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EFFICIENCY OF SUPERPLASTICIZERS IN COMPOSITION OF SELF-COMPACTING CONCRETE MIXTURES

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osInternational Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp. 2170-2177, Article ID: IJCIET_10_04_224
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=04
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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EFFICIENCY OF SUPERPLASTICIZERS IN
COMPOSITION OF SELF-COMPACTING
CONCRETE MIXTURES
Sergey D. Bartenev
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Valery V. Bausin
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Yevgenia V. Ivanova
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Vitaly Yu. Ermakov
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Leonid G. Novikov
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Ksenia Yu. Tkachenko
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Daria V. Gromova
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Vakhtang V. Nikolava
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
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Efficiency of Superplasticizers in Composition of Self-Compacting Concrete Mixtures
Georgiy S. Kazantsev
Institute of Construction and Architecture, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
Aleksandr E. Gerasimov
Department of Construction of Thermal and Atomic Power Stations, Institute of Hydraulic
Engineering and Power Plant Construction, National Research Moscow State University of
Civil Engineering, Moscow, Russian Federation
ABSTRACT
One of the main conditions for producing self-compacting concretes is the use of
superplasticizers with a relatively high content of dispersed materials in the form of
Portland cement, mineral additives, ground fillers and / or very fine sand.
Keywords: Superplasticizers, SNF, SMF, MLST, surfactant, Portland cement,
polymethylene naphthalene sulfonates, mineral additives
Cite this Article: Sergey D. Bartenev, Valery V. Bausin, Yevgenia V. Ivanova,
Vitaly Yu. Ermakov, Leonid G. Novikov, Ksenia Yu. Tkachenko, Daria V. Gromova,
Vakhtang V. Nikolava, Georgiy S. Kazantsev and Aleksandr E. Gerasimov.
International Journal of Civil Engineering and Technology, 10(04), 2019, pp. 21702177
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1. INTRODUCTION
Superplasticizers are organic polyelectrolytes (surface active substances - surfactants), which
function as a dispersed chemical medium in heterogeneous systems [1, 2], while their
effectiveness is manifested in the ability to maintain the technological properties of concrete
mixtures for at least 30 minutes - time, required for molding products [3].
Surfactants are most often used not as in individual products, but in compositions. This is
due to a number of reasons, both economic and physico-chemical nature. For example, a
mixture of high and low molecular weight surfactants. High-molecular surfactants determine
the high stability of dispersed systems due to the creation on the surface of a durable gelatinous
structured adsorption layer with a thickness of tens and hundreds of nanometers. Low
molecular weight surfactants provide a high dispersing effect and greatly reduce the surface
tension at the interface. As is well known [4-9], superplasticizers are divided into four basic
types: the condensation products of sulfonated naphthalene-formaldehyde (SNF), sulfonated
melamine-formaldehyde (SMF), the modified lignosulfonates technical (MLST) and polymers
(II) comprising polyacrylates, polystyrene sulfonates, polycarboxylate esters. The mechanism
of their action on disperse systems, in particular, cement pastes, is closely associated with the
adsorption of clinker minerals on hydration products. Adsorption in cement systems obviously
has its own characteristics - the chemical (spatial) structure of additive molecules or the
structure of the adsorption layer may be of fundamental importance [10].
2. PHYSICAL AND CHEMICAL PROPERTIES OF
SUPERPLASTICIZERS
The main factor determining the adsorption of polar compounds in aqueous solutions is the
ability of water molecules to form hydrogen bonds both with the molecules themselves and
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Sergey D. Bartenev, Valery V. Bausin, Yevgenia V. Ivanova, Vitaly Yu. Ermakov, Leonid G.
Novikov, Ksenia Yu. Tkachenko, Daria V. Gromova, Vakhtang V. Nikolava, Georgiy S.
Kazantsev and Aleksandr E. Gerasimov
with the surface of the adsorbent [11]. In turn, the adsorption mechanism of the plasticizing
action of a surfactant involves the dissociation of ionic groups and their adsorption on the active
centers of the surface of the solid phase and its hydrolysis [12].
