Civil Engineering Reference
In-Depth Information
Fig. 3.17 Position of natural
aggregate (NA) and CDW
aggregates (RCA) in CaO-
SiO
2
-Al
2
O
3
ternary diagram
(Limbachiya et al.
2007
)
Several reports indicate that CDW aggregate contains slightly higher amounts
of chlorides and sulphates than normal aggregate. However, this amount is gen-
erally lower than the limits set for them in standard specifications. Tam and Tam
(
2007
) determined chloride and sulphate contents in several CDW aggregates and
compared the results with standard specifications. Their results suggest that sul-
phate and chloride content in all the aggregates, except one type, meet the standard
specifications. Rahal (
2007
) also found slightly higher amounts of chloride (0.3 %)
in CDW aggregate than in normal aggregate (0.14 %). Corinaldesi (
2009
) did not
find any organic and alkali silica reactive materials in CDW fine aggregate. They
also found low chloride and sulphate contents, which are lower than the standard
specifications. To evaluate the potential surface activity of fine particles (clay,
organic materials and ferrous hydroxides) present in CDW aggregate, Courard
et al. (
2010
) analysed its fine fractions, those passing through the 80 lm sieve, by
measuring the methylene blue value, according to the standard specified method
described in Belgian standard, NBN B11-210. They found very low methylene
blue value, which means that the aggregate is acceptable for use in concrete.
Chemically, CDW aggregate contains lower amounts of SiO
2
and higher
amounts of CaO and Al
2
O
3
, the three major oxides, than the contents of those in
natural fine and coarse aggregates. The CaO-SiO
2
-Al
2
O
3
ternary diagram for these
three major oxides present in CDW and natural aggregate as reported by Lim-
bachiya et al. (
2007
) is presented in Fig.
3.17
. In comparison with CDW aggre-
gates (RCA), the two natural aggregates are found to be at the top of the triangle,
indicating the presence of higher amounts of SiO
2
than the CDW aggregate. The
diagram also shows a comparable composition for all three CDA aggregates,
obtained from three different C&D sources, with a richer composition in Al and Ca
oxides when compared to coarse and fine NAs.
The mineralogical compositions of CDW aggregate are slightly different from
those of natural aggregates due to the presence of different constituents from
different
sources
such
as
hydrated
cement, ceramics
and
natural
aggregates
