Flexural Properties of ECC-Concrete Composite Beam
International Journal of
Flexural Properties of ECC-Concrete Composite Beam
Yanhua Guan 0
Huaqiang Yuan 0
Zhi Ge 0
Yongjie Huang 0
Shuai Li 0
Renjuan Sun 0
0 Department of Transportation Engineering, School of Civil Engineering, Shandong University , Jinan 250061 , China
Rebar corrosion-induced durability issue is a major concern for bridges. )e ECC cover was employed to prevent the intrusion of the corrosive agent. )is paper studied the flexural behavior of ECC-concrete composite beam. )e effects of bonding at the interface and fiber mesh reinforcement on the flexural properties and cracking pattern were investigated. )e strain distribution and midspan deflection were evaluated. Test results show that the bonded composite beam had a higher loading capacity. But the unbonded composite beam showed better postcrack energy absorption capacity with higher midspan deflection. )e fiber mesh reinforcement could further improve the flexural properties regardless of the bonding condition. )e strain at the bottom of the unbonded beam was much smaller than that of the bonded beam. )e penetrated cracks were observed at the ECC layer of the bonded composited beam.
)e long-term durability of bridges has become a major
concern, especially for bridges exposed to aggressive
environmental conditions. In 2015, about 79.6 thousand bridges,
which is 10.2% of the total bridges, were classified as
dangerous in China [
]. )e main cause of bridge deterioration
is the corrosion of reinforcing steel, which results in reduced
service life [
] or even collapse. To prevent steel corrosion,
a certain thickness of concrete cover is designed for
reinforced concrete structures. However, in practice, concrete
cover will definitely crack due to mechanical and
environmental loading, low tensile strength of concrete, and so on,
thereby creating a fast entry path for corrosive agents and
causing corrosion [
]. )erefore, one of the key points of
prolonging bridge service life is to prevent cracking and
reduce the permeability of the concrete cover.
Engineered cementations composite (ECC) developed
based on micromechanics has a high ductility and crack
control capacity (crack widths less than 100 ?m) even at large
]. Besides the excellent mechanical
properties, a large amount of researches show that ECC has much
higher durability than that of normal concrete [
Researches indicate that even strained in tension up to 3%, the
permeability and chloride ion diffusivity of ECC were similar
to that of uncracked concrete [
]. )ese unique
properties make ECC very suitable as concrete cover for bridges
under aggressive environments [
]. Researches have been
carried out to investigate the mechanical properties of the
reinforced ECC-concrete composite beam [
Compared to normal reinforced concrete, properties, including
load-carrying capacity, deformability, crack controlling ability,
and fatigue, of beam with ECC layer were improved
significantly. )e ultimate strength and deflection improvement in
composite beams are mainly dependent on the tensile and
compressive ductility of the matrix .
In most of the current studies, the ECC layer was fully
bonded with the normal concrete. )erefore, these two
layers could deform together and increase the load-carrying
capacity. However, large cracks developed at the concrete
could cause localized cracking in the ECC layer [
Some cracks could still penetrate through the ECC layer,
resulting in an entry path for corrosive agents. In this
situation, the high ductility and durability of the ECC could not
be fully utilized. In order to prevent the penetrated crack in
the ECC cover, the unbound composite beam is proposed in
this paper. A plastic sheet was placed at the interface of
normal concrete and ECC to break the bond. Large strain
caused by the cracking in the normal concrete will be
distributed across the entire ECC layer, avoiding the strain
concentration. A ber mesh reinforcement was also placed
in the middle of the ECC layer to further increase its strength
and ductility. In this paper, the e ects of bonding and
reinforcement of ECC on the exural properties of the
composite beam were investigated.
2. Materials and Methods
2.1. Materials. e cement used was ordinary 42.5# Portland
cement with a 28-day compressive strength of 42.5 N/mm .
e main chemical components of cement are provided in
Table 1. e class F y ash containing 3.88% CaO from Jinan,
Shandong province, was adopted. e characteristics of used
PVA ber are listed in Table 2. e high-range water reducer
(HRWRA) and viscosity-modifying agent (VMA) were
employed simultaneously to obtain the proper workability.
Based on the previous study, the water to cement ratio of
0.32, y ash to cement ratio of 1.2, silica sand to cement ratio
of 0.8, and 2% (by volume) of ber were adopted for ECC
mix. e concrete with the compressive strength of 40 MPa
(C40) was used for the composite beam.
