Preparation And Performance Study Of Nanoparticles Aerogel Cement-based Materials

As the public’s demand for residential comfort increases,leading to an increasing conflict between energy supply and demand,cement-based insulation materials have great potential as building insulation materials due to their simple process,low cost,safety,and fire resistance.However,when the thermal insulation performance and mechanical properties of cement-based insulation materials are optimized,their thermal insulation performance will directly depend on the thermal insulation performance of insulation aggregates,so it is necessary to use insulation aggregates with lower water absorption and thermal conductivity and better heat resistance to reduce energy consumption and improve the thermal insulation performance of buildings.Firstly,in this paper,the surface of hydrophobic SiO₂aerogel particles was modified by using silane coupling agent KH570,and the modified aerogel cementitious composite mortar was prepared by mixing SiO₂aerogel particles into cement mortar using equal volume replacement sand method.The effects of different volume admixtures of SiO₂aerogel on the dry density,compressive and flexural strength,thermal conductivity and pore structure of the cementitious composite mortar were investigated.It was found that the dry density of the cement mortar decreased linearly with the increase of the volume replacement ratio of modified SiO₂aerogel,while the flexural and compressive strengths and thermal conductivity of the cement mortar decreased with the increase of the porosity,and the pores gradually changed from gel pores to capillaries and macropores.The modification of silane coupling agent KH570 can improve the interfacial bond between SiO₂aerogel and cement mortar matrix,so that SiO₂aerogel can be better bonded with cement mortar.However,it was found during the test that when the doping amount of modified SiO₂aerogel particles increased,its dispersion in the cement mortar was not uniform,which affected the thermal insulation performance of the cement mortar,and when the doping amount of aerogel particles exceeded40%,the specimens were harder to be shaped and the cement mortar with lower thermal conductivity could not be prepared.Therefore,SiO₂aerogel dispersion paste with different volume doping was used to prepare SiO₂aerogel dispersion paste cement mortar,and the effects of different SiO₂aerogel dispersion paste doping on the dry density,flexural and compressive strength,thermal conductivity and pore structure of cement-based composite mortar were investigated.It was found that the compressive strength and thermal conductivity of the specimens decreased with the increase of SiO₂aerogel dispersion paste admixture,and the SiO₂aerogel dispersion paste could be uniformly dispersed in the cement mortar,but micro-cracks existed between it and the cement substrate,which increased the percentage of capillary pores and macropores in the cement mortar.Next,freeze-thaw cycle tests were conducted on modified SiO₂aerogel particle cementitious composite mortar and SiO₂aerogel dispersion paste cementitious composite mortar.The changes of compressive strength,dynamic elastic modulus,thermal conductivity and microscopic pore structure of the aerogel cement-based composite mortar during freeze-thaw cycles were studied,and the microscopic morphology of the cement-based composite mortar with different amounts of SiO₂aerogel admixture before and after freeze-thaw was characterized by electron scanning electron microscopy（SEM）.It was found that the strength loss and dynamic elastic modulus loss of cement mortar doped with SiO₂aerogel particles and dispersed paste were smaller than those of cement mortar without SiO₂aerogel,and multiple freeze-thaw cycles would lead to the destruction of the interfacial bond between SiO₂aerogel particles and cement mortar.Finally,the SiO₂-doped aerogel dispersion paste cement mortar was tested at different temperatures（200°C,400°C,600°C,800°C,and 1000°C）for high temperature resistance.The changes of compressive strength,thermal conductivity and mass loss rate of cement mortar after high temperature were investigated,and the deterioration mechanism of SiO₂aerogel cement mortar after high temperature was analyzed from microscopic point of view using low-field nuclear magnetic resonance（NMR）,X-ray diffractometer（XRD）and scanning electron microscope（SEM）tests.It was found that:when the heat treatment temperature was increased from 25℃to 400℃,the surface of the specimen changed slightly in color,the internal free water evaporated,the mass loss rate increased rapidly,the compressive strength and thermal conductivity decreased slightly,no new material was produced inside the specimen,the porosity increased slightly,and the gel pores gradually changed to capillary pores;When the heat treatment temperature was 600℃,the internal hydration products of the specimen decomposed,the mass loss rate continued to When the heat treatment temperature is 600℃,the internal hydration products of the specimen decompose,the mass loss rate continues to increase,the compressive strength and thermal conductivity decrease rapidly,the porosity increases,the gel pores disappear,the transition pores evolve into large pores,and the SiO₂aerogel begins to shrink in volume;Heat treatment temperature of 800℃,the specimen has a large number of internal calcium yellow feldspar generation,porosity continues to increase,the transition hole continues to large hole transformation,high temperature porcelain phenomenon;The mass loss rate was the largest at1000℃,the compressive strength and thermal conductivity continued to decrease,and cracks and spalling appeared on the surface of the specimen,but the specimen remained intact.