Civil Engineering Reference
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by mass (Ginés et al. 2009) and the second is a change in composition,
in that its combustion products (largely oxides) are less likely to change
their volumes due to decomposition after landfilling. The second driver
for incineration is that of energy recovery. Although much of the potential
energy released by combustion of these wastes is used in evaporation of the
water they contain, there is a useful residue to be recovered and energy-from-
waste (EfW) plants have been widely established in industrialized nations.
In addition, one important benefit of waste incineration is the destruction of
pathogens and organic compounds detrimental to health.
The residues of municipal solid waste incineration (MSWI) have some
potential as construction materials such as unbound filler minerals, but
it is their specific use in concrete which is discussed here. This chapter
considers the composition of MSWI ashes, their hydration in concrete, their
performance in service and the environmental implications of incorporating
such residues.
12.2 Composition
Before looking in more detail at the composition of its combustion products,
we should first look at municipal waste before it undergoes incineration. It is
estimated (Chimenos et al. 1999) that in the year 2000, the rate of municipal
waste incineration (MWI) residue produced in Europe, Japan and the United
States was around 25 million tonnes per year. It is surprising, given the wide
variety of materials disposed of as municipal waste throughout the world,
that its bulk composition is relatively uniform. This largely reflects the
modern practice of waste sorting - recovery of useful resources at source.
Some countries are more exacting in their requirements than others, but the
segregation of metals, paper and cardboard, glass, plastics and compostable
materials are, to a greater of lesser extent, separated for individual collection
by the municipal authorities. Combined with electromagnetic and eddy current
separation for metal recovery, waste sorting has increased the value recovery
from waste markedly. The impact on this over the last two decades is very
far-reaching; for example some 80% of domestic paper and cardboard is
recycled in europe, where almost none was recovered 30 years ago. Conversely,
the quantity of metal foil (principally aluminium) used in packaging has
increased substantially over the same period and this has consequences
for the use of MWI bottom ash in concrete - a subject expanded on later.
A detailed discussion of waste composition, waste management practice
and likely developments in waste generation lie outside the scope of this
chapter. However, Parfitt (2002) and Burnley (2007) consider wastes in the
United Kingdom, whilst Bartelings and Sterner (1999) discuss experiences
in Sweden. For a more general reference, the topic
Handbook of Solid Waste
Management
(Tchobanoglous and Kreith (eds) 2002) gives a comprehensive
