Investigation On Preparation,composition And Structure Of High Quality Calcium Silicate Magnesium Board

Calcium silicate board has the advantages of light weight,high strength,low thermal conductivity,fireproof,heat insulation and non-deformation,moistureproof,anticorrosive and mildew-proof,so it is a new type of wall material developed by our country.However,at present,the main product in the market is ordinary calcium silicate board,which usually has great fluctuation in quality and unstable performance.It is difficult to produce high-quality and high-density calcium silicate board.In this paper,graded quartz sand is used to improve the density and strength of calcium silicate board.Based on the research of calcium magnesium silicate cementitious material in our laboratory,magnesium is introduced into calcium silicate board to develop calcium magnesium silicate board.First,quartz sand is sieved in narrow particle size distribution to study the influence on the composition,pore structure and macro properties of calcium silicate board,which can expounds how quartz sand combine with calcium materials.Base on that,the quartz sand with appropriate particle size is selected for gradation,and then the effect of quartz sand gradation on the macroscopic properties of calcium silicate board is evaluated,and the method of preparing high quality calcium silicate plate quartz sand gradation is put forward.On the other hand,the effects of Mg²⁺on the composition,microstructure,microstructure and mechanical properties of calcium silicate board are explored,the formation process of magnesium-containing tobermorite under autoclaved condition is revealed,and the influence mechanism of Mg²⁺on the macro-mechanical properties of calcium silicate board is clarified,which lays a foundation for the application of magnesium-rich minerals in the field of calcium silicate board.The specific work is as follows:（1）Calcium silicate board was prepared by using narrow range quartz sand（40,45,100,200,325,800mesh）.The results show that the finer quartz sand,the faster the formation of hydrated calcium silicate and tobermorite.The hydrochloric acid dissolution method and BSE-IA method show that the reaction amount of 800 mesh quartz sand is 53.98wt%,while the reaction amount of 40 mesh quartz sand is only 4.7%autoclaved at 180℃for 10 h.The density of products prepared by fine quartz sand decreases.As the particle size of quartz sand becomes finer,the flexural strength of the products increases at first and then decreases.Too coarse and too fine quartz sand is not conducive to the improvement of strength.（2）Calcium silicate board are prepared with graded quartz sand.The results show that the content of quartz sand in the range of 100 mesh has a significant effect on the flexural strength of calcium silicate board.Through the gradation of coarser（about 100mesh）and finer particles（more than 200 mesh）,the pore distribution of the product can be optimized,the density of the product can be improved,and the strength of the product can be improved.The product with graded quartz sand 100mesh:200mesh:325mesh=4:4:2 has better pore distribution,higher density（1.62g/cm³）and 45%higher flexural strength（12.2MPa）than that with 325mesh quartz sand（8.4MPa）.（3）Calcium silicate magnesium board was prepared by adding magnesium-containing materials under different autoclaved condition.The results show that the formation of tobermorite from calcium silicate board product goes through the process which is as follows:high alkaline hydrated calcium silicate（Ca/Si>1.4）,low alkaline hydrated calcium silicate（Ca/Si between 1-1.4）to tobermorite.The existence of calcium hydroxide in the reaction products will hinder the formation of low alkaline hydrates and tobermorite.The solid solution of Mg²⁺in calcium silicate hydrate and tobermorite is beneficial to the formation of calcium silicate hydrate with low alkalinity,reduce its alkalinity,and transform to tobermullite.When autoclaved at 180℃for 10h,the maximum solid solution capacity can reach 2.45%.The solid solution of Mg²⁺changed the morphology of tobermorite,resulting in petal-like crystals in flaky tobermorite.According to the results of infrared spectrum（FTIR）and nano-indentation,the addition of magnesium increased the polymerization degree of hydrated calcium silicate,the content of UHD C-S-H phase and HD C-S-H in hydration products,and the micro-modulus and microhardness of hydration products.When a small amount of magnesium is added（the molar ratio Mg/（Ca+Mg）=5%）,the flexural strength of the product is increased from 8.4MPa to 11.02MPa.Through the addition of magnesium and the introduction of graded quartz sand,the density of calcium silicate plate can reach 1.63g/cm³ and the flexural strength can reach 14.7MPa.