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increased with copper slag incorporation due to the high bulk density, glass-like
surface properties and irregular grain shape of copper slag (Shoya et al.
1997
).
Bleeding depends on several factors such as w/c ratio, air content and slag content
in concrete. According to Shoya et al. (
1997
) 40 % copper slag can be used as
partial replacement of aggregates to control the amount of bleeding to less than
5 l/m
2
. The addition of an admixture with cellulose ether and powder-like mate-
rial, such as limestone powder, is highly effective to improve the bleeding per-
formance of concrete with copper slag as aggregates (Shoya et al.
1997
). Hwang
and Laiw (
1989
) obtained a concrete mix with satisfactory workability and
minimal bleeding at the optimum fineness modulus of a mixture of copper slag and
natural fine aggregates, which was roughly equal to 2.6.
The addition of copper slag as fine or coarse aggregates in concrete increases its
fresh density due to the higher bulk density of copper slag than that of NA
(Al-Jabri et al.
2011
; Khanjadi and Behnood
2009
). Al-Jabri et al. (
2011
) observed
an increase in the density of fresh concrete of about 5 % when fine aggregates were
totally replaced by copper slag. Khanjadi and Behnood (
2009
) reported a density
of 2310 and 2668 kg/m
3
for HSC mixes with limestone and copper slag as coarse
aggregates, respectively. Khanjadi and Behnood (
2009
) also observed air-content
values of 2.5 and 2.4 % for natural and copper slag concrete, respectively. The
difference in air content between control concrete and copper slag concrete
increases with addition of silica fume with cement.
4.5.1.2 Hardened Concrete Properties
Al-Jabri et al. (
2011
) observed an increasing trend of 28-day compressive strength
of concrete as the content of copper slag rose up to a 40 % replacement level (mix
No. 4 in Fig.
4.29
) of fine aggregates. Their results are presented in Fig.
4.29
.
Further increment of the content of copper slag decreased the compressive strength
of resulting concrete and at a 60 % replacement level (mix No. 6) it became
slightly higher than the compressive strength of conventional concrete. The mix
with 40 % copper slag content yielded the highest 28-day compressive strength of
47.1 N/mm
2
compared with 45 N/mm
2
for the control mix, whereas the lowest
compressive strength of 34.8 N/mm
2
was obtained for the mix with 80 % copper
slag (mix No. 7). This reduction in compressive strength for concrete mixes with
high copper slag contents was due to the increase in free water content that
resulted from the low water absorption characteristics of copper slag in compar-
ison with sand, which caused a considerable increase in the workability of concrete
and thus reduced the compressive strength as shown in Fig.
4.27
.
In the Birindha and Nagam (
2011
) study, the 28-day compressive strength of
concrete prepared by replacing 40 % of fine aggregates by copper slag aggregates
was 46.7 MPa in comparison to the equivalent compressive strength of 35.1 MPa
for the control concrete. However, at 60 % substitution level of fine aggregates by
copper slag the compressive strength decreased to 39.7 MPa. Similar observations
were reported in some other studies, where copper slag was used as fine aggregates
