1
Indonesian Journal of Science and Technology 4 (1) (2019) 1-16

Indonesian Journal of Science and Technology
Journal homepage: http://ejournal.upi.edu/index.php/ijost/

Carbon Nano Fibre Reinforcements In Concrete
Muhammad Maqbool Sadiq Awan 1, Parviz Soroushian 2, Arshad Ali 1, Muhammad Yousaf Saqid Awan 1
1

CE Wing, MCE, National University of Sciences and Technology, Islamabad, Pakistan
2
Department of Civil and Environmental Engineering, MSU, USA
*Correspondence: E-mail: aliarshad08@yahoo.com

ABSTRACT

ARTICLE INFO

Graphite nanomaterials offer distinct advantages over microscale reinforcing fibers in terms of engineering properties
and geometric attributes. Through dispersion and effective
interfacial interactions of proper functionalization of carbon
nanofibers are the prerequisites for their effective use in
high-performance cementitious matrices. Furthermore, the
use of nano- and micro-scale reinforcements together
provides reinforcing effects at different scales, thus
rendering balanced gains in engineering properties of the
matrix. However, their uses in coarser high-performance
matrices have not been evaluated thoroughly. The results
show improvements in all flexural attributes, impact and
abrasion resistance of concrete with addition of 0.16% of
oxidized and polyacrylic acid physisorbed carbon nanofibers,
over the corresponding properties of plain matrix. The
results also pointed to synergetic effects of hybrid
reinforcements on improving the various engineering
properties of DSP concrete matrix, especially with low
modulus polypropylene microfibers.

Article History:
Submitted/Received 16 Oct 2016
First revised 20 Aug 2018
Accepted 28 Jan 2019
First available online 31 Jan 2019
Publication date 01 Apr 2019
____________________
Keywords:
Carbon Nano Fibre,
Reinforcements In Concrete,
Nanomaterials,
Cementitious matrices,

© 2019 Tim Pengembang Jurnal UPI

1. INTRODUCTION
Advanced technological aspects of
cement based materials have recently
focused on developing high-performance
cementitious composites, which exhibit high
compressive strengths. Such composites,
however, exhibit also extremely brittle

failure, low tensile capacity and appear
sensitive to early age microcracking as a
result of volumetric changes due to high
autogenous shrinkage stresses. These
characteristics of cement based materials are
serious shortcomings that impose constrains
in structural design and affect the long term
durability of structures. To overcome the

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Muhammad Maqbool Sadiq Awan et al., Carbon Nano Fibre Reinforcements In Concrete… | 2

aforementioned disadvantages from the
reinforcement of cementitious materials, it is
typically provided at the millimeter and/or
the micro scale using macrofibers and
microfibers.
Cementitious
matrices,
however, exhibit flaws at the nanoscale,
where traditional reinforcement is not
effective. Graphite Nanomaterials, including
carbon nanofibers (CNFs), present several
distinct advantages as a reinforcing material
for high strength/performance cementitious
composites as compared to more traditional
fibers. First, they exhibit significant greater
strength and stiffness than conventional
fibers, which should improve overall
mechanical behavior. Second, their higher
aspect ratio is expected to effectively arrest
the nanocracks and demand significantly
higher energy for crack propagation. Third,
CNFs are uniformly dispersed. Then, due to
their nanoscale diameter, fiber spacing is
reduced. This has opened a new field for
nanosized reinforcements that should
theoretically hinder the formation and later
propagation of microcracks at the very
beginning. Few attempts have been made to
add different graphite nanomaterials as
reinforcement in cementitious matrices.
Most of the works involving use of
graphite nanomaterials in cementitious
matrices have used very fine matrices to
evaluate
the
efficiency
of
their
reinforcement and reported modest gains in
some of the engineering properties (Makar
and Beaudoin, 2004; Makar and Chan, 2009;
Li et al., 2005; Cwirzen et al., 2009; Cwirzen
et al., 2008; Metaxa et al., 2009; Metaxa et
al., 2010). A comprehensive approach was
taken to evaluate suitably functionalized
carbon nanofibers in high-performance
cementitious materials of higher complexity,
especially concrete. The results of
functionalized
and
nonfunctionalized
graphite nanomaterials in high performance

