The utilization of red mud waste discharged from the Bayer production process used for extracting alumina from bauxite presents a pressing demand in the aluminum industry. This study aims to adopt a chemical modifier to solidify the Bayer red mud for its application in highway subgrade. The mechanism and properties of the modified red mud using a modifier composed of cement, phosphogypsum and organic polymer, were analyzed and investigated. It was found that the optimal modifier dosage of the solidified modifier was 8%. The three-day unconfined compressive strength of the modified Bayer red mud could reach up to 3 MPa and its strength loss when immersed in water at 7 days and 28 days measured less than 20%. For its real application as subgrade, its road performance could be achieved with good bearing capacity, including a resilient modulus value greater than 90 MPa, a dynamic deformation modulus reaching up to 140 MPa and the Falling Weight Deflectometer (FWD) value measuring less than 100 (0.01 mm). Compared with traditional lime or cement stabilized soil, using locally modified Bayer red mud for subgrade filling can reduce the project cost, minimize the consumption of non-renewable resources and reduce the emission of environmental hazards, thus providing an engineering reference for large-scale and resource-based road applications.

The silt in the Yellow River alluvial plain has low clay content, low cohesion and poor structure. Its stability has always been a difficult problem in the engineering field. In order to improve the engineering properties of the silt in the alluvial plain of the Yellow River, a new type of silt composite flexible curing agent was prepared by using sintered red mud and matrix asphalt as the main materials to comprehensively stabilize the silt. The aim of this study was to investigate the effects of sintered red mud-asphalt composite flexible curing agent on aged mechanical properties of treated silt, in which the replacement levels of the flexible curing agent below 10% by weight are compared. Apart from the compressive strength, the drying shrinkage, low temperature freeze-thaw and high temperature self-healing ability are measured. The test results show that the flexible curing agent has a positive effect on improving the mechanical properties of stabilized silt. The flexible curing agent series exhibit higher compressive strength, better water stability, resistance to freeze-thaw and high temperature self-healing ability, and lower drying shrinkage compared to silt and cement stabilized silt. The preferred dosage 4%~6% of the flexible curing agent is obtained by mechanical property analysis. The SEM images show that the incorporation of the flexible curing agent helps the silt form dense cementation and non-connected microporous structure, that is beneficial to the improvement of water stability and frost resistance. The asphalt component in the flexible curing agent can reorganize and diffuse in the soil, fill the internal pores and micro cracks, and realize the repair of soil damage and structural reinforcement.

This study aimed to verify the effect of solidification materials based on solid waste on the shrink-age performance of silt, the main raw materials of solid waste were red mud, zeolite powder, and matrix asphalt. Temperature shrinkage and drying shrinkage tests were conducted to compare and analyze the shrinkage characteristics using three kinds of solidification materials (2%, 4%, and 6%), with 6% cement-solidified soil and plain soil used as control. The results showed that the solidification material based on solid waste effectively reduced the temperature shrinkage strain and temperature shrinkage coefficient of soil; moreover, the material had good resistance to temperature shrinkage deformation. A drying shrinkage test showed that the addition of solidification materials based on solid waste considerably improved the early water retention capacity of the test soil. The water loss process mainly occurred in the first 7 days of the test. Meanwhile, the addition of the solidification material considerably reduced the drying shrinkage strain and drying shrinkage coefficient of the test soil, and the effect was more obvious as the content amount increased. Through NMR and CT scanning tests, the pore size and pore volume of the solidified material mixed with solid waste were found to be significantly reduced. The dominant pore size ranged from 0.01 μm to 1 μm. The solidification material based on solid waste improved the crack resistance of the soil, providing a new reference measure for subgrade and roadbed fillers, as well as a new means for the recycling of solid waste.