Development And Performance Test Of Bayer Red Mud-Based Foamed Lightweight Soil

In recent years,foamed lightweight soil has become an effective method to solve subgrade diseases such as uneven settlement in the traffic field due to its advantages of light weight,high strength,good fluidity and high construction efficiency.The traditional foamed lightweight soil is mainly made of cement as cementitious material,mixed with slag and fly ash,and then prepared by foaming process.With the implementation of strong transportation network,carbon peaking and carbon neutrality,the preparation of foamed lightweight soil using industrial solid waste as cementitious material instead of cement has gradually become a research hotspot.Bayer red mud,as one of the most difficult to utilize industrial solid waste,has a huge storage capacity and continues to increase by tens of millions of tons annually.Research and development of red mud-based foamed lightweight soil and its application in traffic engineering construction can obtain huge engineering value and ecological benefits.Based on the construction demand of subgrade filling engineering,this paper carried out the proportioning design of red mud-based cementitious materials,the performance optimization of composite alkali resistant foaming agent,and the adaptability study of red mud-based cementitious materials and foaming agent,and realized the preparation and performance control of red mudbased foamed lightweight soil.The main research contents and results are as follows:A study was carried out on the change rule of setting time and compressive strength of slurry under the collaborative utilization of high calcium solid waste slag and red mud.The effects of pH value and dilution times on the foaming times of composite foaming agent and the stability of foam were clarified.The optimal ratio of red mud-based foamed lightweight soil was determined as red mud mixed with 60%,slag mixed with 40%,NaOH mixed with 6%,and water-binder ratio of 0.6.Composite foaming agent FM-20AB:XG:W=1:0.2:60,when foam is mixed with 5%,the pores are homogeneous,the 28 d compressive strength is 1.05 MPa,the fluidity is 212 mm,and the wet density is 9.1 kN/m3.The effects of cement,desulfurized gypsum,water-binder ratio and admixtures on the setting time,rheological properties and crack resistance of red mud-based foamed lightweight soil were revealed.Cement can significantly shorten the setting time of red mud-based foamed light soil,the initial setting time of 10%cement content is 168 min,and the initial setting time can be adjusted within 226-331 minutes with a 2%-10%content of desulfurization gypsum.The fluidity of 0.4-0.7 water-binder ratio and naphthalene superplasticizer are the most significant to improve the fluidity of the slurry.The fluidity of 0.45-0.6 water-binder ratio is between 160 mm and 212 mm,which is conducive to the construction pouring.The fluidity of 0.3%naphthalene superplasticizer increases from 165 mm to 176 mm when the water-binder ratio is 0.5.The cracking phenomenon was significantly reduced by 1.5%fiberglass or 12%expansion agent,the crack width decreased by 71.9%and 50%,and the cracking time increased by 513.5%and 408.1%at room temperature,respectively,compared with the control group.Using CCD industrial camera and Image-Pro Plus image processing technology,the effects of various pore structure parameters on the physical and mechanical properties of red mudbased foamed lightweight soil were studied.The porosity and pore size have linear relationship with foam content,and power function relationship with compressive strength.When the content of foam increases from 3%to 7%,the pore distribution curve gradually diverges,the proportion of small pores(<300 μm)decreases,and the proportion of large pores(>600 μm)increases.The roundness decreases from 1.22 to 1.12 and then increases to 1.35.When the content of foam is 5%,the pore shape is the closest to circular,which is conducive to improving the compressive strength.Aiming at the subgrade failure caused by water and freezing action,the influence of pore structure on water stability of red mud-based foamed lightweight soil was studied,and the influence of cycles and melting temperature on the frost resistance was analyzed.When the porosity increased from 19.2%to 68.0%,the pore size increased from 187.5 μm to 316.3 μm,the water absorption rate increased from 17.9%to 65.6%,and the softening coefficient decreased from 086 to 0.20.Under freeze-thaw cycles,mass loss and compressive strength loss increased from 1.0%and 8.2%to 25.5%and 58.6%,respectively.In addition,the greater the melting temperature is,the faster the failure will be.After 25 cycles,the mass loss and compressive strength loss of red mud-based foamed lightweight soil with 3%,4%and 5%foam content are not more than 5%,and not more than 20%,indicating that the specimen has good frost resistance.The pore structure was damaged by freeze-thaw cycles,and the porosity increased from 26.1%to 72.8%and the pore size increased from 211.6 μm to 332.9 μm at the melting temperature of 20℃.The pore distribution developed from small-pore concentration to large-pore concentration.