Ikegawa, Takuya

Kitoh, Hiroaki

Ohuchi, hajime

Saito, Hisashi

Tsunokake, Hisao

Osaka City University Repository

Flexural and Shear Failure Tests of Reinforced Concrete Beams
with Low Grade Recycled Aggregate
Takuya IKEGAWA*, Hisashi SAITO**, Hajime OHUCHI***, Hiroaki KITOH****
and Hisao TSUNOKAKE*****
(Received September 30, 2009)
Synopsis
Under ecological and natural resource shortage aspects, structural behavior of the reinforced concrete beams
using low grade recycled aggregate has been investigated through six static load test specimens with various
moisture conditions and mix proportions of aggregate. Using the recycle aggregate instead of normal aggregate,
no obvious degradation was observed in flexural strength, while 30% reduction in shear strength.
KEY WORDS: Low Grade Recycled Aggregate, Shear Strength, Flexural Strength, Dry Shrinkage
1. Introduction
In the near future, it is expected that the amount of concrete rubble increases with demolishing existing
structures built during mid to late 19th century. Recycled usage of such concrete is highly expected from the
viewpoints of ecological and natural resource shortage. The low grade recycled concrete, however, has not been
applied to structural members, because of problems in the property of flesh concrete and in the larger shrinkage
appearance in comparison with ordinal concrete of normal aggregate.
The purpose of the present study is to examine the applicability of the recycled aggregate to reinforced
concrete structural members. In order to optimum usage of recycled aggregate, we have conducted flexural and
shear failure tests of the six reinforced concrete beam specimens with various moisture conditions and mix
proportions of the aggregate as parameters.
2. Test Specimens and Concrete Mix Proportions
Figure 1 shows two kinds of test specimens of reinforced concrete beams with the same cross sectional area of
200mm in breadth and 260mm in effective depth. Shorter one is for shear test specimen subjected to a symmetric
* Graduate Student, Department of Civil Engineering
** Sumitomo Osaka Cement Co.,Ltd, Japan
*** Professor, Department of Civil Engineering
**** Associate Professor, Department of Civil Engineering
***** Research Associate, Department of Civil Engineering
- 29-
three points loading with 2.3 of a ratio of shear span to effective depth: ald. The other longer on is for bending
test specimen subjected to a symmetric four points loading. Furthermore, the former had larger longitudinal
reinforcement of two deformed steel bars: D19, not to occur a bending failure, than the latter with those of 010.
The nominal cross sectional diameter, yielding point and elastic modulus of the bars of 019 were 19mm,
359N/mm2 and 177kN/mm2, respectively, while the corresponding values of D I0 were lDmm, 361N/mm2 and
164kN/mm2, respectively. The concrete used for the specimens are listed in Table I. In the table, the first
column show tag of each specimen, in which the first character of S or F denotes the specimens for a shear or
bending tests. Furthermore, the rest character indicates the mix proportion of concrete used, which is relevant to
the first column of Table 2.
Four of the shear test specimens were prepared. One of them called as S-NS was only of normal concrete
and the other were of those with the recycle aggregate, testing parameter of which were two moisture condition
and sorting. The formers were oven dry or saturated surface dry states, and the latter was sorting of fine and
coarse aggregates. Two of the bending test specimens, however, were used the recycled aggregate with different
combination of moisture condition and sorting.
Moreover, all the specimens were in water curing for a week after the placement of concrete. After the
curing, they were in air curing, and the time dependent strain history due to dry shrinkage were measured for
some of them until the day of its loading test.
Shear Failure
