循环流化床飞灰合成地聚物过程中的应用基础研究
发布时间：2019-01-08 15:24
【摘要】：循环流化床飞灰中钙、硫组分含量较高,导致其难以在传统水泥行业实现规模化利用。从化学组成和矿物组成上来看,循环流化床飞灰在地聚物合成领域具有广阔的应用前景,然而灰中大量存在的CaCO_3、CaSO_4和CaO使其地聚反应过程的复杂程度远高于偏高岭土基或粉煤灰基地聚反应体系。论文通过在偏高岭土中分别添加CaCO_3,CaSO_4和Ca(OH)_2来对循环流化床飞灰进行模拟。基于SiO_2-Al2O_3-CaO-Na2O体系,首先研究了 Na2O/Al2O_3变化对样品凝结时间和抗压强度的影响,实验发现,体系中Na2O/Al2O_3增加有利于偏高岭土中活性硅、铝组分的溶出,缩短样品凝结时间。当养护至90天后,Na2O/Al2O_3为0.7-1.1的样品中出现八面沸石晶体,而Na2O/Al2O_3为0.6-0.8的样品中出现A型沸石晶体,这些晶体的生成有利于提升样品的后期强度。然而,当Na2O/Al2O_3高于1.0,反应体系中因水化石榴石的生成导致地聚反应历程改变,进而对样品抗压强度产生负效应。当碱激发剂中含有NaCl时,体系中有氯铝酸盐生成,样品抗压强度降低,因此,为获得性能优异的地质聚合物,碱激发剂中需保证一定浓度的OH-离子存在。SiO_2/Al2O_3对样品凝结时间的影响程度高于Na2O/Al2O_3。在反应早期,低SiO_2/Al2O_3(SiO_2/Al2O_32.5)样品中有沸石晶体的生成,这类晶体能够提升样品早期强度;而SiO_2/Al2O_3增加会促使样品中生成的地聚物类型由Na-PS型向Na-PSS型过渡,后者更有利于样品后期强度的提高。值得注意的是,样品中SiO_2/Al2O_3不能过高,否则样品凝结过快,会导致浆体搅拌不均匀,气泡逸出困难,使得样品后期抗压强度发展受到影响。利用熔融玻璃粉部分取代(60%)水玻璃,能够在保持样品整体SiO_2/Al2O_3不变的基础上,延长样品凝结时间,提升高SiO_2/Al2O_3样品机械强度。通过分别研究CaCO_3,CaSO_4和Ca(OH)_2在碱激发偏高岭土体系中的反应历程发现:CaCO_3对反应起到催化作用,加速样品凝结,在养护后期主要起到物理填充作用,对强度影响不大;CaSO_4主要参与钙矾石的形成,钙矾石可以提升样品的早期强度,但在养护后期(28天),钙矾石的生成会导致样品出现裂纹,影响后期强度发展;添加Ca(OH)_2的样品中同时存在火山灰反应和地聚反应。
[Abstract]:The high content of calcium and sulfur in CFB fly ash makes it difficult to realize large-scale utilization in traditional cement industry. In terms of chemical composition and mineral composition, CFB fly ash has a broad application prospect in the field of geopolymer synthesis. However, there is a large number of CaCO_3, in the ash. CaSO_4 and CaO make the process of geopolymerization more complex than that of metakaolin or fly ash base polymerization system. In this paper, CFB fly ash was simulated by adding CaCO_3,CaSO_4 and Ca (OH) _ 2 into metakaolin. Based on the SiO_2-Al2O_3-CaO-Na2O system, the effect of Na2O/Al2O_3 change on the setting time and compressive strength of the samples was studied. It was found that the increase of Na2O/Al2O_3 in the system was beneficial to active silicon in metakaolin. The dissolution of the aluminum component shortens the setting time of the sample. After curing for 90 days, octahedral zeolites were found in samples with Na2O/Al2O_3 of 0.7-1.1, while those with Na2O/Al2O_3 of 0.6-0.8 had A-type crystals. The formation of these crystals is beneficial to the later strength of the sample. However, when the Na2O/Al2O_3 is higher than 1.0, the formation of hydrated garnet in the reaction system results in the change of geopolymerization process, which has a negative effect on the compressive strength of the sample. When the alkali activator contains NaCl, chloraluminate is formed in the system, and the compressive strength of the sample decreases. Therefore, in order to obtain the geopolymer with excellent properties, It is necessary to ensure the existence of certain concentration of OH- ion in alkali activator. The influence of SiO_2/Al2O_3 on the setting time of sample is higher than that of Na2O/Al2O_3.. In the early stage of the reaction, zeolite crystals were formed in the low SiO_2/Al2O_3 (SiO_2/Al2O_32.5) samples, which could enhance the early strength of the samples. The increase of SiO_2/Al2O_3 can promote the transition of polymer type from Na-PS type to Na-PSS type, the latter is more favorable to the later strength of the sample. It is important to note that the SiO_2/Al2O_3 in the sample should not be too high, otherwise, if the sample coagulates too quickly, it will lead to the uneven stirring of the slurry and the difficulty of bubble escape, which will affect the development of the compressive strength in the later stage of the sample. By partially replacing (60%) sodium silicate with molten glass powder, the mechanical strength of high SiO_2/Al2O_3 sample can be improved by prolonging the setting time of the sample on the basis of keeping the whole SiO_2/Al2O_3 of the sample unchanged. By studying the reaction mechanism of CaCO_3,CaSO_4 and Ca (OH) _ 2 in alkali-excited metakaolin system, it is found that CaCO_3 plays a catalytic role in the reaction, accelerates the condensation of the sample, and plays a physical filling role in the later curing period. It has little effect on strength; CaSO_4 is mainly involved in the formation of ettringite, ettringite can enhance the early strength of the sample, but in the late curing period (28 days), the formation of ettringite will lead to cracks in the sample and affect the later strength development. Both pozzolanic reaction and geopolymerization occurred in the samples with Ca (OH) _ 2 addition.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O635
