Experimental Investigation on the Blast Resistance of Fiber-Reinforced Cementitious Composite Panels Subjected to Contact Explosions
International Journal of Concrete Structures and Materials
Experimental Investigation on the Blast Resistance of Fiber- Reinforced Cementitious Composite Panels Subjected to Contact Explosions
This study investigates the blast resistance of fiber-reinforced cementitious composite (FRCC) panels, with fiber volume fractions of 2%, subjected to contact explosions using an emulsion explosive. A number of FRCC panels with five different fiber mixtures (i.e., micro polyvinyl alcohol fiber, micro polyethylene fiber, macro hooked-end steel fiber, micro polyvinyl alcohol fiber with macro hooked-end steel fiber, and micro polyethylene fiber with macro hooked-end steel fiber) were fabricated and tested. In addition, the blast resistance of plain panels (i.e., non-fiber-reinforced high strength concrete, and non-fiberreinforced cementitious composites) were examined for comparison with those of the FRCC panels. The resistance of the panels to spall failure improved with the addition of micro synthetic fibers and/or macro hooked-end steel fibers as compared to those of the plain panels. The fracture energy of the FRCC panels was significantly higher than that of the plain panels, which reduced the local damage experienced by the FRCCs. The cracks on the back side of the micro synthetic fiber-reinforced panel due to contact explosions were greatly controlled compared to the macro hooked-end steel fiber-reinforced panel. However, the blast resistance of the macro hooked-end steel fiber-reinforced panel was improved by hybrid with micro synthetic fibers.
fiber-reinforced cementitious composites; macro hooked-end steel fiber; micro synthetic fiber; contact explosion; blast charge; local damage; fracture energy; panel
Reinforced concrete (RC) structures, which can be used
semi-permanently because of their high strength and high
durability, are used for infrastructure and military facilities.
RC has comparatively good blast resistant performance
compared to other building materials. However, in recent
years, terrorist activities and accidental explosions have
caused damage to RC structures. These incidents result in
the loss of human life and significant damage to properties of
national interest (Luccioni et al. 2004; Osteraas 2006; Islam
and Yazdani 2008). Blast and impact load caused by
explosions and physical conflict must be considered in the
design of protective structure systems for improved safety. In
the case of local damage of RC panels subject to explosive
loads, it is important to suppress the spall of the panel in
terms of secondary damage caused by scattering of concrete
fragments (McVay 1988). In addition, for high-rise buildings
and plant equipment, local damage caused by explosions or
mechanical collisions is likely to lead to continuous collapse,
causing additional loss of life and property damage. In this
scenario, it is especially necessary to enhance the protection
ability of the concrete materials under blast loads.
Research on the anti-blast performance of cement-based
composite materials, such as concrete, which has been
conducted for application to the protective design of military
facilities and infrastructure, has primarily examined the
dynamic behaviors of RC under blast loads (Wang et al. 2013;
Wu et al. 2009; Silva and Lu 2009). In particular, Morishita
et al. (2000), Morishita et al. (2004) and Tanaka and Tuji
(2003) reported that the space between reinforcing bars and
the compressive strength of concrete were not effective
indicators for predicting the local damage and breaking point of a
concrete slab through contact-blast testing. Moreover,
according to the test results performed by Nam et al. (2011),
the blast resistance of RC specimen was obviously not
influenced by the reinforcement of steel bar. The local damage of
RC specimen was exhibited similarly to the results of the
nonfiber-reinforced high strength concrete specimen. These
results indicate that other methods should be considered to
reduce the damage of concrete panels by blast loads.
For decades, previous studies have utilized
fiber-reinforced composites at both material and structural levels to
improve the blast and impact resistance of cement-based
composite materials (Yamaguchi et al. 2011; Silva and Lu
2007; Ohkubo et al. 2008; Ha et al. 2011; Wu et al. 2009;
Mosalam and Mosallam 2001; Razaqpur et al. 2007; Xie
et al. 2014; Ohtsu et al. 2007; Lan et al. 2005; Soe et al.