r~·+·, -,,= ~__-----,,6::::..o00'---__~~1
I----------'-'=="---------~
Bending Failure
Fig.1 Front view of specimens (unit: mm)
650 300
1.800
650
Table I List of specimens
Tag Failure Aggregates Moisture Condition* Sorting
S-NS Normal ODS done
S-RS Shear SSDS ditto.S-RD Recycled ODS ditto.S-RD-O none
F-NS Bending Normal SSDS doneF-RD-O Recycled ODS none
*Moisture condition: Oven Dry State / Saturated Surface Dry State
- 30-
Table 2 Mix proportion of concrete
WIC sla
Unit Weight(kglm3) Fresh Testing
Mix ame Normal Aggregate Recycled Aggregate AE Air Slump
W C AE Water Reducing Agent(%) (%) SI S2 G S G (%) (cm)
NS 58 44.5 174 300 328 474 1026 - - - 3.18 4.0 10.1
RS 47.4 171 295 - - - 731 903 0.0056 071 4.8 9.8
RD 58 47.4 221 381 - 549 715 0.0076 1.91'2 3.8 105
RD-O 60.5" 221 381 - - 1297 00076 4.57'2 3.7 23.0
*1 Calculated from screening test *2 Used special AE water reducing agent for RD and RD-O
3. Results of Loading Tests
3.1 Shear Loading Test
For all of the shear test specimens, Figs. 2 and 3 show the final cracking patterns, and the relation between
applied shear load intensity normalized by an estimated shear strength and deflection at mid-span, respectively.
First, comparing the behavior of the specimen using the recycled aggregate with that using normal aggregate,
the flexural stiffness of the former was lower than that of the latter as same as the corresponding tendency of
both concrete materials. It can also found that initial cracking of the specimen using the recycled aggregate was
earlier and the following crack development and opening were obviously remarkable, owing to lower concrete
tensile strength and also existence of the residual mortal covered over the recycled aggregate surface.
Except for the specimen of S-RO-D, moreover, their shear strength decreased around 30% of that of the
specimen using normal concrete, independent of the recycled aggregate's moisture condition. It should be noted
that no penetration of diagonal shear crack was observed in failure mode of the exceptional specimen of
S-RO-D, which suggested different load carrying mechanism from the another specimen using the recycled
aggregate.
Table 3 Shear test results
Concrete Material Testing Shearing Load
fc' Ec ft initial
Shear Strength
Tag
cracking load Calculated Value Experimental Value Calculated
) (kN/mm2) ) (kN) (kN) (kN) Experimental(N/mm-) (N/mll1-)
S-NS 32.5 28.2 2.88 63.0 95.8 143.8 1.50
S-RS 34.8 19.6 2.44 40.9 98.2 114.3 1.16
S-RD 44.1 22.7 2.58 45.0 106.3 130.8 1.23
S-RD-O 42.4 21.9 2.44 40.1 104.9 162.8 1.55
3.2 Bending Loading Test
For all of the bending test specimens, Figs. 4 and 5 show the final cracking patterns, and the relation
between applied load intensity and deflection at mid-span, respectively. As same as the shear loading test, their
bending strength of the specimen using the recycled aggregate decreased around 10% of that of the specimen
using normal concrete. Furthermore, the similar tendency to the shear loading test of crack initiation,
development and opening was also observed.
- 31 -
Table 4 Bending tests results
Concrete Material Testing Bending Load
fc' Ec ft initial design bending strengthTag
cracking load Calculated Value Experimental Value Calculated
(N/mm2) (kN/mm2) (N/mm 2) (kN) (kN) (kN) Experimental
F-NS 32.5 28.2 2.88 30.0 40.5 55.7 1.38
F-RD-O 43.0 22.8 2.62 18.9 40.6 50.0 1.23
~ S-NS Ii, , V
i, ,Yi
...1.::"""
j-..[ , : '
f
-l S-RD-O: ", '/ ,"-. , , ! , ,
! ,...4 i , i-"""';""i ! ,
I I ,v, ,i "
I I W i I ~:
1"--. I YJ1 I !Ii I ,
" -"',=r, X I , \ , ~,
Fig.2 Final cracking patterns in shear tests
-S-NS --S-RD-O
---S-RS ---S-RD
o 1 2 3 4
center displacement (mm)
5 6
Fig.3 Normalized shear force Ys. central deflection
- 32 -
60
20
o
I--F-NS
---- F-RD-O
20 40 60
center displacement (mm)
FigA Load - deflection relation in bending tests
80
Fig.5 Final cracking pattern in bending tests
- 33-
4. Results of Dry Shrinkage Measurements
4.1 Internal confinement stress of specimen
