Preparation of Cement Admixture with MSWI Ash by Mechanical Milling Technology for Pb Stabilization and Cementitious Modification
| Autor: | Cheng-Gang Chen, 陳政綱 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 This study used mechanical milling to change physical and chemical properties of municipal solid waste incinerator (MSWI) fly ash. The mobility of heavy metals would be reduced by mechanical milling and the amount of inorganic gelwould be also promoted by alkali activation of the MSWI fly ash. After mechanical milling and alkali activation processes, the MSWI fly ash can achieve the aim of detoxification and recovery, and can be a good substitute of Type I ordinary Portland cement (OPC). The crystal structure of MSWI fly ash was destroyed and became the amorphous phase after milling 96 h. At the same time, the leaching concentration of the heavy metals of milled fly ash could be decreased below the detection limit. The paste which partial substituted the OPC by the milled fly ash would increase the amount of gel pores and middle-size pores, and led the paste to become denser than OPC paste. The results of the nuclear magnetic resonance Spectrometer (NMR) test indicated that the milled fly ash can not only increase the amount of C-S-H gel which is caused by the higher hydration reaction, but also can accelerate the pozzolanic reaction. Based on these results, the compressive strength of the paste could rise up in all of the curing times. By 0.2 M PO4 3- of milling solution and 1 h milling time, the calcium phosphate of hydroxyapatite (HAp), tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP) would be produced. However, the dissolution of calcium phosphate compounds and excessive PO4 3- remained in the milled ash, which made the calcium hydroxide of paste be consumed. This result indicate that the milled fly ash by PO4 3- caused the negative impact of the compressive strength of the milled fly ash paste greater than the positive impact, and led the compressive strength lower than the OPC paste. The milled fly ash with 0.002 M PO4 3- would produce a lot of TTCP when it partial substituted OPC paste, which the TTCP would react with water to produce HAp and calcium hydroxide. In addition, the effect of the pozzolanic reaction premature generated by 96 h of milling time still appears and the compressive strength of the milled fly ash paste after 7 days and 28 days of curing also higher than the OPC paste. The effect of metakaolin and washed fly ash on a different mixing ratio by mechanical milling activation (1 M NaOH, 24 h) was evaluated. The results show 1 M NaOH of milling solution was lack of alkali concentration, thus it could not dissolute the silicate of metakaolin. The compounds produced by metakaolin after mechanical milling activation could conduct an ions exchange of heavy metal and achieve the stabilization of heavy metal. When the alkali concentration increased to 5 M, heavy metal would bond with the activated gel. Due to the bonding strength is weak, so the leaching concentration of heavy metal was slightly increased. In addition, the high concentration of sodium hydroxide would cause significant negative influence on the hydration reaction. The milling activation was conducted in 5M of NaOH with the water treatment plant sludge after calcination. The results show that the stabilized chloride crystallization would be increased when the amount of the extracted fly ash was increased. Nevertheless, when the amount of the extracted fly ash was decreased, the type of the bound with chloride ion was the physical stability mechanism, which would lead to poor stability of the paste. From above statement, the milled activated fly ash would form a gel of weak structure for binding with chloride ion and was not conducive to stabilize chloride for the paste in the early curing time. When the water was the milling solution, it would generate many similar Friedel’s salt structure which caused the effect of observably chemical stability. The excellent of the effect of stabilize chloride ion for the paste would be appeared after 7 days of curing. The stabilization and reaction mechanism of chloride ion in the inorganic gel is difference with traditional cement evidently. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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