L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
1005–1009
BASIC PHYSICAL, MECHANICAL AND ELECTRICAL
PROPERTIES OF ELECTRICALLY ENHANCED
ALKALI-ACTIVATED ALUMINOSILICATES
OSNOVNE FIZIKALNE, MEHANSKE IN ELEKTRI^NE
LASTNOSTI ELEKTRI^NO IZBOLJ[ANIH, Z ALKALIJAMI
AKTIVIRANIH ALUMINOSILIKATOV
Luká{ Fiala1, Milo{ Jerman1, Pavel Rovnaník2, Robert ^erný1
1Czech Technical University, Faculty of Civil Engineering, Department of Materials Engineering and Chemistry, Thákurova 7,
166 29 Prague 6, Czech Republic
2Brno University of Technology, Institute of Chemistry, Faculty of Civil Engineering, @i`kova 17, 602 00 Brno, Czech Republic
fialal@fsv.cvut.cz
Prejem rokopisa – received: 2017-05-04; sprejem za objavo – accepted for publication: 2017-07-28
doi:10.17222/mit.2017.051
Alkali-activated aluminosilicates (AAAs) with electrically conductive admixtures are promising competitors to the
cement-based materials enhanced in the same way. The electrical conductivity of these materials dramatically increases with a
sufficient amount of admixtures, which broaden their possible applicability. Electrically optimized materials are typically used
in self-heating, self-sensing or magnetic-shielding systems. However, an increase in the amount of admixtures can negatively
affect the compressive or flexural strength and can lead to an increase in the porosity. Therefore, it is crucial to experimentally
determine the mechanical properties in order to decide whether an electrically enhanced material is applicable in the building
industry. In this research, basic physical, mechanical and electrical properties of AAAs with three types of electrically conduc-
tive admixtures in different dosages are studied. Typical representatives of spherical inclusions, carbon black (CB), graphite
powder (GP) and carbon fibers (CF) as fibrous fillers, are tested. The experimental results reveal that AAAs with CB dosages
higher than 4 % are promising materials that could be utilized in self-heating systems due to their sufficiently high electrical
conductivity.
Keywords: alkali-activated aluminosilicates, electrically conductive admixtures, compressive strength, flexural strength, elec-
trical conductivity
Z alkalijami aktivirani aluminosilikati (AAA) z elektri~no prevodnimi dodatki so obetavni konkurenti materialov, ki izbolj{ani
na enak na~in, temeljijo na cementu. Elektri~na prevodnost teh materialov se drasti~no pove~uje z zadostno koli~ino tak{nih
dodatkov, ki raz{irjajo njihovo mo`no uporabnost. Tipi~na prakti~na uporaba elektri~no optimiranih materialov je v samo-
ogrevanju, samozaznavanju ali magnetno-za{~itnih sistemih. Vendar lahko pove~anje koli~ine dodatkov negativno vpliva na
tla~no ali upogibno trdnost in lahko povzro~i pove~anje poroznosti. Zato je klju~nega pomena, da dolo~imo eksperimentalno
mehanske lastnosti, da bi se odlo~ili, ali se naj elektri~no oja~an material uporablja v gradbeni{tvu. V tem prispevku so
preu~evane osnovne fizikalne, mehanske in elektri~ne lastnosti AAA s tremi vrstami elektri~no prevodnih dodatkov v razli~nih
doziranjih. Eksperimentalni rezultati ka`ejo na dejstvo, da so AAA z odmerki CB, vi{jimi od 4 %, obetavni materiali, ki bi jih
lahko uporabili v sistemih za samoogrevanje zaradi dovolj visoke lastne elektri~ne prevodnosti.
Klju~ne besede: aluminosilikati, aktivirani z alkalijami; elektri~no prevodne dodajne me{anice, tla~na trdnost, upogibna trdnost,
elektri~na prevodnost
1 INTRODUCTION
Alkali-activated aluminosilicates (AAAs, often also
denoted as geopolymers) are promising competitors to
the cement-based materials due to their good mechanical
properties, chemical resistance and enhanced fire resis-
tance.1,2 Moreover, other AAA benefits that cannot be
overlooked are economic aspects and their environmen-
tally friendly nature.3,4
Alkaline activators as components of cementing
materials date back to 1930, when Kuhl investigated the
setting behavior of mixtures of ground slag powder and
caustic potash solution. The first extensive laboratory
study on clinkerless cements consisting of slag and so-
dium hydroxide was performed in 1940s by A. O. Pur-
don.5 Further detailed observations of AAAs were
performed by V. D. Glukhovsky6 who aimed at investi-
gating the binders used in ancient Roman and Egyptian
constructions and concluded that they were composed of
calcium aluminosilicate hydrates similar to the ones of
Portland cement, which explained their durability. Based
on these observations, Glukhovsky developed a new type
of binders, the so-called soil cement, which consists of
aluminosilicates mixed with alkalis-rich industrial
wastes. Another study carried out by R. Malinowski7 re-
vealed the fact that the restoration of ancient construc-
tions with the materials based on Portland cement leads
to their disintegration after 10 years, which is much
lower compared to the durability of the original material.