According to A.M. Koganovsky [13, 14] on hydrophilic surfaces of oxides, hydroxides or
aluminosilicates, the adsorption of polar organic molecules is possible only as a result of a
specific (chemical or Coulomb) interaction, since the displacement of water (several
molecules) requires a significant expenditure of energy. In this regard, the majority of
superplasticizer molecules, which are anionic polyelectrolytes, are adsorbed on the positively
charged minerals of Portland cement С3А and C4AF clinker, as well as their hydration
products as a result of electrostatic interaction [15, 16]. At the same time, in the mechanism of
action of superplasticizers of types SNF, SMF, MLST, the effect of electrostatic repulsion of
cement particles and stabilization prevails, caused by the fact that the adsorption layers of
additive molecules increase the -potential on the surface of cement particles to -23 ... -28 mV
[17 -20]. On the contrary, dispersion and stabilization of cement pastes with the use of spatial
polymeric molecules of modified polyacrylates and polycarboxylates is provided mainly due
to the strong steric effect of repulsion of cement particles [21]. Due to the side hydrophobic
polyether chains of polycarboxylate molecules, the duration of their plasticizing action is 3–4
times longer compared to sulfomelamine, sulfonaphthalene formaldehydes or lignosulfonates
[22-24]. This ability allows not only to increase the mobility of the solution in the early periods,
but also, as a rule, to maintain it for a longer period of time, which has a positive effect on the
timing of transportation of concrete mixtures to the construction sites.
The water-reducing effect of modern superplasticizers based on modified polycarboxylate
esters ranges from 30 to 40% or more, while for modified lignosulfonates its value, as a rule,
does not exceed 15%, and for sulfonated melamine (formaldehyde) formaldehyde condensates
- 25% [2 , 5, 24]. At the same time, as is known, if the first-second generation superplasticizers
are effective in mobile concrete mixtures and give a weak plasticizing effect with a low content
of mixing water, then polycarboxylate superplasticizers provide a high plasticizing effect even
in concrete mixtures with a water-cement ratio less than 0.2, which is a typical composition of
high strength concrete. To achieve a similar effect in such mixtures, the dosage of SMF (SNF)
superplasticizers should be three times higher [23].
However, additives based on polycarboxylate esters have their drawbacks [25]:
- The problem of compatibility with cements of different chemical-mineralogical
composition;
- High sensitivity to low temperatures, which is especially important for the climatic
conditions of Russia [26];
- Increased air entrapment, which can reduce the strength of concrete (1% entrained air
reduces the tensile strength by about 4-5%) - with excessive air entrainment in the concrete
mix, it is advisable to use additives that suppress this process [27];
- Special storage conditions - high humidity and ambient temperature must not be allowed;
- High cost - according to [21], if the cost of type P superplasticizers (polycarboxylate,
polyacrylate polymers) in terms of dry matter is taken as 100%, then the cost of the joint venture
based on SMF condensates is 80%, SNF - 40%, MLST - 20%.
3. COMPATIBILITY IN THE "PORTLAND CEMENT
SUPERPLASTICIZER" SYSTEM
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Efficiency of Superplasticizers in Composition of Self-Compacting Concrete Mixtures
According to [4], compatibility in the "Portland cement superplasticizer" system involves the
following parameters related to cement: chemical and mineralogical composition, in particular
C3A content, alkali content and free lime, composition and type of calcium sulfate (dihydrate,
basanite, anhydride), size cement particles. By taking into account the properties of the
superplasticizer, the following factors matter: the chemical nature and average molecular
weight, degree of polymerization, the amount of additive and the method of introduction into
the concrete mix.
With regard to concrete, the compatibility of additives with cement can be viewed as the
ability of additives to provide the required technological effects and maintain them at a given
level for a certain time, taking into account the action of various factors [28]. The loss of
mobility by the concrete mix at the construction site is one of the main reasons, which leads to
non-uniformity of strength and reduced durability of concrete in structures [29]. Some
combinations of "Portland cement - superplasticizer" provide the level of the required mobility
of the concrete mix for an hour, others - after 10-15 minutes show a tendency to its sharp
decrease [1, 6]. According to [27], to assess the rheological activity of the joint venture in
combination with specific cement, can be used the value of the shear stress limit of the cement
paste.
4. INCOMPATIBILITY IN THE "PORTLAND CEMENT SUPERPLASTICIZER" SYSTEM
The incompatibility in the "Portland cement - superplasticizer" system increases with an
increase in the content of Portland cement in the clinker C3A tricalcium aluminate [30]. In
concrete mixtures with the addition of naphthalene (melamine) formaldehyde condensates with
an increase in the adsorption of superplasticizer on cement minerals and hydration products,
the initial mobility increases. However, over time, the mobility of the mixtures decreases,
which is due to the lack of a “free” superplasticizer in the volume of the pore fluid required for
the electrostatic stabilization of the disperse system [31, 32]. The same picture is observed in
the case of the use of polycarboxylate polymers - the higher the content of C3A, the greater the
critical dose of the additive to achieve the desired plasticizing effect.