2013; Nam et al. 2010; Kim et al. 2015; Li et al. 2016;
Coughlin et al. 2010; Yoo et al. 2015; Kim et al. 2015; Yoo
and Yoon 2016; Nam et al. 2016). Yamaguchi et al. (2011)
reported that polyethylene fiber-reinforced concrete has
superior blast resistance under contact explosions as
compared with normal RC. Silva and Lu (2007) examined the
blast resistance of RC slabs containing fiber-reinforced
polymers (FRP). The fiber reinforcing was applied on one or
both sides and subjected to a close-in blast test. The
explosion resistance of RC slabs was improved by the
inclusion of FRP, and the effect of reinforcement on both
sides was found to have a larger effect than reinforcement of
only one side. Ohkubo et al. (2008) used contact-blast
testing to identify the reduction of spall due to applying a
reinforcing carbon fiber sheet and an aramid fiber sheet on
the back side of a concrete slab. Ha et al. (2011) also used a
close-in blast test to evaluate the reduction of fracture of
concrete panels due to reinforcement with CFRP and
polyuria (PU). To control the destruction and suppressed
cracking, it is necessary to review the blast resistance of the
fiberreinforced cementitious composites (FRCCs). Wu et al.
(2009) evaluated the explosion resistance of slabs
manufactured with both ultra-high performance fiber concrete
(UHPFC) and reinforced ultra-high performance fiber
concrete (RUHPFC). The blast resistance of the RUHPFC slab
was good compared to the other concrete slabs in the
closein blast tests. However, there have been very limited studies
on the local damage of FRCC panels with various blended
fibers and comparison of their blast resistance to that of
For blast tests of cementitious composite materials, the
failure modes are influenced by the standoff distance from the
explosion source. The effect of blast load on the test
specimens decreases with atmospheric pressure and the dispersion
of explosion pressure increases with the distance from the
explosion source. Furthermore, the mass of high explosive
(HE) is also serves as a very important parameter in the failure
modes of cementitious composite materials. Therefore, the
scaled distance with the mass of HE has a significant impact on
the failure modes of cementitious composite materials under
the explosion test. In the close-in blast test, generally induces
global damage of the test specimen, such as flexural failure,
cracking, and shear-punching action, based on the standoff
distance level. However, local damage (i.e., crater, spall, and
breach) also will occur if the combined loads are severe
enough (McVay 1988), although that require larger blast
charge compared to the contact blast test. In contrast, the
failure modes of cementitious composite materials caused by
contact-blast tests tend to be local damage. Thus, the current
study employs contact explosions because various strengths
of blast charge are required; namely, when considering the
explosion tests on a laboratory scale, the local damage of the
concrete panel caused by the close-in blast test is difficult to
perform, whereas the evaluation of local damage is possible
with only a small amount of blast charge in contact explosions.
In particular, the spall damage on the back side of a
structure is closely related to the fracture energy; thus, the
damage of FRCCs under contact explosions must be
evaluated to consider the blast resistance according to the
development of fracture energy. Additionally, since the strain
rates of cementitious composite materials under contact
explosions are approximately 1000–0,000 s-1, it is very
difficult to evaluate the dynamic properties of cementitious
composite materials under contact explosions. Thus, the
static fracture energies of cementitious composite materials
are considered in order to examine the dynamic fracture
energy. The dynamic fracture energy is approximately the
same as the static fracture energy (van Doormaal et al. 1994;
Lee and Lopez 2014).
Due to FRCC indicates superior energy absorption
capacity, very low crack widths, and high ductility, it can be
expected a suitable safety performance as protective
structures more than conventional concrete under extreme
loadings such as high-velocity impacts and explosions. However,
very few investigations of the blast resistance of FRCC
panels under contact explosions have been conducted.
Accordingly, in this study, the local damage of FRCC panels
with blended fibers was investigated after exposure to
contact explosions, and the relationship between the static
fracture energy and failure mode was examined. To clarify
the blast resistances of FRCC panels, plain panels, such as
non-fiber-reinforced high strength concrete (NHC), and
nonfiber-reinforced cementitious composites (NCC) were also
tested. In addition, the hybrid effect of micro synthetic fibers
and macro hooked-end steel fibers in FRCCs was
investigated. Moreover, the experimental results were examined
through comparison with existing damage evaluation
prediction equations for prediction of the limited thickness on
the local damage of panels subjected to contact explosions.
2. Experimental Program
The experiments were designed to evaluate the blast
resistance of FRCC panels compared with plain panels. The
used materials, the test specimen preparations, and the
applied test procedures for the experimental measurements
are discussed in this section.
2.1 Materials and Mixture Proportions
The employed materials are summarized in Table 1. Type
II Ordinary Portland cement (ASTM 2016) was used as the
binder for the cementitious materials. In the case of NCC
and FRCCs, class-F fly ash (ASTM 2015) was used as 15%
of the total binder to improve the workability (Yang et al.
2007; Mahmoud et al. 2013). The mixture proportions for
NHC and NCC are shown in Table 2. The water/binder ratio
(W/B) of NHC was 0.3, and that of NCC was 0.4. The unit
weight of the binder used for NHC was 533 kg/m3, and that
used for NCC was 1129 kg/m3. A polycarboxylic acid-based
high-range water reducer (HRWR) was used to achieve the
target flow for each fresh cementitious composites.
