Civil Engineering Reference
In-Depth Information
group also use untreated bottom ash in a comparative study (
ibid.
) as a partial
replacement for sand. In this case they conclude that satisfactory concrete
could be made with up to 10% by mass of the aggregate being replaced by
MSWI bottom ash. Berg and Neall (1992) describe MSWI bottom ashes as
'marginal aggregates' owing to both their relatively low strength and angular
shapes, which reduce workability of fresh concrete.
Jaturapitakkul and Cheerarot (2003) examined finely ground bottom ash
as a potential pozzolan in blended cement concrete. They also found the
material influenced hydration kinetics in that at all blending ratios considered
(0-30% by mass) the 28 day strengths were significantly lower than control
samples made from conventional concrete. However, at low replacement
levels (<20%) the late age strengths (60 days) were greater than those of
the control samples. Using ground bottom ash, they produced concretes
with strengths of ~30-40 MPa) at 28 days, rising to over 50 MPa at 90
days. Jurič et al. (2006) used ground bottom ash as a replacement for the
binder in concrete and recommend that up to 15% by mass may be used as
a cement replacement material, to produce acceptable strengths (~40 MPa)
at 28 days.
12.6.2 Manufactured aggregates
One option for effective re-use of MSWI ashes in concrete is to process
the material into a manufactured aggregate and this route has attracted
considerable attention in recent times, through both low-temperature and
high-temperature processing. Amongst the most promising approach for
low temperature processing is the rapid carbonation of these materials
either directly or during the early stages of hydration. Fernández Bertos
et al. (2004) reviewed the potential of accelerated carbonation technology
in the treatment of cement-based materials and sequestration of CO
2
. The
review followed their successful production of artificial aggregates using
similar technology and this group went on to stabilise MSWI fly ashes using
accelerated carbonation (Li et al. 2007). Previous work (e.g. van Gerven
et al. 2005) has shown that the leachability of many metals was reduced
during the rapid carbonation of MSWI bottom ash, but others (notably Cr)
were enhanced. Gunning et al. (2010) reviewed the stability of many waste
types (including MSWI) as a result of accelerated carbonation and presented
additional results which confirm these findings. Arickx et al. (2006) found a
marked reduction in leachability of rapidly carbonated bottom ash, but did
not use it in concrete production. Latterly, the first commercial uptake of
accelerated carbonation technology has been announced, in which artificial
aggregates are being produced from APC residues (Gunning et al. 2012;
Hills et al. 2012; Perella 2012). This application is claimed to operate with
an overall consumption of CO
2
in a rapid process (minutes) sequestering
