Structural Behavior of Durable Composite Sandwich Panels with High Performance Expanded Polystyrene Concrete
International Journal of Concrete Structures and Materials
Structural Behavior of Durable Composite Sandwich Panels with High Performance Expanded Polystyrene Concrete
Sandwich panels comprising prefabricated ultra-high performance concrete (UHPC) composites can be used as ecofriendly and multi-functional structural elements. To improve the structural and thermal performance of composite sandwich panels, combinations of UHPC and expanded polystyrene (EPS) beads were investigated. High-performance expanded polystyrene concrete (HPEPC) was tested with various EPS bulk ratios to determine the suitability of the mechanical properties for use as a high-strength lightweight aggregate concrete. As a core material in composite sandwich panels, the mechanical properties of HPEPC were compared with those of EPS mortar. The compressive strength of HPEPC is approximately eight times greater than that of EPS mortar, and the thermal conductivity of approximately a quarter that of EPS mortar. The structural behavior of composite sandwich panels was empirically analyzed using different combinations of cores, face sheets, and adhesive materials. In the flatwise and edgewise compression tests, sandwich panels with HPEPC cores had high peak strengths, irrespective of the type of face sheets, as opposed to the specimens with EPS mortar cores. In the four-point bending tests, the sandwich panels with HPEPC cores, or reinforced UHPC face sheets combined with adhesive mortar, exhibited higher peak strengths than the other specimens, and failed in a stable manner, without delamination.
sandwich panel; structural lightweight aggregate concrete; high performance expanded polystyrene concrete (HPEPC); compression test; four-point bending test
Lightweight concrete can be applied in a number of ways,
such as a reduction in self-weight of structures with smaller
cross sections. The lightweight concrete developed could be
a suitable material for high-rise buildings, with a number of
advantages: cost saving due to extra insulation not being
required, more flexibility for architects and structural
engineers when designing buildings, sustainability due to
relatively easy maintenance, and easier recycling
(Yu et al.
One of the typical applications is as a core material in a
composite sandwich structure. Sandwich structures can
comprise various types of cores and skin materials to create
an optimal design for a specific performance target.
Composite sandwich structures are used widely in
weight-sensitive structures where high flexural rigidity is required,
because of the high-specific strength, stiffness, light weight,
high thermal insulation, and the capability to be formed into
(El Demerdash 2013)
composite sandwich panels comprise a relatively thin, stiff, and
strong skin plate with a relatively thick and light core. To
improve the structural performance of standard composite
sandwich panels, numerous strengthening methods have
been proposed and studied. One was the change of core
materials or configurations to strengthen the elements. The
contribution of core materials with high flexural strength and
shear stiffness is significant.
Expanded polystyrene (EPS) was first used as an
aggregate for concrete in 1957. It is the most well-known core
material because of its low density and high thermal
insulation capacity. As opposed to the limited resources of
lightweight mineral aggregates, EPS aggregates are
commercially available worldwide. Therefore, EPS concrete can
be considered as an alternative lightweight aggregate
(Short and Kinniburgh 1978; Babu and Babu 2003;
Sadrmomtazi et al. 2011)
. The composite sandwich panels
evaluated in this study are constructed with an EPS concrete
core, with face sheets on either side of the panel, as shown in
Fig. 1. Precast concrete sandwich panels are composed of
two concrete wythes separated by a layer of rigid foam
plastic insulation, typically
(PCI Sandwich Wall Committee
. Compared with the typical sandwich panels, EPS
concrete core in the EPS concrete sandwich panels can
provide the dual function of transferring load and insulating
structure in a single element, and enveloped face sheet acts
as a strengthening reinforcement of EPS concrete core.
However, the compressive strength of EPS concrete is
generally less than 10 MPa
(Ravindrarajah and Tuck 1994;
Miled et al. 2004; Babu et al. 2006)
, which makes it difficult
to use as a structural construction material. Additionally,
mixture segregation of EPS beads and mortar during the
manufacturing process easily leads to a deterioration in
quality, and a degradation in durability.
