Study On Strength Characteristics And Microstructure Mechanism Of Red Mud-based Silty Sand

Red mud is a solid waste produced in alumina refining process,which has the characteristics of large discharge,strong pollution and low utilization rate.It is urgent to find a large-scale and comprehensive utilization way of red mud and effectively solve the harm of red mud to social economy and ecological environment.With the development of traffic engineering construction in China,the application of red mud in roadbed filling can consume a large amount of accumulated red mud,reduce the cost of road construction and alleviate the shortage of road construction materials.To explore the red mud for the feasibility of the modified soils used as embankment filling material,based on the bayer process red mud as the research object,with cement,lime and fly ash as the binder and the preparation of red mud modified silty soil,using macro micro test method of combining the strength characteristics of modified soil to study the change rule and the microstructure effect mechanism,The environmental impact of red mud-based modified silty sand was evaluated.The main research contents and achievements are as follows:(1)Firstly,the basic physical properties,oxide content,mineral composition and environmental impact of red mud were studied and evaluated.Red mud belongs to high liquid limit silty clay.Based on the comprehensive evaluation of environmental indicators,red mud belongs to class?general industrial solid waste and meets the requirements of roadbed filling material.(2)Compaction tests were carried out on red mud-based modified silty sand soil with different red mud,cement,lime-ash(lime,fly ash)content.The results show that with the increase of red mud,cement and lime-ash content,the maximum dry density of the modified silty sand decreases and the optimal water content increases,and lime-ash has better improvement effect on the water sensitivity of the modified red mud based silty sand than cement,which is more conducive to the actual construction compaction quality control.(3)Considering the influence of different mixing ratio of red mud,cement and lime-ash and curing age,the unconfined compressive strength and splitting tensile strength tests of red mud-based modified silty sand were carried out.The results show that there are optimal ratios of cement and lime-ash modified red mud based silt.When the red mud content is 20%and cement content is 12%,the strength and deformation characteristics of cement modified red mud based silt are the best.When the red mud content is 23%and the limonite content is20%,the strength and deformation characteristics of red mud-based silty sand modified by limonite are the best.(4)X-ray diffraction,thermogravimetric analysis and scanning electron microscopy were used to analyze the strength formation mechanism of red mud-based modified silt.It is found that the main hydration products of the modified silt are calcium silicate hydrate,calcium aluminate hydrate and Ca(OH)₂.When adding proper amount of red mud,the alkaline environment can obviously promote the hydration reaction.Too much red mud will inhibit the hydration reaction,and will adversely affect the density of soil,so that the strength of modified soil decreased.(5)The environmental indexes such as corrosiveness,heavy metal leaching toxicity and radioactivity of red mud modified silt were detected and evaluated.It was found that the environmental indexes of the modified red mud met the requirements of the specification.Compared with the pure red mud,the environmental indexes of the cement modified red mud and lime-ash modified red mud have been improved.The generation and crystallization of hydration gelled products play a key role in the solidification of heavy metal ions in the red mud.