Sun Yafei et. al.
Letter
ELECTROMAGNETIC WAVE ABSORBING AND MECHANICAL PROPERTIES OF
CEMENT-BASED COMPOSITE PANEL WITH DIFFERENT NANOMATERIALS
Sun Yafei1,2, Gao Peiwei1,*, Peng Hailong1, Liu Hongwei1,2, Lu Xiaolin1, Song Kai1
Department of Civil Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
2
Department of Civil Engineering, Yancheng Institute of Technology, Yancheng, 224051, China)
1
*Author to whom correspondence should be addressed: e-mail: [email protected]
Received 2 November 2016; accepted 21 November 2016
ABSTRACT
This paper presents the microstructures and mechanical and absorbing properties of double and triple layer, cement-based,
composite panels. The results obtained show that the frequency range in 2-18GHz had less than -10dB effective bandwidth,
which correlates with 3.7and 10.8GHz in double and triple layer cement-based composite panels. Furthermore, the double
layer panel’s compressive strength at 7 and 28 days was 40.2 and 61.2MPa, respectively. For the triple layer panel, the strength
values were 35.6MPa and 49.2MPa. The triple layer panel’s electromagnetic wave (EMW) absorbing properties were superior
compared to the properties of the double layer panel. However, the triple layer panel’s mechanical performance was inferior to
that of the double layer panel. This study proposes that carbon nanotubes can effectively improve the compressive strength and
interface structure of cement-based composite panels.
Keywords: Cement-based panel; electromagnetic wave absorption properties; multi-walled carbon nanotubes(MCNTs); nanoFe2O3; nano-NiO
1. INTRODUCTION
Presently, electrical equipment is universal and widely
applied. It is capable of releasing electromagnetic radiation while operating, which can affect its efficacy and
service life, while also negatively affecting the human
body, increasing the risk of illness [1], and even potentially releasing confidential information and location
coordinates[2,3]. Therefore, abundant research has been
conducted, particularly in electromagnetic wave absorption and shielding [4,5], in order to reduce the harmful
effects of electromagnetic radiation on the environment
[6]. “Shielding” refers to the use of a high-conductivity
material to form a seal around the conductive path to prevent the penetration of electromagnetic waves. However,
this method does not fundamentally weaken or eliminate
electromagnetic waves[7]. Moreover, it is possible for reflected electromagnetic waves on the material’s surface to
release secondary pollution[8]. This method is able to reduce the harm of electromagnetic radiation in cases where
electromagnetic energy is converted into other energy
forms by utilization of EMW-absorbing materials. These
materials include ferrite wave absorption agents, ceramic
wave absorption agents, fibre wave absorption agents, and
carbonaceous wave absorption materials, such as carbon
fibre, and graphite[9-13]. MCNTs is a potentially valuable
wave-absorbing filler with good conductivity, thermal stability, and a highly specific surface area [14,15].
Research shows that MCNTs with a high elastic modulus
and a unique spiral or tubular structure is formed by 2D
planar graphene coaxial layers. Once MCNT is incorporated into cement, it has a greater impact on the mechanical
properties of composites[16]. However, few reports exist
Advanced Composites Letters, Vol. 26, Iss.1, 2017
on MCNTs being used in cement as the nano-absorbing
material. Single layer cement-based panels with nanomaterials show inefficient results and require high production
costs. Multilayer, composite, cement-based panels used as
wave-absorbing material will therefore become a main focus of future research. The present study investigates the
incorporation of MCNTs, nanometre iron oxide (NanoFe2O3), nanometre nickel oxide (Nano-NiO), and ceramic
granule into prepared double and triple layer cement-based
composite panels as wave-absorbing material. We tested
different layers of thickness to replace single layer cementbased composite panels with nano-function materials. We
conducted experiments to explore the different panels’ absorption and mechanical performance within a 2-18 GHz
frequency range of electromagnetic waves. We also performed theoretical research to investigate the application
of composites.
