts with silicates and other compounds to form cementitious products. LS exhibits pozzolanic activity, which refers to its ability to react with calcium hydroxide and water to form additional cementitious compounds. This reaction, known as the pozzolanic reaction, produces calcium silicate hydrates (CSH) gel, which contributes to the strength of the stabilized soil. LS interacts with clay minerals in soils, causing chemical and physical changes to the soil structure. This reaction decreases the plasticity of the clay minerals while enhancing their stability [59]. This reaction enhances the soil characteristics, including strength, workability, and load-bearing capacity. LS can be utilized as a stabilizing agent to enhance soil properties, mainly claycy or cohesive soils. When LS is added to these soils, it reacts with the clay minerals, resulting in improved compaction characteristics, reduced soil plasticity, increased strength, reduced swell-shrink behavior, and enhanced load-bearing capacity [60]. Lime sludge can be self-cement or self-harden when mixed with water. This property allows it to bind and stabilize soil particles, improving cohesion and strength within the stabilized soil or construction material [61]. Utilizing lime sludge in soil stabilization as a waste management solution provides a means of repurposing a waste material that might otherwise pose disposal challenges. It offers an opportunity for sustainable waste management practices and reduces the demand for traditional construction materials. When RHA and LS are used together, LS provides the calcium needed for stabilizing clay, while RHA increases the soil's strength and durability by contributing additional pozzolanic reactions. This combination reduces soil plasticity, minimizes shrink-swell behavior, and improves compaction, making it suitable for infrastructure projects in areas with clay soils. The process involves blending appropriate amounts of LS and RHA with the soil and allowing time for curing to achieve optimal soil stabilization [62]. The produced waste of rice husk ash and lime sludge can have detrimental environmental effects [63]. Proper management and disposal of RHA and LS byproducts are essential. Inadequate disposal methods, such as open dumping or uncontrolled release, can lead to soil and water pollution, posing ecosystem risks [64]. Both RHA and LS can have environmental implications if not properly managed. RHA may contain heavy metals, such as lead, cadmium, arsenic, and mercury; if not properly managed, these metals can leach into the soil or water bodies, posing a risk to ecosystems and human health.