| As one of the by-products of coal combustion,fly ash is a light,porous loose body whose main mineral components are mullite and quartz.In recent years,the large amount of fly ash produced by burning coal in our country has caused problems such as its large storage and occupation of land and environmental pollution due to its low comprehensive utilization rate.Huainan City is located in the north-central part of Anhui province and has extremely rich coal resources.Thermal power generation is the main coal consumption structure.The coal power industry in Huainan is extremely developed,and the utilization and treatment of fly ash in Huainan area is particularly important.Based on this,the article first discusses the basic mechanical properties of fly ash,focusing on the liquefaction characteristics and changing laws of fly ash under vibration load;then use direct shear tester,universal testing machine and carbonization box to study the static mechanical properties of the cured fly ash samples with cement curing agent,combined with XRD and SEM experiments,the microscopic mechanism of cement cured fly ash was further revealed.The relevant research results are as follows:(1)The chemical composition,particle gradation composition and liquid-plastic limit of the fly ash used in the test were analyzed.The test results show that the fly ash has a low calcium oxide content of only 2.337%,which is a low-calcium fly ash;its particles are uniform but poorly graded,and its particle size composition is similar to sand;its liquid and plastic limits are large but the plasticity index is small,indicating the porous properties of fly ash from another aspect.(2)The liquefaction characteristics of saturated fly ash stratum under vibration load were simulated through indoor model tests based on a small shaking table,and the liquefaction deformation law was analyzed.The test results show that under the action of vibration load,the saturated fly ash formation has a macroscopic "sand blasting water" liquefaction phenomenon,and the formation has subsided significantly after the test;the pore water pressure of the saturated fly ash formation gradually increases with the increase of the burial depth.The pore water pressure at the initial burial depth of 80mm,160mm and 240mm shows a linear trend to rise sharply before reaching the extreme ’values of 1.2kPa,1.6kPa and 2.0kPa,and then it increases slowly and stabilizes after reaching the peak value of 1.4kPa,2.0kPa and 2.8kPa;the pore pressure ratio of saturated fly ash formation gradually decreases with the increase of buried depth,that is,the pore pressure ratio at the buried depth of 80mm is the largest,and it is easier to liquefy compared with the buried depths of 160mm and 240mm,indicating that the liquefaction trend gradually diffuses from the upper layer to the middle and lower layers,and the pore pressure ratios at different buried depths finally reached 1.0 or higher,indicating that the saturated fly ash formation has been completely liquefied at this time.(3)The solidified fly ash samples with cement content of 12%,18%,24%and 30%were subjected to direct shear,unconfined compression,split tensile and carbonization tests,and explored the static mechanical properties of the solidified fly ash sample,the failure morphology and strength change law of the sample under different test conditions were analyzed.The test results show that the shear strength of the solidified fly ash samples improve with the increase of cement content;the unconfined compressive stress-strain curve of the solidified fly ash sample has good plastic properties at 12%and 18%cement content,while the compressive stress-strain curve gradually shows brittle failure characteristics with the increase of curing age at 24%and 30%cement content.After carbonization treatment,the compressive stress-strain curves of samples with 12%,18%and 24%cement content shows a clear yielding stage after undergoing the elastic phase compared with the uncarbonized samples;the split tensile stress-strain of the carbonized and uncarbonized cured fly ash specimens all drop immediately after reaching the peak value,which is a typical brittle failure;the unconfined compressive and split tensile strength of the solidified fly ash sample will increase with the addition of cement content and the extension of the curing age.The maximum compressive and tensile strengths are 14.27MPa and 1.28MPa.Under the same cement content and curing age,the compressive and tensile strengths of the carbonized samples are lower than those of the untreated samples.(4)The solidified fly ash samples with cement content of 12%,18%,24%,30%were subjected to XRD and SEM tests under 7d,30d,60d,90d curing age conditions and carbonization treatment conditions,the microstructure characteristics of solidified fly ash samples were explored,and the solidification reaction mechanism was analyzed.XRD results show that the cement content,curing age and carbonization treatment have a significant impact on the amount of hydration products produced in the solidified fly ash sample,but the type of hydration products has little relationship with it;SEM results show that with the deepening of the chemical reaction of solidified fly ash samples,the gel hydration product generated by the reaction effectively wraps and fills the fly ash float beads and their pores,to strengthen the overall connection of the sample,thereby increasing its strength,which explains the microscopic mechanism of cement-solidified fly ash.A large number of pores generated on the surface of the sample after carbonization destroy the integrity of its original structural system,resulting in a decrease in the strength of the sample.Figure 50 Table 11 Reference 81... |
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