A further qualitative enhancement of AAAs repre-
sented by an increased electrical conductivity can be
achieved with an addition of electrically conductive
Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009 1005
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 67.017:666.762.1:661.34 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(6)1005(2017)
admixtures, which was already observed for the cement-
based materials.8–10 With an appropriate amount of such
admixtures, at around the percolation threshold, an elec-
trically conductive network is built up in the solid
matrix. Therefore, the electrical conductivity signifi-
cantly increases and naturally electrically non-conduc-
tive materials become electrically conductive, which
broadens their practical utilization. Such materials can
then be used in many practical ways, e.g., in self-
heating11 or self-sensing12 systems.
In the past, various electrically conductive admix-
tures based on metallic particles or fibers, such as nickel
powder (NP) and steel fibers (SF), or on carbon-based
materials, such as carbon black (CB), carbon fibers (CF),
carbon nanotubes (CNT) or graphite powder (GP) were
studied. A comprehensive review of widely used admix-
tures suitable for self-sensing concrete was given by B.
Han et al.13
In this paper, the basic physical, mechanical and
electrical properties of reference AAAs and several types
of electrically enhanced AAAs with different dosages of
conductive admixtures, namely, carbon black (CB),
carbon fibers (CF) and graphite powder (GP) are studied.
The main aim is to determine the relation of the amount
of electrically conductive admixtures with the electrical
conductivity, the compressive strength and the flexural
strength and to identify the most appropriate AAA mixes
that allow satisfactory electrical and mechanical para-
meters.
2 EXPERIMENTAL PART
The studied AAA materials were based on SM[ 380
produced by Kotou~ [tramberk s.r.o. It is a dry, granu-
lated blast-furnace slag with a fineness of 380 m2 kg–1
fulfilling the requirements of ^SN EN 197-1. The
second component, the Britesil C205 waterglass with the
SiO2/Na2O molar ratio equal to 2.07, was used for the
alkali activation. The filler was represented by three
normalized CEN fractions of the quartz sand (PG1, PG2,
PG3) produced by Filtra~ní písky, Ltd., Czech Republic,
which complies with ^SN EN 196-1. The particle size
distribution of the used sand is given in Figure 1.
Within the study, fifteen different types of AAA
samples were prepared: the reference sample without any
conductive admixture, samples with CB in amounts of
(0.89, 2.22, 4.44, 6.67 and 8.89) % of mass fractions,
samples with CF in amounts of (0.56, 1.11, 1.67 and
2.22) % of mass fractions, and samples with GP in
amounts of (1.78, 3.33, 4.44, 6.67 and 8.89) % of mass
fractions. The compositions of the analyzed AAA mixes
are given in Tables 1–3.
The samples were prepared as follows: Firstly, water-
glass was mixed with water. The solution was then
mixed with the suspension of an electrically conductive
admixture. CB was incorporated into the mixture in the
form of a 20 % mass-fraction homogenized suspension
(relative to the slag mass), GP in the form of 10 %
mass-fraction and 20 % mass-fraction suspensions and
CF in the form of a 5 % mass-fraction suspension. Op-
tionally, additional water was added to ensure good
workability of the mix. Other components were added in
the following order: slag, a fine fraction of sand (PG1), a
medium-coarse fraction of sand (PG2), a coarse fraction
of sand (PG3). The final mixture was put into 40 mm ×
40 mm × 160 mm molds and vibrated. The samples were
demolded after 24 h, cured in water for additional 28 d
and dried in an oven.