Table 1 Material properties.
Fly-ash (used for NCC and FRCCs)
River sand (used for NHC)
Silica sand (used for NCC and FRCCs)
Crushed coarse aggregate (used for NHC)
Ordinary Portland cement (Type II), density: 3.15 g/cm3, fineness:
Class-F type, density: 2.30 g/cm3, fineness: 3228 cm2/g
Density: 2.54 g/cm3, absorption ratio: 1.01%
Density: 2.64 g/cm3, absorption ratio: 0.38%, class-7
Maximum size: 20 mm, density: 2.65 g/cm3, absorption ratio: 1.39%
Table 2 Mixture proportions of plain specimen.
NHC non-fiber-reinforced high strength concrete, NCC non-fiber-reinforced cementitious composite.
a High-range water reducer, target value of flow in NHC: 550 ± 50 mm, target value of flow in NCC: 170 ± 20 mm.
Except for the blended fibers, the mixed materials of the
FRCCs were the same as those of the NCC, as described
in Table 1. Table 3 shows the properties of the fibers used
in this study. Pictures of the used fibers are shown in
Fig. 1. Two kinds of micro synthetic fibers, i.e., polyvinyl
alcohol (PVA) fiber and polyethylene (PE) fiber, were
used in the preparation of the PVA fiber-reinforced
cementitious composite (PVACC) and the PE
fiber-reinforced cementitious composite (PECC), respectively.
Additionally, macro hooked-end steel fibers of 30 mm in
length and 0.7 mm in diameter were used for the steel
fiber-reinforced cementitious composite (SCC) panels.
Table 4 shows the mixture proportion of the FRCCs. The
fibers were blended at 2% of the total volume, and other
properties, such as W/B and binder, were applied to the
panels under the same conditions as the NCC panels.
Moreover, hybrid FRCC panels were manufactured with
the micro synthetic fibers and macro hooked-end steel
fibers. The hybrid FRCC panels are denoted with
PVASCC (indicating a hybrid of micro PVA fibers and
macro hooked-end steel fibers) and PESCC (indicating a
hybrid of micro PE fibers and macro hooked-end steel
fibers) followed by the hybrid fibers type, and the
proportions of the hybrid materials were composed in a 1:1
ratio. This series was considered for the hybrid effects of
micro and macro fibers under contact explosions.
Table 3 Properties of fibers.
Specific density (g/cm3)
Tensile strength (MPa)
Fig. 1 Pictures of fibers; a polyvinyl alcohol (PVA), b polyethylene (PE), c hooked-end steel.
Table 4 Mixture proportions of FRCC specimen.
PVACC PVA fiber-reinforced cementitious composite, PECC PE fiber-reinforced cementitious composite, SCC Steel fiber-reinforced
cementitious composite, PVASCC Hybrid fiber-reinforced cementitious composite (PVA fibers ? Steel fibers), PESCC Hybrid fiber-reinforced
cementitious composite (PE fibers ? Steel fibers).
a The total volume (share of PVA fiber).
b The total volume (share of PE fiber).
c High-range water reducer, target value of flow in FRCCs: 170 ± 20 (mm).
2.2 Test Setup and Procedure
2.2.1 Static Mechanical Tests
Figure 2 shows the experimental set up for compression
and static fracture energy testing of the cementitious
composite specimens. The compressive strength and the elastic
modulus were evaluated in accordance with ASTM C 39
(ASTM 2015) and ASTM C469 (ASTM 2014), and
determined from standard cylindrical specimens of 100 mm in
diameter and 200 mm in height. The compression tests were
performed using a universal testing machine (UTM) and a
compressometer with linear voltage differential transformers
(LVDTs). The flexural properties of each notched specimen
were performed according to RILEM 50-FMC Draft
Recommendation (RILEM 50-FMC Draft Recommendation
1985) to determine the facture energy of the fiber-reinforced
concrete. Each specimen had a notch at the center of the
prismatic specimen, which were cut by using a circular
diamond concrete saw. The fracture energy (energy
absorption capacity) was determined using Eq. (1):
GF ¼ ðW0 þ mgd0Þ=Alig:
where GF is the fracture energy (Nm/m2), W0 is determined
from the crack-mouth opening displacement (CMOD) based
on the area of the load (Nm), m is m1 ? 2m2, m1 is the mass
of the specimen between the supports (kg), m2 is the mass of
the part of the loading arrangement that is not attached to the
machine, g is acceleration due to gravity (9.81 m/s2), d0 is
the final deformation of the specimen (m), and Alig is the
cross-sectional area of the fracture (m2).
