Red soil exhibits a high susceptibility to geological disasters and engineering instability owing to its significant dispersibility and substantial strength attenuation upon exposure to water. Consequently, there is an urgent necessity to enhance its engineering properties. As an environmentally friendly and cost-effective industrial by-product, building gypsum powder demonstrates significant potential in improving the mechanical properties of red soil. It not only reduces the burden of landfilling and lowers material costs but also achieves efficient waste utilization and resource recycling, substantially cutting expenses related to soil stabilization and improvement. It is expected to provide a scientific basis for the analysis of geological hazards such as debris flows, landslides, and collapses in red soil regions, as well as offer guidance for selecting appropriate types and dosage of soil modifiers in practical engineering projects.
Recently, a team led by Yinlei Sun from Yunnan University in Yunnan Province, China, has investigated the impacts of wet-dry cycling and chemical contamination on the improvement of red soil using building gypsum powder, aiming to advance research in the field of red soil modification. Building gypsum powder, which is environmentally friendly, cost-effective, and exhibits remarkable modification effects, stands as an ideal choice for red soil amendment. Utilizing gypsum powder derived from demolished construction waste for soil improvement not only reduces the landfill burden and lowers material costs but also achieves efficient waste utilization and resource recycling. Current research endeavors are focused on revealing the intrinsic relationships between the shear strength, compressibility, and microstructure of both undisturbed and modified red soils, as well as delving into the macroscopic mechanical properties such as shear strength and compressibility of modified red soil and the underlying modification mechanisms. This holds significant importance for refining the macroscopic mechanical theory of red soil and addressing practical engineering application challenges.
The team published their review in Civil Engineering Sciences on 23 February 2026.
"In this study, we have outlined the efforts made by our research team in investigating the impact of dry-wet cycles and chemical contamination on red soil improved with building gypsum powder. This study focuses on the mechanical properties and microstructural evolution of the improved red soil under complex environmental conditions, systematically exploring the influence of acetic acid, sodium hydroxide, and sodium sulfate on the mechanical properties of building gypsum powder-improved red soil under dry-wet cycles, as well as their underlying mechanisms. The study found that when the improved red soil is exposed to various chemical contaminants, there are significant differences in its mechanical properties (including cohesion, internal friction angle, shear strength, and compressive strength)," said Professor Yin-Lei Sun from the School of Architecture and Planning at Yunnan University (the corresponding author of this study).
Building gypsum powder, known for its environmental friendliness, cost-effectiveness, and remarkable improvement effects, serves as an ideal modifier for red soil. Given the high susceptibility of red soil to geological disasters and engineering instability due to its significant dispersibility and substantial strength attenuation upon exposure to water, there is an urgent necessity to enhance its engineering properties. "The utilization of building gypsum powder not only improves the mechanical properties of red soil but also promotes resource utilization and waste recycling by employing gypsum waste from demolished buildings, thereby reducing landfill burdens and material costs," Professor Yin-Lei Sun added.
The research team conducted a series of direct shear and consolidation tests on red soil specimens amended with building gypsum powder, combined with microscopic techniques such as SEM, XRD, and XRF, to analyze the mineral composition and microstructural alterations. "Our findings indicate that acetic acid leads to the dissolution of gypsum components, initiating pore development and substantially reducing soil strength. In contrast, sodium sulfate, at low concentrations, crystallizes to fill pores and augment strength, whereas high-concentration crystallization results in expansion and structural damage. Sodium hydroxide triggers the thickening of the double electric layer and colloid precipitation, thereby cementing the soil skeleton and mitigating the adverse effects of dry-wet cycles," explained Zhen Li, the first author of this study.
The study also revealed that as the number of dry-wet cycles increased, soil pores expanded, the soil structure loosened, and both shear and compressive resistance diminished. "By utilizing gray correlation analysis and fractal theory, we established a quantitative relationship between microstructural parameters and disintegration, elucidating the predominant role of pore characteristics in determining macroscopic mechanical properties and the underlying mechanism of mineral component alterations," stated Xian-Wei Zhang, a corresponding author from the State Key Laboratory of Geomechanics and Geotechnical Engineering at the Chinese Academy of Sciences.
The research team expects that this study will provide a theoretical foundation and strategic guidance for the prevention and control of red soil disasters, as well as the optimization of geotechnical reinforcement materials. "Looking ahead, we anticipate that the application of building gypsum powder in red soil improvement will become more widespread and practical. Future research will focus on optimizing the modifier dosage, exploring long-term performance under complex environmental conditions, and developing cost-effective and environmentally friendly improvement techniques," Zhen Li concluded.
Other contributors to this study include Qing-Ru Du,Xuan-Chen Lin, and Jian-Bin Xie from the School of Architecture and Planning at Yunnan University.
This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 525608054, 42372313, and 12462033); the Natural Science Foundation of Yunnan Province, China (Grant No. 202401CF070174); the Open Research Fund of Key Laboratory of Flood and Drought Disaster Defense, Ministry of Water Resources (Grant No. wx20241100518); the Xingdian Talent Support Program (Grant No. C619300A130); and the Practical Innovation Project of Postgraduate Students in the Professional Degree of Yunnan University (Grant No. ZC-24249614).