DSP paste and mortar matrices have been
mentioned elsewhere (Alkhateb et al., 2013).
Based on previous studies (Awan et al.,
2017; Asmara et al., 2018; Awan et al., 2017),
the focus of this research paper is on the use
of high-performance (DSP) concrete as the
matrix in which the reinforcement efficiency
of suitably functionalized carbon nanofibers
and/ or different microfibers is evaluated.
The larger aggregate size and content in
concrete, when compared with mortar and
paste, adds to complexity of behavior and
failure modes by introducing an interfacial
zone, generating interactions between
aggregates and propagating microcracks, and
the need to disperse nanomaterials in the
space between aggregates.
Evaluation of the reinforcement
efficiency of carbon nanofibers in a coarser
cementitious matrix, high-performance
concrete, was undertaken to see the effect of
increased particle size on the interaction of
nano reinforcements with the relatively
coarser matrix. This has also highlighted the
filler effect and dimensional stability brought
about by use coarser aggregates in a well
graded matrix. Furthermore, micro-scale
fibers along with their hybrid combination
with carbon nanofibers were evaluated to
achieve desired balance of performance and
cost efficiency.
Cementitious materials are essentially
particulate composites, which are rarely used
without aggregates (particulates). Given the
micro- to millimeter-scale dimensions of the
sand and gravel particles used in DSP
concrete, hybrid reinforcements which
complement the reinforcing and dimensional
stabilizing actions of particulates with multiscale reinforcement mechanisms could
produce particularly positive effects. In the
past, the concept of using hybrid (micro- and
millimeter-scale) reinforcement has been
explored by the concrete industry for
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achieving balanced gains in material
properties (O'Connell et al., 2001; Banthia
and Sappakittipakorn, 2007; MoranvilleRegourd, 2002; Lawler et al., 2005).
2. MATERIALS AND METHODS
2.1. Materials
Oxidized (CNF-OX) and polyacrylic acid
physisorbed (CNF-PAA) carbon nanofibers,
carbon microfibers (CMF) and polypropylene
microfibers (PP) at different volume fractions
were used in Densified with Small Particles
(DSP) concrete matrix, as seen in Figure 1.
These carbon nanofibers have an outer
diameters in the 60-150 nm range and
lengths ranging from 30 to 100 μm, 50-60
m2/g specific surface area (SSA), ~1.95 g/cm3
true density, and >95% purity. These pristine
and oxidized nanofibers were purchased
from Pyrograf Products, Inc. and PAA was
physisorbed on to pristine nanofibers using a
procedure described in the subsequent
section. Carbon microfibers (CMF) with 6mm length and 6-μm diameter were
obtained from Toho Tenax America, Inc., US.
Polypropylene microfibers (PP) with 19 mm
in length and 39 μm in diameter were
obtained from New Nycon, Inc., US.
Poly(acrylic acid) (PAA, average Mw of about
100,000, 35 wt.% of H2O) was purchased
from Sigma-Aldrich, US. Deionized (DI) water
was used for all solution preparations and
were purchased from PT Rumah Publikasi
Indonesia, Indonesia.
2.2. Dispersion of Nanotubes in Water
The nanomaterial dispersion procedure
comprised the following steps:
(1) Add the required amount of CNF-OX and
CNF-PAA (carbon nanofibers and poly
acrylic acid 1:1 by weight) to the mixing
water of cementitious materials in order
to achieve the targeted nanofiber
volume fraction.

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(2) Stir the mixture overnight (12 to 15
hours).
(3) Sonicate the mixture using a probe as
follows: (i) Sonicate for ten minutes at
different amplitudes (30%, 45%, 65%
and 75%) with 1-minute breaks between
different amplitudes; (ii) Pulse (1 minute
on and 30 seconds off) for 10 minutes at
85% amplitude; (iii) Turn off the sonic
probe for 2 minutes, and repeat the
pulsing cycle two more times; and (iv)
Repeat the whole sonic probing cycle
one more time.
(4) For the microfiber and hybrid
reinforcement systems, the microfibers
were added to the mixing water without
using the above dispersion procedure.
Microfibers were added to the mixing
water half an hour before mixing it with
other ingredients of the DSP concrete in
mixer.
2.3. Cementitious Matrices
Dense cement-based matrices with a
smooth particle size gradation covering
nano- to micro-scale range promise to
effectively mobilize the tremendous
mechanical
qualities
of
graphite
nanomaterials
within
cementitious
nanocomposites. One category of cementbased matrices meeting these requirements
is referred to as Densified with small particles
(DSP). DSP cement-based materials comprise
micro-scale cement and nano-scale silica
fume particles, dispersed and densified with
a superplasticizer, which is shown in Figure 2
(Guerrini, 2000).
Using this basic concept and introducing
other
ingredients
(e.g.,
high-quality
aggregates and discrete reinforcement), it is
possible to obtain highly desired
combinations of mechanical performance
and durability suiting demanding fields of
application (Guerrini, 2000). Based on a
comprehensive review of the literature on
DSP (Aı ̈tcin, 2000; Badanoiu et al., 2003;