The mechanical properties were evaluated after ageing for
28 days following curing in an environmental chamber at a
temperature of 23 ± 2 C and a relative humidity of
60 ± 5%.
2.2.2 Contact-Blast Tests
The damage of plain panels under contact explosions was
evaluated for failure modes such as crater, spall, and breach.
The failure modes of the plain panels were obtained
according to amount of blast charge for the contact blast tests
using emulsion explosives. Observations of how the amount
of blast charge affected the failure mode of plain panels were
made, and a suitable amount of blast charge for damage
evaluation was determined. From evaluating the damage
results of plain panels, the amount of blast charge for contact
blast tests of FRCC panels was determined. In this study,
emulsion explosives (NewMITE Plus) were used in contact
blast tests because they are chemically very safe and easy to
cast (Hanhwa Corporation/Explosive 2016). For emulsion
explosives, the thermal energy is 4.61 MJ/kg, which is
calculated by heat of explosion (1100 kcal/kg) of NewMITE
Plus. In addition, the value of the thermal energy of TNT
was used 4.29 MJ/kg with reference to the previous work by
Morishita et al. (2000, 2004). Thus, the ratio of the thermal
energy between TNT and emulsion explosives is 1.07. In
later discussions, the mass of the emulsion explosive is
converted to equivalent TNT mass by means of this ratio.
As shown in Fig. 3, the dimensions of the plain and FRCC
panels were 1000 mm 9 1000 mm 9 100 mm. To conduct
the contact blast tests, emulsion explosives with a
semielliptical shape were placed in the centers of the upper surfaces
of the panels and connected with an electric detonator. Based
on the pre-investigations for the influences by installation
direction of the electric detonator, the range the mass of the
blast charges used in the contact explosions, the influences
of the detonator is regarded not prominent and can be
neglected. Emulsion explosives of 50, 75, 100, 200, 400, and
800 g were used for the contact blast tests of the NHC, and
emulsion explosives of 50 and 100 g were used for the NCC.
The contact explosions of the FRCC panels were performed
with blast charges of 100 and 200 g. The design of the blast
charges for the FRCC panels was based on the failure modes
of the plain panels, which will be discussed in Sect. 3.2.
Figure 4 shows the method for evaluating the local
damage, such as crater, spall, and breach, in the front and back
sides of a panel. The diameter and depth of the local damage
were calculated from the mean values for the crater and spall
measurements. The extent of the surface damage to each
panel was quantified graphically by mapping the local
damage on the front and back sides and comparing the
damage area, A2, to the total area, A1 ? A2.
3. Experimental Results and Discussion
3.1 Static Mechanical Properties
The test results were presented as the mean of the values
obtained for each of the three specimens. The static
Fig. 4 Measurement of damage areas in the panels.
mechanical properties of cementitious materials are shown in
Table 5. The compressive strength of NHC was 64.3 MPa
and that of NCC was 43.7 MPa. The compressive strength in
all of the FRCCs was less than that of the NCC, and the
range of compressive strengths was 27.9–36.7 MPa. The
compressive strengths of PVASCC and PESCC were
evaluated at 35.8–36.7 MPa, respectively; moreover, the steel
fibers in the hybrid samples provided a strength-enhancing
effect as compared to the specimens that only used PVA fiber
or PE fiber. The elastic modulus of the FRCCs were less than
those of plain specimens, following almost similar
proportions as the compressive strength. Generally, the blended
fibers did not improve the elastic modulus of the FRCCs
because the cementitious matrix was made without coarse
aggregate (Atis¸ and Karahan 2009; Naaman 2003). In
addition, these results can be explained by the interfacial
transition zone (ITZ) between the cementitious matrix and
the blended fiber, as the ITZ was made in a relatively weak
layer and large pores due to the blended fibers exist in the
cementitious composites matrix (Li and Stang 1997).
Meanwhile, the fracture energy of all of the FRCCs
increased as compared to NHC and NCC. For FRCCs, the
fracture energy, which was calculated by the area below the
Fig. 3 Experimental setup of blast resistance; a dimension of panel, b contact explosion.
Table 5 Test results of static mechanical properties (standard deviation).
Compressive strength (MPa)a
Elastic modulus (GPa)a
Fracture energy (N m/m2)a
a An average value of three time tests at 28 days.
load—CMOD curve, was higher in PVACC and PECC
compared to SCC. This is ascribed to the higher post-crack
stress and residual stress of PVACC and PECC, given that
fracture energy greatly depends on the stress-sustaining
capacity along with the maximum flexural stress. In addition,
the fracture energy of hybrid FRCCs decreased as compared
with PVACC and PECC. When compared with PVACC or
PECC, the reduction of the fracture energy by hybrid of
blended fibers in PESCC is greater than that of PVASCC.