In this study, high performance expanded polystyrene
concrete (HPEPC) is proposed in place of EPS concrete. It
was found that the rate of strength development of concrete
increased with an increasing percentage of silica fume
and Babu 2003; Sadrmomtazi et al. 2011)
. Therefore, the
combination of EPS beads and ultra-high-performance
concrete (UHPC) matrix is expected to be stronger than EPS
concrete. An optimized core material and composite
sandwich system was proposed to produce an eco-friendly,
lightweight system with highly resistant mechanical
properties and good thermal insulation. To investigate the
mechanical properties of HPEPC, the compressive strength,
flexural strength, modulus of elasticity, and Poisson’s ratio
were measured, with varying percentages of EPS beads, to
evaluate different densities. After determining the optimum
mixture composition of HPEPC as a high-strength
lightweight concrete, the mechanical and thermal properties of
possible components in composite sandwich panels were
investigated. Compressive and flexural behavior tests of the
various composite sandwich panels, using developed
lightweight concrete, were conducted to investigate the potential
for applications as walls, slabs, and other components in
2. Development of High Performance
Expanded Polystyrene Concrete (HPEPC)
2.1 Experimental Program for HPEPC
EPS concrete is a lightweight, low-strength material with
good energy-absorbing characteristics. However, due to the
light weight of EPS beads, and their hydrophobic surfaces,
EPS concrete is prone to segregation during casting,
resulting in poor workability and lower strength. Fine silica fume
greatly improved the bond between the EPS beads and
cement paste, and increased the compressive strength of EPS
(Cook 1972; Chen and Liu 2004)
. Fine silica
powder is one of the main binders of UHPC, therefore the
combination of UHPC and EPS aggregates is expected to
perform better than normal concrete without silica fume.
Density is known to be an important parameter
determining numerous physical properties of EPS concrete, and it
is determined primarily by the volume fraction of
polystyrene aggregates. The strength of EPS concrete increased
with increasing concrete density and decreasing EPS volume
fractions (Chen and Fang 2011). The thermal resistance of
EPS concrete can also increase with an increase of EPS
volume fractions, due to the decreased density
et al. 2014; Real et al. 2016)
. To evaluate optimized HPEPC
as a core element in a sandwich panel, the mechanical
properties of HPEPC, according to the replacement ratio of
UHPC and EPS in a unit volume, were investigated. The
tested range of the EPS volume fraction in this study ranged
from 30 to 70%. The mix composition of UHPC and the
material properties of EPS, used in this study, are presented
in Tables 1 and 2, respectively.
The design compressive strength of the given mix
composition of UHPC is 180 MPa
(Richard and Cheyrezy 1995;
Wille et al. 2011; KCI 2012)
. The Portland cement was Type
I, as designated by ASTM C150. The silica fume used was
made in Norway, and had a particle size distribution of
45–800 lm. Typically the silica fume/cement ratio used for
UHPC is 0.25 considering the optimum filling performance,
enhancement of the lubrication effect, and the complete
consumption of total hydration of the cement
. Filler, sized between cement and silica
fume sizes, improves the compressive strength of concrete
by increasing the poured density. A mean particle size of the
filler in Table 1 is 2.2 lm and the filler, as an Australian
product, composed ([ 99%) of SiO2 components was used.
Super plasticizer, that has a specific gravity of 1.01 g/cm3,
was used. EPS beads were used as artificial lightweight
aggregates for decreasing the weight of the concrete, and
producing different grades of EPS concrete. The diameter of
85% of the EPS particles was approximately 3.5 mm, and
their actual density was 50.58 kg/m3. Bulk density of EPS
beads is less than half of true density, which means that EPS
beads per unit volume have large pore space. The curing
method involved removing the specimens 1 day after
pouring, and then subjecting them to 90 C high-temperature
steam for 48 h. Figure 2 shows the cylindrical specimens
with different EPS bulk ratios. Bulk ratios of HPEPC of 30
and 40% show that EPS plays a role in lightweight
aggregates within the UHPC matrix, but HPEPC with bulk ratios
greater than 50% shows that UHPC cannot completely fill
the gaps between the EPS. Specimens with an EPS bulk ratio
of 70% have massive pores in their structure. With
increasing EPS replacement ratios, the HPEPC is expected
Bulk density (kg/m3) True density (kg/m3) Bead diameter (mm)
to be lighter and more thermally resistant, but the
compressive strength is expected to decrease.