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Bayard and Plé, 2003; Bonneau at al., 1996;
Bonneau et al., 2000; Chan and Chu, 2004;
Cheyrezy et al., 1995; Dattatreya et al., 2007;
Dili and Santhanam, 2004; Feylessoufi et al.,
1996; Ju et al., 2007; Kaufmann and
Hesselbarth, 2002; Lee et al., 2007; Matte

and Moranville, 1999), the cementitious
concrete matrix introduced in Table 1 was
selected for evaluation of the merits of
graphite nanomaterials and/or microfibers in
cement-based materials.

Figure. 1. DSP cementitious paste, mortar and concrete (Guerrini, G. L., 2000).

a

b

c

d

Figure. 2. TEM micrographs of CNF with OD of 8-15 nm and length of up to 50 µm, PAA physisorbed
CNF-PAA (a); Oxidized nanofibers CNF-OX (b); SEM micrograph of carbon microfibers (TT
143) with 6 mm in length (c); and polypropylene microfibers (d).

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Table 1. Starting material selections and mix proportions (weight ratios) of high-performance
cementitious concrete matrix.
Ingredient
Silica Fume/Binder
Water/Binder
Superplasticizer/Binder
Silica Sand (0 – 0.18 mm) / Binder
Silica Sand (0.18 -0.6 mm) / Binder
Granite Gravel (1 mm – 9 mm) / Binder

The materials selected for use in cementbased matrices included Type I Portland
cement
(Lafarge-North
America),
undensified silica fume (Norchem, Inc.) with
the average particle size of 200 nm, the
specific surface area of 15 m2/g, and
minimum 7-day pozzolanic activity index of
105%, silica sands (Fairmount Minerals) with
average sizes of about 39 and 350 μm,
comprising >99.5% of silica, granite gravel
ranging in sizes of from 1 mm to less than 9
mm (average particle size of 3.55 mm).
ADVA® Cast 575 is a polycarboxylate-based
Type F ASTM C 494 superplasticizer.
Cementitious materials (with and
without
carbon
nanotubes
and/or
microfibers dispersed in the mixing water via
sonication) were prepared using following
the ASTM C 192 and C 305 procedures. The
specimens were moist-cured inside molds
after casting (ASTM C 192) over a 24-hour
period, and were then demolded and
subjected to 48 hours of steam curing at
70oC. The samples were subsequently
conditioned at 50% of relative humidity for
seven days prior to testing. At least two
batches were casted with at least four
specimens for each test condition in each
batch for all reinforcement conditions and
engineering properties.
2.4. Experimental Methods
The test procedures employed to
determine the engineering properties of
cement-based materials are described in this
section. Compression tests (ASTM C 109)
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DSP Concrete
0.20
0.20
Adjusted for diff reinf
0.36
0.86
0.50

were performed on 50 mm of cube
specimens. Flexure tests (ASTM C 1185) were
performed on 12.5 x 50 x 150 mm specimens
by center-point loading on a span of 125 mm
using a deflection-controlled mechanical test
system, with load and deflection data
collected using a data acquisition system.
Impact tests (ASTM D 7136) were performed
on 12 x 150 x 150 mm specimens. Abrasion
tests (ASTM C 944) were conducted on the
surface of cylindrical specimens with 100 mm
in diameter (and 50 mm in height). Scanning
electron microscopy (SEM) was also
employed to gain further insight into the
structure and failure mechanisms of cementbased nanocomposites. Experimental results
were evaluated using the analysis of variance
(ANOVA)
and
pair-wise
comparison
techniques. Response surface analysis (RSA)
was used to identify reinforcement volume
fraction,
which
provides
optimum
reinforcement and gains in various
engineering properties of the cementitious
matrix.
3. RESULTS AND DISCUSSION
Acid-oxidized (CNF-OX) and Poly-acrylic
acid
physisorbed
(CNF-PAA)
carbon
nanofibers were used as reinforcement at
0.16 vol.%; polypropylene (PP) and carbon
microfibers (CMF) were used at 0.24 vol.%.
Combinations of polypropylene and carbon
microfibers with PAA physisorbed carbon
nanofibers were also used as hybrid
reinforcement for concrete, with PP/ CMF