However, the fluctuations in the chemical-mineralogical composition of cement, and
especially the alkali content, are less susceptible to thinners based on sulfonated naphthalene
formaldehyde condensates. At the same time, there is an inverse relationship between the
amount of adsorbed polymethylene naphthalene sulfonate and the range of mobility values of
cement pastes, which decreases with increasing adsorbed superplasticizer, and loss of mobility
increases. According to researchs of N.M. Zaichenko [33], S. Jiang, C. Jolicoeur, B. Kim, T.
Nawa, and others, the addition of sodium sulfate contributes to an increase in the mobility of
cement paste as a result of a decrease in the adsorption value of the superplasticizer. In the
presence of alkaline sulfate, adsorption on C3A and C4AF is inhibited and increased by C3S
and β-C2S, and the total amount of adsorbed plasticizer decreases, its concentration increases
in the liquid phase of the concrete mix, which causes dispersion of particles and decrease in
viscosity of cement paste [28].
This fact suggests that, under certain conditions, superplasticizers based on polymethylene
naphthalene sulfonates can be successfully used in self-compacting concrete mixtures, despite
the fact that [34] states that only PCE superplasticizers can be used for these purposes.
It should also be noted that SNF-superplasticizers to a lesser extent affect the air
entrainment in the concrete mix. So, according to [35], regardless of the type of air-entraining
surfactant additive used, the SNF-superplasticizer reduces water separation and does not have
air-entraining action, and also has almost no effect on air entrapment caused by the airhttp://www.iaeme.com/IJCIET/index.asp
2188
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Sergey D. Bartenev, Valery V. Bausin, Yevgenia V. Ivanova, Vitaly Yu. Ermakov, Leonid G.
Novikov, Ksenia Yu. Tkachenko, Daria V. Gromova, Vakhtang V. Nikolava, Georgiy S.
Kazantsev and Aleksandr E. Gerasimov
entraining surface-active additive. However, on the other hand, it has been shown [36] that the
use of SNF superplasticizers in conjunction with cellulose ethers leads to the formation of
hydrogen bonds between additives and a reduction in the water-reducing effect of the
plasticizing additive. In addition, increasing the dosage of the stabilizing additive with a
constant amount of plasticizer and the normal resistance to delamination of self-compacting
concrete mixture leads to a slight decrease in the strength characteristics of concrete.
Therefore, self-compacting concrete mixes with polymethylene naphthalene sulfonates
need to be manufactured according to the first type - powder, using a large amount of finegrained mineral materials. Yu.M. Bazhenov and P.G. Komokhov noted that the effectiveness
of the additive superplasticizer depends largely on the method of its introduction into concrete.
The best results are obtained, for example, when the mineral additive is silica fume or a mixture
of silica fume with fly ash, mixed with superplasticizer in advance. This approach became the
basis for the creation of complex modifiers on an organic-mineral basis using superplasticizers
of a new generation, active and low-active mineral additives.
M.M Alonso and other researchers. In their studies noted that polycarboxylate is well
adsorbed not only by grains of cement, but also by mineral fillers. At the same time, the amount
of additive adsorbed on the surface of fly ash and blast furnace slag is slightly less than on the
surface of limestone. Due to the presence of negatively charged functional sulfo groups,
molecules of polymethylene naphthalene sulfonates are also capable of adsorbing on the active
centers of the surface of mineral additives. With an increase in the surface charge, the
adsorption of additives increases [37].
The research of Yu.V. Degtev [38] showed that the amount and type of mineral additives,
as well as the dispersion of all components of the composite binder, form its capacity by
adsorption of a superplasticizer. By trying to increase this capacity, i.e. maximum value of the
effective dosage, due to the mineral additives in the composition of the composite binder, it is
possible to increase their suitability for use in the compositions of self-compacting concrete
mixtures.
The adsorption activity of mineral additives (fillers) is also associated with their hydraulic
activity. According to [39], the presence of low hydraulic activity of mineral additives in
concrete enhances the plasticizing effect of the C-3 superplasticizer, and a smaller amount of
additive is required to produce cast concrete mixes, on the contrary, the plasticizing effect of
C-3 in concrete mixtures with highly active mineral additives is lower, and the effective dosage
C -3 increases dramatically. Thus, concrete mixtures containing microsilica as an additive, even
at a dosage of up to 10%, require an increased consumption of superplasticizers [40].
5. CONCLUSION
The introduction of mineral additives - thermo-activated kaolin, microsilica or ground
limestone together with a superplasticizer provides less loss of mobility of the concrete mix
during the first two hours after preparation, than without a mineral additive.
Modifying mineral additives allows changing the nature of their surface (hydrophilicity,
electric charge, electrical double layer structure, concentration of surface active centers) to
widely activate the process of structure formation of cement dispersions and the formation of
the microstructure of the binder stone.
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Efficiency of Superplasticizers in Composition of Self-Compacting Concrete Mixtures
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