Z E M C H 2 0 1 2 I n t e r n a t i o n a l C o n f e r e n c e
662
As shown in Table 2, the required average strength of the concrete in the experiment
was set to be 25MPa, and the water and cement ratio was approximately 60%. The
slump of the concrete fabricated using natural aggregate was measured to be 170mm,
while the slump of the concrete fabricated using 100% recycled coarse aggregate was
measured to be 160mm. The air content of the concrete was found to be about 6%,
which was within the target range of
5.0±1.5%.
A cylindrical specimen was fabricated with a dimension of Φ150×300mm. 28 days after
placement, a compressive strength test was conducted in accordance with KS F 2405
(compressive strength test for concrete); the NA-P specimen made of natural coarse
aggregate was observed to have a compressive strength of 28MPa, whereas the RF-P
specimen made of recycled coarse aggregate had a compressive strength of 29.1MPa.
The stress-strain relationship for each of the specimens is shown in Fig. 1(a).
As for the transverse reinforcement used in the experiment, a circular spiral reinforced
bar with a diameter of 4.5mm was used. The yield strengths of the spirals were 472MPa
and 1,430MPa. The properties and stress-strain relationship of the materials are shown
in Table 3 and Fig. 1(b), respectively.
Table 1 Properties of Aggregate
Aggregate type
Max size
(mm)
Specific gravity
(g/cm
3
)
Absorption
(%)
Fineness modulus
(%)
Coarse
aggregate
Natural
25
2.61
0.68
6.60
Recycle
25
2.53
2.55
6.58
Fine aggregate
5
0.64
2.39
2.94
Table 2 Concrete mix proportions
Table 3 Properties of spiral reinforcements
0
10
20
30
40
-0.004 -0.002 0.000 0.002 0.004
NA
RF
Strain (
ε
)
Stress (MPa)
0.00
0.01
0.02
0.03
0
400
800
1200
1600
2000
472MPa
1430MPa
Stress (MPa)
Axial strain
(a) Concrete (b) Steel bar
.Fig. 1 Experimental results of specimens
Specimens
ck
f
(MPa)
W/C
(%)
S/a
(%)
Unit weight (kg/m
3
)
W
C
S
G
AD
0
25
61.9
50
177
257
891
898
2.00
100
59
270
885
892
1.8
Type
Yield strength
(MPa)
Tensile strength
(MPa)
Yield strain
(ε
y
)
Modulus of Elasticity
(GPa)
Normal strength
472
553
0.0024
197
Ultra high strength
1430
1522
0.0072
199
