Mix Proportion Design Of Bayer Red Mud Based Foamed Lightweight Soil And In The Application And Research Of Subgrade Engineering

In China as a new light roadbed filling material,Cast-in-place foamed lightweight soil has the advantages of light weight,vertical casting and intensity adjustment.It can effectively reduce the load exerted on the foundation,and its unique advantages can effectively deal with highway construction problems such as settlement of soft roadbed and bumping at bridge head.Red mud is a fine alkaline solid waste discharged from the production of alumina from bauxite.The production and discharge of red mud occupy a large number of land resources,which brings a series of hidden dangers,and directly affects the sustainable development of alumina industry.From the perspective of reducing the cost of foamed lightweight soil,combined with the urgent needs of solid waste recycling of red mud,relying on the subgrade project of the Linlin Expressway experimental section,the research and development of foamed lightweight soil with Bayer red mud as the main cementitious material has important significance for the development of circular economy.Research shows:(1)The composition,micro morphology and product structure of raw materials such as red mud were analyzed.Based on the principle of alkali excitation and orthogonal experimental design,the mix proportion optimization test of new red mud based cementitious material was carried out.The optimal mix proportion was determined as 26% slag powder,4% quicklime,3% sodium sulfate,52% Bayer red mud and 15% cement.The cementitious mechanism of the cementitious material system was analyzed.(2)According to the test section roadbed requirements,the compressive strength and flow value of red mud based lightweight soil are tested.The laboratory test results show that the water-binder ratio of red mud based foamed lightweight soil is 0.70,the design wet density is800kg/m~3,and the 28 d compressive strength of the lightweight soil test block in the laboratory is 0.93 MPa,which meets the requirement of 0.8MPa for the 28 d strength of the embankment.When the water-binder ratio is 0.70 and the design wet density is 1000kg/m~3,the 28 d compressive strength of the light soil test block in the laboratory is 1.29 MPa,which meets the requirement of the 28 d strength of the roadbed position of 1.20 MPa.Based on the analysis of range and variance,the influence of design wet density and water binder ratio on the compressive strength and flow value of the material is explored.(3)The results of SEM show that the microstructure of the material is mainly composed of pore wall framework structure.The results show that the design wet density mainly determines the number of pores,pore size and distribution of internal structure;the water binder ratio mainly affects the change of internal free water content,and both of them comprehensively affect the macro mechanical properties.Through the immersion test,it is concluded that the red mud based lightweight soil under room mix parameters has a water absorption rate of 25% and a softening coefficient of more than 0.75,which all in accord with the engineering technical requirements.Based on the test and analysis of casting technology,it is pointed out that appropriate parameters such as stirring time,stirring rate and casting thickness can improve the strength of materials and the quality of finished products.(4)In this paper,the effect of red mud based lightweight soil is analyzed by numerical simulation to study the stress and displacement response law of red mud based lightweight soil subgrade under different working conditions.The results show that,compared with the conventional filling subgrade,the red mud based light soil subgrade can make the foundation settle integrally and reduce the settlement by 65.10% and the base stress of 55.23%.Meanwhile,the settlement difference of the subgrade increases with the increase of the filling height and the design wet density.The simulation results show that under the optimal mix proportion design,the problem of effective settlement of uneven ground settlement and additional stress by red mud foamed lightweight soil material is provided,which provides a theoretical basis for the development of the field test section in the next stage.(5)The project research team successfully carried out the subgrade engineering of the red mud foam lightweight soil test section,and analyzed and summarized a complete set of construction technology plan and quality control for the construction preparation,construction technology and key points of the roadbed construction process.The results of the test section show that the wet density,strength,flow value and defoaming rate of the red mud based foamed lightweight soil meet the technical requirements of the roadbed of the expressway.Compared with conventional foamed lightweight soil,red mud based lightweight soil has a 20% advantage over cost.The experimental section saves about 4.6207 million yuan of material cost and consumes about 23029.5 tons of Bayer red mud,achieves the goal of red mud resource utilization and project cost reduction,which has the value of popularization and application..