دانلود رایگان مقاله رفتار ژئوپلیمریزاسیون کسر غنی از آهن خاکستر قهوه ای

Abstract

Iron rich brown fly ash has been segregated into (a) coarse, and (b) fine size fractions using air classification. The suitability of fine iron-rich fly ash (CFA) has been evaluated for the synthesis of geopolymer. The behavior of CFA based geopolymer in relation to reactivity, NaOH concentration and sodium silicate to sodium hydroxide (S/H) ratio has been studied. The concentrations of NaOH (6, 8, 10 and 12 M) and S/H ratios (0.33, 1.0 and 3.0) were the variable parameters. Calorimetric studies revealed that the total heat release increased with NaOH concentration, but decreased with the increase in S/H ratio. The geopolymer synthesis was done by thermal curing at 60 °C for 24 h. It was found that the compressive strength increased with an increase in the NaOH concentration. The increase in S/H ratio from 0.33 to 1.00 resulted in a significant increase in the compressive strength, but a further increase from 1.00 to 3.00 resulted in a slight decrease in compressive strength. High strength geopolymer mortar up to 70 MPa at 28 days was obtained, when the mixture was formulated with 12 M NaOH and S/H ratio of 1.00. From SEM-EDS studies, an increase in the degree of reaction and formation of geopolymer gel was observed with increase in NaOH concentration. Also it revealed that the geopolymer gel obtained was ferro-sialate based polymers with chemical formula close to [Ca, Na]-[-Fe-O-]x-[-Si-O-Al-O-]1−x-[-Si-O-]y, wherein “x” is less than or equal to 0.5, and “y” is a value between 0 and 25. Formation of the compact microstructure has resulted in improved strength properties of geopolymer.

4. Conclusions

Iron rich fly ash, particularly fine fraction fly ash, has been used in making geopolymer binders. The utilization of fine iron-rich fly ash resulted in several positive effects on the properties of geopolymer binders. The effects of factors such as NaOH concentration and S/H Ratio on the properties of fine iron-rich fly ash geopolymer were investigated. The setting time increases with the increase in NaOH concentration, while it decreases with the S/H ratio. The increase in NaOH concentration also results in more heat of geopolymerization. Whereas, the increase in S/H ratio delays the geopolymerization and produces less heat. The compressive strength also increases with the increase in NaOH concentration. The increase in S/H ratio gives no definite trend. The compressive strength first increases with S/H ratio in the range of 0.33–1.00 and then decreases with S/H ratio in the range of 1.00–3.00. The morphology of hardened geopolymer samples consists of partially reacted fly ash and geopolymer gels rich in Na, Ca and Fe. The geopolymer binders obtained are of poly (ferro-sialate-siloxo) and poly (ferrosialate-disloxo) polymer type binders with Ca2þ and Naþ as charge-balancing cations. The increase in NaOH concentration results in more compact microstructure of geopolymer. The fine iron-rich fly ash can be used for manufacturing high strength geopolymer binder. There is no negative effect of high iron content on the compressive strength of geopolymer mortars. The iron rich fly ash geopolymers mainly differ in their microstructural compositions as observed in SEM-EDS.