Study On Preparation Of Metakaolin-Natural Hydraulic Lime Cementitious Material And Modification Of Light Aggregate

As one of the unique types of cultural relics in the history of human development,the grotto temple sites has very significant historical,artistic and scientific worth.Nevertheless,during the preservation of many grotto temple sites,factors such as stress and human damage in nature have caused weathering,cracks,surface pollution,and improper restoration of the rock mass.Therefore,the protection of the grotto temple site is imminent,and the research on the appropriate protection of gelling materials has become the key.In this paper,the failure mechanism of Leshan Giant Buddha traditional repairing materials were studied.In order to ensure the structural uniformity of the repair materials,metakaolin(MK)and natural hydraulic lime(NHL)were selected as raw materials to prepare MK-NHL cementitious material.On this basis,in order to ensure the overall compatibility of the light aggregate modified MK-NHL cementitious material as the fracture grouting material,coal-based kaolin and natural hydraulic lime were used as raw materials to prepare the ceramsite light aggregate.The effects of homemade ceramsite light aggregate and clay ceramsite light aggregate on the properties of MK-NHL cementitious materials were studied.Use modern testing techniques and methods to study material properties,phase composition and microstructure.The properties,phase composition and microstructure of the materials were studied by modern testing methods.The main conclusions are as follows:(1)The main reasons for the failure of the hair curls of Leshan Giant Buddha's repair materials are water seepage,acid rain,CO2 concentration and the uniformity of the repair material itself.(2)In the MK-NHL cementing material,with the increase of the content of metakaolin,it helps to promote the hydration reaction rate of the cementing material and improve the overall performance of the material.When the content of metakaolin is 50 wt%in the cementitious material,the flexural and compressive strength of the sample after 28 days of curing reaches the maximum,which are 2.43 MPa and 5.98 MPa.The increase of metakaolin content promoted the hydration reaction of Ca(OH)2,suppressed its carbonization reaction,and slowed down the hydration reaction of dicalcium silicate.The content of hydrated calcium silicate in the gelled material increased with the increase of the amount of metakaolin.The morphology of hydrated calcium silicate changes from needle-like to network-like and continuously extends,making the structure inside the material uniform and dense.(3)Using coal-based kaolin and natural hydraulic lime as raw materials,ceramsite light aggregates meeting the requirements of high-strength light aggregates in the chinese standard were successfully prepared.The content of coal-based kaolin in the experimental formula is 80 wt%,and the content of natural hydraulic lime is 20 wt%.The calcination system is kept at 1100? for 20 minutes.The particle size range of the prepared ceramsite is 4-5 mm,and the bulk density is 1070 kg/m3,water absorption rate is 12.4%,cylinder pressure strength is 18 MPa,which meets the strength requirements of the national standard density level of 1100.(4)The self-made ceramsite and clay ceramsite were used to prepare ceramsite light aggregate modified MK-NHL cementing materials.When MK-NHL cementitious material is added with ceramsite aggregate,it can increase the fluidity of the cementitious material slurry and reduce the shrinkage and water absorption of the cementitious material.The homemade ceramsite can obviously improve the compressive strength of MK-NHL cementitious material,while the addition of clay ceramsite will reduce the compressive strength of the cementitious material.The introduction of ceramsite lightweight aggregates in cementitious materials can improve their resistance to sulfate attack.Among them,the self-made ceramsite light aggregate modified gelling material has better anti-sulfate corrosion resistance than the clay ceramsite light aggregate modified gelling material.Comparing the microstructures of the two ceramsite modified cementitious materials in the interface transition zone,the bonding of the homemade ceramsite and the slurry material is relatively close,while the interface has a gap between the clay ceramsite and the slurry material.