1. Physical and chemical performance of
treated MSWI bottom ash (fine fraction)
as sand replacement in concrete
Author: Arno Keulen1,2
1: Eindhoven University of Technology. 2: MINERALS (part of Renewi)
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The dry treated ash was the input for the wet treatment (separating and washing), which significantly lowered the content of fine particles <63µm and reduced contaminant leaching of salts, soluble organic structures and heavy metals, results shown in Fig 3.
Results concrete production
Treated BA aggregate 0-2/3 mm was characterized and is in compliance with the standard EN aggregates for concrete. Additionally, a course BA aggregate fraction 2-12mm was also produced, which is already tested in previous (published) research.
Earth-moist concrete was composed, on a factory production pilot scale, producing pavement tiles, replacing the natural sand fraction with 20 wt.% BA aggregate. The strength results of Fig. 4, indicate no significant differences between the BA and reference concrete strength development.
Finally, leaching of monolithic state concrete and that of granular state materials (recycled as aggregate) was tested, and is in compliance with the Dutch Soil Quality Decree (regulations for quality of building material products). No significant differences in leaching were found between the BA and the reference concrete.
Introduction
MSWI bottom ash is a potential waste stream considered for re-use. The fine fraction (0-2/3mm) contains various contaminants which cause increased elements leaching and hamper the re-use possibilities. The aim of this study was to improve the quality of the fine fraction bottom ash (BA) to a fine aggregate to promote the re-use potential within concrete. BA was treated within special dry and wet treatment processes obtaining a high quality aggregate, applicable for natural sand replacement in Portland cement concrete mixtures. The treatment involved:
Step 1: Weathering of fresh MSWI bottom ash.
Step 2: Crushing, dry separation and metal recovery of BA into a fine and course fraction (specially designed plant).
Step 3: Wet separation and washing treatment of BA, towards an aggregate (specially designed plant).
Leaching of contaminants and the effects of the treatment processes on the BA aggregate properties were studied. BA was applied in concrete, replacing the initial natural sand fraction. The concrete products were tested on leaching in accordance to the standards.
Results granulate production
The dry treatment largely extracted unburnt material and metallic metals. Although, the remaining BA fraction still contains relatively high leachable concentrations of potentially hazardous elements. Observed trends between element release and a smaller particle size and their leaching behavior are shown in Fig 2.
(a)
(b)
Fig 3: pH dependent element leaching, of the dry- and wet treated 0-2/3 mm BA fraction, in accordance with EN 14997
Fig 1: From fresh bottom ash to BA aggregate to BA concrete products.
Fig 2: Element release of dry treated BA particle size, as function of particle size, measured with batch leaching test NEN-EN (L/S 10).
Fig 4: Flexural strength of pavement tiles (dished line: 35 d. strength limit value 4.9 N/mm2).
Poster nr. S4.5