These results can be explained by the difference of the
fracture energy between PECC and SCC. Similar
observations were previously reported by Ahmed et al. (2007). In
the case of a hybrid fiber-reinforced cementitious composite,
the reduction of the flexural capacity is dependent on the
hybrid ratio between high performance and low performance
under identical volume ratio of fiber reinforcement. PECC
has fracture energy about 3 times greater than that of SCC,
whereas PVACC has fracture energy about 1.5 times greater
than that of SCC. Thus, it can be said that the reduction of
the fracture energy in PESCC was clearly observed
compared to that of PVASCC. Nevertheless, PESCC has fracture
energy about 2 times greater than that of SCC, which shows
the significant influence of hybrid macro and micro fiber on
FRCC flexural performance.
3.2 Blast Resistance
3.2.1 Appearance of the Damage
The results of the contact blast tests of NHC and NCC are
shown in Fig. 5. For the NHC panels, spall failure was
observed for blast charges of 50, 75, and 100 g. Similar
observations were previously reported by Ohkubo et al.
(2008): in the case of TNT blast charges of 50 g, significant
large spall was apparent in the concrete panel. As seen in
Fig. 5, breach failure of the NHC panel occurred in the case
of contact explosion with a blast charge of 200 g. Therefore,
the primary failure mode of the local damage in the NHC
panels transitions between 100 and 200 g of blast charge. In
addition, for blast charges of 400 and 800 g, the quantitative
failure modes of crater, spall, and breach were not observed
in NHC panels under contact explosions. This also means
that it is inappropriate to compare failure modes with the
local damage of FRCC panels at these blast charge masses.
Furthermore, the failure modes of NCC panels were also
investigated. The NCC panels had the same mixture
proportions as compared with FRCC panels except for the
blended fibers. For NCC panels, breach failure was observed
at both 50 and 100 g of blast charge. The local damage in the
NCC panels increased according to the amount of blast
charge. Therefore, these results on the local damage of NCC
panels are useful for comparison with the failure mode of
FRCC panels. When the failure mode of NCC panels was
compared with NHC panels at both 50 and 100 g of blast
charge, NCC panels, breach failure was observed with
severe cracks. Whereas the failure mode of breach was not
generated in NHC panels. These results can be explained by
the difference of the compression behaviors and used
materials. NHC has an approximately 1.5 times greater
compressive strength and elastic modulus than those of
NCC. In addition, NCC panel does not contain coarse
aggregate of high rigidity. It is believed that the difference of
the compression behaviors and used materials between NHC
and NCC in contact explosions without fiber reinforcement
which in turn may influence the failure modes at the
identical blast charges. Based on the above discussion regarding
the local damage in the NHC and NCC panels, the amount of
blast charge for damage evaluation of FRCC panels
subjected to contact explosions should be less than 400 g of
emulsion explosive; thus, FRCC panels were investigated
with blast charges of 100 and 200 g.
The external damage of FRCC panels with blended fibers
is shown for each blast charge in Fig. 6. The results of the
NHC panels were plotted for comparison with the failure
modes of FRCC panels. Hence, the blast resistance of the
FRCC panels under contact explosions can be clarified from
the figure. For each FRCC panels that used a blast charge of
100 g, spall failure was not observed in the overall panels. It
is evident from the figure that the blast resistance of the
FRCC panels was significantly improved compared to the
NHC panels. Additionally, among the FRCC panels, the
SCC panels exhibited crack patterns on their back sides that
were more significant than the other FRCC panels,
indicating that the static flexural behavior, such as strain-hardening
performance, of SCC contributed to the crack pattern under
dynamic blast loading. Generally, macro hooked-end steel
fiber reinforced composites have low strain-hardening
capacity as compared to micro synthetic fiber reinforced
Fig. 5 Appearance of the damage in NHC and NCC panels for each blast charge.
cementitious composites. However, amount of cracks in the
SCC panel was reduced by hybrid with micro synthetic
fibers. This improvement was provided from a one-to-one
hybrid ratio of macro hooked-end steel fibers and micro
synthetic fibers. In addition, all FRCC panels experienced
spall failure mode in the case of contact explosions using
200 g blast charges, but the degree of spall was very slight
compared to the plain panels.