Figure 6 shows time-dependent shortening of the specimen of RD before the loading test, in which open
circles indicate measurement values at the ages of zero, one, three, seven, twenty eight and fifty six day from its
concrete placement and an approximate curve based upon the measured values is also drawn. True of the
internal confinement stresses of the specimen were calculated from both the approximate curve in Fig.6 and
also the dry shrinkage of the specimen during air curing. Last, Fig.8 shows a picture of the specimen just before
its loading test, in which a mesh of initial cracking due to dry shrinkage could be seen.
'""" 0~
~ -200
~
.....
~;....
\..)
-400:;::
C)
\..)
'C3'
-600
~
~
s::
-800......
;....
~
":l
i:' -1000Q 0
approximate curve
10 20 30 40 50 60
drying concrete age (day)
Fig.6 Dry shrinkage of specimen RD
--------------------------
tensile strength of ~oncrete
:ft = 2.58N/mm
6010 20 30 40 50
drying concrete age (day)
Fig.7 Internal confinement stress of concrete
- 34-
Fig.8 Cracks due to dry shrinkage
4.2 Relationship between drying shrinkage cracks and due to loading
Fig.9 and]°describe the relationship has been caused by drying shrinkage cracks and cracks that occurred
during the loading test. When loading test, many of the cracks occurred in the initial loading, the crack is
advancing along the drying shrinkage. Dry shrinkage helped the progression of bending crack.
Than this, as in Fig.9 drying shrinkage cracking is to promote the development of flexural cracks. However,
Fig.] 0, diagonal shear cracks that occurred during the shear failure was unaffected by the drying shrinkage
cracks. This is the diagonal shear cracking shear failure will occur when cracks to occur rapidly and probably
little affected the shrinkage cracks. Unlike bending clack, independent of shear cracks lead to destruction.
Fig.9 Bending cracks progress along the
drying shrinkage cracking
- 35 -
Fig.lO Diagonal shear cracks occur suddenly
5. Concluding Remarks
From four shear failure and two flexural failure loading tests of the reinforced concrete beams with low
grade recycled aggregate, followings are concluded:
(1) From the shear failure tests, the recycled aggregate usage specimens provides 30% reduction III shear
strength compared with those using normal aggregate.
(2) No obvious influence of the moisture conditions as well as the sorting of the recycle aggregates was
observed in shear strength.
(3) From the bending failure test, initial crack load and growth were in the earlier loading stage in case of the
low grade recycled aggregate usage. However, both strength and yielding stiffness of the test beams using
the recycled aggregate were as well as those using the normal aggregate.
(4) Dry shrinkage affected the cracking damage of concrete using the low grade recycled aggregates before
loading test, and helped the progression of bending crack while independent of shear cracks lead to
destruction.
(5) In order to understand more deeply the effect of drying shrinkage, we should be fUliher examined using the
finite element analysis.
Refel·ellces
1) Japan Concrete Institute: Current status and future prospects of recycled concrete 2006
2) T. Fumoto: Study on the material propeJiies and the applicability to concrete of the recycled fine aggregate
and power crushing, Dissertation submitted to Osaka City University 2004 (in Japanese)
3) S.Nagato: Research on material properties of low-grade recycled aggregate concrete, Department of Civil
Engineering, Osaka City University, 2008 (in Japanese)
4) Japan Society of Civil Engineers: Standard Specification for Concrete Structures-2007, Design (in Japanese)
- 36 -


Flexural and Shear Failure Tests of Reinforced Concrete Beams with Low Grade Recycled Aggregate

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Flexural and Shear Failure Tests of Reinforced Concrete Beams with Low Grade Recycled Aggregate

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