Civil Engineering Reference
In-Depth Information
ground ash was re-wetted (24% water by mass) and pelletized (8-10 mm)
before oven drying and firing at 900-1080 °C. Examination of the product
revealed considerable transformation to pyroxene (diopside: CaMgSi
2
O
6
and
clinoestatite: Mg
2
Si
2
O
6
) in a glassy matrix containing minor albite feldspar
(NaAlSi
3
O
8
) and wollastonite (CaSiO
3
). Leach testing proved that some
improvement (especially lead and zinc) was achieved but for other species,
sintering made little long term difference in their mobility.
Appenido et al. (2004) melted MSWI bottom ash at higher temperatures
(initially 1100 °C, rising to 1450 °C for 12 hours, then cooling to 1100 °C
and final air quenching) finding a similar mineral assemblage to the above,
containing corundum, feldspars (anorthite, CaAl
2
Si
2
O
8
and albite, NaAlSi
3
O
8
),
pyroxenes (diopside, Ca(Mg,Al)(Si,Al)
2
O
6
, augite, Ca(Fe,Mg)Si
2
O
6
) and
traces of metallic aluminium. These glassy ceramics were crushed and
graded, being used as aggregates in cement and mortar samples (Ferraris
et al. 2009; Fig. 12.22) which showed similar strength development curves
to reference samples up to 180 days of curing where the particle size was
coarse. Finer material (<5 mm diameter) showed a reduction in unconfined
compressive strengths between around 10 and 30% in comparison with
reference materials where the sintered aggregate replacement level varied
between 25 and 75% by volume. In this case, where the manufactured
aggregate is a direct replacement for sand in the concrete, they recommend a
replacement level not exceeding 25% by volume and suggest the cause of the
strength reduction is due to reduced integrity of the cement paste-aggregate
bond, reflecting the smooth surface of the glass. Importantly, these authors
used a finely ground fraction (<50 mm) as a filler material replacing part of
the cement fraction. They found no evidence of alkali silica reaction after
two years (using ASTM method C289), which suggests that the nature of
(a) (b)
12.22
Vitrified bottom ash (left) and a core of concrete containg
vitrified bottom ash aggregate. After Ferraris et al. (2009).
