Preparation And Properties Of Cement-based Porous Materials Based On SiO₂

Cement-based porous materials have many advantages,such as simple process,low cost,fire-resistance,and safety,making them great potential for using as high performance thermal insulation materials.Most of the existed processes prepared cement-based porous materials are introducing pore structure into cement matrix.Although the thermal insulation performance of the material is improved,the mechanical properties of the material are greatly weakened,which hinders its development and application in the field of building thermal insulation.Based on the current research status,this paper proposes to use silica sol and aerogel slurry as the pore forming agent to produce cement-based porous materials by building nanopore structure inside the cement-based material.The pore structure and basic properties of the materials were conducted in the study,and the main results are as follows:Silica sol can form a three-dimensional network structure of SiO₂ in cement paste,and strengthen by interacting with hydration products.After drying,micropores and nanopores can be obtained in the cement matrix.Eventually,the cement-based porous materials based on silica sol（S-CPM）were successfully obtained.Using silica sol as a pore-forming agent,the S-CPM with a cumulative pore volume of 0.124 cc/g¹.440 cc/g,a porosity of 24.5%⁷5.6%,and an average pore diameter of 22.6 nm³6.2 nm was obtained.Cement-based porous materials prepared by introducing aerogel slurry as a pore-forming agent（A-CPM）have a cumulative pore volume of 0.337 cc/g².010 cc/g,and a porosity of 42.8%⁷7.6%.The average pore diameter is 47.5 nm¹89.4 nm.By contrast,the pore size distribution of the cement-based porous material prepared based on the modified aerogel slurry（MA-CPM）is relatively concentrated,the cumulative pore volume of MA-CPM is 0.304 cc/g¹.738 cc/g,the porosity is 24.5%⁷5.6%,and the average pore diameter is 43.8 nm¹70.9 nm.The fresh S-CPM is a pseudoplastic fluid with a fluidity of 65 mm.With the increase of silica sol,the consistency coefficient of S-CPM decreases from 50.9 Pa to 2.5 Pa,the rheological property is improved.Increasing the amount of pore forming agent,the dry density of cement-based porous materials decreases from 1741 kg/m³ to 488 kg/m³,the 28-day compressive strength decreases from 51.0 MP to 0.5 MPa,and thermal conductivity decreases from 0.081W/（m·K）to 0.552 W/（m·K）.The increase of aerogel slurry reduces the fluidity of the fresh A-CPM from 90.5 mm to 69.6 mm,and the yield stress decreases from 28.0 Pa to 18.1 Pa.The dry density of A-CPM is 355 kg/m³¹251 kg/m³,28-day compressive strength is 0.9 MPa²4.1 MPa,thermal conductivity is 0.066 W/（m·K）⁰.353 W/（m·K）.MA-CPM prepared with modified aerogel slurry has a fluidity of 72.0 mm¹00.5 mm,a yield stress of 4.9 Pa¹7.2Pa,and a dry density of 390 kg/m³¹280 kg/m³,and 28-day compressive strength and thermal conductivity of MA-CPM are 1.0 MPa³3.2 MPa and 0.067 W/（m·K）⁰.337 W/（m·K）,respectively.Due to the formation of micropore and nanopore,the compressive strength of these two kinds of cement-based porous materials prepared in the study is higher than that of other cement-based porous materials,and the thermal conductivity is lower than that of other cement-based porous materials.Therefore,the contradiction between the good mechanical properties and the efficient thermal insulation performance of cement based porous materials is alleviated.