| China is the world’s largest coal producer and consumer,and coal occupies an important position in the current energy consumption.In order to improve the level of clean and efficient utilization of coal resources,circulating fluidized bed(CFB)combustion as a clean combustion technology has been rapidly promoted and used in China,but it also brings a large number of coal-fired solid waste called CFB fly ash.In order to recycle CFB fly ash,this research uses CFB fly ash to replace pulverized coal furnace fly ash as siliceous material to prepare autoclaved aerated concrete(AAC).The foaming process was preliminarily optimized by orthogonal test with aluminum powder content,curing temperature,W/S ratio,CFB fly ash replacement rate and stirring time as factors.The effects of C/S ratio,steam curing temperature,steam curing time,CFB fly ash substitution rate and cement content on the physical properties of AAC were studied,the preparation process parameters were determined,and the formation law of ettringite in AAC was discussed.The physical properties of AAC were optimized by controlling the initial slurry expansion and adjusting the content of foam stabilizer and PCE,and the water absorption and frost resistance of the product were investigated.The main conclusions are as follows:Through orthogonal test,it was found that the change of W/S ratio and CFB fly ash replacement rate on the initial slurry expansion has obvious influence on the foaming height,so the foaming process parameters of AAC with CFB fly ash are preliminarily determined as follows:the initial slurry expansion is 198±2mm,the stirring time is 50min,the curing temperature is 40℃;the C/S ratio,steam curing temperature,steam curing time,CFB fly ash replacement rate and cement content have significant influence on the compressive strength of the sample,but the C/S ratio,steam curing temperature and steam curing time have little influence on the dry density.The optimal preparation parameters are determined as follows:the C/S ratio is 0.8,the steam temperature is 170℃,the steaming time is 8h,the CFB fly ash replacement rate is 40%,and the cement content is 20%.The autoclaved curing process can inhibit the formation of delayed ettringite.Only a small amount of delayed ettringite is formed when AAC is cured in air,while the amount of delayed ettringite can reach 4.46%under water curing condition.The initial slurry expansion,the content of foam stabilizer and PCE have significant effects on pore structure.The increase of initial slurry expansion and the decrease of the content of foam stabilizer and PCE are beneficial to the increase of the average pore diameter.When the appropriate amount of foam stabilizer is used in combination with PCE,the compressive strength of the sample can be increased and the bulk density can be reduced.Considering the physical properties of the samples,the optimal initial slurry expansion is 198±2mm,the optimal content of foam stabilizer and PCE are 3‰ and 1‰,respectively.Under these conditions,the bulk density of AAC is 498kg/m3,and the compressive strength is 3.5MPa.which met the requirements of the national standard "Autoclaved Aerated Concrete Blocks"(GB/T 11968-2006)for B05 grade superior quality products.The water absorption of AAC increases rapidly at first and then slowly.The increase of PCE content is helpful to decrease the water absorption of AAC.At the initial stage of water absorption,the water absorption decreased with the increase of the foam stabilizer content,and after 72 hours of water absorption,the water absorption rate increased significantly with the increase of the foam stabilizer content.The addition of PCE can effectively improve the frost resistance of AAC by increasing the initial strength of sample and improving the pore structure.Under the optimal process conditions optimized in Chapter 4,the mass loss and strength loss of the product are 1.6%and 15.64%respectively,which met the requirements of the frost resistance in "Autoclaved Aerated Concrete Blocks"(GB/T 1168-2020). |
PDF Full Text Request