Preparation And Performances Of Light-weight Autoclaved Aerated Concrete With Ceramic Residue Powder

Autoclaved aerated concrete,a kind of porous heat preservation silicate material with light weight,is widely used in industrial and civil buildings.However,the performances can not meet the new requirements of building energy efficiency standards due to the high bulk density(?500kg/m3)and high thermal conductivity(?0.14W/(m?K)).Therefore,it is urgent to develop new building materials with low density,high strength and heat-insulating performances.On the other hand,ceramic wastes produced in the production process of building ceramics occupy a great amount of land and cause serious environmental pollution and resource waste.It is environmentally and economically to prepare light-weight autoclaved aerated concrete using ceramic wastes.In this paper,the light-weight autoclaved aerated concrete was fabricated using ceramic wastes.On the base of series of experiments and analysis,the preparation method and influence factors of multiaperture silicate material were studied,the function and influence of each composition was investigated,the suitable mix proportion of raw material was identified,and the mechanical strength was enhanced by adding fibers.The influence of steam pressure system on the autoclaved aerated concrete was discussed.And the using performances of autoclaved aerated concrete were also explored and evaluated.The results show that the mechanical and thermal insulation can be improved by good pore structure.Dry density can be reduced by increasing aluminum powder dosage.But too much aluminum powder will result in bubbling and collapse mode.Matching among fluidity of slurries,thickening rate and gas velocity of aluminum powder paste is beneficial for forming of good pore structures.A dequate addition of Na2CO3 is beneficial for forming good pore structures due to the increased alkalinity of slurries and concentrated gas caused by hydrolyzed OH-.Besides,OH-can destroy chemical bond of Si-O and Al-O andform free unsaturated bond,which are easily react with Ca(OH)2,to form hydrated calcium silicate and hydrated calcium sulphoaluminate,thus significantly improving the strength of samples.In the experimental conditions,the addition amount of Na2CO3 is conformed as 8‰.Diffierent raw materials play different roles during the process of matrix formation.Si O2 derived from ceramic waste powders react with Ca O via hydrothermal reaction to form tobermorite hydrates(mainly CSH(I)gel,hydrogarnet and tobermorite).The combination of tobermorite hydrates and unreacted particles constitutes the structural strength of aerated concrete.It is shown that the optimized formulation for B03 is that the mass ratio of ceramic waste residue,lime,cement,gypsum is 70?18?9?3,and the ratio of starting materials to water is 0.80.The addition of 4% autoclaved aerated concrete waste fine powders as seed crystal,can induce the growth of tobermorite and make the pore wall structure more compact,thus improving the strength and thermal insulation performance of the products.The strength of products was usually limited by the porosity(above 86%)of light-weight autoclaved aerated concrete.Carbon fiber,basalt fiber and glass fiber were taken as reinforcing agents and compared in this paper.The results show that the compressive strength of products has no obvious change with the addition of fiber,but flexural strength is obviously improved.Among these fibers,the basalt fiber exhibits the best reinforcing effect.The flexural strength i ncreases from 0.49 MPa to 0.74 MPa,and the ratio of flexural to compressive strength reaches up to 0.4 3 by adding 2‰ of basalt fiber with the length of 6 mm,thus,the application effect is effectively improved.Autoclave curing is the necessary condition for hydrothermal synthesis,and the structure and performance of products are determined by steam pressure parameters such as temperature,pressure and time.Generally,forming temperature of tobermorite is 174.5 ? under the condition of 0.88 MPa.At a lower temperature/pressure,little tobermorite is formed and the crystallization is not complete,leading to a poor product performance.More Si O2 can be dissolved with autoclave time extending and autoclave pressure increasing,thus promoting the formation of tobermorite and improving the comprehensive perform ance.Experiments show that high performance of B03 autoclaved aerated concrete can be prepared at the temperature of 188? for 6 h under the pressure of 1.2MPa.For B03 products(bulk density?325kg/m3),the compressive strength and thermal conductivity are 1.82 MPa,0.064W/(m?K)respectively,which is superior to that of the national standard of GB11968-2006.The water absorption and natural carbonation experiments show that the compressive strength decreases sharply with the increase of water content,when the water contentis less than 10%.The compressive strength decreases lowly with the increase of water content,when the water content is in the range of 10%~30%.The compressive strength tends to stabilize,when the water content is higher than 30%.The thermal conductivity increases sharply with the increase of water content,when the water contentis less than 15%.The thermal conductivity increases slowly with the increase of water content,when the water content is higher than 15%.After natural carbonation for 18 months,the compressive strength of products slightly increases at the first 6 months,and then decreases.The range of these compressive strength values are less than 0.1MPa,and all the compressive strengths are higher than 1.0MPa,still better than that of the national standard of GB11968-2006,showing excellent application performances.Environmental problems caused by ceramic wastes can be solved by producing light-weight autoclaved aerated concrete using ceramic waste powders,thus realizing their high value-added utilization,and providing heat-keeping building material with excellent performances for modern architecture.