Civil Engineering Reference
In-Depth Information
Table 4.5
Content of conductive admixture, slump fl ow, compressive strength
and fl exural strength
Content
of NCB
(kg/m
3
)
Content
of CF
(kg/m
3
)
Slump
fl ow,
d
(mm)
Compressive
strength (
f
cu
)
(MPa)
Flexural
strength
(
Mixture/samples
σ
u
) (MPa)
Plain concrete
PC
0
0
620
42.55
4.44
Concrete with
NCB only
NCB01
0.3733
0
600
43.53
4.52
NCB02
0.7467
0
540
43.67
4.71
NCB03
1.1200
0
390
44.17
4.79
NCB04
1.4933
0
330
45.45
4.83
Concrete with
CF only
CF04
0
1.4933
590
43.49
5.10
CF08
0
2.9866
570
44.37
5.19
CF10
0
3.7333
550
45.10
5.22
CF13
0
4.8533
520
44.6
5.30
CF16
0
5.9733
500
44.76
5.31
Concrete with
BF (NCB
+
CF)
BF14
0.3733
1.4933
590
43.78
4.90
BF18
0.3733
2.9866
540
44.01
4.94
BF24
0.7467
1.4933
480
43.54
5.02
BF28
0.7467
2.9866
410
43.98
5.13
the average diameter in the slump fl ow test. It may be seen from Table 4.5
that fresh PC (plain concrete without any conductive admixtures) corre-
sponds well to the requirements of self-compacting concrete. There is very
good fl owability and no segregation. However, the workability of fresh
concrete declines with an increase in NCB or CF content. The slump fl ow
of BF28 is only about 410 mm. This means that the content of diphasic
conductive admixtures (0.747 kg/m
3
(NCB)
2.99 kg/m
3
(CF)) is less than
the lower limit (450 mm) of the workability of highly fl owable concrete. The
fl ow behaviour of NCB03, NCB04, and BF28 is much less fl uid than that of
other mixtures due to the relatively high content of CF and NCB.
The average values of compressive strength
f
cu
and fl exural strength
+
σ
u
after 28 days may be found in Table 4.5. The increment of compression
strength ranges between 2.2% and 6.2%. This indicates that the addition of
NCB, CF and BF shows some positive effect on the compressive strength
of concrete, but does not amount to a signifi cant trend of improvement.
4.3.2 Infl uence of conductive admixtures
on fl exural strength
When a beam is subjected to bending, strains are produced. These strains
create compression stress at the top of the beam and tension at the bottom.
The load is applied until a crack is imminent. If the beam section does not
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