M. MA£EK et al.: CHARACTERIZATION OF NEW FILLER ADDITIONS AFFECTING ...
399–403
CHARACTERIZATION OF NEW FILLER ADDITIONS AFFECTING
THE MECHANICAL STRENGTH OF CONCRETE
KARAKTERIZACIJA DODAJANJA NOVIH POLNIL, KI VPLIVAJO
NA MEHANSKO TRDNOST BETONA
Marcin Ma³ek
1*
, Mateusz Jackowski
1
, Wojciech ¯yciñski
1
, Marcin Wachowski
2
1
Military University of Technology, Faculty of Civil Engineering and Geodesy, 2 Generala Sylwestra Kaliskiego Street, 00-908 Warsaw,
Poland
2
Military University of Technology, Faculty of Mechanical Engineering, 2 Generala Sylwestra Kaliskiego Street, 00-908 Warsaw, Poland
Prejem rokopisa – received: 2018-07-15; sprejem za objavo – accepted for publication: 2018-12-20
doi: 10.17222/mit.2018.155
In this work, the results of a chemical modification of concrete based on Portland cement by zeolite, metakaolinite and micro-
metakaolinite in amounts of (5, 10 and 15) w/%, and mass fractions of the concrete amount included in the mixture as a filler
were summarized. The influence of the w/%, or mass fractions, of new commercial fillers on the concrete’s mechanical strength
was measured. The reference recipe of concrete contained three parts of aggregates: 0.125–0.250 mm, 0.250–0.500 mm and
0.500–1.000 mm. For the concrete production, white cement (42.5 MPa), water and a deflocculant based on polycarboxylate
were used. To characterize the basic properties of the studied concrete, SEM observations, chemical compositions, slump-cone
test results and time setting were widely investigated. Samples of the concrete were characterized with the compressive-strength
and bending tests after (1, 7, 14 and 28) d of the curing process. The obtained results were compared with the reference samples
of the concrete without chemical additions. This study proved that all the chosen modifiers had an increased effect on the final
mechanical strength of the researched concrete samples and that they are very promising for applications in civil engineering
and new building technologies in the future.
Keywords: concrete strength, zeolite, metakaolinite, micrometakaolinite, admixtures
Avtorji opisujejo rezultate kemi~nih modifikacij betona na osnovi portland cementa z dodatkom (5, 10 in 15) masnih dele`ev
zeolita, metakaolinita oz. mikrometakaolinita. Raziskovali so vpliv teh dodatkov na mehansko trdnost novih betonov.
Referen~ni recept betona brez dodatkov je vseboval tri velikostne dele`e agregatov: 0,125–0,250 mm, 0,250–0,500 mm in
0,500–1,000 mm. Za izdelavo betona so uporabili cement (42,5 MPa), vodo in deflokulant na osnovi polikarboksilata. Osnovne
lastnosti izdelanega betona so analizirali s pomo~jo SEM. Dolo~ili so tudi kemijske sestave betonov in izvedli testa posedanja s
sto`cem in utrjevanja betona. Vzorcem betona so dolo~ili {e tla~no in upogibno trdnost po razli~no dolgem ~asu staranja, to je
po (1, 7, 14 in 28) dneh. Rezultate so primerjali z referen~nim betonom, ki ni imel dodanih polnil. S {tudijo so dokazali, da so
vsa polnila izpolnila pri~akovanja glede izbolj{anja kon~ne mehanske trdnosti ter opozorili na perspektivnost njihove uporabe v
gradbeni{tvu in v prihodnosti novih gradbenih tehnologij.
Klju~ne besede: trdnost betona, zeolit, metakaolinit, mikrometakaolinit, dome{avanje
1 INTRODUCTION
According to the definition, admixtures are natural or
manufactured substances, which can be added to con-
crete to maintain or modify its properties. Admixtures
are added to concrete immediately before or during the
mixing process.
The reason for using admixtures is to obtain special
properties of fresh or hardened concrete. Admixtures
may enhance the durability, workability or strength of a
given concrete mix. They are used to overcome difficult
construction situations, such as hot or cold weather
placements, early-strength requirements or very low
water-cement ratio specifications.
1–3
In conclusion, the major reasons for using admixtures
are:
• to reduce the costs of concrete constructions;
• to maintain certain properties of concrete more
effectively than by other means;
• to maintain the quality of concrete during the stages
of mixing, transporting, placing and curing in adverse
weather conditions;
• to overcome certain emergencies during concreting
operations.
Another important issue is the fact that admixtures
are usually provided in the liquid form. Some admix-
tures, such as pigments, pumping aids and expansive
agents, are typically added manually from pre-measured
containers as the amounts used are very small.