2. MATERIALS AND EXPERIMENTAL PROGRAM
2.1 Materials and apparatus
For the experiments, we used type P·II 42.5 grade Portland
cement manufactured by Dalian Nanjing Cement Factory,
and MCNTs with> 200m²/g specific surface area, 5-10 nm
inner diameter, and 10-20 nm outer diameter with 10-30
μm length and <0.01Ω·cm resistivity manufactured by
Nano Times. We purchased nano-Fe2O3 with >99% purity
and >60 m2/g specific surface area, 20 nm average particle size, and 1594.5°C melting point from Baomanbio. We
also purchased nano-NiO with >99.9% purity, >58m2/g
specific surface area, 60nm average particle size, and 6.6
g/cm3 density from Shanghai Xangtian Nanomaterial Co.
Ltd. We obtained ceramic granule with 1480 kg/m3 apparent density, 31.6% water absorption in 1 hour, and 31.7%
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Sun Yafei et. al.
water absorption in 24 hours from Huainan Jinrui New
Building Materials Factory. We also used fluvial sand with
2550 kg/m3 apparent density, 3.0 fineness modulus, and
<1.0% clay contents. We purchased silica fume with>105%
activated index, >15m2/g specific surface area, >85% SiO2
contents, and<1.5% alkali contents from Shanghai Ledem
Silica Fume Co, Ltd. We were provided with super plasticizer with polycarboxylic acid-based in approximately
45% water-reducing rate from Shanghai Sunrise Polymer
Material Co, Ltd. Lastly, Shanghai Shliangxing provided
us with white floss like dispersant, easy dissolving in water.
We used several main apparatus and facilities for our experiments, including: -160A grouting machine and JJ-5
cement mortar mixer manufactured by Wuxi Jianyi Instrument & Machinery Co, Ltd.; ZP-4 standard concrete vibrator manufactured by Xinxinag Golden Harvest Machinery
Co., Ltd.; CF-B Standard thermostatic bath tank manufactured by Beijing KangdaZte Co., Ltd; DHG-9146A electrothermal thermostatic blasted drying oven manufactured
by Shanghai Jing Hong Laboratory Instrument Co., Ltd;
WDW-E2000 universal microelectronic controlled testing
machine manufactured by Jinan Shijin Group; S4800 Field
Emission Scanning Electron Microscope manufactured by
Hitachi (Japan); HP8722ES vector network analyser manufactured by Xintongrui; and BS-110S electronic analytical scale with 6kg weight and 0.1g weight sensor manufactured by Beijing Saiduolisi Balance Co., Ltd.
2.2 Experimental mix proportions
According to the absorbing mechanism of composites, the
wave-absorbing element of cement-based panels is mainly
based on the upper and bottom layers of the panel. The
mechanism is achieved by amplitude reflection that is
equivalent to the opposite phase, as well as electromagnetic wave loss absorption conducted by the nanomaterial itself. Nano-Fe2O3 and Nano-NiO are suitable materials for
the wave-absorbing layers, since they have good frequency
particularity with less relative permittivity and greater permeability. In this experiment, our aim was to devise double
and triple layer, cement-based, wave-absorbing panels to
ensure that the basic mechanical properties would match
with wave impedance at a void within the panel and, there-
Letter
fore, produce a favourable electromagnetic wave loss particularity. We manufactured upper and bottom layers with
14 mm thickness for the double layer panel structure. The
upper layers were mixed with appropriate amounts of MCNTs, whereas the bottom layers were mixed with appropriate amounts of Nano-Fe2O3 and Nano-NiO. For triple
layer panels, we used layers of 6mm, 11mm, and 11mm
thickness, respectively. The upper layers for these were
mixed with ceramic granule; the middle layers with appropriate amounts of MCNTs; and the bottom layers with appropriate amounts of Nano-Fe2O3 and Nano-NiO. Table 1
shows the experiment mixture proportions combined with
our research results.
2.3 Experimental method
Our specimen preparation was conducted as follows.