Table 1: Compositions of the reference AAA mixture and AAA mix-
tures with CB
Component/
Admixture
Refe-
rence
CB
0.89 %
CB
2.22 %
CB
4.44 %
CB
6.67 %
CB
8.89 %
Slag (g) 450 450 450 450 450 450
Waterglass (g) 90 90 90 90 90 90
Sand PG1 (g) 450 450 450 450 450 450
Sand PG2 (g) 450 450 450 450 450 450
Sand PG3 (g) 450 450 450 450 450 450
Admixture
suspense (%) 0 20 20 20 20 20
Amount of
suspense (g) 0 20 50 100 150 200
Additional
water (g) 0 190 170 130 90 105
Table 2: Compositions of the AAA mixtures with CF
Component/
Admixture
CF
0.56 %
CF
1.11 %
CF
1.67 %
CF
2.22 %
Slag (g) 450 450 450 450
Waterglass (g) 90 90 90 90
Sand PG1 (g) 450 450 450 450
Sand PG2 (g) 450 450 450 450
Sand PG3 (g) 450 450 450 450
Admixture
suspense (%) 5 5 5 5
Amount of
suspense (g) 50 100 150 200
Additional
water (g) 150 100 50 0
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
1006 Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: Particle size distribution of the Chlumský reference sand
Table 3: Compositions of the AAA mixtures with GP
Component/
Admixture
GP
1.78 %
GP
3.33 %
GP
4.44 %
GP
6.67 %
GP
8.89 %
Slag (g) 450 450 450 450 450
Waterglass (g) 90 90 90 90 90
Sand PG1 (g) 450 450 450 450 450
Sand PG2 (g) 450 450 450 450 450
Sand PG3 (g) 450 450 450 450 450
Admixture
suspense (%) 10 10 20 20 20
Amount of
suspense (g) 80 150 100 150 200
Additional
water (g) 140 70 130 90 50
As the fundamental physical material characteristics,
the bulk density v (kg m–3), the open porosity  (–) and
the matrix density mat (kg m–3) were measured using the
water-vacuum-saturation method. In the first step, the
samples were dried in a drier to remove the majority of
the physically bound water. Subsequently, the samples
were placed into a desiccator. In three hours, the air was
evacuated with a vacuum pump from the desiccator. The
samples were then kept under water for 24 h. From the
mass of water-saturated sample mw (kg) and the mass of
immersed water-saturated sample ma (kg), volume V of
the sample was determined, and the basic physical pro-
perties were calculated.
Mechanical properties were measured on three sam-
ples with dimensions of 40 mm × 40 mm × 160 mm
according to the Czech Standard ^SN EN 196-1 (Figure
2). At first, three samples of each mixture were cured in
a water bath for 28 d. Then the flexural strength was
determined with the three-point-bending test. The span
length between supports was 100 mm, and the loading
rate was 0.15 mm/min. The compressive strength was
then determined on six halves of the prisms from the pre-
vious flexural-strength tests.
Electrical properties were determined on samples
with dimensions of 40 mm × 40 mm ×10 mm cut from
40 mm × 40 mm × 160 mm prisms. In order to achieve
good contact of the tested materials with the measuring
apparatus, two lateral sides (40 mm × 40 mm) playing
the role of electrodes were painted with a conductive-
carbon paint produced by SPI Supplies, together with a
copper adhesive tape that was connected to the conduc-
tors. The samples dried in an oven were put into the
dessicator for a couple of days in order to achieve dry
state with no residual water. Finally, the electrical resis-
tance was determined with a Fluke 8846A 6-1/2 digit
precision multimeter in a 4-electrode configuration (Fig-
ure 3) and the electrical conductivity was calculated with
respect to the shape ratio of the samples.
3 RESULTS AND DISCUSSION
The basic physical properties are presented in Fig-
ures 4 to 6. The bulk density of the reference material
(Figure 4) was 2164 kg m-3. It decreased with the in-
creasing amount of all the tested electrically conductive
admixtures. In the case of CB, the decrease was in a
range of 3.3–8.7 % compared to the reference material.
The highest decrease of 8.7 % was observed for the
AAAs with 8.89 % of CB. Concerning the AAA samples
with CF and GP, the decrease in the bulk density was in
ranges of 3.1–4.9 % and 2.9–4.5 %, respectively.
The matrix density (Figure 5) was highest for the
reference material (2673 kg m–3). Concerning the AAA
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009 1007
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: Bulk density of electrically enhanced AAAsFigure 2: Three-point bending and compressive-strength experiment
Figure 3: Electrical-resistivity measurements
admixtures, which was already observed for the cement-
based materials.8–10 With an appropriate amount of such
admixtures, at around the percolation threshold, an elec-
trically conductive network is built up in the solid
matrix. Therefore, the electrical conductivity signifi-
cantly increases and naturally electrically non-conduc-
tive materials become electrically conductive, which
broadens their practical utilization. Such materials can
then be used in many practical ways, e.g., in self-
heating11 or self-sensing12 systems.
In the past, various electrically conductive admix-
tures based on metallic particles or fibers, such as nickel
powder (NP) and steel fibers (SF), or on carbon-based
materials, such as carbon black (CB), carbon fibers (CF),
carbon nanotubes (CNT) or graphite powder (GP) were
studied. A comprehensive review of widely used admix-
tures suitable for self-sensing concrete was given by B.
Han et al.13
In this paper, the basic physical, mechanical and
electrical properties of reference AAAs and several types
of electrically enhanced AAAs with different dosages of
conductive admixtures, namely, carbon black (CB),
carbon fibers (CF) and graphite powder (GP) are studied.
The main aim is to determine the relation of the amount
of electrically conductive admixtures with the electrical
conductivity, the compressive strength and the flexural
strength and to identify the most appropriate AAA mixes
that allow satisfactory electrical and mechanical para-
meters.