The failure modes of all panels are summarized for each
blast charge in Fig. 7. As the damage of the investigated
panels increased with the amount of explosives, spall and
breach become the critical failure modes. However, from the
figure, the failure modes of the FRCC panels were one stage
less severe compared to the NHC and NCC panels. This
demonstrates that FRCCs have superior blast performance
compared to NHC and NCC under contact explosions of the
same blast charge. Therefore, FRCCs should provide more
blast resistance when used as a protective material.
3.2.2 Diameter, Depth, and Superficial Damage
To clarify the effect of fiber reinforcement on the blast
resistance of FRCC panels, quantitative damage results were
provided through measurements of diameter, depth, and
superficial damage. The measured diameters of crater and
spall are shown for each blast charge in Fig. 8. It is clear
from the figure that the damage diameters of the FRCC
panels were significantly smaller than the plain panels after
contact explosions using blast charges of 100 g. In addition,
in the case of a 200 g blast charge, the diameter of spall in all
FRCC panels was less than 300 mm, which is approximately
half of that of the NHC panel. Compared with the PVACC
and PECC panels, the hybrid FRCC panels exhibited larger
Fig. 6 Appearance of the damage in NHC and FRCCs panels for each blast charge.
spall diameters. The hybrid FRCC panels can have a
relatively small specific surface area between the fibers and
cementitious matrix as compared to the PVACC and PECC
panels in the same conditions. The number of blended fibers
in the hybrid FRCC is approximately half that of the PVACC
and PECC panels. Previous research (Yamaguchi et al.
2011), on fiber-reinforced concrete specimens subjected to
contact blast tests showed that as fiber volume fractions
increase, the damage diameters of the back sides decreased.
This implies that the specific surface area between the
blended fibers and the cementitious matrix is strongly
correlated with the diameter of local damage.
The depth of the crater and spall due to the contact
explosions of the 100 and 200 g blast charges are shown in
Fig. 9. For FRCC panels under contact explosions using
100 g blast charges, the crater depth was less than that of the
NCC panel, and that of the spall was immeasurable.
Figure 10b describes the depths of the crater and spall for each
panel after contact explosions using 200 g blast charges.
From this figure, the fiber reinforcements make the depths of
the crater and spall slightly smaller than those of the NHC
panel. The resistance effect of FRCC panels on the depths of
crater and spall was not clearly observed compared to
resistance observed for the diameters in the 200 g blast
charge (see Fig. 8). The resistance for crater depth in the
panels was likely influenced both by the fiber reinforcements
and by the compressive strengths of the test materials. Even
though the compressive strengths of the FRCC panels were
less than those of the plain panels, the crater depths of the
FRCC panels were also less than those of the plain panels.
Figure 10 shows the ratio of the crater depth to panel
thickness (Cd/T) for the failure modes of the plain and FRCC
Fig. 7 Failure mode of all panels for each blast charge.
Fig. 8 Diameter of damaged areas for each blast charge; a 100 g, b 200 g.
Fig. 9 Depth of damaged areas for each blast charge; a 100 g, b 200 g.
Fig. 10 Failure mode of panels by relationship between Cd/T
and each blast charge.
panels. The NCC panel experienced breach failure with a Cd/
T of 0.26 at 50 g of blast charge. For the NHC panels, the
spall failure had a Cd/T less than 0.4, whereas the breach
failure had a Cd/T greater than 0.4. In contrast, for the FRCC
panels, crater failure occurred in the range of Cd/T values for
which spall failure was observed in the NHC panel, and spall
failure occurred in the range of Cd/T values for which breach
failure was observed in the NCC panel. Therefore, the
blended fibers in the FRCC panels play an important role for
blast resistance under contact explosions.
Figure 11 shows the superficial damage on the front and
back sides of the panels for each blast charge. The superficial
damage on the back side of the FRCC panels, when using
the 100 g blast charge, was calculated from the lengths and
widths of the cracks. Among the FRCC panels, the SCC
panel exhibited the most superficial damage under contact
explosions using 100 g of blast charge. However, the
amount of superficial damage in the SCC panel was only
approximately 1%, which occurred on both the front and
back sides. Moreover, this value is very small compared to
superficial damage to the NCC panel. Furthermore, in the
cases of contact explosions using 200 g blast charge, the
FRCC panels experienced significantly less superficial
damage compared to the NHC panel. For the FRCC panels,
the superficial damage on the back side was less than 5%,
whereas that of NHC panel was approximately 18%. Based
on the obtained results, the superficial damage was
proportionally related to the damage diameter. Therefore, the fiber
reinforcement in the FRCCs also helps restrain the surface
progress of local damage.
