C o n f i n e m e n t E f f e c t o f C o n f i n e d C o n c r e t e
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Specimen Design and Experimental Methods
In this experiment, a specimen made of natural aggregate and a specimen made of
recycled coarse aggregate were fabricated in order to determine the confinement
performance of concrete made using recycled coarse aggregate. A ratio of transverse
reinforcement of 0.0175 was equally applied to both specimens, and a longitudinal bar
was not reinforced in order to obtain the pure confinement performance. Also, the yield
strengths of the transverse reinforcements were 472MPa and 1430MPa. Three
specimens were fabricated for each type under the same conditions with a total of 18
specimens. The details of the specimen design are shown in Table 4.
As shown in Fig. 2 the specimens were fabricated as a cylinder with diameter of
150mm and height of 300mm. The spaces between the transverse reinforcements was
25mm, and a gauge was mounted at 120° on the traverse reinforcement located in the
central part of the experiment section (200mm) to measure the strain in the transverse
direction. Also, in order to measure the strain in the longitudinal and transverse
directions, three LVDTs were installed in each of the longitudinal and transverse
directions at 120°. The longitudinal LVDTs were mounted on the steel rod fixed at the
50-mm points so as to make the experimental section 200mm long. The transverse
LVDT was mounted on the upper steel road to measure the strain in the transverse
direction at mid-point. Loading was performed using a universal testing machine (UTM)
of 2,000kN capacity, with the load being applied in a displacement control method to
produce a 0.006-mm displacement per second. The load was continuously applied until
the specimen failure.
Fig. 2 Detail of specimens Fig. 3 Test setup configuration
Results
Stress-strain relationship
As for the NA specimens made of natural coarse aggregate, the NA-NS series with spiral
yield strength of 472MPa showed an increase in strength by 24% compared to the
unconfined NA-P series, and all of the transverse reinforcements yielded upon
application of maximum strength. The NA-US series with spiral yield strength of
1,430MPa showed an increase in strength by 97% compared to the P series, and only
one of the specimens had a yielding transverse reinforcement upon application of
maximum strength.
As for RF specimens made of recycled coarse aggregate, the RF-NS series with spiral
yield strength of 472MPa showed an increase in strength by 29% compared to the RF-P
series, and all of the transverse reinforcements yielded upon application of maximum