本文编号：2404798
[Abstract]:The high content of calcium and sulfur in CFB fly ash makes it difficult to realize large-scale utilization in traditional cement industry. In terms of chemical composition and mineral composition, CFB fly ash has a broad application prospect in the field of geopolymer synthesis. However, there is a large number of CaCO_3, in the ash. CaSO_4 and CaO make the process of geopolymerization more complex than that of metakaolin or fly ash base polymerization system. In this paper, CFB fly ash was simulated by adding CaCO_3,CaSO_4 and Ca (OH) _ 2 into metakaolin. Based on the SiO_2-Al2O_3-CaO-Na2O system, the effect of Na2O/Al2O_3 change on the setting time and compressive strength of the samples was studied. It was found that the increase of Na2O/Al2O_3 in the system was beneficial to active silicon in metakaolin. The dissolution of the aluminum component shortens the setting time of the sample. After curing for 90 days, octahedral zeolites were found in samples with Na2O/Al2O_3 of 0.7-1.1, while those with Na2O/Al2O_3 of 0.6-0.8 had A-type crystals. The formation of these crystals is beneficial to the later strength of the sample. However, when the Na2O/Al2O_3 is higher than 1.0, the formation of hydrated garnet in the reaction system results in the change of geopolymerization process, which has a negative effect on the compressive strength of the sample. When the alkali activator contains NaCl, chloraluminate is formed in the system, and the compressive strength of the sample decreases. Therefore, in order to obtain the geopolymer with excellent properties, It is necessary to ensure the existence of certain concentration of OH- ion in alkali activator. The influence of SiO_2/Al2O_3 on the setting time of sample is higher than that of Na2O/Al2O_3.. In the early stage of the reaction, zeolite crystals were formed in the low SiO_2/Al2O_3 (SiO_2/Al2O_32.5) samples, which could enhance the early strength of the samples. The increase of SiO_2/Al2O_3 can promote the transition of polymer type from Na-PS type to Na-PSS type, the latter is more favorable to the later strength of the sample. It is important to note that the SiO_2/Al2O_3 in the sample should not be too high, otherwise, if the sample coagulates too quickly, it will lead to the uneven stirring of the slurry and the difficulty of bubble escape, which will affect the development of the compressive strength in the later stage of the sample. By partially replacing (60%) sodium silicate with molten glass powder, the mechanical strength of high SiO_2/Al2O_3 sample can be improved by prolonging the setting time of the sample on the basis of keeping the whole SiO_2/Al2O_3 of the sample unchanged. By studying the reaction mechanism of CaCO_3,CaSO_4 and Ca (OH) _ 2 in alkali-excited metakaolin system, it is found that CaCO_3 plays a catalytic role in the reaction, accelerates the condensation of the sample, and plays a physical filling role in the later curing period. It has little effect on strength; CaSO_4 is mainly involved in the formation of ettringite, ettringite can enhance the early strength of the sample, but in the late curing period (28 days), the formation of ettringite will lead to cracks in the sample and affect the later strength development. Both pozzolanic reaction and geopolymerization occurred in the samples with Ca (OH) _ 2 addition.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O635
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