2.2 Test Results
The compressive strength tests were carried out in
accordance with ASTM C109. On the seventh day, the strength of
the cubic specimens (50 9 50 9 50 mm3) was measured
using a universal testing machine. The specimens were
subjected to displacement at a loading rate of 1 mm/min.
The unit weight of the HPEPC was measured according to
standard KS F 2462, that contains a method for determining
the unit mass of structural lightweight concrete.
To determine the modulus of elasticity and Poisson’s ratio,
cylindrical concrete specimens, 100 mm in diameter and
200 mm high, were tested according to ASTM C469 (2014).
A compressometer was used to measure the modulus of
elasticity. The mean strain was measured by two strain
gauges, opposite each other halfway up the specimen,
parallel to the vertical axis. The specimens were tested, and
maintained within the defined curing state, within 1 h after
removal from the mold. The transverse strain was
determined by an unbonded extensometer, with an accuracy of
0.5 lm, that measured changes in diameter at the mid-height
of the specimen. A combined compressometer and
extensometer was used to obtain Poisson’s ratio.
The test results are summarized in Table 3. The
compressive strength and density of UHPC measured on the 7th
day were 196.83 MPa and 2311.07 kg/m3, respectively, for
the same curing conditions as the other specimens. The
density and compressive strength of HPEPC decreased with
increasing EPS bulk ratios. The density of HPEPC decreased
almost linearly with increase EPS bulk ratio till 60%, but the
density of HPEPC with EPS bulk 70% decreased steeply.
The massive pores in the specimens with EPS bulk 70% in
Fig. 2 supports these test results. The compressive strength
of HPEPC decreases at a rate greater than the rate of increase
of the EPS bulk ratio. Figure 3a shows the normalized
compressive strength and density, by material properties, of
UHPC that contained no EPS. The modulus of elasticity
shows tendencies similar to the compressive strength, but the
Poisson’s ratio decreases negligibly compared to the other
properties. Figure 3b shows all the test results, except for the
average values, that indicate that the standard variation of
Poisson’s ratio increases with an increase in the EPS bulk
ratio, despite the relatively constant average value, 0.6.
From the test results, HPEPC with a 40% EPS bulk ratio
was chosen as a core material for the composite sandwich
panels, taking into consideration the decreased rate of
compressive strength, modulus of elasticity, and density as a
function of the EPS bulk ratio.
This can be regarded as a high strength lightweight
concrete. According to fib Model Code 2010, it is recommended
that lightweight aggregate concrete for structural
applications have a density in the range 800–2000 kg/m3, and high
strength concrete is typically accepted to have a
characteristic compressive strength greater than 50 MPa
3. Experimental Investigation of Component
Materials in Composite Sandwich Panels
3.1 Test Program for Composite Sandwich
As can be seen in Fig. 1, composite sandwich panels
comprise a prefabricated core and a prefabricated face sheet,
with glue between them. To investigate the optimized
composite sandwich panels using HPEPC cores, three types
of face sheet materials, ultra-high-performance
fiber-reinforced concrete (UHPFRC), UHPC with a glass fiber
reinforced polymer (GFRP) mesh, and GFRP were tested with
both adhesive mortar and epoxy bond as a glue. Specimens
with EPS mortar cores were also tested, for comparison with
the specimens with HPEPC cores. EPS mortar in this study
is distinguished by EPS concrete by no silica fume, no
coarse aggregates. EPS mortar was composed by ready
mixed cement mortar and EPS beads. The mechanical
properties of EPS mortar was targeted for structural
applications. The test program is presented in Table 4. The first
letter of the specimen ID is the core material, and the second
letter the face sheet material.
The test set-ups and dimensions of the specimens are
shown in Fig. 4. The thickness of the core and face plate are
55 and 5 mm, respectively, and the specimens are 65 mm
thick. Results of flatwise compression tests can be used for
the applications of the support zones under concentrated
loads. To compare core compressive behavior only,
specimens with two different cores, with GFRP face sheets, were
tested. For applications of load bearing walls and slabs in
high-rise buildings, specimens bonded by adhesive mortar
were tested for edgewise compressive loading, as well as for
flatwise flexural loading
(Manalo et al. 2010)
. In addition,
specimens with different face sheets, with their HPEPC
cores bonded by epoxy, were tested to investigate
delamination between cores and face sheets. Flexural behavior
testing was planned for all composite sandwich panels, but
the face sheet of the M-U2 specimen detached before the test
was conducted, and the flexural test results of that specimen
are not recorded.