Figure 12 shows the relationship between the fracture
energy and the superficial damage on the back side of the
panels for each blast charge. It is clear from the figure that
the growth of the fracture energy of the FRCCs contributed
to constraining the superficial damage. In both cases, the
reduction of superficial damage is highly correlated with
fracture energy. In addition, in the case of a 100 g blast
charge, the superficial damage of the SCC panel was
improved by hybrid with PVA or PE fibers, as the fracture
energy of the PVASCC and PESCC was significantly higher
than that of the SCC. The increase of the fracture energy in
the FRCCs contributed to the development of their flexural
capacity, which greatly reduced the local damage caused by
the contact explosion to the back side of the panel. It can be
said that the mechanism of spall failure in cementitious
composites is different from the static mechanical
characteristics, however, the improvement of the static fracture
energy can have an indirect effect to enhance the blast
resistance under contact explosions. Previous studies on the
effectiveness of fracture energy for improving the spall
resistance of cementitious composite materials subjected to
contact explosions are very limited. However, in some
studies on the impact resistance of cementitious composites
under dynamic loading, the effects of fracture energy on
scabbing resistance are observed (Leppa¨nen 2006;
Mechtcherine et al. 2011; Zhang et al. 2009; Habel and
Gauvreau 2008; Mindess et al. 1987). Improving the fracture
energy of cementitious composites has a large effect on the
reduction of scabbing failure, which especially has a
significant influence on the reduction of the diameter compared
to the depth of local damage. Additionally, because the
fracture energy depends on the loading rate, the dynamic
fracture energy in blast loading, such as contact explosions,
Fig. 11 Superficial damage of panels for each blast charge; a 100 g, b 200 g.
Fig. 13 Fragment of the back side of the PVASCC panel in case of blast charge of 200 g.
can affect the local damage characteristics of cementitious
composites compared to those of static loading conditions.
A fragment of the back side of the PVASCC remained
attached to the panel, as shown in Fig. 13. From the figure,
the spall fragment bulged approximately 45 mm from the
panel and did not detach completely. Likewise, the blast
resistance of the hybrid FRCC panels under contact blast
tests using 200 g of blast charge exhibited equivalent
performance as compared with those of the PVACC and PECC
panels. Based on the obtained results, it is obvious that the
hybrid effect of the blended fibers and their characteristics
plays an important role in the blast resistance of PVASCC
and PESCC panels. The hybrid effect of the macro and
micro fibers in the FRCCs is discussed in several previous
studies: the hybrid blend of macro and micro fibers
improved the mechanical properties of FRCCs (Shu et al.
2015; Lawler et al. 2003). The cementitious composite
materials reinforced with a hybrid blend of macro and micro
fibers showed better mechanical performance than those that
were only reinforced with macro fibers. Consequentially,
these aspects explain the improvement of the blast resistant
performance of hybrid FRCC panels. For the FRCC panels,
the reduction of spall is dependent on the control of macro
cracking under blast load. Figure 14 shows a schematic of
the hybrid blend effects of macro and micro fibers on the
blast resistance of FRCCs. In the hybrid FRCC panels, the
micro fibers were most effective at limiting the widening of
Fig. 14 Influence of hybrid fiber reinforcement on the spall
cracks. Furthermore, the micro fibers assisted the strain
capacity of the macro fibers in the FRCC panels. In addition,
the improvement of flexural performance significantly
influenced the local damage reduction of the FRCCs. From
the results previously described in Sect. 3.1 on the
comparative evaluation of the flexural properties between
FRCCs and plain specimens, the fracture energy of FRCCs
significantly increased as compared to NHC and NCC.
3.2.3 Relationship Between Diameter and Depth
of Local Damage
To clarify the resistance of FRCC panels to critical local
damage, such as spall, the diameter and depth of local
damage are compared in Fig. 15. It is clear from the
figure that the diameter/depth ratio of local damage for the
Crater and spall 2:0
where Cd (cm) is depth of the crater and Sd (cm) is depth of
Figure 16 compares the experimental results of the failure
mode with the empirical equations. From the figure, it can be
seen that although the failure modes of the NHC and NCC
panels by the experimental results are well agreed with the
empirical equations, whereas the blast resistance of FRCC
panels are underestimated. Similar observations were
previously reported by Li et al. (2016): the failure modes of
micro steel-fiber-reinforced ultra-high performance concrete
slabs are underestimated compared to normal strength
concrete subjected to contact explosions, which are predicted
from the empirical equations by Li et al. (2016) analyzed to
be due to empirical predictions do not consider the effects of
fiber reinforcement, which affect the local damage of
concrete slabs. Therefore, the blast resistance of FRCCs
calculated from empirical predictions are underestimated
compared to that of real performance of FRCCs.