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microfibers and CNF-PAA used at 0.24 and
0.16 vol.%, respectively.
3.1. Flexural Performance
The flexural attributes test results for the
high-performance concrete reinforced with
different volume fractions of carbon
nanofibers
and/or
microfibers
are
summarized in Table 2. Significant gains in all
flexural performance characteristics of
concrete are observed with carbon nanofiber

reinforcement used alone or in combination
with microfibers. Polymer wrapping of
nanofibers improves their reinforcement
efficiency in concrete. The most desired
balance of properties for a single
reinforcement system was realized with 0.16
vol.% of PAA-physisorbed carbon nanofibers
(CNF-PAA). The corresponding improvements in flexural strength, energy absorption
capacity and maximum deflection versus
plain concrete were 20.9, 134, and 120%,
respectively.

Table 2. Mean values of flexural attributes of plain high-performance concrete and those reinforced
with different nano- and/ or micro-scale reinforcement systems.
Reinforcement Condition

Plain
Carbon microfiber, 0.24 vol.% (CMF-0.24)
Polypropylene microfiber, 0.24 vol.% (PP-0.24)
Carbon nanofiber, 0.16 vol.% (CNF-0.16)
Carbon nanofiber, 0.16 vol.% (CNF-PAA-0.16)
Polypropylene microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.%
(CNF+PP)
Polypropylene microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.%
(CNF-PAA+PP)
Carbon microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.%
(CNF+CMF)
Carbon microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.% (CNFPAA+CMF)

The experimental data generated in the
past pointed at the positive effects of hybrid
(nano- and micro-scale) reinforcement
systems in high-performance cementitious
materials (Peyvandi et al., 2013). The test
data presented here suggest that micro-scale
fibers of lower modulus and lower cost
(when compared with high-modulus carbon
microfiber) could effectively complement the
reinforcing effects of polymer-wrapped
carbon nanofibers in high-performance (DSP)
concrete. These lower-modulus microfibers,
when used as hybrid reinforcement together
with both treated and untreated carbon

Flexural Deflection Energy
Strength (mm)
Absorption
(MPa)
(N.mm)
13.4
0.71
92
12.8
1.01
111
13.0
4.55
383
15.4
1.52
193
16.2
1.56
215
17.4
5.30
400
18.2