3.2 Mechanical and Thermal Properties
of Component Materials
3.2.1 Mechanical Properties of Component
Mechanical properties of component materials, except for
UHPC reinforced by GFRP mesh, are presented in Table 5.
The compressive strength of EPS mortar was measured on
the twenty-eighth day after pouring. The mechanical
properties of HPEPC were written on the seventh day according
to Table 3. The compressive strength after the 90 C heat
treatment for 48 h can be regarded as a result of fully
(Fehling et al. 2014)
, and the compressive
strength after the heat treatment tends to maintain their
strength regardless additional curing duration
(Kang et al.
. For the same density and 40% EPS bulk ratio, the
compressive strength of HPEPC was approximately eight
times higher than that of EPS mortar. The compressive
strength of UHPFRC, with a 2% steel fiber volume fraction,
was greater than 190 MPa, for the same UHPC mix
composition and curing conditions as the HPEPC. The mix
compositions are presented in Table 1, and the most
commonly used steel fiber, with a diameter of 0.2 mm,
13 mm long, and 250 MPa tensile strength was used.
Three-point bending tests were conducted on the beam
specimens to determine their flexural strength
(160 9 40 9 40 mm3). Figure 5 shows the EPS mortar and
HPEPC flexural test results. The crack face of the EPS
mortar specimen shows that EPS beads had segregated from
the mortar, which meant that cracks had generated along the
EPS beads. On the other hand, the crack face of the HPEPC
specimen shows that EPS beads were fractured, and that
cracks had gone through the EPS beads. These crack faces
are similar to typical crack faces of normal strength concrete
and high strength concrete with coarse aggregates,
(Mohamed and Richard 1999)
. The flexural strength
of UHPFRC is greater than 32 MPa, with considerable
tensile strain, and the post-peak behavior shows outstanding
In addition to the tested components in Table 5, UHPC
with GFRP mesh and GFRP plates were applied as face
sheets on composite sandwich panels (Fig. 6). Fabric-type
GFRP, as a GFRP mesh, was used to maximize the tensile
strength by ensuring the smoothness of the shell and the
convenience of installation
(Fam and Sharaf 2010; Correia
et al. 2012)
. The mesh was affixed to the form prior to
pouring, to ensure adhesion to the concrete. UHPC
reinforced by GFRP mesh was expected to be lighter and more
ductile than UHPFRC (Shams et al. 2014). The GFRP plates
used in this study were manufactured from three different
types of mats, laminated, and embedded in a polyester resin
matrix: surface mats of 30 g/m2, chopped mats of 380 g/m2,
and roving cloth mats of 570 g/m2. The face sheets were
produced using a hand lay-up technique. Adhesive mortar
and epoxy bond were used as adhesive materials. The
adhesive strength of both materials, from technical data, is
approximately 2.0–2.1 N/mm2 after 28 days.
3.2.2 Thermal Properties of Component Materials
The thermal properties focused on were thermal
conductivity (k), thermal resistance (R), and thermal transmittance
(U). These term are defined in ASTM C168 (2017): thermal
conductivity is the rate of steady state heat flow through a
unit area of a material induced by a unit temperature gradient
in a direction perpendicular to the unit area; thermal
resistance is the quantity determined by the temperature
difference, at steady state, between two defined surfaces of a
material that induces a unit heat flow through a unit area; and
thermal transmittance is the heat transmission in unit time
through a unit area of a material and the boundary air films,
induced by unit temperature differences between the
environments on each side. Thermal conductivity and resistance
are indices of heat flow from surface to surface, but thermal
transmittance is an index from environment to environment;
therefore, the environmental temperatures of both sides must
be well defined. Lower thermal conductivity, lower thermal
transmittance, and higher thermal resistance ensure efficient
thermal insulation performance of a sandwich panel.
The specimens were prepared in accordance with ISO
9869-1 (2014). All components used for the structural tests
were made of panels sized 300 9 300 9 20 mm3.