3–5
Chemical admixtures are classified according to the
basic effects obtained with their use – listed in the
European standards:
6
• reduction in the amount of mixing water,
• significant reduction in the amount of mixing water,
• increase in the water binding,
• aeration,
• acceleration of the binding,
Materiali in tehnologije / Materials and technology 53 (2019) 3, 399–403 399
UDK 620.1:67.017:666.97 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(3)399(2019)
*Corresponding author e-mail:
marcin.malek@wat.edu.pl

• acceleration of the hardening,
• delay in the binding,
• increase in the water resistance (sealing),
• multifunctional (comprehensive) effect.
Nowadays, chemical components are very important
elements of concrete mixtures. In contrast to the old
components, modern admixtures are designed and
manufactured to be used in cement slurries, mortars or
concretes to obtain a specific effect of the final product.
The main purposes of using chemical admixtures are to
change the properties of a fresh mix and to modify the
parameters of a hardened cement paste, mortar or
concrete. The correlations given in the literature usually
differ from one another and are valid only for limited
ranges of operating parameters, e.g., an admixture
addition allows us to produce a concrete mix with a rela-
tively small amount of water, but a sufficient degree of
liquidity allows us to mix it correctly into the concrete.
7–9
A relatively small amount of water used to produce a
mixture based on a given mass of cement may contribute
to the improvement of several parameters of hardened
concrete, including:
4
• strength,
• waterproofness,
• resistance to environmental impacts,
• resistance to corrosion, including corrosion of the
concrete reinforcement,
• absorbability.
On the other hand, when using chemical admixtures,
sometimes more than one property of a fresh or hardened
mixture are modified. An example is the use of aeration
admixtures, which, on the one hand, contribute to the im-
provement of the hardness of concrete and, on the other
hand, reduce the density and strength of the material.
Chemical admixtures are mostly added during the
production of a concrete mix (during the mixing pro-
cess). According to the PN-EN 934-2 standard, admix-
tures should be used in an amount not greater than 5 %
of the cement mass in concrete. However, new research
about the chemical modification of concrete shows that
an admixture addition of more than 5 % increases some
of the properties. At the same time, a reduced amount of
cement is needed for the production of concrete.
10–13
There are no universal methodologies describing how
to select chemical admixtures to obtain optimal final pro-
perties. The dosing of many products can be direct – into
the mixer, after the cement, water, possible additives and
aggregate have been introduced. Some products need to
be mixed with water (technological), then this water is
added to the other ingredients during the mixing process.
In any case, a proper distribution and dispersion of the
chemical admixture in the volume of a mixed material is
important to obtain the required and reproducible para-
meters.
In this paper, the effects of an admixture addition
(zeolite, metakaolinite and micrometakaolinite) in
amounts of (5, 10 and 15) w/% and mass fractions were
characterized. The obtained results are very promising
for future applications in new civil-engineering technolo-
gies.
2 MATERIALS AND METHODS
This study presents the effects of three commercial
admixture additions – zeolite, metakaolinite (MK) and
micrometakaolinite (MMK) – on the final properties of
concrete samples.
Parameters such as the morphology and chemical
composition were analysed with a SEM JEOLJSM-6610
at a voltage equal to 5 kV. Additionally, the particle size
of the used admixtures was determined with the
laser-diffraction method.
Concrete mixtures were fabricated using aggregates
of Portland cement (42.5 MPa), water and quartz sand
(0.125–0.250 mm; 0.250–0.500 mm and 0.500–1.000 mm),
a deflocculant based on polycarboxylate and an admix-
ture addition in amounts of (5, 10 and 15) w/%. A refe-
rence sample was prepared without the admixture
addition. The time of mixing was 5 min in laboratory
conditions (52 % humidity and 22 °C). After the mixing
process, the concrete mixture was transformed into steel
and compacted with the vibration method in 45 sec.
Time setting and slump-cone test results for the concrete
mixtures were analysed according to the PN-EN
12350-2:2011 standard.
The compressive strength of concrete depends on
many factors such as water-cement ratio, cement
strength, quality of the concrete material, quality control
during the production of concrete etc. The compressive
strength is the ability of a material or structure to carry
loads on its surface without getting any cracks or def-
lection.
The conditions and method of performing a com-
pressive-strength test of concrete are described in the
PN-EN 12390-3:2011 standard. The samples for the
testing were cube-shaped. The dimensions of the
samples were as follows: 150 mm × 150 mm × 150 mm.
Concrete was poured into moulds and tempered properly
to eliminate any voids. After 24 h, the moulds were re-
moved and test specimens were put into water for curing.
To measure the compressive strength, 10 specimens were
tested after (1, 7, 14 and 28) d of the curing process.
The compressive-strength test of concrete was carried
out using a Form + Test Prûfsysteme testing machine in
laboratory conditions of 21 °C and 52 % humidity. The
samples were loaded with a displacement of 0.5 kN/min.
