Hydraulic activity of municipal solid waste incinerator fly-ash-slag-blended eco-cement

The melting of municipal solid waste incinerator (MSWI) fly ash can produce an extremely stable glassy slag that exhibits pozzolanicity if activated. Such slag, therefore, could be recovered in more valuable form as a cement replacement than as a roadbed aggregate. This study investigates the hydrau lic activity, compressive strength development. composition variation, and heavy metal leachability of such fly-ash-slag-blended cement (FASBC). The r esults indicate that FASBC pastes. with cement replacement ratios of less t han 20%, show a smaller early strength but a larger later strength at the a ge of 28 days. It was found that early cement hydration, Followed by the br eakdown and dissolving of the slag, enhanced the formation of calcium silic ate hydrates (C-S-H), which contributes to the later strength. The XRD and Si-29 MAS/NMR results also indicate that, after 28 days, both the hydration degree and the average length of the linear polysilicate anions would incr ease with an increasing cement replacement ratio, implying an increased str ength development. On the other hand, the targeted heavy metal leaching con centrations in the synthetic slag and the FASBC paste were significantly lo w; thus clearing the EPA's regulatory thresholds. These factors suggest the Feasibility and safety of using MSWI fly ash slag in blended cement. (C) 2 001 Elsevier Science Ltd. All rights reserved.