Physical and chemical performance of
treated MSWI bottom ash (fine fraction)
as sand replacement in 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 reuse 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.
Author: Arno Keulen1,2
1:
Eindhoven University of Technology.
2: MINERALS (part of Renewi)
Contact:
• [email protected]
• [email protected]
• www.Renewi.com
• Tel: 0031-613209271
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.
(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
Results concrete production
Fig 1: From fresh
bottom ash to BA
aggregate to BA
concrete products.
Treated BA aggregate 0-2/3 mm was characterized and is in
compliance with the standard EN 12620 aggregates for concrete.
Additionally, a course BA aggregate fraction 2-12mm was also
produced, which is already tested in previous (published) research.
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.
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.
Fig 2: Element release of dry
treated BA particle size, as
function of particle size,
measured with batch leaching
test NEN-EN 12457-3 (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