The bending-strength test was carried out using the
same testing machine and conditions, in accordance with
the PN-EN 12390-5:2011 standard. The bending force
was analysed after (1, 7, 14 and 28) d of the curing pro-
cess. For this research, 10 steel samples were prepared
(40 mm × 40 mm × 160 mm). The section below dis-
cusses bending force vs time observed during the curing
M. MA£EK et al.: CHARACTERIZATION OF NEW FILLER ADDITIONS AFFECTING ...
400 Materiali in tehnologije / Materials and technology 53 (2019) 3, 399–403

process. The bending force was calculated with Equation
(1):
F = f
c
·A
c
(1)
where
F – the final bending force [kN]
f
c
– the bending strength [MPa]
A
c
– the cross-sectional area of a sample [mm
2
]
3 RESULTS
The morphology and chemical composition of the
investigated admixtures (cement, zeolite, microkaolinite
– MK and micrometakaolinite – MMK) are presented in
Figures 1 and 2.
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Materiali in tehnologije / Materials and technology 53 (2019) 3, 399–403 401
Figure 1: Morphology of the investigated admixtures – (a – cement, b – zeolite,c–MK,d–MMK)
Figure 4: Sieve curve of the used aggregates
Figure 2: Chemical composition of the investigated admixtures – (a –
cement, b – zeolite, c – MK, d – MMK)
Figure 3: Average particle sizes of the investigated admixtures

The average particle sizes of the researched admix-
tures are shown in Figure 3. The sieve curve of the used
aggregates is shown in Figure 4. Additionally, the time
is presented in Figure 5.
The basic characterizations of this study are shown in
Figures 1–4. The morphologies of the tested admixtures
are very significant. Sharp-edge particles and agglome-
rates were observed on SEM images. The chemical
compositions of all the chosen admixtures are based on
oxides of silicone and aluminium. The rest of the com-
pound was formed during the production process. Only
the zeolite admixture comes from a natural environment,
additionally including Ca, Mg and K.
The average particle sizes of the investigated admix-
tures are different. For zeolite and MK, they are similar –
45 μm. MMK exhibits the smallest particle size–5μm.
The sieve curve was prepared for the quartz sand of
Polish origin. The most common particle size was ob-
served to be in a range of 1–8 mm. Its highest amount,
47 w/%, was found for 5.6-mm grains.
To characterize the basic parameters of the concrete
mixture, a slump-cone test was done and time setting
was widely examined. The concrete mixture exhibits the
S1 class of consistency. No significant changes were ob-
served in the time setting of the concrete samples. All the
tested admixtures needed almost 240 min to be fully
cured.
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402 Materiali in tehnologije / Materials and technology 53 (2019) 3, 399–403
Figure 5: Time distribution for the investigated admixture additions
Figure 7: Compressive-strength distribution for the investigated
samples Figure 6: Bending-strength distribution for the investigated samples

The mechanical-strength characterization including
the bending force and compressive strength is presented
in Figures 6–7.
The obtained results show that the chemical modifi-
cation of the concrete significantly changes the final
mechanical properties of the concrete samples. All the
added admixtures exhibit an increased effect on the
mechanical strength of the samples. As it can be seen,
the relative values of the bending force are small in
relation to the compressive strength. The highest effect
on the mechanical compressive strength was measured
for the 10 w/% MMK, amounting to almost 100 MPa.
The lowest effect was observed for the sample with the
5 w/% MK addition.
4 DISCUSSION
This paper summarizes the results of the chemical
modification of the concrete samples including zeolite,
metakaolinite and micrometakaolinite. The application
of this type of compounds allowed us to obtain the
highest values of mechanical strength already after1dof
the curing process. The presented results (Figures 6-7)
show that the admixture addition significant increases
the final mechanical properties of the tested samples. For
the MK and MMK materials, the highest level of in-
crease was noted. During the bending test, values three
times higher than that of the reference sample were
observed. Cement can also be replacement with a new
commercial filler. In accordance with the PN-EN 934-2
standard, more than 5 w/% of admixtures were added
into the matrix of the concrete samples and no damage of
the concrete structure was observed. It was proven that
the fabrication of a new concrete composite with the
highest amounts of admixtures is possible and does not
require a special method of production. New synthesized
commercial admixtures available on the international
markets meet the requirements of new building techno-
logies in civil engineering.
5 CONCLUSIONS
In line with our assumptions, the final effect of the
addition of new commercial admixtures to the matrix of
concrete on the composite properties was proven and
characterized in this paper. An addition of admixtures
significantly improved the mechanical strength of the
concrete composite. No problems were noted in the
process of mixing and the composite could be prepared
under ordinary environment conditions. This study pro-
ved that it is possible to produce a new concrete com-
posite using new commercial admixtures and obtain
higher values of its final mechanical properties. Addi-
tionally, the cement replacement is more environ-
mentally friendly, emitting less CO
2
gas (produced in the
process of cement fabrication) into the atmosphere.
Acknowledgment
The paper was prepared within the Statutory
Research Work no. 934 at the Faculty of Civil
Engineering and Geodesy of the Military University of
Technology.
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