| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 90 === Abstract
As the current percentage of the national population served by a sewer system in Taiwan is as low as 6.5%, a "National Development Sewer System Plan" has been launched, aimed at pushing forward sewer system development on the island. Pursuant to this development plan, it is estimated that by the years 2003 and 2009, the national average served by sewer systems should reach 15% and 33%, respectively, generating an estimated 180,000 m3/day and 400,000 m3/day of sewage sludge to be disposed of, which is expected to have significant impact on the environment. From the viewpoint of substantial waste management, zero-discharge for MSW incinerators, and the add value of the recovery of waste for green products, the resource and recovery of sewage sludge ash, for producing lightweight foaming concrete,should be a feasible and novel alternative.
This study investigates the feasibility of producing foaming concrete as an insulator, using sewage sludge ash as a main component, and evaluates its heat-insulating efficiency. The work focuses on the characterization of the sewage sludge ash, the mix design, the bloating mechanism, and the heat-transfer properties of the sludge-ash-based insulator. Sewage sludge cakes were collected from the Bali and Minsheng sewage treatment plants (STPs) respectively, representing a typical primary and a secondary STP. The sludge cake was first incinerated at 900℃ to produce ash. Aluminum powder was used as a foaming agent, combined with pulverized scrap ( more than 90% Aluminum) small amount of OPC was used as a binder.
The characterization of the main components of the sludge ash indicate that, for sludge cakes with polymers, the ash content of the primary sludge ash(PSA) was higher than that of the secondary sludge ash(SSA), whereas the relationship was reversed for the water content. The specific surface areas of the PSA and SSA were 4,657 m2/kg and 10,193 m2/kg respectively, showing the greater fineness of the effect of sludge ash on the workability of the pastes. In general, the PSA has higher SiO2 content but lower P2O5 content than the SSA, whereas the other components were about equal to each other. Furthermore, the PSA had higher pozzolanic activity than did the SSA. These results suggest the greater economic feasibility of recycling PSA rather than SSA.
Various mix designs were tested showing that the sludge-ash-based foaming concrete had a specific gravity of less than 1.2, meeting the ASTM for lightweight concrete(LC). The foaming mechanism was mainly due to hydrogen gas being by the reaction of aluminum with hydroxyl radicals, generated by the hydration of the cement. The cellular structure was solely composed of micro pores about 1μm in diameter.
LC samples prepared according to the mix design adopted in this study showed a porosity distribution ranging from 51% to 71% for PSA-based LC, and 54% to 63% for SSA-based LC. The higher porosity of the latter resulted in a lower heat transfer(0.0880-0.2507 W/m-oK) compared to that of the former(0.0763-0.1510 W/m-oK). Therefore it is suggested that the SSA-based LC should outperform PSA-based LC in heat-insulating efficiency.
It can be concluded, from the results of this study, that PSA is more economically feasible than SSA, whereas the SSA based LC showed better heat-insulating performance than did PSA- based LC.
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