2 EXPERIMENTAL PART
The studied AAA materials were based on SM[ 380
produced by Kotou~ [tramberk s.r.o. It is a dry, granu-
lated blast-furnace slag with a fineness of 380 m2 kg–1
fulfilling the requirements of ^SN EN 197-1. The
second component, the Britesil C205 waterglass with the
SiO2/Na2O molar ratio equal to 2.07, was used for the
alkali activation. The filler was represented by three
normalized CEN fractions of the quartz sand (PG1, PG2,
PG3) produced by Filtra~ní písky, Ltd., Czech Republic,
which complies with ^SN EN 196-1. The particle size
distribution of the used sand is given in Figure 1.
Within the study, fifteen different types of AAA
samples were prepared: the reference sample without any
conductive admixture, samples with CB in amounts of
(0.89, 2.22, 4.44, 6.67 and 8.89) % of mass fractions,
samples with CF in amounts of (0.56, 1.11, 1.67 and
2.22) % of mass fractions, and samples with GP in
amounts of (1.78, 3.33, 4.44, 6.67 and 8.89) % of mass
fractions. The compositions of the analyzed AAA mixes
are given in Tables 1–3.
The samples were prepared as follows: Firstly, water-
glass was mixed with water. The solution was then
mixed with the suspension of an electrically conductive
admixture. CB was incorporated into the mixture in the
form of a 20 % mass-fraction homogenized suspension
(relative to the slag mass), GP in the form of 10 %
mass-fraction and 20 % mass-fraction suspensions and
CF in the form of a 5 % mass-fraction suspension. Op-
tionally, additional water was added to ensure good
workability of the mix. Other components were added in
the following order: slag, a fine fraction of sand (PG1), a
medium-coarse fraction of sand (PG2), a coarse fraction
of sand (PG3). The final mixture was put into 40 mm ×
40 mm × 160 mm molds and vibrated. The samples were
demolded after 24 h, cured in water for additional 28 d
and dried in an oven.
Table 1: Compositions of the reference AAA mixture and AAA mix-
tures with CB
Component/
Admixture
Refe-
rence
CB
0.89 %
CB
2.22 %
CB
4.44 %
CB
6.67 %
CB
8.89 %
Slag (g) 450 450 450 450 450 450
Waterglass (g) 90 90 90 90 90 90
Sand PG1 (g) 450 450 450 450 450 450
Sand PG2 (g) 450 450 450 450 450 450
Sand PG3 (g) 450 450 450 450 450 450
Admixture
suspense (%) 0 20 20 20 20 20
Amount of
suspense (g) 0 20 50 100 150 200
Additional
water (g) 0 190 170 130 90 105
Table 2: Compositions of the AAA mixtures with CF
Component/
Admixture
CF
0.56 %
CF
1.11 %
CF
1.67 %
CF
2.22 %
Slag (g) 450 450 450 450
Waterglass (g) 90 90 90 90
Sand PG1 (g) 450 450 450 450
Sand PG2 (g) 450 450 450 450
Sand PG3 (g) 450 450 450 450
Admixture
suspense (%) 5 5 5 5
Amount of
suspense (g) 50 100 150 200
Additional
water (g) 150 100 50 0
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
1006 Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: Particle size distribution of the Chlumský reference sand
Table 3: Compositions of the AAA mixtures with GP
Component/
Admixture
GP
1.78 %
GP
3.33 %
GP
4.44 %
GP
6.67 %
GP
8.89 %
Slag (g) 450 450 450 450 450
Waterglass (g) 90 90 90 90 90
Sand PG1 (g) 450 450 450 450 450
Sand PG2 (g) 450 450 450 450 450
Sand PG3 (g) 450 450 450 450 450
Admixture
suspense (%) 10 10 20 20 20
Amount of
suspense (g) 80 150 100 150 200
Additional
water (g) 140 70 130 90 50
As the fundamental physical material characteristics,
the bulk density v (kg m–3), the open porosity  (–) and
the matrix density mat (kg m–3) were measured using the
water-vacuum-saturation method. In the first step, the
samples were dried in a drier to remove the majority of
the physically bound water. Subsequently, the samples
were placed into a desiccator. In three hours, the air was
evacuated with a vacuum pump from the desiccator. The
samples were then kept under water for 24 h. From the
mass of water-saturated sample mw (kg) and the mass of
immersed water-saturated sample ma (kg), volume V of
the sample was determined, and the basic physical pro-
perties were calculated.
Mechanical properties were measured on three sam-
ples with dimensions of 40 mm × 40 mm × 160 mm
according to the Czech Standard ^SN EN 196-1 (Figure
2). At first, three samples of each mixture were cured in
a water bath for 28 d. Then the flexural strength was
determined with the three-point-bending test. The span
length between supports was 100 mm, and the loading
rate was 0.15 mm/min. The compressive strength was
then determined on six halves of the prisms from the pre-
vious flexural-strength tests.