2.2. Experiment Design. e 100 ? 100 ? 400 mm composite
beam with a 20 mm ECC layer at the bottom was casted for
the study. Two types of the ECC layer were considered. One
is the pure ECC layer and the other is the reinforced ECC
layer with ber mesh reinforcement in the middle. Two
interface bonding conditions, fully bonded and unbonded,
between normal concrete and ECC layer were designed.
erefore, four di erent types of ECC-concrete composite
beams were studied. During the four-point bending testing,
the strain at di erent locations and midspan de ection was
monitored. e con gurations of the strain gauges are
shown in Figure 1.
2.3. Specimen Preparation. e C40 concrete was rst mixed
according to GB/T 50081-2002  and casted in the mold.
e reinforcing steel was then embedded into the concrete.
After cured for 24 hours, the ECC was mixed and casted on
top of the normal concrete. e beam was then cured in the
standard curing room with 20 ? 2?C temperature and 95%
humidity for 28 days. For the unbonded composite beam,
a plastic sheet was place on top of the normal concrete before
placing ECC to prevent the bonding between ECC and
normal concrete. e ECC layer was anchored at both ends.
For the reinforced ECC layer, the ber mesh was placed at
the middle of the ECC layer before casting ECC.
2.4. Testing Methods. e uniaxial tensile and four-point
bending tests were conducted to evaluate the properties of
ECC. e 15 mm ? 50 mm ? 350 mm specimen was used for
both tests. e LVDT displacement sensors were employed
to measure displacement. e universal testing machine
(WDW-100E) was used for loading. e loading rates were
0.1 mm/min and 0.5 mm/min for direct tensile and four-point
bending tests, respectively. e testing setups are shown in
Figure 2. For the composite beam, the four-point bending
test was carried out by using the microcomputer-controlled
electronic universal testing machine under displacement
control at the rate of 0.5 mm/min until its failure. e strain at
di erent locations was collected by DH3818-4 strain
acquisition box. e midspan de ection was measured by LVDT.
3. Results and Discussion
3.1. Properties of ECC Material. Figures 3 and 4 show that,
under both uniaxial tensile and flexural loading, ECC
exhibits strain hardening behavior. )e first cracking strength
was 2.9 MPa. After the first cracking, the load continued to
increase without fracture localization. Sequentially, more
cracks developed, resulting in the inelastic strain at increasing
stress. )e ultimate tensile strength and tensile strain capacity
were 4.4 MPa and 4.5%, respectively.
)e flexural behavior was similar to that under uniaxial
tensile loading (Figure 4). )e four-point bending test could
be used as an indirect evaluation method for the
strainhardening properties of ECC [
]. )e midspan deflection
reached 20.5 mm at failure. )e first cracking strength and
flexural strength were 7.7 and 14.7 MPa, respectively, which
were much higher than those of normal concrete.
)e typical microcracking patterns of specimen under
uniaxial tensile and flexural loading are shown in Figure 5.
As observed in the figures, microcracks with very tight crack
width were uniformly distributed with an average spacing
less than 1 mm. )e cracking pattern also indicated that the
ECC had a very good strain-hardening property.
3.2. Flexural Behavior of Composite Beam. As shown in
Figure 6, both composite beams show elastic and plastic
behavior under the flexural loading. At the beginning, the
midspan deflection increased linearly with the flexural
loading. At the end of the linear portion there was a force
drop, it could be caused by the cracking of ECC and yielding
of reinforcement steel. After that, more deflection occurs.
Figure 6 also indicates that, regardless of whether the fiber
mesh was embedded in the ECC layer, the type of bonding
between the concrete and ECC layer had significant effect on
both the flexural loading capacity and midspan deflection.
Since the ECC had high tensile strength and ductility, it will
carry the tensile strength together with the steel reinforcement
after concrete cracks, resulting in higher strength. )is trend
is consistent with other research works [
15, 18, 19
Differently, the unbonded composite beam showed a great
postcrack energy absorption capacity due to the deformation
of the ECC layer. )e unbonded ECC cover could be treated
as an external strengthening reinforcement. Since slip at the
interface was allowed, the longitudinal strain was distributed
across the ECC cover, thereby, allowing higher deflection.
)is finding is similar to Kamada and Li?s research. )ey also
found that the interface property could affect the flexural
behavior of the composite beam. )e smooth surface
specimen was able to redistribute the load and utilize more
materials than rough surface specimens. )erefore, the
deflection of the smooth beam was larger than that of the
rough beam [
Placing a fiber mesh in the middle of the ECC layer could
further increase its tensile strength and ductility, which in
turn increased the loading capacity and midspan deflection
at failure (Figure 7). is e ect is more prominent for the
bonded composite beam. e increments were 50% and 70%
for the loading capacity and midspan de ection at failure,
respectively. e midspan de ections were 2.1 and 3.0 mm
for the unbonded beam with and without ber mesh
3.3. Load-Strain Pattern of Composite Beams. e load
versus strain at di erent locations of the bottom is plotted in
Figure 8. ese two types of beam possessed totally di erent
patterns. For the unbonded composite beam, the tensile
strains at points 1 and 2 were negligible due to very small
stress and bending moment. e major strain occurred at the
Point 01 Point 03 1,300 Strain (??)
middle of the span. Di erently, the strain at point 1 of the
unbonded composite beam was close to that of point 3.