We weighed experiment materials based on our pre-determined mixture proportions. We then mixed different
batches of dry cement for 3 minutes with MCNTs, nanoFe2O3, nano-NiO, and ceramic granule. After, we added
water, plasticizer, and dispersant to each mix and combined the ingredients for 2-3 minutes. We then used iron
molds with a difference scale of 180mm×180mm×28mm
and 70.7mm×70.7mm×70.7mm, and marked a certain
thickness at the inner part of each mold after filling them
with the well-stirred cement mixtures. We then vibrated
the mixtures at the vibration platform and calibrated the
specimen surfaces while curing them indoors at 20 for 1
day. After mold removal, we cured them again at 20±2,
and then again at 7 and 28 days with a standard requirement of relative humidity above 95%. After all of these
steps were completed, we tested the specimen’s mechanical properties and reflectivity.
We performed reflectivity testing to measure the accuracy of each specimen’s reflection system. We set a signal
source and used a vector Network Analyser (HP8722ES)
as well as antenna testing, based on the testing standards in
radar, wave-absorbing materials (GJB2038-2011)
3. RESULTS AND ANALYSIS
3.1 Mechanical properties analysis
Fig. 1 shows the wave-absorbing materials in double
and triple layer cement-based panels (upper, middle, and
Table 1: Double and triple absorbing material mix proportions /g
Item
Ce
NF
NN
Thickness
(mm)
Up
945
/
/
4.725 253
7.56
3.78 /
14
Do
Down
675
283 94
/
256.5
5.40
/
/
14
Up
360
/
/
/
70
2.52
0
150
6
Tri Middle 540
/
/
2.7
140.4
4.32
2.7
/
11
Down
540
228 75.6 /
205.2
4.32
/
/
11
Note: Do- double layer, Tri- triple layer, Ce- Cement, NF- Nano-Fe2O3, NN- Nano-NiO, CN- Carbon
Nanotubes, W-water, Su- Superplasticizer, Di- Dispersant, Ci- Ceramicite, Up- upper layer, Middlemiddle layer，Down- bottom layer
Advanced Composites Letters, Vol. 26, Iss.1, 2017
CN
W
Su
Di
Ci
7
7d
28d
70
60
50
40
30
20
10
0
Down
Up
All
Compressive strength/ MPa
Compressive strength/ MPa
Sun Yafei et. al.
Based
（a）Double
Letter
7d
28d
70
60
50
40
30
20
10
0
Down
Up
Middle
All
Based
（b）Three
Fig. 1: Compressive properties of cement-based absorbing materials
bottom layer expressed as up; middle layer expresses as
down), as well as the overall panel (expressed as all) at
7 and 28 days’ compressive strengths. These values are
compared with an unmixed, nanomaterial, testing block
(expressed as based).
Fig. 1(a) shows that the compressive strengths of the bottom panel in the triple layer cement-based panel were 23.0
and 33.0 MPa at 7 and 28 days, respectively. We may explain these values by the incorporation of Nano-Fe2O3,
and Nano-NiO to the bottom layer with smaller granules.
Therefore, this kind of cement is difficult to completely fill
in between nanomaterials and to disperse uniformly. The
upper layer panel’s compressive strengths are significantly
high, with 46.6 and 69.0MPa values at 7 and 28 days, respectively. This may due to the incorporation of 0.5wt%
MCNTs into the cement, which can generate larger hydration crystals by reacting with C3S, C2S, and C3A in the
paste. The crystals will attach to the surface of the MCNTs,
compacting the composites. MCNTs with large specific
surface areas can also effectively improve the interface
structure and compressive strength of cement-based panels
via larger Van der Wales forces[17]. Moreover, the overall
compressive strengths of double layer cement-based panels are 40.2 and 61.2MPa, while the standard strengths for
the testing panel are 52.8 and 58.1MPa at 7 and 28 days,
respectively. Clearly, the overall strength of the double
A
layer cement-based panel was increased by 5.3% when
compared to the standard testing panel’s values.
Fig. 1(b) shows the compressive strengths of the triple layer cement-based panel. The upper layer panel’s values are
4.6 and 7.0MPa, and the middle layer panel’s values are
46.4 and 68.8MPa. The bottom layer panel exhibits values
of 22.9MPa and 33.2MPa. All of these were taken at 7 and
28 days, respectively. Basically, the compressive strengths
of the middle and bottom layers in the triple layer structure panel are the same as those of the double layer panel.
