Preparation And Key Properties Of Lightweight Insulated High Ductility Cementitious Composites

Foamed concrete has the advantages of light weight,fireproofing,heat preservation and sound insulation performance,but there are also problems that need to be solved urgently in engineering applications.When applied to the fields of external wall internal insulation and exterior insulation,the material is susceptible to cracking due to the additional tensile stress caused by the surrounding structural component during drying shrinkage because of its poor ductility.Moreover,due to the low compressive strength and poor crack resistance,the breakage rate of the prefabricated thermal insulation board is high.In order to solve the problems of low compressive strength,poor ductility and poor crack resistance of foamed concrete to meet the needs of different insulation wall applications,Lightweight Insulated High Ductility Cementitious Composites(LI-HDCC)were prepared by utilizing the advantages of HDCC materials combined with the preparation principle of foamed concrete.Firstly,A11(dry density is not more than 1100kg/m~3)LI-HDCC was prepared by three processes of hydrogen peroxide foaming,air entraining agent foaming and plant foaming agent foaming,and the effects of foaming agent dosage,water-binder ratio and fiber content on the key properties were studied.The results show that the air entraining agent foaming is the best process for preparing A11 LI-HDCC,and the LI-HDCC with dry density of 903kg/m~3～1253kg/m~3 and compressive strength of 20.73MPa～37.83MPa is prepared.As the density increases,the water absorption rate gradually decreases and the thermal conductivity increases.A11 LI-HDCC is prepared with a mixing ratio of 0.23Y0.22W2F,the physical performance of which is about dry density 1108kg/m~3,water absorption 2.3% and thermal conductivity 0.19W/(m·K),the mechanical properties of which is about compressive strength 32.33MPa,flexural strength 7.64MPa and the ultimate tensile strain 0.60%.After experiencing 300 freeze-thaw cycles,A11 LI-HDCC has a mass and compressive strength loss rate of 3.0% and 20.4%,indicating that LI-HDCC has better antifreeze performance.The drying shrinkage strain at the 90d age is 1153με.Secondly,based on the synergistic effect of compressive strength and dry density,plant foaming agent foaming was preferred for preparing LI-HDCC with dry density of430kg/m~3～650kg/m~3 and compressive strength of 2.82MPa～6.21MPa.The effects of silica fume content,sand-binder ratio,water-binder ratio,curing regime,PVA fiber content and dry density on the key properties of LI-HDCC were studied,and the pore structure change and distribution of LI-HDCC were analyzed with the X-CT technology.The results indicate that the compressive strength of LI-HDCC increases first and then decreases with the increase of silica fume content,which is the highest with the silica fume content of 7%because of the narrowest pore size distribution range and the more concentrated keyhole distribution in LI-HDCC.Steam curing at 60℃ for 7 days is more conducive to the development of compressive strength of LI-HDCC.At the same time,the compressive strength of LI-HDCC can also be improved by increasing the fiber content to some extent.It is preferred to prepare 630kg/m~3 LI-HDCC with a compressive strength of 5.82 MPa,the ultimate tensile strain of 0.90%,a thermal conductivity of 0.10W/(m·K),a shrinkage strain of about 1781μεat 90 days,and an early crack resistance rating of I.Finally,Image J software was used to process the X-CT image to obtain the parameters such as pore size distribution,average aperture and pore roundness of LI-HDCC,and the relationship between physical and mechanical properties and pore characteristics of A11 and A07(dry density is not more than 700kg/m~3)LI-HDCC was investigated.The results show that the compressive strength of LI-HDCC decreases linearly,the thermal conductivity decreases nonlinearly,and the water absorption increases with the increase of porosity and average aperture.At the same time,the relationship between compressive strength,thermal conductivity,water absorption and porosity,average aperture is obtained.If the proportion of pores with a pore diameter of less than 0.4 mm and a roundness of 0.8-1 is larger in LI-HDCC,the water absorption of LI-HDCC is lower and the compressive strength is higher.The relationship between LI-HDCC compressive strength,thermal conductivity,water absorption and the proportion of aperture and roundness in each interval is obtained.