Measurement periods were at least 72 h on the outside of the
specimens, to comply with the ISO 9869 norm. For
measurements where the inside structure varied, the
measurement time was extended, considering the importance of
constant conditions according to the ISO norm. The test
results are presented in Table 6.
The thermal conductivity of concrete depends primarily on
its density and water content, and tends to increase with
increasing density and water content
(Holm and Bremner
. According to
Holm and Bremner (2000)
, the thermal
conductivity of structural lightweight aggregate concrete,
with an average density of approximately 1850 kg/m3,
typically ranges from 0.58 to 0.86 W/(m K). In normal-weight
concrete of approximately 2400 kg/m3 density, the thermal
conductivity can vary from 1.4 to 2.9 W/(m K). A typical
thermal conductivity value for concrete with quartzite
aggregate is 3.5 W/(m K)
(Metha and Monteiro 2006)
thermal conductivity of EPS concrete, with an EPS bulk
ratio of 55–60%, was 0.50–0.56 W/(m K) at a density of
approximately 1100 kg/m3
(Schackow et al. 2014)
comparing the typical values of lightweight concrete and
EPS concrete, the thermal properties of EPS mortar in this
study were found to be lower than anticipated. However, the
HPEPC specimens exhibited outstanding thermal insulation
performance. The U- and k-values of HPEPC are
approximately 3.34 times lower than those of EPS mortar, despite
the similar density of the two specimens. For face sheet
components, UHPC reinforced by GFRP mesh has a 1.43
times higher U-value, and lower R-value, than those of
UHPFRC. It can be concluded that HPEPC exhibits better
thermal resistance than typical structural lightweight
concrete, and the thermal resistance of UHPFRC is greater than
that of normal concrete of similar density.
4. Structural Behavior of Composite
4.1 Compressive Behavior of Flatwise and Edgewise Composite Sandwich Panels
The flatwise compression tests were conducted in
accordance with ASTM C365 (2016). Compressive strength tests
were performed on three sandwich specimens,
100 9 100 9 65 mm3, for the EPS mortar core and the
HPEPC core. The load was applied with a universal test
machine, with a 2000 kN capacity. The ultimate flatwise
compressive strengths, based on the averaged test results, are
8.89 MPa for the M-G specimen, and 45.23 MPa for the
U-G specimen (Table 7). The failure modes of both
specimens are core compression failure, as shown in Fig. 7. When
comparing the material properties of the core materials in
Table 5, the ultimate compressive strength of the M-G
specimen is greater than the compressive strength of EPS
mortar, but the ultimate compressive strength of the U-G
specimen is significantly lower than that of the HPEPC
specimen. The material compressive strength of HPEPC is
approximately eight times greater than that of EPS mortar,
but the flatwise compressive strength of the U-G specimen is
approximately five times greater than that of the M-G
specimen. This phenomenon might be interpreted by size
effect and high strength effect. The compressive strength of
EPS concrete decreases significantly with an increase in EPS
bead size for the same concrete porosity
(Miled et al.
2004, 2007; Le Roy et al. 2005; Babu et al. 2006)
observed that the EPS beads size effect is very pronounced
for low porosity concretes. In addition, for 6.3 mm EPS
beads concrete, unlike 2.5 mm beads EPS concrete, the
compressive strength can be affected by specimen size
(Miled et al. 2007). HPEPC has much less porosity than
general EPS concrete and the EPS bead size applied in this
study was 3–5 mm, which can lead to the specimen size
Edgewise compression tests determine the compressive
properties of structural sandwich construction in a direction
parallel to the sandwich facing plane. The tests, to evaluate
the in-plane compressive behavior of the sandwich panels
made of both core materials, were carried out in accordance
with ASTM C364 on specimens with nominal dimensions of
250 9 250 9 65 mm3. The loaded surfaces (250 9
65 mm2) were levelled to avoid any non-uniform or
transverse loading. The load was applied with the same testing
machine used in the tests described above. The test results in
Table 7 show that the maximum strength of the specimens
with EPS mortar core depends on the type of face sheets, but
the maximum strengths of the specimens with HPEPC cores
are greater, irrespective of the type of face sheets.