The triple layer panel’s overall compressive strengths were
35.6 and 49.2MPa at 7 and 28 days, respectively. However, by the 28th day the intensity had decreased by 15.3%,
compared with the standard testing panel. This may be
caused by the incorporation of a certain amount of the porous and loose structure of ceramic granule to the upper
layer, thereby causing the overall compressive strength to
decrease.
3.2 Scanning electron microscopy (SEM) observations
We used the middle layer of the cement-based triple layer
panel to analyse the influence of mechanical properties after the addition of nano-function materials.
Fig. 2 shows our SEM analysis of the middle layer in the
triple layer, cement-based, wave-absorbing materials at 3
B
（a）Double
（b）Three
Fig. 2: SEM observations of cement-based absorbing materials
Advanced Composites Letters, Vol. 26, Iss.1, 2017
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Sun Yafei et. al.
3.3 Analysis of absorption properties
Due to its absorbing mechanism, electromagnetic wave
absorbing material is able to absorb both waves and interferences. To operate, absorption material relies mainly on
internal electromagnetic wave loss. However, interference
absorbing material suppresses electromagnetic waves by
the principle that reflected waves on the absorbing layer’s
surface have the same amplitude as but opposite phase to
the bottom layer’s reflected waves. The absorption material can also be divided into dielectric and magnetic medium types, according to its absorbing properties. Nano-NiO
and Nano-Fe2O3 are magnetic media fillers with high magnetic permeability. They absorb electromagnetic waves via
a mechanism of relaxation through electron polarization,
ionic polarization, molecular polarization, and interfacial
polarization. According to the theory of electromagnetic
shielding, incident waves are partly reflected by the material. When launching into the material, electromagnetic
waves are partly absorbed and partly consumed by the
multiple reflections. The residual electromagnetic waves
transmit along their incident direction (Transmitted Wave,
TW). Fig. 3 is an absorption and shielding schematic diagram of electromagnetic waves in multilayer materials.
The total shielding effectiveness expression[18] we used
is:
SEtotal  SEA  SER  SEM
(1)
Where SEA =absorption loss; SER =reflection loss; and
SEM =inner multiple reflections loss. When SEA>15dB,
SEM is negligible and equation (1) can be modified to
SEtotal=SEA+SER, and SEA is a function of the material’s
electrical conductivity and magnetic permeability[19]:
SE A (dB)  20d (
ur 1/ 2
) log10 (e)
2
Advanced Composites Letters, Vol. 26, Iss.1, 2017
(2)
Where d is thickness of sample (cm), e is a constant of
2.718, σ is conductivity, ur is relative magnetic permeability, and ω is the angular frequency. From equation (2), we
may determine that SEA increases with electrical conductivity and magnetic permeability. When evaluating absorption properties, reflectance is a key indicator. Electromagnetic wave absorbing and shielding materials can be used
in general construction when the absorbing material’s reflectance is less than -5dB. To use shielding materials in
critical military equipment and/or facilities, the absorbing
material’s reflectance should be less than -7dB[20]. Fig.
4 shows our reflectivity test results for double and triple
layer cement-based panel.
Fig. 3: Absorption and shielding schematic diagram of electromagnetic wave
-2
-4
-6
-8
Reflectivity/ dB
and 28 days. Fig. 2(a) shows the clear production of acicular AFt and C-S-H flakes. The curing of cement slurry
with MCNTs after 3 days is visible in rare crystal size,
since AFt length is around 0.5 - 1um and the crystals are
only slightly connected in between. As Fig. 2(b) shows,
AFt and C-S-H grow up significantly after curing for 28
days, whereas AFt and C-S-H grow approximately 1-5 µm
and gradually become connected in a network structure.
MCNTs is affected by smaller size, surface, quantum size,
and macroscopic quantum tunnelling efficiency. The slurry mixed with MCNTs does not only exhibit good absorbing properties; it is also characterized by a huge surface
ratio. In addition, it presents a larger path ratio and favourable tensile modulus, which potentially provides sites for
crystal growth and for C-S-H gel to fill the gaps of cement
hydration products. This can improve the efficiency and
strength of the products. Therefore, we may conclude that
the testing panel with 0.5wt% MCNTs shows significant
improvement in compressive strength.