Electrical properties were determined on samples
with dimensions of 40 mm × 40 mm ×10 mm cut from
40 mm × 40 mm × 160 mm prisms. In order to achieve
good contact of the tested materials with the measuring
apparatus, two lateral sides (40 mm × 40 mm) playing
the role of electrodes were painted with a conductive-
carbon paint produced by SPI Supplies, together with a
copper adhesive tape that was connected to the conduc-
tors. The samples dried in an oven were put into the
dessicator for a couple of days in order to achieve dry
state with no residual water. Finally, the electrical resis-
tance was determined with a Fluke 8846A 6-1/2 digit
precision multimeter in a 4-electrode configuration (Fig-
ure 3) and the electrical conductivity was calculated with
respect to the shape ratio of the samples.
3 RESULTS AND DISCUSSION
The basic physical properties are presented in Fig-
ures 4 to 6. The bulk density of the reference material
(Figure 4) was 2164 kg m-3. It decreased with the in-
creasing amount of all the tested electrically conductive
admixtures. In the case of CB, the decrease was in a
range of 3.3–8.7 % compared to the reference material.
The highest decrease of 8.7 % was observed for the
AAAs with 8.89 % of CB. Concerning the AAA samples
with CF and GP, the decrease in the bulk density was in
ranges of 3.1–4.9 % and 2.9–4.5 %, respectively.
The matrix density (Figure 5) was highest for the
reference material (2673 kg m–3). Concerning the AAA
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009 1007
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: Bulk density of electrically enhanced AAAsFigure 2: Three-point bending and compressive-strength experiment
Figure 3: Electrical-resistivity measurements
mixtures with electrically conductive fillers, the samples
with a GP admixture exhibited a higher matrix density
(2599–2636 kg m–3) compared to the samples with CF
and CB. In the case of the samples with CB, the matrix
density ranged between 2590–2618 kg m–3. In the case of
CF, the decrease was higher than for the reference mate-
rial and the matrix density ranged between 2570–2600
kg m–3. The maximum decrease (3.9 %) was observed
for the samples with 0.56 % of CF admixture.
The total open porosity of the mixtures ranged bet-
ween 0.193–0.244 % (Figure 6). A significant increase
in the porosity was observed for the AAA mixtures with
6.67 % of CB and 8.89 % of CB.
The dependence of the flexural strength on the
amount of electrically conductive admixtures is pre-
sented in Figure 7. The flexural strength of the reference
AAAs was 7.43 MPa and it slightly increased up to 8.03
MPa for the 4.44 % CB dosage for the materials with a
CB admixture (an 8 % increase compared to the refe-
rence AAAs). For higher dosages of the CB filler, the
flexural strength decreased to 6.88 MPa (a 7.4 %
decrease compared to the reference AAAs). In the case
of the CF admixture, the flexural strength was higher
than that of the reference AAAs, which was due to the
fibrous nature of such an admixture. The increase to the
maximum of 9.9 MPa (a 33.2 % increase compared to
the reference AAAs) was observed for the mixture with
CF in the amount of 2.22 %. GP exhibited a systematic
increase in the flexural strength of up to 10.47 MPa
(40.9 % compared to the reference AAAs) for 6.67 % of
GP and then a slight decrease to 10.17 MPa (a 36.9 %
increase compared to the reference AAAs) was observed
for GP in the amount of 8.89 %.
The dependence of the compressive strength on the
amount of electrically conductive admixtures is pre-
sented in Figure 8. The highest compressive strength
equal to 66.38 MPa was observed for the reference
AAAs. With the increase in the amount of electrically
conductive admixtures, a decrease in the compressive
strength was observed. The electrically conductive
admixtures reduced the workability of the mixes and
therefore a higher amount of the mixing water led to a
higher total open porosity, which negatively affected the
above mechanical property. Comparing the types of
admixture, CF exhibited the lowest maximum decrease
of 58.67 MPa for the samples with CF in the amount of
1.11 % (an 11.6 % decrease compared to the reference
AAAs), 24.77 MPa for the samples with CB in the
amount of 6.67 % (a 62.7 % decrease compared to the
reference AAAs) and 37.34 MPa for the samples with
GP in the amount of 6.67 % (a 43.7 % decrease com-
pared to the reference AAAs).