Because of the slip at the interface, there was limited shear
resistance. e load carried by the ECC layer would pass to the
anchors at both ends. In this case, all ECC layers were under
tension and had similar tensile strain at the longitudinal
direction. is means that under the same de ection, the ECC
layer of the unbonded composite beam had smaller strain and
lower risk of cracking than that of the bonded beam.
Figure 9 shows the strain distribution at the midspan
section of the composite beam. Figure 9(a) indicates that the
bonding between the ECC and normal concrete was strong and
no slip occurred. e trend is similar to the current research
]. But for the unbonded composite beam, the strain of
the ECC layer increased slowly with the load. When loaded at
15 kN, the strain was 1328 ?? at point 7. But the bottom strain
at point 3 was only 227 ??. e high-strain value at point 7 was
caused by the cracking of normal concrete. Figure 9 also
indicates that under the same loading the strain at the bottom of
the unbonded beam was much smaller than that of the bonded
beam. is further proves that the ECC layer of the unbonded
composite beam had lower risks of cracking, making the ECC
suitable as concrete cover for corrosion resistance.
3.4. Cracking Pattern of the Beams. Figures 10 and 11 show
the cracking pattern of di erent beams. Even though ECC
had very high ductility, localized cracks still occurred at the
ECC cover of the bonded composite beam (Figure 10) due to
the concentrated strain. A major crack right beneath the
crack of the normal concrete penetrated through the
ECC cover. Although the ECC cover improved the beam?s
mechanical performance, there were still risks of corrosion of the
rebar inside the beam and reduction of service life of the bonded
composite beam. Differently, there were no cracks penetrating
through the ECC cover for the unbonded composite beam. Also,
the crack?s width at the ECC cover was limited due to the high
crack control capacity. )e average crack widths at failure were
115 and 98 ?m for the unbonded composite beam without and
with fiber reinforcements, respectively. )erefore, even though
there were cracks at the ECC cover, the permeability would be
limited due to very small crack width, resulting in high
durability. Figure 11 also shows cracking at the left end of the ECC
layer. Since the ECC layer could be treated as the external
reinforcement of the unbonded composite beam, the force
provided by the ECC layer is transferred to the normal
concrete in the compression mode through end anchors,
resulting in tensile stresses in the end anchors. If the stress is
large enough, it will lead to cracking and failure of the anchor.
)is paper studied the effects of bonding and fiber mesh
reinforcement on the flexural properties and cracking
pattern of the composite beams. )e following findings and
conclusions can be drawn:
(1) ECC exhibits strain-hardening behavior. )e first
cracking strength, ultimate tensile strength, and tensile
strain capacity were 2.9 MPa, 4.4 MPa, and 4.5%,
(2) )e bonded composite beam had a higher loading
capacity. But the unbonded composite beam showed
a better postcrack energy absorption capacity. )e fiber
mesh reinforcement could further improve the flexural
properties, regardless of the bonding condition
(3) )e unbonded ECC layer had the ability to distribute
the strain across the beam. Under the same loading,
the strain at the bottom of the unbonded beam was
much smaller than that of the bonded beam
(4) Localized cracking could penetrate through the ECC
cover of the bonded composite beam. )e average
cracking widths were controlled at 115 and 98 ?m for
unbonded composite beam without and with fiber
)e results of this study indicate that the unbonded ECC
cover is more effective in terms of controlling the cracking
and preventing the corrosion-induced damage. )erefore,
the unbonded composite beam could be used for bridges
under aggressive environments to enhancing its service life.
However, further study is needed to quantify the effect of the
bonding on the beam behavior and to explore the durability
of the composite beam.
Conflicts of Interest
)e authors declare that they have no conflicts of interest.
)e financial support is provided by Tai?an Tong Da
Investment Co., Ltd., Ji Nan Tong Da Highway Engineering
Co., Ltd., and the Natural Science Foundation of China of
Shandong (ZR2016EEM03). Sincere acknowledgements are
also given to Nan Gao, Changjin Tian, and Yida Wang for
their great assistance.
Hindawi Publishing Corporation
Control Science and
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