Lukuttsova N.P, Pykin
A.A., Pustovgar A.P.
Bryansk State Academy of
Engineering and Technology, Bryansk, Russia
Physical and mechanical properties of
fine-grained concrete with admixture nanodispersed schungite
Physical and mechanical properties of fine-grained
concrete modified by nanodispersed admixture such as water suspension of
schungite (Karelia, Russia) are investigated. Schungite is a natural petrified
organic silica gel with 51-67% silica dioxide and carbon 28-32%. Admixture was
obtained by ultrasonic dispersion reduced to powder
schungite in water in the presence of the stabilizer.
Nowdays in Russia and abroad the urgent task of
nanotechnology in concstruction industry is to discover cheap and efficient
methods of obtaining nanomodifying admixtures which make it possible, at
nano-and microlevels, to control the
processes of structure formation of composite materials and concrete among
them.
Promising scientific and technical area is the
accumulation of knowledge and experience in cavitation technology. Examples of
practical application of these technologies is obtaining nanoparticles in
exploding cavitation bubbles, hyperfine dispersion of organic and inorganic
materials in liquid media, ultra-fine aerosols for the needs of nanoelectronics
and chemical industry, coating, obtaining nanosuspensions and nanoemulsions,
compacting nanopowders, cleaning and so on.
The
aim of this work is to investigate the dependence of the particle diameter of
schungite water suspensions on the time of ultrasound and the presence of the
stabilizer and as well as to study the effect of the suspension on physical and
mechanical properties of fine-grained concrete (FGC).
A characteristic feature of schungite is the
structure of its carbon, which is the globule size from 6 to 10 nm. Scientists
have determined the morphological similarity of schungite carbon globules and
fullerenes: presence of an inner cavity and a two-dimensional hexagonal cell of
carbon atoms. The carbon part of sñhungite
is described by formula: C690-2300H100N5-14O5-16S1-12.
The
specificity of schungite structure is also in the fact that silicon dioxide and
carbon form a strong interpenetrating nets. Therefore, each particle of
schungite powder contains a nonpolar carbon and polar mineral components.
Schungite
make it possible to produce electroconducting construction materials on its
basis (mechanical strength, abrasion resistance, freeze-thaw resistance, electrical
conduction, corrosion stability).
Besides,
the unique features of schungite are used to create on its basis structural
radio waves shielding materials [1].
In
order to obtain schungite powder with a
specific surface of particles 320-350 m2/kg grinding of schungite
gravel fraction 3-10 mm was being conducted for 1 h in a vibratory mill. The
particle size of schungite powder was being determined by method of laser
granulometry with «MicroSizer 201».
Then, the schungite powder was added to water in the amount of 1% and
treated by ultrasonic at frequency of 22 kHz from 15 till 30 minutes. The same
was done with schungite powder which particles surface was treated with
molecules of stabilizer of naphthalene-formaldehyde type (NF) at combined dry
grinding of schungite and NF composition 1:0.5.
The size of the particlesobtained after USD suspension was determined
with the help of a multilevel system 90Plus/Bi-MAS. This system designed to
determine the particle size of concentrated suspensions of macromolecules.
To study the effect of nanodispersed schungite on mass specific gravity,
water absorption, ultimate compressive strength and initial modulus of
deformations of fine-grained concrete test beams of 4×4×16 cm size
were produced. They were made of portland cement M 500 R0 and quartz sand with
fineness modulus 1.5 composition of 1:3. Supplements were admixtures in the
amount of 1% from cement mass with water. These test beams were hardened under
normal conditions.
To determine the initial modulus of deformation of test fine-grained
concrete were modified by microdispersed schungite at 5% from cement mass and
subjected to static and dynamic loads.
Figure 1 shows that the optimum time of ultrasonic dispersion of
schungite powder in water without stabilizers is 15 minutes. It helps to obtain
a suspension with particle from 201 to 5112 nm.
