Research On Preparation And Performance Of Thermal Insulation Composite Materials Based On SiO₂ Aerogel

With the continuous improvement of China’s requirements for building energy efficiency and building fire protection,traditional thermal insulation materials are difficult to meet the application requirements.SiO₂aerogel has the characteristics of high porosity,high specific surface area,low density,low thermal conductivity and superior fire resistance.The thermal insulation and fire resistance of the inorganic cementing materials can be significantly improved after the addition of SiO₂aerogel,and it is safe and fireproof,which exhibits great potential in the field of building thermal insulation materials.However,the poor compatibility of SiO₂aerogel with the inorganic cementing materials hinders its application in the field of building energy efficiency.Based on these,in this dissertation,the thermal insulation composite materials AIP were successfully prepared by using SiO₂aerogels,inorganic cementing materials and expanded polystyrene（EPS）particles.Among them,the inorganic cementing materials adopted the gypsum-based composite cementing system with great thermal insulation performance,the SiO₂aerogel slurries were made by dispersing SiO₂aerogels into aqueous solutions after surface modification,and the insulation aggregates were expanded polystyrene particles.The purpose was to minimize the thermal conductivity,besides,improved the mechanical properties and the grade of combustion properties.At the same time,the hydration products and reaction mechanism of inorganic cementing materials,the performance changes and interface bonding properties of SiO₂aerogel-inorganic cementing materials,the performance changes of AIP,as well as building energy consumption were analyzed.The specific contents include:（1）Taking gypsum as the main cementing material,gypsum was modified by adding inorganic admixtures.The cement-gypsum binary cementing system and the gypsum-cement-fly ash-lime quaternary cementing system were constructed,respectively.The effects of the addition amount of inorganic admixtures on various properties of the cementing systems were analyzed.The results sho wed that the mechanical property and water resistance of the gypsum can be improved by adding a certain proportion of inorganic admixtures,but both of which will be reduced when the addition amount of inorganic admixtures was excessive.Additionally,the mechanical properties and water resistance of the quaternary cementing system were better than those of the pure gypsum and the binary cementing system.The performances of the inorganic cementing materials were further improved by adding water reducing agent.When the amount of water reducing agent added was 0.6 wt%,the properties of the quaternary cementing system were higher than other samples.The compressive strength,the flexural strength,and the softening coefficient for 28days were 47.51 MPa,10.43 MPa and 0.83,respectively.（2）The surface modifications of SiO₂ aerogel powders were carried out by using surfactants,and the powders were dispersed into aqueous solutions to prepare the SiO₂aerogel slurries.The SiO₂aerogel-inorganic cementing materials with excellent thermal insulation and mechanical properties were prepared by combining the SiO₂aerogel slurries with inorganic cementing materials.The surface modification mechanisms of different surfactants on the SiO₂aerogel were analyzed,and the influences of different types and amounts of SiO₂aerogel slurries on the properties of inorganic cementing materials were also studied.The results showed that the SiO₂aerogel slurry（A4）modified by cationic surfactant/nonionic surfactant/inorganic nano-materials（CNSI）had great compatibility with inorganic cementing materials.When the addition amount of SiO₂aerogel was 3 wt%,the dry density of the sample C4 was 1136.4 kg/m³,the thermal conductivity was 0.1889 W/（m·K）,the compressive strength was 17.16 MPa,and the flexural strength was 4.34 MPa.When the addition amount of SiO₂aerogel in inorganic cementing materials exceeded 10 wt%,the variation amplitude of each performance decreased.（3）The thermal insulation composite materials AIP was prepared by adding EPS insulation aggregates into the composites of SiO₂aerogel and the inorganic cementing materials.The influences of different factors on the performances of AIP were discussed through orthogonal tests.The results mainfested that the main factors affecting the performances of AIP were the addition amounts of EPS particles and SiO₂aerogel.Through performance optimization,the prepared AIP exhibited great thermal insulation,mechanical,and fire resistance properties.The density of AIP was 147 kg/m³,the compressive strength was 0.23 MPa,the flexural strength was 0.21 MPa,the thermal conductivity was 0.0411W/（m·K）,and the combustion performance was A2 grade.（4）The AIP was applied to building engineering in the form of the compound insulation system of AIP external formwork.Taking a residential building in Taiyuan as the model,the energy consumption of the residential building without external wall insulation measures and with EPS system,TEPS system and AIP system for external wall insulation is calculated by using the Energy Plus software.The results evidenced that the energy consumption of the residential building mainly came from the heating energy consumption.Compared with the absence of external wall insulation measures,the energy consumption of the residential building was significantly reduced after external wall insulation measures were taken.The heating energy consumption,cooling energy consumption and total energy consumption of the residential building were the lowest when the external wall insulation adopted AIP system.