The electrical conductivity of the reference AAA
material was 1.27 × 10–6 S m–1. Such a material is prac-
tically electrically non-conductive. The electrical con-
ductivity of the samples with any type of the studied
electrically conductive admixtures increased compared
to the reference material (Figure 9). However, the in-
crease was by just about one order of magnitude (10–5)
and remained constant for all the dosages of the CF and
GP admixtures. In the case of CB, the electrical conduc-
tivity increased significantly by about three and half
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
1008 Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 7: Flexural strength of electrically enhanced AAAsFigure 5: Matrix density of electrically enhanced AAAs
Figure 8: Compressive strength of electrically enhanced AAAsFigure 6: Total open porosity of electrically enhanced AAAs
orders of magnitude with the percolation threshold close
to 4 % of CB.
4 CONCLUSIONS
Fifteen different AAAs were analyzed in the study,
namely the reference AAAs and the AAAs with CB, CF
and GP admixtures in different dosages. Basic physical
properties represented by the bulk and the matrix density
were determined by means of the water-saturation
method. The total open porosity was then calculated with
respect to the determined basic physical properties. Me-
chanical properties were measured according to the
Czech Standard ^SN EN 196-1 on different types of
samples (reference samples and the samples with a given
dosage of electrically conductive admixture). Electric
properties represented by the electrical conductivity were
determined by measuring the electrical resistance in a
4-electrode set-up and calculating the electrical conduc-
tivity with respect to the shape ratio of the samples.
The highest increase in the electrical conductivity of
about three and half orders of magnitude was observed
for the samples with the CB admixture in an amount
higher than 4 %, which is promising in terms of possible
applications in self-heating systems. The total open poro-
sity of the AAA samples with 4.44 % of CB remained at
the same level as for the reference sample. The total
open-porosity increase of about 17 % and 22.6 %, res-
pectively, was observed in the case of the AAA samples
with 6.67 % and 8.89 % of CB. The increased total open
porosity negatively influenced the flexural and
compressive strength of the AAAs with a 6.67 % dosage
of CB; a decrease in the flexural strength of about 4.8 %,
to 7.07 MPa, and a decrease in the compressive strength
of about 62.7 %, to 24.77 MPa, were observed. For the
AAAs with an 8.89 % dosage of CB, the strengths
decreased by 7.4 %, to 6.88 MPa, and 51.7 %, to 32.03
MPa. The decrease in the compressive strength of these
materials is particularly significant. However, with
respect to the enhancement of electrical properties and
the fact that CB is a waste product, such a material can
find applications in building practice. In the case of the
AAAs with CF and GP admixtures, electrical properties
were not enhanced significantly, and the electrical con-
ductivity increased by just about one order of magnitude.
However, the AAAs with a CF admixture exhibited an
increased flexural strength and only a low decrease in the
compressive strength when compared to the reference
AAAs.
Based on the results presented in this paper, the
AAAs with a CB admixture exhibited the best electrical
properties. Therefore, they are promising candidates in
the field of smart materials. These materials will be
subjected to a deeper investigation in terms of their
applicability for self-heating elements.
Acknowledgment
This research was supported by the Czech Science
Foundation, under project No. 16-00567S.
5 REFERENCES
1 J. Davidovits, Geopolymers and geopolymeric materials, Journal of
Thermal Analysis, 35 (1989) 2, 429–441, doi:10.1007/BF01904446
2 J. Davidovits, Geopolymers – inorganic polymeric new materials,
Journal of Thermal Analysis, 37 (1991) 8, 1633–1656, doi:10.1007/
BF01912193
3 P. Marc, I. Costescu, Industrial wastes used in pavement layers, Jour-
nal of Environmental Protection and Ecology, 14 (2013) 1, 187–195
4 T. Kim, S. Tae, C. U. Chae, K. Lee, Proposal for the Evaluation of
Eco-Efficient Concrete, Sustainability, 8 (2016) 8, 705–724,
doi:10.3390/su8080705
5 A. O. Purdon, The action of alkalis on blast furnace slag, Journal of
the Society of Chemical Industry, 59 (1940), 191–202
6 V. D. Glukhovsky, Soil Silicates, Gostroyizdat Ukrainy Publishing,
Kiev, USSR, 1959
7 R. Malinowski, Concretes and mortars in ancient aqueducts,
Concrete International, 1 (1979) 1, 66–76
8 P. Xie, P. Gu, J. J. Beaudoin, Electrical percolation phenomena in
cement composites containing conductive fibers, Journal of Materials
Science, 31 (1996) 15, 4093–4097, doi:10.1007/BF00352673
9 M. Chiarello, R. Zinno, Electrical conductivity of self-monitoring
CFRC, Cement & Concrete Composites, 27 (2005) 4, 463–469,
doi:10.1016/j.cemconcomp.2004.09.001
10 J. Song, D. L. Nguyen, C. Manathamsombat, D. J. Kim, Effect of
fiber volume content on electromechanical behavior of strain-harden-
ing steel-fiber-reinforced cementitious composites, Journal of
Composite Materials, 49 (2015) 29, 3621–3634, doi:10.1177/
0021998314568169
11 J. P. Won, C. Kim, S. Lee, J. Lee, R. Kim, Thermal characteristics of
a conductive cement-based composite for a snow-melting heated
pavement system, Composite Structures, 118 (2014), 106–111,
doi:10.1016/j.compstruct.2014.07.021
12 F. Azhari, N. Banthia, Cement-based sensors with carbon fibers and
carbon nanotubes for piezoresistive sensing, Cement & Concrete
Composites, 34 (2012) 7, 866–873, doi:10.1016/j.cemconcomp.