Figure 1. Histogram of schungite particles distribution according to their sizes
after
the
USD in water during 15 minutes
An increase in the USD up to 30 minutes leads to
particle aggregation and formation of more coarse suspensions with particle size ranges from 220.82 to 8767.95 nm (Figure 2).
Figure 2. Histogram of schungite particles distribution according to their sizes
after
the USD in water during 30
minutes
Aqueous suspensions of schungite are
kinetic polydisperse and unstable regardless of the time of ultrasonic
treatment. Sedimentation of aggregated particles is observed after 1-2 hours [2].
The smallest diameter of schungite particles
in water suspension, the absence of their aggregation and sedimentation are
observed in the dry depositing of molecules of the stabilizer of naphthalene-formaldehyde
type on the surface of schungite particles under the combined grinding components
according to USD. Ultrasonic dispersion of such particles during 15 minutes
helps to obtain a suspension with a particle diameter from 62 to 716 nm (Figure
3).
Figure 3. Histogram of schungite particles distribution according to their sizes
after
the USD in water
during 15 minutes in the presence of NF stabilizer
FGC
maximum strength is observed with the introduction of the suspension of
nanodispersed schungite suspension, which is stabilized by dry deposition NF
stabilizer on the surface of schungite particles before ultrasonic dispersion
(Table 1).
According to the table 1 maximum strength of modified concrete exceeds
the strength of the control composition in 2.8 times after 3 days and 2.1 times
after 28 days of hardening.
The results showed an increase in mass
specific gravity from 1760 to 2242 kg/m3 and a decrease
of water absorption from 2.4 to 0.9% in the strength of fine-grained concrete
with nanodispersed schungite admixture.
When introducing in FGC microdispersed schungite in the amount of 5% an
increase in initial dynamic modulus of the strain up to 45% takes place [3]. It
is especially important in the construction of buildings and structures in the
areas of high seismic activity.
Table 1. Physical and mechanical properties of fine-grained concrete modified by
suspensions
nanodispersed schungite
|
¹ |
Composition of the
FGC, the dispersion of admixture, the presence of the stabilizer |
C/W |
Mass specific grayity,
kg/m3 |
Absorption of water,
% |
Ultimate compression
strength MPa, after days of hardening |
||
|
3 |
7 |
28 |
|||||
|
1 |
FGC control |
0.43 |
1960 |
2.4 |
9.2 |
16.4 |
23.8 |
|
2 |
FGC with 1% schungite 201-5112 nm without stabilizer |
0.43 |
2085 |
1.9 |
12.1 |
19.9 |
34.0 |
|
3 |
FGC with 1% schungite 62-716 nm with stabilizer NF |
0.43 |
2242 |
0.9 |
25.7 |
33.0 |
50.0 |
A
positive impact of nanodispersed schungite on the strength and deformation
properties of fine-grained concrete was determined. This method is
characterized by high productivity and easy hardware.
The
composition of the modified fine-grained concrete with nanodispersed schungite
stabilizer in the presence of NF is recommended for covering the extra strong
floors, construction elements of the urban slum (curbing, paving flag, etc.),
as well as structures and constructions, resistant to bending loads.
References:
1. Sokolov V.A., Kalinin Y.K.,
Dyukkiev E.F., Schungite – the new carbon materials, Petrozavodsk, 1984 (in
Russian).
2. Lukuttsova N.P., Pykin A.A., Chudakova O.A. Modification of fine-grained
concrete with micro-and nanosize particles of titanium dioxide and schungite, Journal BSTU V. Shuhov, pp. 73-76,
Belgorod, 2010 (in Russian).
3. Shablinsky G.E., Lukuttsova N.P., Pykin A.A., Tsvetkov K.A. Investigation
of dynamic strength and rigidity of products from fine-grained concrete
modified by nanostuctured schungite aggregate, Journal MSSU, pp. 231-236, Moscow, 2010 (in Russian).