| Red mud is the industrial waste of aluminum oxide plant.For every 1 ton of alumina produced in industry,about 0.8-1.5 tons of red mud are produced.On the one hand,the accumulation of red mud occupies a large amount of land resources,and on the other hand,it may cause serious pollution to soil,water system and atmosphere.Large-scale consumption and utilization of red mud can not only reduce the damage to the natural environment,but also have great social and economic benefits.The utilization of red mud in road is an effective way to large-scale consumption of red mud.But at this stage for solidification/stabilization technology of red mud in the road engineering is not widely used,mainly exist the following problems:(1)the activity of red mud composition is low,the excitation effect of curing agents for red mud in current study is poor,the strength increase is not obvious.Besides,the red mud is mainly used for curing the subgrade filling materials,it is hard to satisfy the standard of the strength of the road base materials.(2)Literature shows that cement,lime and GGBS are all alkaline curing agents.In the process of curing red mud,the p H value of the red mud solidified body leach is bound to increase.Therefore,solving the problem of high alkalinity of red mud has always been an international problem.(3)Bayer red mud has fine particles,large specific surface area,high dispersion and strong water holding capacity.Stabilizing/solidifying red mud requires a lot of curing agents,which reduces the economic benefit of red mud utilization.It is urgent to select a reasonable ratio to meet the requirements of road performance and cost.Therefore,based on the modified red mud road base materials as the research object,through indoor experiment,research,the effects of additives(cement,lime,phosphogypsum)on the physical properties and strength properties of modified red mud road base material were studied,the durable performance under the action of F-T and W-D cycle and the road base materials properties under driving load were studied.The main research contents and results of this paper are as follows:(1)According to the previous research results and the strength requirements of the road base,cement,lime and phosphogypsum were selected as three kinds of admixants,and the effects of different cement,lime-cement and phosphogypsum contents on the physical properties and strength performance of the modified red mud were studied through three groups of material optimization tests.The strength formation mechanism of the modified red mud materials was analyzed as follows: the cement effect of hydration products C-S-H,C-A-S-H,N-A-S-H gels and the filling effect of ettringite.It is confirmed that ettringite expansion has a dual character,and the pore filling mechanism of ettringite for the modified red mud is clear:ettringite mainly fills the pores with pore sizes of 0.1μm-1μm,and the microcrack pores produced by volume expansion are mainly pores with pore sizes of 1μm-10μm.(2)By W-D and the F-T cycle test,research durability of modified red mud with different phosphorus gypsum content,analyze the influence of W-D and F-T cycles on UCS,p H,dry density and micro pore structure of modified red mud,confirm the external environment and the intensity attenuation mechanism of modified red mud in the W-D and F-T cycle,discuss the correlation between the macroscopic strength and the microscopic pores and dry density.The results show that the strength guarantee rate of samples with 2% phosphogypsum content after five cycles of W-D and F-T is above 85%.The optimal ratio of phosphogypsum modified cement and lime stabilized red mud is Rm: PC: Lm :PG= 100:8:2:2.It was found that the proportion of micropores(0.01-0.1μm)in the modified red mud samples decreased due to WD and F-T cycles,while the proportion of small pores(0.1-1μm)and medium pores(1-10μm)increased,and the accumulated mercury content increased.W-D had a more significant effect on the strength of the modified red mud than that of F-T cycles.The UCS of the modified red mud sample was positively correlated with the percentage of pore volume < 0.1μm and dry density.(3)The splitting test was used to evaluate the tensile properties,the compressive resilience modulus test was used to evaluate the ability mud to resist vertical deformation under the action of vertical load,and the shrinkage test was used to evaluate the resistance of the material to shrinkage.Based on the above experimental parameters,the calculation model of pavement structure was established by Abaqus to analyze the road condition of the base of different thickness and modulus under driving load,calculate the tensile stress and tensile strain of the base and complete the checking calculation of bending and tensile stress.The results show that the elastic modulus and splitting strength of the modified red mud meet the requirements.Both economic benefits at the same time,the numerical simulation results reveal the tensile stress at the grass-roots level and decreased as the basic unit thickness,with the increase of compressive modulus of resilience increases,the allowable tensile stress at the grass-roots level is greater than the actual tensile stress,tensile strength meet the engineering requirements,the optimal thickness of secondary highway phosphogypsum modification cement-lime road base is 35 cm. |
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