Study On Preparation And Performance Of Basic Magnesium Sulfate Cement Composite Foamed Material

With the substantial increase in building energy consumption in recent years,China is comprehensively promoting building energy-saving projects.Foamed cement is a building material filled with a large number of closed pores.It has the characteristics of low density,heat insulation,sound insulation,and low elastic modulus.There is high energy consumption and a large amount of CO₂released during the preparation process of traditional silicate-based foamed cement materials.The raw materials of magnesium-based foamed cement are easily available and the energy consumption is low in the preparation process.Among them,the basic magnesium sulfate foamed cement（abbreviated as BMS foamed cement）is a new type of foamed cement whose pore walls are composed of a large number of interlaced needle-shaped crystals.It has the advantages of light weight,high strength,green,good corrosion resistance,etc.Therefore it has a good development prospect.The cost of magnesium oxide,the raw material of basic magnesium sulfate foamed cement,is higher than that of Portland foamed cement.The cost can be reduced by adding inexpensive mineral admixtures.In addition,foamed cement is brittle due to its porous structure,and it is easy to break during processing or actual use process.Fibers can be added to enhance its crack resistance.Therefore,this paper selected two mineral admixtures,fly ash（FA）and metakaolin（MK）,and mixed them to prepare BMS foamed cement.Furthermore,ceramic sand,polyvinyl alcohol fiber（PVA）and polypropylene fiber（PP）were added for related research.The main research contents are as follows:（1）Using active magnesium oxide,magnesium sulfate,citric acid as the main raw materials,and adding hydrogen peroxide,potassium iodide,calcium stearate to prepare BMS foamed cement with a density of450-1500 kg/m³.By changing the amount of foaming agent and activator,the density grade of BMS foamed cement can be effectively controlled.The foaming agent H₂O₂was added to the BMS foamed cement,and the influence of the amount of H₂O₂on the performance of the BMS foamed cement was investigated.The results showed that the dry density and compressive strength of the BMS foamed cement decreased with the increase of the amount of H₂O₂.When the amount of H₂O₂is 2.5%of magnesium oxide,the dry density of BMS foamed cement is 624.6 kg/m³,and the compressive strength of 28d is 1.68 times that of the B06 premium product.The activator KI was added to the BMS foamed cement to investigate the influence of the amount of KI on the performance of the BMS foamed cement.The results showed that the dry density and compressive strength of the BMS foamed cement decreased with the increase of the amount of KI.When the amount of KI is 8%,the dry density of BMS foamed cement is 473.5 kg/m³,and the compressive strength of 28d is 1.20 times that of the B05 superior product.（2）Using FA and MK as mineral admixtures,BMS foamed cements with density grades of B06～B08 and water absorption grades of W30～W40 were prepared to study the influence of different mineral admixtures on the properties of BMS foamed cement.Incorporating appropriate mineral admixtures can effectively improve the mechanical properties of BMS foamed cement.When the FA content is 40%,the 28d compressive strength of BMS foamed cement is2.06 times the strength of B06 superior product.When the MK content is20%,the 28d compressive strength of BMS foamed cement is 1.19 times the strength of B07 superior product.The reason for the difference in dry density and compressive strength of the BMS foamed cement prepared by doped FA and MK may be due to the difference in particle size and morphology of the two admixtures.（3）Adding ceramic sand,PVA fiber,and PP fiber to BMS foamed cement can significantly improve the compressive strength of foamed cement.With 1.5%ceramic sand and 1.5%PP,the 28d compressive strength of BMS foamed cement is increased by 24.3%.Incorporating PVA and PP fibers can enhance the crack resistance of foamed cement and improve the compressive strength of foamed cement.The reinforcing effect of PVA is better than that of PP.This is because the binding force between hydrophilic fibers and foamed cement is higher than that of hydrophobic fibers.Mixing 1.5%ceramic sand and 1.5%PVA into foamed cement can reduce the water absorption rate of foamed cement and increase the softening coefficient;adding PP fiber can reduce the water absorption rate of foamed cement,but cannot increase the softening coefficient.