Research On Key Technologies Of Preparation Of High Performance Foamed Concrete Materials

Foamed concrete is a kind of building thermal insulation material with the advantages of light weight,thermal insulation,fire prevention and sound insulation,which is widely used in engineering practice.In recent years,due to the improvement of building energy conservation requirements and the innovation of structural forms,higher requirements are put forward for the performance of foamed concrete.Under the condition of ensuring compressive strength,the preparation of foamed concrete with lower thermal conductivity has become one of the main problems restricting the application of foamed concrete.In this thesis,high performance foamed concrete was prepared by physical foaming method with fly ash,silica fume,polypropylene fiber and graphene oxide as reinforcement materials.The main research contents and results are as follows :(1)The effects of water-binder ratio,foamed content,fly ash content and polypropylene fiber content on dry density,thermal conductivity and compressive strength of foamed concrete were studied,and the mechanism of the above factors in foamed concrete was obtained.The results show that when the water-binder ratio is 0.6 and the foamed content is4 %,the foamed concrete slurry has appropriate fluidity and the proportion of cementitious materials,which ensures that the foamed concrete has high compressive strength and low thermal conductivity.When the content of fly ash is 25 % and the content of polypropylene fiber is 0.2 %,fly ash mainly plays the role of filling pores and promoting hydration reaction,polypropylene fiber mainly plays the role of skeleton and inhibiting cracks,which makes the pore structure of foamed concrete improved,the microstructure is more dense,and the cement hydration is more complete,which improves the compressive strength of foamed concrete and reduces the thermal conductivity.(2)On the basis of the above single factor test,the mix proportion was optimized by orthogonal test,and the influence of various factors on the performance of foamed concrete and the optimal mix proportion of foamed concrete were obtained.The results show that fly ash content and silica fume content are the main factors affecting the thermal conductivity and compressive strength of foamed concrete.The optimum mix proportion of high performance foamed concrete determined by comprehensive balance method is : water-binder ratio is 0.6,fly ash content is 30 %,silica fume content is 8 %,polypropylene fiber content is 0.1 %,the compressive strength of foamed concrete is 2.60 MPa,and the thermal conductivity is 0.113W/(m·K),which is high performance foamed concrete.(3)The effects of graphene oxide on hydration reaction,microstructure,mechanical properties and thermal insulation properties of foamed concrete were studied.The mechanism and dosage range of graphene oxide in foamed concrete were obtained.XRD,TG-DSC and isothermal calorimeter were used to determine the type,content and hydration reaction rate of graphene oxide foamed concrete.The test results show that graphene oxide has no significant effect on the hydration process of foamed concrete.The microstructure of graphene oxide foamed concrete was analyzed by SEM.The experimental results show that graphene oxide mainly plays a role of template and crack resistance in foamed concrete.When the content of graphene oxide is 0.02 %,the foamed concrete has high compressive strength and low thermal conductivity,and high performance graphene oxide foamed concrete can be obtained.(4)The stress-strain curves of foamed concrete and graphene oxide foamed concrete were studied,and the constitutive equation was obtained.The constitutive equations of foamed concrete and graphene oxide foamed concrete were obtained by fitting according to the failure mode and the variation law of stress-strain curve of the test block under axial compression.