5.28

433

17.2

1.55

274

17.5

1.65

269

microfibers, produced balanced gains in the
flexural performance attributes of the highperformance (DSP) concrete by interacting
with and arresting the cracks developing in
matrix at different scales. The hybrid
reinforcement of low-modulus polymer
(polypropylene) microfibers with nanofibers
produced particularly pronounced gains in
the mechanical properties of DSP concrete.
The best balance of flexural attributes was
realized with the hybrid reinforcing material
comprising
PAA-physisorbed carbon
nanofibers (0.16 vol.%) and polypropylene
microfiber (0.24 vol.%) (which were
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produced to have 35.8, 644, and 371%) rise
in the flexural strength, maximum deflection,
and energy absorption capacity of the highperformance concrete.
The hybrid reinforcement systems also
overcame the adverse effects of microfibers
on flexural strength, as reported earlier. The
synergistic reinforcing action of nano- and
micro-scale reinforcement was further
enhanced by polymer wrapping of carbon
nanofibers. The effectiveness of hybrid
reinforcement was also evident for highmodulus carbon microfibers when used with
different
PAA
physisorbed
carbon
nanofibers. This hybrid reinforcement
resulted in improvement of all engineering
properties versus plain matrix and also
versus a similar hybrid reinforced materials
incorporating untreated carbon nanofibers.
The experimental results were subjected
to statistical analysis of variance (ANOVA).
Due to the large number of observations,
ANOVA only gives the general trends in test
results. The ANOVA outcomes indicate that
there are statistically significant (at 0.05
significance level) improvements in all
flexural attributes of high-performance
concrete due to the addition of nano-scale
and hybrid reinforcement systems. Pair-wise
comparisons were carried out in order to
assess the statistical significance of the
effects associated with the addition of nanoand/or micro-scale reinforcement systems.
These results indicate that nano-scale
reinforcement systems at 0.16 vol.%
produced
statistically
significant
improvements in all flexural attributes of the
plain matrix at 0.05 of significance level when
compared with plain concrete. Both
microfibers
produced
statistically
insignificant drops in flexural strength (0.297
and 0.481 of significance levels for carbon
and polypropylene microfibers, respectively).
Pair-wise analysis also pointed at statistically
insignificant gains in energy absorption
capacity (0.502 of significance level) and
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maximum deflection (0.402 of significance
level) realized with 0.24 vol.% of carbon
microfiber. The use of low-modulus
polypropylene microfiber as well as highmodulus carbon microfiber in conjunction
with different surface functionalized carbon
nanofibers reversed any negative trends in
the effects of individual reinforcement,
producing balanced gains in the engineering
properties of high-performance DSP
concrete at significance levels varying form
0.000 to 0.047. The lower values of
significance level were only for maximum
deflection when carbon microfibers were
used in conjunction with carbon nanofibers.
3.2. Compressive Strength
The compressive strength test results
(mean values and standard errors) for highperformance concretes with nano- and/or
micro-scale reinforcement systems are
presented in Table 3. As was the case with
DSP paste and mortar (Alkhateb et al., 2013),
PAA physisorbed carbon nanofibers as well
as both microfibers produced relatively small
and statistically insignificant (at 0.05 of
significance level) effects on the compressive
strength of high-performance concrete.
Outcomes of pair-wise comparisons also
indicate the effects of nano- and microscale
reinforcement systems on compressive
strength are not statistically significant (at
0.05 of significance level). The use of hybrid
reinforcement systems comprising carbon or
polypropylene microfiber and carbon
nanotubes restored the compressive
strengths of DSP concrete by inducing
interactions with matrix and its cracks at
different scales. The hybrid reinforcement
system comprising functionalized carbon
nanofibers and micro-scale polypropylene
fiber produced a small rise in the
compressive strength of high-performance
concrete.

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3.3. Impact Resistance
The impact test data are summarized in
Table 4. All nano- and/or micro-scale
reinforcement
systems
produced
improvements in the impact resistance of
high performance concrete. The maximum
rise in impact resistance realized with a single
reinforcement (69%) was for 0.16 vol.% of
CNTF-PAA. In the case of micro-scale fibers,
polypropylene produced a higher gain (60%)
in the impact resistance of high-performance
DSP concrete.

All hybrid nano- and micro-scale
reinforcement systems produced further rise
in the mechanical properties of highperformance concrete when compared with
individual
(nanoor
micro-scale)
reinforcement used alone. A significant
(0.000 significance level) increase in impact
resistance was observed for the hybrid
reinforcement comprising polypropylene
microfiber with CNF-PAA, which confirms the
effectiveness of hybrid reinforcement.

Table 3. Mean values and standard errors of the compressive strength test results for plain DSP
concrete and those reinforced with nano- and/ or microscale reinforcement systems.
Reinforcement Condition

Mean
Compressive
Strength
(MPa)

Standard Error
(MPa)

Plain

151

7.75

Carbon microfiber, 0.24 vol.% (CMF-0.24)

139

13.5

Polypropylene microfiber, 0.24 vol.% (PP-0.24)

137

18.4

Carbon nanofiber, 0.16 vol.% (CNF-0.16)

140

8.75

Carbon nanofiber, 0.16 vol.% (CNF-PAA-0.16)

144

8.23

Polypropylene microfiber,
0.24
Carbon nanofiber, 0.16 vol.% (CNF+PP)

vol.%

and

148

12.3

Polypropylene microfiber,
0.24 vol.%
Carbon nanofiber, 0.16 vol.% (CNF-PAA+PP)

and

148

4.33

Carbon microfiber, 0.24 vol.% and Carbon nanofiber, 0.16
vol.% (CNF+CMF)

