Study On The Preparation And Strength And Thermal Conductivity Of Ultra-light Cement-based Composite Thermal Insulation Material

Cement as cementing material,EPS particles,admixts,foams and modifiers,water is the main raw material,using the physical foaming process to prepare dry apparent density is not greater than 120kg/m~3 of ultra-light cement-based composite thermal insulation material(Referred to as UCIM)has good mechanical properties and thermal properties.The structure of UCIM is composed of EPS particles and foamed concrete matrix interpenetrating.The incorporation of EPS particles into the foamed concrete matrix can improve the stress distribution of UCIM under stress state,improve the mechanical properties,and ensure that UCIM has a good thermal performance.In view of this,the preparation,pore structure and properties of UCIM were systematically studied in this paper.Firstly,based on the comprehensive comparison of the foam stability,settling distance,bleeding rate and the compressive strength of the foamed concrete,the suitable foaming agent for this study was selected.Secondly,the strength of UCIM under different water content states was studied.It was found that the existing standard test method of building materials industry,i.e.the strength under absolutely dry condition,was convenient to represent the mechanical properties of materials.However,the measured strength test results of the specimens were too low to reflect the actual strength of the specimens in use.Therefore,this paper determined that the moisture content of the specimen should be controlled within the range of(30±5)%when testing the strength of UCIM.The effects of EPS particles content on the pore structure(pore size distribution and average pore size),mechanical properties and thermal properties of UCIM were studied when the dry apparent density of UCIM was constant at 120 kg/m~3.It is found that the appropriate dosage of EPS particles can significantly improve the compressive strength and tensile strength of UCIM,but at the same time,it will increase the thermal conductivity of UCIM.By controlling the volume ratio of EPS particles and foam concrete matrix,the mechanical properties and thermal properties of UCIM can be coordinated through the synergistic effect.With excellent thermal properties,the mechanical properties can meet the practical requirements,so as to realize the high performance of UCIM.It is also found that EPS particles with good gradation can optimize the stacking structure inside UCIM,thus improving the related properties of materials.Admixtures are very important for the preparation of UCIM with excellent properties.It was found that when the mineral powder and metakaolin were used as admixtives,the stratified segregation of UCIM slurry appeared to varying degrees,and the strength of the specimen was low.When silica fume was used as admixture,no stratification and segregation occurred in UCIM slurry.The appropriate silica fume content can make the pore size distribution of UCIM move towards the direction of smaller pore size,reduce the thermal conductivity and improve the mechanical properties.Due to the large aspect ratio and specific surface area of polypropylene fiber,the appropriate fiber content can improve the mechanical properties of UCIM,but the fiber content should not be too much,otherwise the mechanical properties of UCIM will decline.Further research shows that the average pore size of foamed concrete matrix increases first and then decreases when fiber is added into UCIM,and then the thermal conductivity increases first and then decreases,which makes UCIM have good thermal insulation performance.