| China is currently in a period of rapid social and economic development,and there are serious problems such as excessive consumption of resources and energy,huge solid waste reserves and difficulties in utilization,and increased ecological damage and degradation.At the same time,building energy consumption is increasing year by year,which makes environmental pollution and energy crisis intensify,and building energy saving becomes an urgent task.It is of great significance to research wall materials with high waste efficiency and light weight.Based on the open subject of State Key Laboratory of Solid Waste Resource Utilization and Energy-saving Building Materials(SWR-2020-007),this paper investigates the preparation of autoclaved aerated concrete(AAC)based on calcium silica solid waste: calcium carbide slag and granite stone powder as the main materials.The preparation technology and performance control method of autoclaved aerated ultralight concrete(AAC)were investigated.Firstly,we systematically studied the effects of calcium carbide slag,granite powder and multiple solid waste compounding on the slurry properties and physical and mechanical properties of AAC,and used SEM,XRD,FT-IR and other microscopic testing methods to reveal the effects of solid waste substitution on the hydration products of the product and to determine the ratio of the highly beneficial waste system.Through the synergistic study of slurry gas generation rate and thickening rate,we realized the stability control of the billet formation process.To study the influence of the autoclave temperature and time on the performance of the products and to determine the suitable autoclave system.On the basis of this study,the optimization and regulation of the billet formation process,pore size distribution and pore wall strength were carried out by means of additives and nano-reinforced materials,which provide a reference for the lightweight and high reinforcement of low-activity solid waste-based ultralight wall materials.The main work and research results of this paper are as follows:1.Effect of calcium and silicon solid waste on the performance of AACUsing siliceous solid waste granite powder to replace the Yellow River extra-fine sand,with the increase of the content,the amount of tobermorite in the product is significantly reduced,and the mechanical properties of the product are significantly reduced.When the maximum replacement amount is 60%,The mechanical strength of the product is 3.02 MPa,and the absolute dry density is 523kg/m3.The increase of the replacement amount of calcareous solid waste has a great influence on the stability of the slurry.With the increase of the replacement amount,the exothermic effect of quicklime hydration is weakened,the reaction rate of the slurry in the early stage is weakened,and the gas generation volume is reduced from 230 ml to 198 ml.The absolute dry density increases.The increase in the amount of substitution slowed down the pre-gassing rate of the slurry,the amount of slurry gassing decreased from 223 ml to 192 ml,and the absolute dry density of the product increased from 525 kg/m3 to 536 kg/m3.The increase in the amount of calcium material and the decrease in the amount of silica material increased the alkalinity of the slurry and increased the pre-gassing rate,and the increase in the amount of substitution of solid waste led to the decrease in the hydration products.2.Factors influencing the performance of calcium carbide slag-granite stone powder based AACThe fineness of the raw material directly affects its reaction activity and slurry stability.The granite powder has low activity,its fineness has less influence on the slurry outgassing rate and outgassing generation,but more influence on the slurry fluidity,when the specific surface area increases from 328m2/kg to 385m2/kg,its fluidity decreases from 270 mm to 235 mm.When the specific surface area increased from 282m2/kg to 368m2/kg,the reactivity increased,the exotherm increased,the pre-gassing rate of the slurry increased significantly,and the fluidity increased from 240 mm to 262 mm.372m2/kg and 356m2/kg were the preferred values for granite powder and calcium carbide slag fineness,respectively.When the water material ratio is 0.54~0.60,the slurry fluidity increases from 238 mm to 258 mm,and the slurry stability is better.When the water to material ratio is between 0.60~0.64,the slurry consistency is too small,and the gas generation has been completed within 40 min,and the gas generation speed is much larger than the thickening speed,and it slows down the thickening speed of the slurry.Therefore,the ratio of water to material is chosen as 0.60.The pouring temperature of the slurry determines the rate of hydration reaction of the material.The pouring temperature increases from 30℃ to 80℃,and the fluidity of the slurry decreases from 258 mm to 223 mm.When the pouring temperature is 30~40℃,the pre-expansion of the slurry is too slow.When the pouring temperature is higher than 60℃,the rate of gas generation of the slurry accelerates,and the volume expansion tends to level off after 35 min.Therefore,the pouring temperature is chosen to be 50~60℃.The doping amount of aluminum paste affects the rate of gas generation and the amount of gas generation of the slurry,when the doping amount is 0.12%~0.17%,the early gas generation rate increases,but the impact on the liquidity of the slurry is small.When the doping amount increased from 0.15% to 0.17%,the pre-reaction rate of the slurry was too fast,and the gas generation was completed in 35 min,and the phenomenon of bubbling and collapse appeared.In order to ensure the stability of the billet formation process,the doping amount of aluminum paste is 0.15%.Based on the above parameters,the strength reached the maximum value of 3.36 MPa and the absolute dry density of 529 kg/m3 when the autoclave temperature was 195℃ and the holding time was 8h.3.Calcium carbide slag-granite stone powder based AAC light weight and high reinforcement study Porosity and pore structure are the key factors to determine the capacity and strength of AAC.Polycarboxylic acid water reducing agent and HPMC were selected as admixtures for product porosity and pore structure optimization.On the premise of satisfying the flowability of casting requirements,the amount of water reducing agent and HPMC is changed to further improve the processability of the slurry,optimize the matching between the gas generation rate and thickening rate of the slurry,make the pore distribution more uniform and reduce the proportion of large pores in the product.The solid fraction outside the pores in AAC has the main contribution to the strength of the product.Enhancement modification of the pore wall was studied using nano-silica,and the strength of the products was significantly enhanced when the nano-silica doping amount was increased from 0.2% to 0.8%.Microscopic analysis showed that the incorporation of nano-silica significantly affected the formation of C-S-H gels with tobe mullite crystals. |
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