150

9.87

Carbon microfiber, 0.24 vol.% and Carbon

151

13.1

nanofiber, 0.16 vol.% (CNF-PAA+CMF)

The maximum increase in impact
resistance (115%) was brought about by
hybrid use of 0.16 vol.% of CNFPAA and 0.24
vol.% of PP microfiber. Outcomes of ANOVA
and pair-wise comparisons point at the
statistical significant (0.000 to 0.012
significance levels) of nano- and/ or microscale reinforcement effects on the impact
resistance of high-performance concrete.
When compared with high performance
cement paste and mortar (with nano-scale

reinforcement), concrete (with nano-scale
reinforcement) provides higher levels of
impact resistance; this observation points at
the well-known contributions of aggregates
(in concrete) to the toughness of
cementitious matrices.
3.4. Abrasion Resistance
The abrasion test results produced for
high-performance concrete with different
volume fractions of graphite nanomaterials
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and/ or microfiber reinforcement
summarized in Table 5.

are

As shown in Table 5, CNF-PAA at 0.16
vol.% produced the greatest improvement
(reaching 40.0%) in the abrasion resistance of
high-performance DSP concrete. All nanoand/or microscale reinforcement systems
produced marked gains in the abrasion
resistance of this high-performance concrete
matrix, which were statistically significant at
0.05 of significance level. Outcomes of pairwise comparisons confirmed that each of the
reinforcement conditions considered here
produced
statistically
significant
improvements in the abrasion resistance of
high-performance concrete (with the value

of significance levels ranging form 0.006 to
0.000).
3.5. Response Surface Analysis
The test data on high-performance
concrete with nano- and/or micro-scale
reinforcement systems was subjected to
response surface analysis. The objective of
this analysis was to identify optimum
reinforcement conditions which maximize
the benefits to specific engineering
properties of high-performance concrete.
This section presents optimization of
concrete nanocomposites for enhancing
specific engineering properties, and also for
simultaneous enhancement of several
engineering properties.

Table 5. Mean abrasion weight losses of DSP concretes with and without
nano- and/ or micro-scale reinforcement systems.
Reinforcement Condition

Loss of
Mass (grams)

Plain

1.50

Carbon microfiber, 0.24 vol.% (CMF-0.24)

1.15

Polypropylene microfiber, 0.24 vol.% (PP-0.24)

1.05

Carbon nanofiber, 0.16 vol.% (CNF-0.16)

0.97

Carbon nanofiber, 0.16 vol.% (CNF-PAA-0.16)

0.98

Polypropylene microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.% (CNF+PP)

0.99

Polypropylene microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.% (CNF-PAA+PP)

0.99

Carbon microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.% (CNF+CMF)

1.00

Carbon microfiber, 0.24 vol.% and Carbon nanofiber, 0.16 vol.% (CNF-PAA+CMF)

1.01

Response surface analysis (RSA) of the
test data was conducted considering the
volume fractions of nano- and micro-scale
reinforcement systems as input variables.
Flexural strength, energy absorption
capacity, maximum deflection and impact
resistance were used as response variables.
The RSA process started with evaluating the
effects of input variables on response
variables, and was followed with desirability
analyses considering means of response
variables, using both canonical and ridge
analyses.
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RSA conducted for each of the flexural
strength, energy absorption capacity,
maximum deflection and impact resistance
test data indicated that an optimum
reinforcement system comprising 0.12 vol.%
of CNFPAA and 0.24 vol.% of PP microfiber
maximizes subject properties. Optimal
Response for flexural strength as
calculated to be 17.20 MPa with 95% of
confidence Interval (16.02 nd 18.18 MPa),
Optimal Response for energy absorption
capacity is 482.78 N/mm with 95% of
confidence Interval (336.69 and 508.86

Muhammad Maqbool Sadiq Awan et al., Carbon Nano Fibre Reinforcements In Concrete… | 10

N/mm), Optimal Response for maximum
deflection is 5.101 mm with 95% of
confidence Interval (4.79,5.41 mm), and
Optimal Response for maximum impact
resistance is 2.90 mm/mm with 95% of
confidence Interval (2.75 and 3.63 mm/ mm).
All stationary points are saddle points which
do not give a maximum but a general
direction to follow in which targeted
properties can be maximized.
The ridge analysis outcomes can be used
to adjust the reinforcement condition for
achieving further gains in engineering
properties, shown in Table 6. The analyses
for flexural attributes and impact resistance
show that the current hybrid reinforcement

is the appropriate combination to maximize
these properties of the matrix.
Desirability analysis of test data was also
conducted in order to identify reinforcement
conditions which yield a desired balance of all
the engineering properties considered here.
Desirability analyses were conducted using
mean values obtained through both
canonical and ridge analyses. These outputs
indicate that maximum values of all response
variables can be achieved with 0.11; 0.12
vol.% CNF-PAA and 0.26; 0.24 vol.% PP
microfiber. These values are closer to what is
being used as hybrid reinforcement in this
high-performance concrete matrix.