Failure mode is important in edgewise compression test
results, and commonly observed failure modes of composite
sandwich panels can be categorized as face sheet failure,
comprising buckling or compression failure, or core failure,
comprising compression or shear failure (ASTM C364
Table 7 Flatwise and edgewise compression test results for composite sandwich panels.
CEoPreS mmaotretrairal Face UshHePeFtRmCaterial PmFalxa–t(wkNis)e compreFssaiiolunre–temst ode PmE2ad5xg6(e.k1wNis)e compBreuFscaskiiloluinnrpegltaemtoseftodfaece
UHPC wmiethshGFPR – – 110.2 Compreosfsifoancefailure
GFRP plate 88.9 Core compression 95.2 Compreisnsicoonrefailure
HPEPC UHPFRC – – 447.0 Bucklinpglatoef face
UHPC wmiethshGFPR – – 463.3 Compreosfsifoancefailure
GFRP plate 452.3 Core compression 471.6 Compreisnsicoonrefailure
2016). In this study, it was observed that the specimens
sheeted by GFRP plate experienced core failure, and the
other specimens face sheet failure. In all specimens, initial
cracking was observed in the core, and the M-G and U-G
specimens suffered core failure, with severe delamination
between the face sheets and cores. The other specimens
behaved differently after core cracking, depending on the
types of face sheets. The specimens sheeted with UHPFRC
resisted additional compressive loading with less stiffness,
but failed with face sheet buckling. The specimens sheeted
by UHPC with GFRP mesh did not resist additional
compressive loading, but ductile behavior was observed with
constant compressive loading. The failure modes of the
specimens with HPEPC cores, as shown in Fig. 8, depend on
the face sheets. The U-U1 specimen failed by UHPFRC
buckling in a brittle way, and the U-U2 specimen failed by
compressive failure in the face sheet. Shear failure in the
HPEPC core was observed in U-G specimen.
4.2 Flexural Behavior During Four-Point
Bending Tests on Composite Sandwich Panels
Flexural tests were conducted in a four-point bending
configuration. The bond capacity between the face sheet and
core plays an important role in the flexural capacity of a
sandwich panel. The separation of the facing from the core
in the adhesive bond zone is one of the most frequent failure
modes for sandwich panels with concrete facings
et al. 2014)
. Using externally bonded reinforcement as
shown in Fig. 1a, the bond between the adhesive and the
concrete often fails once the tensile strength of the concrete
has been exceeded. Following the local debonding of
externally bonded reinforcement and the concrete, the results
mostly induces a total failure of the bond between the
externally bonded reinforcement
(Zilch et al. 2014)
representative stress distribution depending on the bond
capacity between the face sheet and core can be explained by
non-composite section and fully composite section in Fig. 9.
For a non-composite sandwich panel, the three concrete
wythes act independently, so that the distribution of loads is
based on the relative flexural stiffness of each wythes. For a
fully composite panel, the entire panel acts as a single unit in
bending and the flexural design of fully composite panels
can be considered as I-shaped section applying transformed
(PCI Sandwich Wall Committee 1997)
There are numerous techniques, for instance the shear
connection between the outer face sheets, for ensuring linear
composite behavior in the cross sections
(Benayoune et al.
2008; Shams et al. 2014)
. To consider the importance of
bond behavior between prefabricated concrete, epoxy bond
as an adhesive material was also tested for the U-U1 and
Table 8 and Fig. 10 shows the failure modes of the
specimens. The flexural capacity of the specimens with
EPS mortar cores, and the specimens with epoxy bonds,
was significantly less than the flexural capacity of the
specimens with HPEPC cores. The peak loads of the
specimens with epoxy bonds was 0.3–0.6 times the peak
loads of the specimens with the same components, but with
different adhesive materials. Therefore, it can be concluded
that the epoxy bond is not appropriate as an adhesive
material in prefabricated concrete panels. Whether
delamination was observed before the peak load is also indicated
in Table 8, as delamination induces not only a decrease in
the flexural capacity, but also occasional brittle structural
behavior. Both specimens sheeted with GFRP plate, and the
specimens with epoxy bonding, were clearly delaminated
before the peak load, as shown in Fig. 10. For the
specimens with a delamination, core cracking tends to govern
the overall flexural capacity, which means that the
maximum stresses in the EPS core determines the peak load
without externally bonded reinforcement’s role as shown a
non-composite section in a Fig. 9. On the other hand, the
delamination in U-U2 specimen was observed after the
peak load in a partial region, which induces ductile
behavior till a total failure.
