Civil Engineering Reference
In-Depth Information
2.2.2 Silica fume (SF)
Total world silica fume (SF) production was estimated to be 900 ¥ 10
3
t /
year in 2006 (aCi, 2006). in the USa the estimated SF production in 2004
was between 100 and 120 ¥ 10
3
t (ePa, 2008). This accounts for less than
0.01% of total cement production making the analysis of silica availability
unnecessary. Due to this reason, and the fact that it is a very expensive
material, approximately US$800/t (malhotra, 2005), it is only used in some
special concretes.
2.2.3 Fly ash (FA)
Coal plants are still the world's most important energy source at present.
Humphreys and Mahasenan (2002) evaluated total world fly ash (FA)
availability and concluded that, by 2020, the average annual production
will be 205 ¥ 10
6
t. WBCSD (2009) estimates a total of 500 ¥ 10
6
t/year
of Fa in 2006. USGS (2010a) shows that the Fa production in the USa
was near 56.9 ¥ 10
6
t in 1999, increasing to a peak of 65.7 ¥ 10
6
t in 2006
and, decreasing to 57.2 ¥ 10
6
t in 2009. india produced about 100 ¥ 10
6
t
in 2005 (malhotra, 2005). Considering that both countries are among the
six largest coal producers in the world and that not all Fa produced winds
up in cement production, the rough estimate of humphreys and mahasenan
(2002) seems to provide a good insight as to the magnitude of the amount
of Fa worldwide available for concrete.
Considering that the total annual world cement production expected for
the same year (2020) is more than 3 ¥ 10
9
t, the maximum average clinker
replacement content by Fa will be 7% or so. as for making this expectation
worse, if it is true that coal production is increasing and will increase in
the medium term, it is also true that a significant and quick decrease in its
production from 2020 onward should be expected (höok et al. 2008), as is
shown in Fig. 2.2. So, a world Fa production decrease is only a matter of
time.
allocation of Co
2
to fly ash is also under discussion (Chen et al. 2010)
since for every ton of fly ash produced, from 2.9 to 5.2 t of CO
2
are released
into the atmosphere (Yamamoto et al. 1997). again, except for technical or
localized reasons, there seems to be no need to promote the use of higher
amounts of pozzolans in cement mixtures. Fly ash must also be considered
a scarce material.
2.2.4 The need for additional supplementary
cementitious materials
in considering the relative scarcity of traditional supplementary cementitious
materials, the development of new supplementary materials becomes a
