Study On The Influence And Improvement Of Red Mud On The Nerformance Of Fly Ash Autoclaved Aerated Concrete

China is a major producer of alumina,and the accumulated red mud has accumulated to hundreds of millions of tons,and most of them are handled by open dam construction.This red mud handle method not only occupies land resources,but also causes soil pollution and affects the health of humans,animals and plants Aerated concrete is a new type of building material,which has the advantages of light weight,good thermal insulation,good sound insulation,and secondary use of solid waste.The Bayer process red mud has high alkalinity(pH value>12),fine particles,and a certain self-cementing ability,and has the properties suitable for the aerated concrete pulping and curing process.However,there are few studies on the use of red mud in autoclaved aerated concrete,and the influence mechanism of the addition of red mud is not perfectIn order to solve these problems,this paper first makes an experimental study on the basic properties of red mud;secondly,it studies the influence of red mud content on the performance of aerated concrete;finally,22.5%red mud content is selected to prepare the autoclaved aerated concrete which meets the national standard by improving.The main conclusions are as follows:(1)Red mud chemical analysis and mineral composition analysis show that the content of Fe2O3 in the red mud is as high as 32.5%,the content of A1203,CaO,SiO2 is only 11-17%,the main mineral components are hematite,calcium nepheline,aluminum monohydrate Stone,etc.,so red mud has low gelation activity;alkaline tests show that the PH value of the suspension with red mud:water=1:10 is 12.4,so the red mud has higher alkalinity;Particle size analysis shows that the particle size of red mud is mainly distributed in lum-10um,so the particles of red mud are fine,and mixing red mud into cement slurry will increase the viscosity of the slurry;the gelation activity test shows that the activity index of red mud is 0.672,which is lower than the activity index of the pulverized coal witch is 0.772(2)The experiment of using red mud to replace fly ash to prepare autoclaved aerated concrete shows that with the increase of red mud content from 0%to 45%,the fluidity of the slurry of aerated concrete decreases from 17.9cm to 10.9cm,the density of the products increases by about 11%,the strength decreases by 26.3%-34.5%,and the thermal conductivity increases by 30%.Further research shows that one of the reasons for this phenomenon is the poor gas generation of aluminum powder,and the pores tend to be lateral and connect with each other.On the other hand,the study of microstructure shows that the inherent reason for the decrease of strength of aerated concrete is that the content of tobermorite increases with the addition of red mud,and it is a large area intergrowth with less contact points,with poor crystallinity and weak cementation ability.(3)For the purpose of using as much red mud as possible,this paper improve the aerated concrete mixed with 22.5%red mud(of witch compressive strength is 4.0MPa,density is 629kg/m3,thermal conductivity is 0.1604 W/mK),the results show that adding 0.025%Superplasticizer or adjusting the water-material ratio to 0.675 can increase the fluidity of the slurry,witch makes the gas generation efficiency of aluminum powder adapt to the thickening speed of slurry,improves the pore structure,reduces the thermal conductivity,and there is no significant negative impact on the strength of the product.Based on the above test,the improvement method for adjusting the water-to-material ratio is selected.The main performance indexes of the improved autoclaved aerated concrete meet the performance requirements of the A3.5B06 autoclaved aerated concrete in national standard.