Cement soil stabilization is widely used in civil engineering to improve the performance of soils subjected to freeze-thaw (F- T), wet-dry (W-D), and sulfate attack (SA). Due to the negative impacts associated with manufacturing cement, the development of eco-friendly and sustainable additives is highly desirable. Coal-derived char is a cost-effective byproduct of the coal pyrolysis process. In this study, the influence of coal char on mineralogical, microstructural, physical, and mechanical properties of cement stabilized soils (with cement contents of 0%-20% and char contents of 0%-30%) subjected to F-T cycles, W-D cycles, and SA is investigated. Compared to cement stabilized soils, char-cement stabilized soils exhibit up to 60.8% fewer volume changes during F-T cycles and 31.6% fewer during W-D cycles. The compressive strength of char-cement stabilized soils with cement contents of 5%, 10%, and 20% are on average 7.9%, 17.6%, and 11.0%, respectively, higher than that of cement stabilized soil subjected to F-T cycles, W-D cycles, or SA. The inclusion of char promotes cement hydration and results in the formation of more amorphous hydration products that fill voids or cover soil minerals. The findings indicate the promising potential of coal char in enhancing soil performance under a range of challenging environmental conditions.

Cement soil stabilization is a commonly used method to improve in -situ soil properties catering to different geotechnical applications. However, cement manufacturing is typically associated with high CO2 emissions and energy consumption. Coal char is a sustainable and environmentally friendly material derived from the coal pyrolysis process. Traditionally used for combustion and gasification, recent research has revealed its potential to improve the engineering performance of cement-based construction and building materials. This study explores the innovative use of coal char in cement soil stabilization. Examining various cement contents (5%, 10%, and 20%) and char contents (10%, 20%, and 30%), the properties of char-cement stabilized soils, including mineralogy, density, water content, thermal conductivity, unconfined compressive strength (UCS), and mechanical properties under triaxial compression, are comprehensively investigated and compared with cement stabilized soil. It is found that char promotes both cement hydration and reaction between soil minerals and cement. The thermal conductivity and UCS of char-cement stabilized soil are 0-9% lower and 8-16% higher, respectively than that of cement stabilized soil. Under triaxial compression, the addition of char in stabilized soil leads to 23.7% increase in shear strength, 17.7% increase in cohesion, and 16.7% increase in the angle of internal friction. In conclusion, the introduction of coal char into traditional cement soil stabilization demonstrates a novel approach to achieving sustainability and enhancing engineering performance in relevant geotechnical applications.