Design and Application Basic Research on the Magnesium Oxychloride Cement Foam Concrete

Author:Zheng Wei Xin

Supervisor:zhou yuan xiao xue ying

Database:Doctor

Degree Year:2019

Download:51

Pages:147

Size:7098K

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Exploiting the magnesium resources of salt lakes has drawn much attention of the government as well as researchers and investors.The magnesium resource of Qinghai Qarham Salt Lake boasts high grade,huge reserve,low impurity content and easy exploitation.It is ideal raw material to manufacture MOC products.MOC is an air-hardening binding material made from magnesium chloride solution mixed with lightly-burnt magnesia powder.It is widely applied in many fields for such advantages as high density,high intensity,excellent anti-saline performance,quick solidification and easy curing.MOC foam concrete made from bischofites,a byproduct of salt lakes,Not only can a large amount of magnesium chloride be directly applied to building materials so as to achieve comprehensive utilization of resources,but also maximize economic value through nearby utilization of resources,so it is a feasible approach easy to promote in farming and stockbreeding areas.Especially in Qinghai area,developing the research and application of MOC foam concrete has many economic,environmental and social benefits.Therefore,this paper takes the design,manufacture and application of MOC foam concrete as the research target,conducts systematic research to the forming conditions,mix ratio,property improvement,etc.,and demonstrates the results through the application examples in alpine regions,providing theoretical guidance for the production and engineering application of MOC foam concrete in alpine regions.The main research contents and conclusions are as follows:1.The effect of fly ash + phosphoric acid + nano-silica on the water resistance of MOC was studied.The effects of different incorporation methods of nano-silica,phosphoric acid,fly ash and other admixtures on the setting time,hydration and heat release process,compressive strength,water resistance,thermal stability,hydration products and microstructure of MOC materials were studied.It was found that incorporation of industrial grade fly ash or nano-silica respectively could not improve the softening coefficiency of MOC,and incorporation of phosphoric acid + fly ash could significantly improve the softening coefficiency of MOC,while addition of nano-silica on the basis of incorporation of phosphoric acid + fly ash further improved the water resistance of MOC matrix.At the same time,two incorporation methods of fly ash + phosphoric acid + nano-silica and fly ash + phosphoric acid in MOC foamed concrete system were studied.The results show that the two incorporation methods can improve the water resistance of MOC foam concrete,the strength retention coefficient of 28 d can reach at least 75%,which can meet the requirements of MOC foam concrete in basic applications.2.This paper discusses the influence factors of foaming method on MOC foamed concrete,and analyzes the influence of different foaming agents on the pore structure,mechanical properties,unit weight,dissolution mechanism and formation mechanism of MOC foamed concrete.The results showed that the MOC concrete obtained by chemical foaming method presented the phenomenon of uneven pores size in the upper and lower layers,while the MOC concrete obtained by physical foaming method had more uniform pores,which was more suitable for the application of MOC materials.MOC foamed concrete obtained by animal protein foaming agent in physical foaming agent,between Mechanical properties or structural stability and water resistance(density of the material matrix),all performed well.At the same time,combinating with physical foaming agent and different incorporation methods of foam,the relationships among unit weight,compressive strength and thermal conductivity of MOC foam concrete with caustic dolomite powder were studied.The results showed that MOC foam concrete products have similar properties and stable physical properties,when the proportions of caustic dolomite powder and light burnt magnesia powder were 3:1,4:1 and 2:1.When the raw material is 4:1,both the quality and economics of MOC foam concrete can be guaranteed.3.Through the experiment of the physical properties of bischofite in water,the difference between the mass concentration and baume degree of solution was obtained.Based on the constant difference,the traditional calculation method is improved,and a simplified mathematic model about MOC bittern dosage is established.On this basis,a calculation model of water-cement ratio of MOC foamed concrete was established.According to the model,the free water consumption and regulated water consumption of MOC foamed concrete were calculated.Combined with the test,the optimal water-cement ratio and the optimal water-cement ratio after adding additives were determined.4.Based on the above research,The MOC foamed concrete with different strength grades was taken as an example for calculation.The results show that the design values were consistent with the experimental results.At the same time,the results were applied to the production and application of large volume MOC foamed concrete.The cracking and pulverization of mass MOC foam concrete were analyzed,The results show that the cracking and pulverization were caused by the large temperature gradient inside the MOC foamed concrete.By changing the active parameters of magnesia and restraining the impact of external environment temperature on the interior of foamed concrete,the yield of mass MOC foamed concrete was improved.