# Use of Lignin, Waste Tire Rubber, and Waste Glass for Soil Stabilization
## 1 Introduction  
In recent years, the recycling of waste materials has become increasingly important due to its sustainability and environmental benefits. For this reason, the use of waste materials in ground improvement applications has been put on the agenda [1]. The use of waste materials in construction works not only saves money by reducing the amount of construction materials used but also reduces the demand for natural construction materials [2]. Therefore, researchers have been trying to reuse granite waste in construction and protect natural resources for several years [3]. Industrial waste was used as aggregates or cement for concrete production. Waste materials are also used in geotechnical engineering for soil improvement [4, 5]. In roadway construction, the traditional options for improving the subgrade are lime/cement-stabilized subgrade and geosynthetically reinforced subgrade. Stabilization is a method by which the properties of the soil are altered to improve its performance [6]. To increase the bearing capacity and the shear strength of the soil, the soil properties are either physically altered (by vibration) or a more resistant material is added or incorporated. In recent decades, intensive efforts have been made to develop economical,environmentally friendly, and durable soil stabilizers such as lime, cement, fly ash, and others [7; 8; 9; 10; 11; 12; 13]. Conventional stabilizers such as soil stabilizers treated with lime and cement have been investigated for their stabilizing effect and their suitability as geomaterials for road construction [14; 15]. Although these stabilizers have shown significant improvement in soil capacity and durability, their high cost, potential shrinkage, and high alkalinity are still critical issues that prompt geotechnical engineers to look for other alternatives. In recent years, there has been a great deal of interest in the use of non-traditional stabilizers for this purpose [16]. With the pursuit of sustainable development, there is an increasing need for environmentally friendly building materials with improved properties, which has drawn the attention of researchers to the use of used tires, glass powder, lignin, etc., and has led to increased research on this topic [6; 17; 18; 19]. Due to the increase in waste production, researchers have started to use waste materials in different areas to reduce the amount of industrial waste thrown into nature. Waste materials can be used in various areas of construction. Lignin as a waste material can be used effectively in subgrade improvement to increase the strength and stability of the soil, and it offers a sustainable and environmentally friendly solution for construction applications. In recent years, studies on the use of lignin in soils with poor engineering properties have increased [20; 21]. Various researchers have reported that the use of lignin has achieved positive results in soil parameters, especially in problematic soils with a low bearing capacity [22; 23; 24; 25; 26]. [PERSON] et al. [27] conducted the shear wave test and unconfined compression test to evaluate the shear modulus and unconfined compressive strength of lignin-stabilized silty soil. They found that the shear modulus and compressive strength of the lignin-treated soil increased logarithmically with the curing time. In addition, they pointed out that the interaction mechanism between lignin and soil and the durability of the soil still needs to be investigated and confirmed by additional laboratory tests. Lignin may initially increase the strength of the soil by coating the particles with an adhesive film, but long-term effects may include a reduction in strength due to the dispersion of clay particles caused by the negative surface charge of the lignin [16; 28]. Every year, around 1.5 billion tires are thrown away at the end of their useful life, and this figure is expected to rise to 5 billion by the end of 2030. This leads to various environmental problems such as soil and air pollution.