Study On Preparation Technology And Mechanism Of Red Mud Magnesium Cement Building Materials

In order to realize resource utilization of red mud and develop green building materials,in this paper,Bayer red mud was used as the main filling material and combined with magnesium oxychloride cement（MOC）system as well as magnesium oxysulfate cement（MOS）system to prepare red mud magnesium cement composite materials.The effect of red mud on the properties of magnesium cement and the consolidation effect of magnesium cement on soluble alkali in red mud were studied,and the interaction mechanism between red mud and magnesium cement was analyzed.Red mud magnesium cement building materials were prepared by experimental study.The study reached the following conclusions:（1）The effects of red mud on the properties of MOC and MOS were studied with the curing age of 200 days as the time scale.The results showed that adding 50%red mud had little effect on the strength of MOC,but significantly improved the water resistance of MOC at the early stage（28days）.The addition of red mud significantly improved the compressive strength and water resistance of MOS during the whole study period.This was because the addition of red mud played a physical filling role in the pores of magnesium cement,and an amorphous gel was formed between red mud and magnesium cement,which made the matrix more compact and improved the mechanical properties and water resistance of magnesium cement.Meanwhile,magnesium cement solidifies soluble alkali in the red mud and inhibit the frosting phenomenon.（2）Magnesium oxychloride cement building materials with high red mud ratio were prepared.Chromium slag was added as auxiliary supporting aggregate,and the effects of red mud dosage and Mg O/Mg Cl₂molar ratio on the performance of the samples were investigated.The modifiers with good MOC improvement effect were selected and the optimal ratio of modifier was obtained by adding the modifier separately and adding the modifiers with orthogonal method.On this basis,fly ash was added to further improve material properties.At the same time,considering the environmental impact and production cost,the optimal raw material ratio is determined as follows:the mass ratio of chromium slag to red mud is 1:1,the magnesium content is20%,the molar ratio of Mg O/Mg Cl₂is 5,the compound modifiers areⅠ1%,Ⅱ1%,Ⅲ0.5%,the fly ash content is 20%.The red mud MOC building materials with 7.37MPa flexural strength,35.7MPa compressive strength and0.91 softening coefficient have been prepared.（3）Red mud magnesium oxysulfate cement foamed concrete was prepared.The foaming properties of different foaming agents were tested.The results showed that foaming agent c had the best foam stability and consistency with slurry.Water content,foam content and magnesium content had obvious effects on the pore structure and properties of foamed concrete.Using iron tailings as reinforcement aggregate.The optimum mix ratio of raw materials is determined as follows:the mass ratio of red mud to iron tailings is1:1,the magnesium content is 33%,the water content is 44%,the volume of foam（L）/the mass of dry powder（kg）is 1.67.Foamed concrete with dry density of 0.8g/cm³and compressive strength of 2.4 MPa was prepared.The foamed concrete produced is light weight and high strength and has a good application prospect.