2012.04.007
13 B. Han, S. Ding, X. Yu, Intrinsic self-sensing concrete and struc-
tures: A review, Measurement, 59 (2015), 110–128, doi:10.1016/
j.measurement.2014.09.048
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009 1009
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 9: Electrical conductivity of electrically enhanced AAAs
mixtures with electrically conductive fillers, the samples
with a GP admixture exhibited a higher matrix density
(2599–2636 kg m–3) compared to the samples with CF
and CB. In the case of the samples with CB, the matrix
density ranged between 2590–2618 kg m–3. In the case of
CF, the decrease was higher than for the reference mate-
rial and the matrix density ranged between 2570–2600
kg m–3. The maximum decrease (3.9 %) was observed
for the samples with 0.56 % of CF admixture.
The total open porosity of the mixtures ranged bet-
ween 0.193–0.244 % (Figure 6). A significant increase
in the porosity was observed for the AAA mixtures with
6.67 % of CB and 8.89 % of CB.
The dependence of the flexural strength on the
amount of electrically conductive admixtures is pre-
sented in Figure 7. The flexural strength of the reference
AAAs was 7.43 MPa and it slightly increased up to 8.03
MPa for the 4.44 % CB dosage for the materials with a
CB admixture (an 8 % increase compared to the refe-
rence AAAs). For higher dosages of the CB filler, the
flexural strength decreased to 6.88 MPa (a 7.4 %
decrease compared to the reference AAAs). In the case
of the CF admixture, the flexural strength was higher
than that of the reference AAAs, which was due to the
fibrous nature of such an admixture. The increase to the
maximum of 9.9 MPa (a 33.2 % increase compared to
the reference AAAs) was observed for the mixture with
CF in the amount of 2.22 %. GP exhibited a systematic
increase in the flexural strength of up to 10.47 MPa
(40.9 % compared to the reference AAAs) for 6.67 % of
GP and then a slight decrease to 10.17 MPa (a 36.9 %
increase compared to the reference AAAs) was observed
for GP in the amount of 8.89 %.
The dependence of the compressive strength on the
amount of electrically conductive admixtures is pre-
sented in Figure 8. The highest compressive strength
equal to 66.38 MPa was observed for the reference
AAAs. With the increase in the amount of electrically
conductive admixtures, a decrease in the compressive
strength was observed. The electrically conductive
admixtures reduced the workability of the mixes and
therefore a higher amount of the mixing water led to a
higher total open porosity, which negatively affected the
above mechanical property. Comparing the types of
admixture, CF exhibited the lowest maximum decrease
of 58.67 MPa for the samples with CF in the amount of
1.11 % (an 11.6 % decrease compared to the reference
AAAs), 24.77 MPa for the samples with CB in the
amount of 6.67 % (a 62.7 % decrease compared to the
reference AAAs) and 37.34 MPa for the samples with
GP in the amount of 6.67 % (a 43.7 % decrease com-
pared to the reference AAAs).
The electrical conductivity of the reference AAA
material was 1.27 × 10–6 S m–1. Such a material is prac-
tically electrically non-conductive. The electrical con-
ductivity of the samples with any type of the studied
electrically conductive admixtures increased compared
to the reference material (Figure 9). However, the in-
crease was by just about one order of magnitude (10–5)
and remained constant for all the dosages of the CF and
GP admixtures. In the case of CB, the electrical conduc-
tivity increased significantly by about three and half
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
1008 Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 7: Flexural strength of electrically enhanced AAAsFigure 5: Matrix density of electrically enhanced AAAs
Figure 8: Compressive strength of electrically enhanced AAAsFigure 6: Total open porosity of electrically enhanced AAAs
orders of magnitude with the percolation threshold close
to 4 % of CB.
4 CONCLUSIONS
Fifteen different AAAs were analyzed in the study,
namely the reference AAAs and the AAAs with CB, CF
and GP admixtures in different dosages. Basic physical
properties represented by the bulk and the matrix density
were determined by means of the water-saturation
method. The total open porosity was then calculated with
respect to the determined basic physical properties. Me-
chanical properties were measured according to the
Czech Standard ^SN EN 196-1 on different types of
samples (reference samples and the samples with a given
dosage of electrically conductive admixture). Electric
properties represented by the electrical conductivity were
determined by measuring the electrical resistance in a
4-electrode set-up and calculating the electrical conduc-
tivity with respect to the shape ratio of the samples.
