| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 101 === Municipal solid waste incineration (MSWI) fly ash and flue gas desulfurization (FGD) gypsum are common residues with rich calcium and silica elements, so that they have the potential to be used in the production of autoclaved aerated concrete (AAC) as an alternative raw material. But they also contain large quantity of chloride and sulfate which may cause corrosion and durability problems to the cementitious products, therefore the reusability was restricted. Due to these reasons, there are three objectives in this study which are: (1) to investigate the effects of chloride and sulfate on the production of AAC, (2) reuse of MSWI fly ash and FGD gypsum to produce AAC, (3) understanding the leachability of heavy metal, chloride and sulfate from AAC products.
The results show that NaCl has the most serious impact on the density and compressive strength of AAC products. When the chloride content is about 0.18 wt.%, the strength of the sample with NaCl addition reduce 6 MPa and the sample contain CaCl2•2H2O decrease 2.29 MPa as well, which indicate that chloride has the negative effect on AAC products. In addition, the sample with CaSO4•2H2O addition lower the strength of sample as well, it means sulfate does not benefit to the strength development of AAC product.
On the other hand, the appropriate water to solid ratio is 0.65 L/kg when utilizing MSWI fly ash in AAC production, which could extend the replacement ratio to 20 wt.% with better AAC properties and meet ASTM AAC specification. Besides, the proper water to solid ratio for AAC product made by FGD gypsum is 0.70 L/kg, although the sample properties is worse than the AAC with 0.65 L/kg, it could increase the replacement ratio up to 20 wt.% and meet ASTM standard.
In terms of leaching test, the leaching concentration of heavy metals of AAC products meet TCLP and green building material limit when the conditions are at DI (deionized) water, acid rain and acetic acid. Besides, according to tank leaching test, excepting Ca, Si, Na and K elements, the leaching concentration of 15 heavy metals of building material decree (BMD) are not detected. Which indicate that there is no doubt that the utilization of MSWI fly ash and FGD gypsum in AAC will not have leaching toxicity of heavy metals.
The chloride and sulfate leaching properties could be determined by cumulative leaching percentage. The FGD gypsum products perform obvious leaching properties among of batch tests, but different leaching trend was observed in the tank leaching test, that is, the AAC products with MSWI fly ash easily leach out chloride, and FGD gypsum products show clear leaching property of sulfate.
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