Civil Engineering Reference
In-Depth Information
Fig. 3.13 Grading curve of fine CDW aggregate along with limits for M grading according to BS
EN12620 (Yang et al.
2011
)
3.5.6 Grading Size
The size distributions of coarse and fine CDW aggregates are generally different
from the corresponding fractions of natural aggregates. However, in a production
plant and also in several studies, CDW aggregate is produced by adopting crushing
and screening processes and therefore CDW aggregate generally falls within the
limits of mixing gradation for preparation of required types of concrete. The use of
similar crushing technique with the same maximum size (or if the crusher is set a
specific opening) generates CDW aggregates with almost similar grading behav-
iour (Katz
2003
; Chen et al.
2003
). Yang et al. (
2011
) compared the sieve analysis
results of fine CDW aggregate with the grading limits from British standard, BS
EN12620, and concluded that fine CDW aggregate used in their study could be
categorised as medium class, as the passing percentage of 150 lm fraction of fine
CDW aggregate fell in the region of medium grading limits (Fig.
3.13
).
The particle sizes of the fine CDW aggregates used by Khatib (
2005
) are similar
but coarser than those of natural class M sand. Tangchirapat et al. (
2008
) and
Zaharieva et al. (
2003
) also reported that the CDW fine aggregate is generally
coarser than normal sand. The fineness modulus of CDW and natural aggregates,
reported in various references, are presented in Table
3.11
.
Chen et al. (
2003
) found similar grade size distributions in the fine and coarse
fractions of two types of CDW aggregates, which are slightly different in their
compositions but processed by similar crushers with the same maximum size
(Fig.
3.14
).
Corinaldesi et al. (
2002
) and Vieira et al. (
2011
) found different grading curves
for natural and CDW fine aggregates, which are presented in Fig.
3.15
. For this
reason, Vieira et al. (
2011
) separated various fractions of CDW aggregates so that
the grading curve of CDW aggregate matched the grading curve of natural
aggregate with similar fineness modulus. Although this type of procedure is dif-
ficult in practical terms, it enables comparisons between mix compositions with