Table 6. Outcomes of Ridge analysis of the flexural attributes and impact resistance test data
for high performance concrete with nano- and/or microscale reinforcement (Ridge

Analysis for Maximizing Flexural Strength)
Coded Radius Estimated 95.00% Confidence Interval Uncoded Factor Values
Response Upper
Lower
CNF-PAA
PP
0.000
15.604
15.024
16.183
0.080
0.120
0.100
15.847
15.264
16.429
0.088
0.123
0.200
16.093
15.502
16.684
0.095
0.127
0.300
16.344
15.739
16.949
0.103
0.131
0.400
16.600
15.976
17.225
0.110
0.136
0.500
16.861
16.212
17.511
0.111
0.141
0.600
17.128
16.449
17.807
0.112
0.147
0.700
17.400
16.686
18.115
0.113
0.152
0.800
17.678
16.924
18.433
0.116
0.208
0.900
17.963
17.164
18.762
0.118
0.225
1.000
18.253
17.404
19.103
0.120
0.240

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Table 6 (continue). Outcomes of Ridge analysis of the flexural attributes and impact resistance
test data for high performance concrete with nano- and/or microscale reinforcement
(Ridge Analysis for Maximizing Flexural Strength)

(a) Flexural Strength
Ridge Analysis for Maximizing Energy Absorption Capacity
Coded Radius Estimated 95.00% Confidence Interval Uncoded Factor Values
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700

Response Upper

Lower

CNF-PAA

PP

282.779
295.584
308.239
320.761
333.167
345.477
357.712
369.893

308.865
321.800
334.843
348.000
361.276
374.667
388.171
401.783

0.080
0.082
0.084
0.086
0.087
0.087
0.098
0.108

0.120
0.132
0.143
0.155
0.167
0.179
0.191
0.203

256.693
269.367
281.635
293.521
305.059
316.288
327.254
338.003

Ridge Analysis for Maximizing Energy Absorption Capacity
Coded Radius Estimated 95.00% Confidence Interval Uncoded Factor Values
Lower
CNF-PAA
PP
Response Upper
0.800
0.900
1.000

382.042
394.181
406.334

348.582
359.037
369.406

415.501
429.326
443.263

0.117
0.0119
0.120

0.215
0.228
0.240

(b) Energy Absorption Capacity
Ridge Analysis for Maximizing Maximum Deflection
Coded Radius
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.900
1.000

Estimated

95.00% Confidence Interval

Uncoded Factor Values

Response Upper

Lower

CNF-PAA

PP

3.101
3.296
3.492
3.687
3.882
4.076
4.271
4.465
4.659
4.853
5.046

3.408
3.605
3.805
4.008
4.213
4.420
4.630
4.841
5.054
5.268
5.484

0.080
0.082
0.083
0.085
0.086
0.088
0.089
0.091
0.092
0.109
0.119

0.120
0.132
0.143
0.155
0.167
0.179
0.191
0.202
0.214
0.226
0.238

2.793
2.987
3.178
3.366
3.551
3.733
3.912
4.089
4.264
4.437
4.608

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Muhammad Maqbool Sadiq Awan et al., Carbon Nano Fibre Reinforcements In Concrete… | 12

Table 6 (continue). Outcomes of Ridge analysis of the flexural attributes and impact resistance
test data for high performance concrete with nano- and/or microscale reinforcement
(Ridge Analysis for Maximizing Flexural Strength)