Consequentially, in the current study, it is also clear that the
experimental results of the total depth of local damage in the
FRCC panels were significantly lower than those in the plain
panels. This implies that the FRCC panels experience not
only reduced crater damage, but also reduced spall damage,
which reduces the allowable limit thickness for each failure
mode under contact explosions.
Fig. 15 Relationship between crater and spall calculated
from diameter/depth ratio.
plain panels was more closely distributed in spall areas under
contact blast tests in the cases of both 100 and 200 g of
explosives, which means that the spall of the back side
contributed most of the damage. Conversely, the diameter/
depth ratio of local damage for the FRCC panels was more
closely distributed in crater areas. It is obvious from the
figure that the diameter/depth ratio of the local damage
increased proportionally, but the amount of spall area is not
critical in contrast to that of the plain panels. Based on the
above discussion, FRCCs should experience a reduced
damage area on the back side of panels even if spall or
3.2.4 Comparison of Experimental Results
with Empirical Equations for Failure Mode
Morishita et al. (2000, 2004) proposed useful equations for
estimating the failure mode in normal RC slabs subjected to
contact explosions. In the following discussions, the
experimental results of local damage are compared to the
equations of Morishita et al.
The scale thickness of a concrete panel (T/W1m/3) using
emulsion explosives can be obtained as given in the
where T is thickness of concrete, Wm is the substitution
amount of explosive, KTNT is Chapman–Jouguet (C–J)
thermal energy (=4.29 MJ/kg) of TNT, and K is the C–J
thermal energy (MJ/kg) of the used explosive. The C–J
thermal energy of emulsion explosives is 4.61 MJ/kg.
The range of the local damage is limited, depending on T/
W1m/3, for crater, spall, and breach. It can be calculated from
the following equations:
Fig. 16 Comparison of experimental results with empirical
equations for failure mode.
The objective of this study was to experimentally clarify the
effect of fiber reinforcements on the local damage of FRCC
panels subjected to contact explosions. Five kinds of FRCCs
were investigated in the study. Based on the experimental
results, the main findings of this study, which are useful
information for blast resistance of FRCCs, are drawn as follows:
1. For FRCCs, the fracture energy of PVASCC and PESCC
is greater than that of SCC, which shows the influence of
hybrid macro and micro fiber on FRCC flexural
performance. Additionally, comparing the flexural performance
of FRCCs to that of the plain specimens, the fracture
energy of FRCCs is significantly larger than that of NHC
and NCC. By having increased fracture energy, FRCCs
have superior resistance to local damage under contact
explosions, which suppresses the propagation of wide
radial cracks to the back sides of the panels.
2. The experimental results revealed that FRCC panels have
high resistance to failure under contact explosions as
compared with plain panels. Specifically, for contact
explosions using 100 g of blast charge, the cracks observed
on the SCC panel were more prevalent than for the other
FRCC panels, but these cracks were still controlled by
hybrid blending with micro synthetic fibers (1 vol.% macro
hooked-end steel fibers and 1 vol.% micro synthetic fibers).
Therefore, the hybrid blending of fibers plays an important
role in the blast resistance of FRCC panels.
3. The fiber reinforcements of FRCC panels significantly
reduce the damage diameter and amount of superficial
damage as compared to depth of the local damage. This
implies that the influence of fiber reinforcement in FRCCs
on the blast resistance is associated with the restraint of the
lateral progress of local damage. Based on the relationship
between crater and spall, the diameter/depth ratios of local
damage in FRCC panels were more closely distributed in
crater areas in contrast to those of plain panels. Thus,
FRCCs should experience a reduced damage area on the
back side of panels even if spall or breach occurs.
4. Finally, the experimental results presented useful data
for comparison to empirical equations for prediction of
limited thickness on the local damage subjected to
contact explosions. The experimental results for the total
depth of local damage in the FRCC panels were
significantly lower than those in the plain panels, which
implies that the FRCC panels restrain the critical local
damage. However, it should be noted that these
empirical methods tend to greatly underestimate the
blast resistance of FRCC panels due to do not consider
the effects of fiber reinforcements.
This work was supported by the Basic Science Research
Program through the National Research Foundation of
Korea (NRF) funded by the Ministry of Science, Information
and Communications Technologies (ICT) & Future Planning
This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License (
http://creativecommons.org/licenses/by/4.0/), which permits
unrestricted use, distribution, and reproduction in any
medium, provided you give appropriate credit to the original
author(s) and the source, provide a link to the Creative
Commons license, and indicate if changes were made.
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