Civil Engineering Reference
In-Depth Information
(close to 10-15 wt%) make BCSAF a potential alternative to oPC with
expected prices only slightly larger than those of oPC cements.
Very much related with the above issue, bauxite cost and scarcity
(Scrivener and Kirkpatrick, 2008; Juenger et al., 2011; Schneider et al.
2011) are serious problems. Bauxite is necessary in large amounts for CSA
and BCSAA fabrications and this will certainly prevent their applications
for large-scale uses. However, for BCSAF the primary aluminum source
may be aluminum silicates and bauxites or aluminum-rich wastes are used
as correctors to reach the right Al
2
o
3
content. Therefore, bauxite cost and
availability are not that critical for BCSAF. Furthermore, the current value
of C
4
A
3
S
content, ~30 wt%, implies ~15-16 wt% of Al
2
o
3
in the clinker.
research is ongoing in order to develop belite-active BCSAF with ~20 wt%
of C
4
A
3
S
which would lead to ~10 wt% of Al
2
o
3
but cement performances
must be maintained.
18.2.2 Laboratory-prepared yeelimite-containing cements
Mehta (1977) presented some compositions ranging ~20 wt% of C
4
A
3
S
,
25-45 wt% of C
2
S, 15-40 wt% of C
4
AF and 15-20 wt% of anhydrite. Those
materials containing higher values of C
2
S gained mechanical strengths up to
50 MPa at 28 days. Most laboratory studies were mainly devoted to revealing
the relationship between mineralogical composition of clinkers and some
final performances. This fact becomes even more relevant if waste materials
were included in the raw mixtures for producing CSA and BCSAF clinkers
(Beretka et al., 1993; Arjunan et al., 1999; Katsioti et al., 2006; Seluck et
al., 2010). These studies concluded that the use of waste materials such as
bag house dust, low-calcium fly ash, phosphogypsum or scrubber sludge
successfully yielded to the preparation of CSA or BCSA clinkers at low
temperatures, i.e. 1200-1300 °C. Moreover, final performances, i.e. setting
times, consistency, expansion and mechanical strengths were similar to those
obtained with the cements prepared using reagent grade raw materials.
Senff et al. (2011) presented the use of the design of experiments for the
formulation of clinkers with mineralogical composition ranging 30-70 wt%
of C
2
S, 20-60 wt% C
4
A
3
S
and 10-25 wt% C
4
AF and mathematical models
to predict properties. They concluded that mechanical strength at early ages
strongly increases with higher amounts of C
4
A
3
S
, as expected. However,
these authors do not deal with activation of BCSAF. aBCSAF materials
were successfully prepared in the laboratory (Cuberos et al., 2010; Aranda
et al., 2011; Álvarez-Pinazo et al., 2012). In these works, the main goal was
the quantitative demonstration of a¢
H
-C
2
S polymorph stabilization by borax
addition to BCSAF clinkers, and that this polymorph hydrates much faster
than b-C
2
S polymorph.
Figure 18.2 gives rietveld plots of two BCSAF, (a) without any activator