The highest increase in the electrical conductivity of
about three and half orders of magnitude was observed
for the samples with the CB admixture in an amount
higher than 4 %, which is promising in terms of possible
applications in self-heating systems. The total open poro-
sity of the AAA samples with 4.44 % of CB remained at
the same level as for the reference sample. The total
open-porosity increase of about 17 % and 22.6 %, res-
pectively, was observed in the case of the AAA samples
with 6.67 % and 8.89 % of CB. The increased total open
porosity negatively influenced the flexural and
compressive strength of the AAAs with a 6.67 % dosage
of CB; a decrease in the flexural strength of about 4.8 %,
to 7.07 MPa, and a decrease in the compressive strength
of about 62.7 %, to 24.77 MPa, were observed. For the
AAAs with an 8.89 % dosage of CB, the strengths
decreased by 7.4 %, to 6.88 MPa, and 51.7 %, to 32.03
MPa. The decrease in the compressive strength of these
materials is particularly significant. However, with
respect to the enhancement of electrical properties and
the fact that CB is a waste product, such a material can
find applications in building practice. In the case of the
AAAs with CF and GP admixtures, electrical properties
were not enhanced significantly, and the electrical con-
ductivity increased by just about one order of magnitude.
However, the AAAs with a CF admixture exhibited an
increased flexural strength and only a low decrease in the
compressive strength when compared to the reference
AAAs.
Based on the results presented in this paper, the
AAAs with a CB admixture exhibited the best electrical
properties. Therefore, they are promising candidates in
the field of smart materials. These materials will be
subjected to a deeper investigation in terms of their
applicability for self-heating elements.
Acknowledgment
This research was supported by the Czech Science
Foundation, under project No. 16-00567S.
5 REFERENCES
1 J. Davidovits, Geopolymers and geopolymeric materials, Journal of
Thermal Analysis, 35 (1989) 2, 429–441, doi:10.1007/BF01904446
2 J. Davidovits, Geopolymers – inorganic polymeric new materials,
Journal of Thermal Analysis, 37 (1991) 8, 1633–1656, doi:10.1007/
BF01912193
3 P. Marc, I. Costescu, Industrial wastes used in pavement layers, Jour-
nal of Environmental Protection and Ecology, 14 (2013) 1, 187–195
4 T. Kim, S. Tae, C. U. Chae, K. Lee, Proposal for the Evaluation of
Eco-Efficient Concrete, Sustainability, 8 (2016) 8, 705–724,
doi:10.3390/su8080705
5 A. O. Purdon, The action of alkalis on blast furnace slag, Journal of
the Society of Chemical Industry, 59 (1940), 191–202
6 V. D. Glukhovsky, Soil Silicates, Gostroyizdat Ukrainy Publishing,
Kiev, USSR, 1959
7 R. Malinowski, Concretes and mortars in ancient aqueducts,
Concrete International, 1 (1979) 1, 66–76
8 P. Xie, P. Gu, J. J. Beaudoin, Electrical percolation phenomena in
cement composites containing conductive fibers, Journal of Materials
Science, 31 (1996) 15, 4093–4097, doi:10.1007/BF00352673
9 M. Chiarello, R. Zinno, Electrical conductivity of self-monitoring
CFRC, Cement & Concrete Composites, 27 (2005) 4, 463–469,
doi:10.1016/j.cemconcomp.2004.09.001
10 J. Song, D. L. Nguyen, C. Manathamsombat, D. J. Kim, Effect of
fiber volume content on electromechanical behavior of strain-harden-
ing steel-fiber-reinforced cementitious composites, Journal of
Composite Materials, 49 (2015) 29, 3621–3634, doi:10.1177/
0021998314568169
11 J. P. Won, C. Kim, S. Lee, J. Lee, R. Kim, Thermal characteristics of
a conductive cement-based composite for a snow-melting heated
pavement system, Composite Structures, 118 (2014), 106–111,
doi:10.1016/j.compstruct.2014.07.021
12 F. Azhari, N. Banthia, Cement-based sensors with carbon fibers and
carbon nanotubes for piezoresistive sensing, Cement & Concrete
Composites, 34 (2012) 7, 866–873, doi:10.1016/j.cemconcomp.
2012.04.007
13 B. Han, S. Ding, X. Yu, Intrinsic self-sensing concrete and struc-
tures: A review, Measurement, 59 (2015), 110–128, doi:10.1016/
j.measurement.2014.09.048
L. FIALA et al.: BASIC PHYSICAL, MECHANICAL AND ELECTRICAL PROPERTIES OF ELECTRICALLY ENHANCED ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 1005–1009 1009
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 9: Electrical conductivity of electrically enhanced AAAs