Letter
-10
-12
-14
Two
Three
-16
-18
-20
-22
-24
2
4
6
8
10
12
14
16
18
Frequency /GHz
Fig. 4: Reflectivity of cement-based absorbing plate
As Fig. 4 shows, the reflected ratio of the double layer,
cement-based panel is lower than -5.4dB at the frequency range of 2-18GHz. Minimum reflectance occurs at
3.7GHz, which achieves a -13.4 dB value. When the effective bandwidth is less than -7dB, a 16.5GHz surplus is
achieved. When the effective bandwidth is less than -10
dB, a value of 3.7GHz is achieved.
The triple layer cement-based panel’s reflectivity is lower
than -5.9dB at a 2-18GHz frequency range. Its minimum
reflected ratio occurs at 4.5GHz, and achieves a value of
-22.4 dB. When the effective bandwidth is less than -7dB,
a value of 16.1GHz surplus is achieved. When the bandwidth is less than -10 dB, a value of 10.8GHz is achieved.
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Sun Yafei et. al.
The wave-absorbing, cement-based, triple layer panel’s
reflectivity shows significant reduction compared with
the same value for the double layer panel. Therefore, ceramic granule with low electromagnetic parameters and
greater porosity (as well as wave impedance) appropriately matches the gaps after a ceramic granule supplement
is added to wave-absorbing materials in a double layer
panel. This is done to increase the incidence ratio of electromagnetic waves. Additionally, the porous structure of
ceramic granule provides multi-transmission paths for incident electromagnetic waves. This increases the incident
electromagnetic wave-absorbing materials at the inner reflection, scattering, and interference, while also increasing
electromagnetic wave absorption loss. The intermediate
layer should be designed for transition with semiconductor
material. When mixing cement-based panels with appropriate amounts of MCNTs, the cement will form a closed
conducting network in its interior. Meanwhile, part of the
electromagnetic wave will be converted to a thermic wave
through a vortex generated in the material’s inner section.
The bottom layer should be devised as an absorbing layer
with Nano-Fe2O3 and Nano-NiO, which possess favourable electromagnetic wave absorption properties.
4. CONCLUSIONS
We found that the double layer, cement-based panel’s overall compressive strength was 61.2 MPa at 28 days. This
showed a 5.3% increase when compared with the experiment’s standard panel. For the triple layer cement-based
panel, compressive strength was 49.2 MPa at 28 days,
which showed a decrease of 15.3% when compared with
the standard panel. Cement slurry mixed with MCNTs
and cured for 3 days generated AFt and C-S-H. Hydration
products tended to increase gradually with hydration time,
producing a network to fill the gaps of cement hydration
products. Thereby, the mechanical properties and compacting efficacy were improved.
Minimum reflectance in the double layer cement-based
panel’s absorbing material occurred at 3.7 GHz, achieving
a value of -13.4 dB. When the effective bandwidth was less
than -10dB, a value of 3.7GHz was achieved. The minimum reflectance in the triple layer cement-based panel’s
absorbing material occurred at 4.5GHz, achieving a value
of -22.4 dB. When the effective bandwidth was less than
-10dB, the value of 10.8GHz was achieved. Therefore, we
conclude that the triple layer, cement-based panel’s wave
absorption capacity is more favourable.
Our research shows significant results for wave absorption
at 2-18GHz in double and triple layer cement-based panels mixed with nanomaterials. We also found less variation in compressive strength. Thus, our formulation can be
used as wave-absorbing material in panels or as a special
coating applied to military installations and vital civilian
installations.
Advanced Composites Letters, Vol. 26, Iss.1, 2017
Letter
ACKNOWLEDGEMENTS
We wish to express our gratitude to: National Natural Science Foundation of China(51478408); Six talent team
project of Jiangsu Province, China(XCL-CXTD-007); The
IUR joint innovation Fund of Jiangsu Province of China
(No. BY2016065-27); The Post-doctoral fund of China and
Jiangsu (under contract No. 1301057B, 2014M551588).
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