| dc.description.abstract | This study investigated the pozzolonic reactions and engineering properties of municipal solid waste incinerator (MSWI) ash modified slag blended cements (SBC) with various replacement ratios. The modified slags were characterized by melting the MSWI ash mixtures at 1,400℃ for 30 min. The mixtures were composed of different types of MSWI ash, including fly ash, scrubber ash and bottom ash, with various formulas. Bottom ash and scrubber ash, in general, have higher melting points, and are more energy intensive to melt than fly ash. Therefore, fly ash was used to modify the mixtures. The obtained slags were divided into three series based on the experimental ash mixtures. Following further pulverization, these slags were blended with cement at cement replacement ratios ranging from 10% to 40%. The slags thus obtained were quantified and the characteristics of their SBC pastes examined, including the pozzolanic activity, compressive strength, hydration activity, gel pores, crystal phases, species, and the microstructure at various ages.
The results indicate that the slag contained 27～34% CaO, 29～39% SiO2, and 8～23% Al2O3, and approximately 47～67% non-calcium compounds, thus meeting the ASTM C grade for fly ash, which is similar to that of the blast furnace slag.
The 90-day compressive strength developed by SBC pastes with a 10% and 20% cement replacement by slags generated from the modification of scrubber ash, outperformed that of ordinary Portland cement(OPC) by 1-7 MPa, whereas the slags generated from the modifications of bottom ash series were comparable to OPC with a difference of less than 0.5MPa.
From the pore size distribution, as shown by the MIP results, it was found that, with increasing curing ages, the gel pores increased and the total porosity and capillary pores decreased — a result that shows that hydrates had filled the pores.
XRD and DTA species analyses indicated that the hydrates in SBC pastes were mainly CH, the calcium silicate hydrate C-S-H(C-S-H) gel, and C-A-H salts, like those found in OPC paste. TG analysis also indicated that the slag reacted with CH to form C-S-H and C-A-H. The average length (in terms of the number of Si molecules) of linear polysilicate anions in C-S-H gel, as determined by NMR, indicated an increase in all SBC pastes with increasing curing age, which outperformed that of OPC at 90 days. The generation of C-S-H gel, with intersections forming a network structure, as observed by SEM from the surface reaction with CH, also indicated the later development of strength in SBC pastes enhanced by the slag. It can be concluded from the study results that MSWI ash can be modified and processed by melting to recover reactive pozzolanic slag, which may be used in SBC to partially replace cement. | en_US |