| Aluminum industry is the pillar industry of Guangxi industrial development,and the alumina capacity of Guangxi accounts for 14.9%of the total alumina capacity in China.A large amount of bauxite tailings(BTs)will be produced in the process of alumina production and stored in the tailing reservoirs for a long time,which will make the tailing reservoirs become a high potential dangerous source of artificial debris flow,not only threatening the safety of life and property of the downstream people and environment,but also occupying a large number of land resources.There are 14 existing large-scale tailing reservoirs in Guangxi,with a total capacity of 1145×10~4 m~3～6181×10~4 m~3.If a large number of BTs can be utilized as resources,it can not only implement the national and local policy requirements for the reduction of industrial solid waste and the construction of ecological civilization,but also the urgent need of sustainable economic and social development.BTs contains a lot of kaolin with high viscosity,which is non-toxic and harmless.It can replace some fine sand and cementitious materials as raw materials for concrete and other materials.It can bring good economy,but the utilization rate of BTs is low at present.The foamed mixture lightweight soil(FMLS)is widely used because of its good light weight,density and intensity adjustment,but the price of raw materials for FMLS is rather high.Therefore,it is a new attempt to prepare FMLS with BTs(FMLSB).It not only accelerates the process of BTs utilization,but also provides a kind of green and practical light material for civil engineering field,which can greatly alleviate the shortage of land resources and environmental pollution,and has significant economic benefits and environmental benefits.Through the orthogonal test of FMLSB,sensitivity analysis is carried out on the factors affecting fluidity,wet density and unconfined compressive strength of FMLSB.The changes law of the physical and mechanical properties,durability and microstructure of FMLSB with density are revealed,and the relationship between them is established.The change law of the physical and mechanical properties,durability and microstructure of FMLSB with the BTs content,fly ash content and water glass modulus are mainly discussed from multi-scale(macro-,meso-and micro-scale),and the mechanism of performance change is revealed.Finally,the FMLSB was obtained to meet the requirements of strength,and has good fluidity,light weight and low cost,providing scientific basis and technical reserve for the resource utilization of a large amount of BTs.The main conclusions are as follows:(1)The results of range analysis and variance analysis showed that the sensitivity of factors affecting fluidity of FMLSB was ranked as BTs content>cement content>foam content,and the sensitivity of factors affecting wet density and unconfined compressive strength was ranked as foam content>cement content>BTs content.The unconfined compressive strength is between 0.4MPa～3.15MPa when the wet density of FMLSB is changed between 450 kg/m~3～1080 kg/m~3.With the increase of wet density,the area porosity of FMLSB decreases exponentially,the unconfined compressive strength increases exponentially,and the volume water absorption decreases linearly.The relationships among the wet density,unconfined compressive strength,volume water absorption and area porosity are established based on the experimental data.The results show that the compressive strength of FMLSB can be adjusted according to the density,and it has wide applicability.(2)When the BTs content is 10%,20%,30%and 40%,the fluidity of FMLSB is in the range of 160mm～180mm,and the wet density is between 489kg/m~3 and 527 kg/m~3,it has better lightness compared with the FMLS with fly ash(FMLSF).With the addition of water glass,the fluidity of FMLSB increases significantly,and the wet density decreases with the increase of the water glass modulus.With the increase of BTs content,the volume water absorption increased from 25.7%to 43.1%,and the water stability coefficient decreased from0.859 to 0.710.However,when water glass is added,the volume water absorption increases obviously,especially when the BTs content is 20%,the corresponding volume water absorption is up to 112.52%～115.96%,while the water stability coefficient is relatively small.The volume water absorption of FMLSB is between 25.7%and 43.1%and the water stability coefficient is greater than 0.7,indicating that the FMLSB has good lightweight and durability.(3)Under the low density of about 500 kg/m~3,the unconfined compressive strength of FMLSB is in the range of 0.31MPa～0.71MPa,the 7d and 28d unconfined compressive strength of FMLSB is as high as 73%～83%,which is larger than that of FMLSF.After adding water glass,when the BTs content is 20%,the ratio of 7d and 28d unconfined compressive strength is at a high level.The higher the content of BTs and fly ash,the more significant the effect of water glass on early strength improvement.There is strain softening and strain hardening behavior after the destruction of FMLSB,indicating that it has obvious ductility.Based on the distribution function of Weibull and thr model of Avalle,a one-dimensional damage constitutive model of FMLSB was studied,and the relationship between the model parameters and the BTs content was established.It shows that the FMLSB has higher early strength and buffering capacity,and has great advantages in practical engineering application.(4)When the BTs content is between 10%～30%,the pore distribution of FMLSB is uniform,and the area porosity of cell wall is 11.72%～20.33%.After adding water glass,the pores in the FMLSB are larger,and there is a phenomenon of pore wall rupture and pore connectivity.When the water glass modulus is 2,the area porosity of cell wall is the smallest.Due to the large surface area of BTs and the rich oxide of Si O2,Al2O3 and Fe2O3,the volcano effect of BTs in alkaline environment is significant,and plays a key role in improving the pore structure,mechanical properties and durability of FMLSB. |
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