(c) Maximum Deflection
Ridge Analysis for Maximizing Impact Resistance
Coded RaEsti95.00% Confidence Interdius
mated
val
Response Upper
Lower
0.000
2.500
2.375
2.625
0.100
2.567
2.441
2.693
0.200
2.633
2.506
2.761
0.300
2.700
2.569
2.831
0.400
2.767
2.631
2.902
0.500
2.833
2.693
2.974
0.600
2.900
2.752
3.048
0.700
2.967
2.811
3.123
0.800
3.034
2.868
3.199
0.900
3.100
2.925
3.276
1.000
3.167
2.979
3.355
(d) Impact Resistance

3.6. Scanning
Evaluation

Electron

Microscope

Failed surfaces of flexure and
compression test specimens were evaluated
under a high-precision scanning electron
microscope (JOEL 7500F). All samples were
coated with Osmium (Using Osmium Coater
Neoc-AN, Meiwa Shoji) prior to SEM
observations. Figure 3 shows SEM images of
DSP concrete samples.
The density of the DSP matrix is apparent
in Figures 3a and 3b. Figure 3a also highlights
the positive effective of coarser particles in
the matrix like sand and gravel. Figures 3c to
3e points at the uniform dispersion of
nanotubes and their bridging/pullout actions
across a fine (nano-scale) crack within the
cementitious matrix. Figures 3f and 3g

Uncoded Factor Values
CNTF-PAA
0.080
0.086
0.092
0.099
0.105
0.111
0.117
0.124
0.130
0.136
0.120

PP
0.120
0.127
0.135
0.142
0.150
0.157
0.165
0.172
0.180
0.227
0.240

present evidence of micro-fiber pullout from
the matrix. Scanning electron microscope
(SEM) observations of cementitious concrete
matrices
reinforced
with
hybrid
reinforcement (carbon nanofibres and microfibres) also indicated that the presence of
nanofibers in the matrix around micro-fibres
enhanced the interaction of matrix with
micro-fibres (Figure 3g), thus benefiting the
gains in matrix performance with hybrid
reinforcement. This strong interaction of
matrix with micro-fibres was not observed in
samples reinforced with only micro-fibre
reinforcement. These observations provide
some insight into the synergistic action of
nano- and micro-scale reinforcement
systems in cementitious matrices. All these
observations support the results of various
engineering properties mentioned in earlier.

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13 | Indonesian Journal of Science and Technology, Volume 4 Issue 1, April 2019 Page 1-16

a

b

c

d

e

f

g

Figure 3. SEM images of sample: (a) crack deflection around sand particle; (b)
dense structure of paste; (c) and (d) pulled out nanofibers at fractured
surface; (e) distribution of nanofibers within the matrix (f) carbon
microfibers in the matrix; and (g) carbon nanofibers interacting with
carbon microfibers
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Muhammad Maqbool Sadiq Awan et al., Carbon Nano Fibre Reinforcements In Concrete… | 14

4. CONCLUSIONS
The experimental results generated for
high performance cementitious concrete
reinforced with both oxidized and (CNF-OX)
PAA physisorbed carbon nanofibers (CNFPAA), polypropylene (PP) microfibers, carbon
microfibers (CMF) and their hybrids casted at
various/ optimum volume fractions and with
carboxyl-based superplasticizers yield some
conclusions, namely proper use of nano-scale
reinforcement can produce improvements in
high-performance concrete mechanical
properties which surpass those realized with
micro-scale reinforcement. Nano- and microscale reinforcement render complementary
reinforcing effects in high-performance
concrete. Among the individual reinforcement conditions evaluated in high
performance concrete, CNF-PAA produces
significant improvements in the mechanical
properties of high-performance concrete.
CNF-PAA act synergistically with micro-scale
reinforcement towards enhancement of the
mechanical properties of high-performance

concrete. The refined hybrid reinforcement
produced results which further demonstrated the synergetic action of nano- and
micro-scale
reinforcement
systems.
Statistical analyses, ANOVA and pair-wise
comparison of test results generally
confirmed the statistical significance of the
results and trends identified.
5. ACKNOWLEDGEMENTS
This project was sponsored by the U.S.
Army Contract # W912HZ-08-C-0009. The
authors are thankful to Richard Haskins for
his support and feedback throughout the
project. We also acknowledge Norchem, Inc,
BASF and W. R.
Grace and Company for donating
materials for the research.
6. AUTHORS’ NOTE
The author(s) declare(s) that there is no
conflict of interest regarding the publication
of this article. Authors confirmed that the
data and the paper are free of plagiarism.

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