Figure 11 shows that load–displacement curves for the
specimens except the specimens bonded by epoxy material.
All panels exhibited an approximately linear behavior up to
initial cracking in the core. Of the specimens with an EPS
mortar core, despite the small peak load, the M-U1 specimen
resisted in a stable manner, and failed by the UHPFRC plate
yielding at the bottom, as shown in Fig. 11a. Figure 11b
shows the load–displacement curves of the specimens with
HPEPC cores. Depending on the type of face sheets, the
elastic region before initial cracking in HPEPC cores showed
some scatter. The initial cracking strength in the core of the
U-G and U-U2 specimens differed, but the peak loads were
similar. However, the load–displacement relationship of the
U-G specimen shows behavior that is too brittle, so it is not
recommended for practical applications. On the other hand,
the U-U1 specimen also shows brittle behavior in the load–
displacement relationship, but it did not collapse, as the
Fig. 11 Force–displacement relationship of flexural tests for composite sandwich panels; a comparison of test results for the
specimens with UHPFRC plate and b comparison of test results for the specimens with HPEPC core.
UHPFRC face resisted after the peak load, without
delamination. The post-peak behavior of the U-U2 specimen is
outstanding, ensuring conservative flexural loading, and the
specimen failed by the yielding of the GFRP mesh in the
Measured strain values in Fig. 12 demonstrate the flexural
behavior in detail. The specimens reinforced by UHPFRC
face sheets shows partially composite flexural behavior. For
for U-U1 specimen and M-U1 specimen, the initial crack
was observed in a core and face at the same time and the
final failure was related to the face yielding or bending. On
the other hand, the specimens reinforced by GFPR plates
shows non-composite flexural behavior. The face sheets in
U-G specimen and M-G specimen hardly resist flexural
Fig. 12 Measured strain values of composite sandwich panels; a U-U1 specimen, b U-G specimen, c M-U1 specimen, and d M-G
loads, so that the initial crack was caused by tensile stress at
the bottom of the core and the compressive stress in the top
of the core induces the final failure. The provision in ACI
318-11 requires that reinforced flexural members need at
least 1.2 times additional load beyond cracking to reach its
flexural strength to prevent abrupt flexural failure developing
immediately after cracking
(ACI Committee 318 2011)
U-U1 specimen and M-U1 specimen satisfy the statement,
and U-G specimen also satisfies that in spite of almost single
resistant behavior of HPEPC core.
5. Summary and Conclusions
To investigate the mechanical properties of HPEPC, the
compressive strength, flexural strength, modulus of
elasticity, and Poisson’s ratio were measured for various densities
obtained by altering the amount of EPS beads. It was found
that HPEPC with 40% EPS bulk ratio was suitable for high
strength lightweight concrete. HPEPC exhibits better
mechanical and thermal resistance than typical structural
lightweight concrete. The HPEPC had compressive strength
and thermal conductivity 8 and 0.25 times, respectively,
those of EPS mortar. The lightweight and thermal insulation
characteristics is suitable for HPEPC to be applied as core
material in sandwich panels. To qualify the structural
behavior in composite sandwich panel, flatwise and
edgewise compression tests, and four-point bending tests, were
conducted on various composite sandwich panels. The
HPEPC and EPS mortar were considered as core materials in
composite sandwich panels, and specimens sheeted by three
types of faces, UHPFRC plate, UHPC plate reinforced by
GFRP textile mesh, and GFRP plate were tested for each
core material. The structural test results indicated that the
sandwich panel with an HPEPC core and UHPFRC face
sheet can be used for high-strength lightweight elements,
and the sandwich panel with EPS mortar and UHPFRC face
sheet can be used as structural lightweight concrete.
This research was supported by a Grant (13SCIPA02) from
Smart Civil Infrastructure Research Program funded by
Ministry of Land, Infrastructure and Transport (MOLIT) of
Korean Government and Korea Agency for Infrastructure
Technology Advancement (KAIA).
This article is distributed under the terms of the Creative
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