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Development of refractory concrete for extreme conditions
Article in IOP Conference Series Materials Science and Engineering · December 2011
DOI: 10.1088/1757-899X/25/1/012001
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Development of refractory concrete for extreme conditions
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2011 IOP Conf. Ser.: Mater. Sci. Eng. 25 012001
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
Development of refractory concrete for extreme conditions
I Pundiene1), VAntonovich2), R Stonys3), I Demidova-Buiziniene4)
Vilnius Gediminas Technical University, Sauletekio av. 11, LT-10223 Vilnius
Email: rastine@vgtu.lt
Abstract. Comparative analysis is provided for the properties of medium-cement refractory
concrete with microsilica based on mullite filler in relation to different type of deflocculant.
The effect of different deflocculants on refractory concrete structure formation, hydration,
rheology, strength and heat resistance is discussed. Corrosion resistance test determined that
samples with hybrid deflocculant showed better resistance for slag penetration than samples
with only the sodium tripolyphosphate or polycarboxylate ether deflocculant. Moreover, a
composition of hybrid deflocculant let to control the rate of the hydration process and to get
features of refractory refractory concrete.
1. Introduction
Recently in Lithuania is being planned to build numerous energetic facilities (special furnaces,
incinerators), which run on local fuel (wood sawdust, polish dust, tires, plastics, municipal waste and
medicine waste, glycerol, peat, straw etc.) and combustive aggregates for combustion of different runoff (domestic, hazardous waste). Lining service conditions of such sets are extremely hard, because
the temperature can vary 1000-1500°C, the lining is exposed to slag and waste gases, mechanical
affecting and thermal shock, that is the reason why the lining working lifespan is very short [1].
Frequent stopping of thermal sets for their maintenance (lining repair and cleaning) are very costly, so,
it is necessary to work out and create new technological refractory concrete with increased life
durability in extreme conditions.
For creation of technological refractory concrete with controllable rheological and physical
characteristics using of deflocculants is needed [2-4]. At present a wide range of such additives is
available for investigators and manufacturers, however those additives differ significantly by their pH
and electric conductivity in water solution. Thus, for sodium tripolyphosphate – pH 8,5-9,3, electric
conductivity µ= 0,9-1,3 µS/сm; for DARVAN D811 – pH 7,9–8,1, µ= 0,39–0,45 µS/сm; for
polycarboxilate ether Castament FS-20 - pH 4,3–4,6, µ= 0,25–0,3 µS/сm. It is clear, that those
deflocculant characteristics influence pH and electric conductivity of entire concrete system and affect
the process of cement hydration [5-7, 9, 12]. In this connection the use of composite (mixed)
deflocculants in refractory concrete appears quite interesting, it widens the abilities of material
structure and hydration regulation, by that allowing to improve physical and mechanical and other
properties of concrete. However for this purpose investigations of each deflocculant influence on
castable rheological characteristics, aluminate cement hydration process and concrete service qualities
are needed. S. Otroy’s [8, 10, 11 ] investigations have proved that the use of hybrid deflocculant
(sodium tripolyphosphate and polycarboxylate ester) can significantly elevate the endurance of selfspreading refractory concrete with spinel fillers – from 30 to 40 МPа after drying and from 90 to 170
МPа after firing at a temperature of 1500 ºС.
Published under licence by IOP Publishing Ltd
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
The objective of this work is investigation of individual deflocculants (polycarboxylate ester
Castament FS-20, sodium tripolyphosphate) and their combinations influence on rheological
properties of cement paste, refractory concrete hydration and initial structure formation processes and
creation of slag resistance sustainable medium cement refractory concrete (MCC-type refractory
concrete ) with hybrid deflocculant.
2. Experimental
For research was used the following materials: microsilica RW-Fuller made by “RW Silicium GmbH”,
Germany (SiO2 content of 96 ± 1.5 %). Average particle size is about 150 nm (see Figure 1).
Figure 1. The image of RW-Fuller SiO2 microsilica
Aluminate cement "Gorkal-40" manufactured in Poland (Al2O3 is not less than 40%); mullite
aggregate was made by crushing of mulite bricks (Al2O3 ≤65%) and sieving on sieves; dispersive
mullite was made by grinding of mullite of same type in the laboratory mill; deflocculant - Castament
FS 20 (FS-20), depends to polycarboxilate ether group manufactured by BASF (Germany) and sodium
tripolyphosphate Na5P3O10 (technical) (NT).
In order to reveal the influence of deflocculants FS-20 and NT content (varying from 0 to 0,5% of
cement amount) on rheological properties of cement paste (V/C=0,25), cement paste samples with
deflocculant were prepared. The investigation of hybrid deflocculant was conducted by the following
scheme: while the concentration of one deflocculant was constant (e.g. NT=0,1%), the concentration
of other changed from 0,1 to 0,5%. For concrete mix dynamic viscosity assessment SV-10 Vibroviscometer (Japan) was used.
3. Results and discussion
In order to reveal the influence of deflocculants on physicomechanical properties of a concrete
sample three compositions of medium-cement refractory concrete based on mullite filler with
additions of NT (composition Nr 1), FS-20 (composition Nr 2) and composite deflocculants
(composition Nr 3) were prepared (Table 1). In hybrid deflocculant Castament FS-20: NT proportion
was 1:2. The doses of water and deflocculants are added to 100 percent of dry material.
Similar concrete sample, but with different deflocculants concentration and proportion in it was
used to determine the exothermic effect temperature in hardening concrete, using the procedure,
created by the firm “Alcoa”.
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
Table 1. The percentage [%] of additives in composition of refractory concrete
Composition number
1
2
3
Aluminate cement
10
10
10
Microsilica
5
5
5
Milled mullite
20
20
20
Mullite (0-10 mm)
65
65
65
Sodium tripolyphosphate (NT)
0,1
--
0,2
Polycarboxilate ether FS-20
--
0,1
0,1
Water
7
7
7
Concrete specimens preparation, sample treatment, concrete consistention and principal physico
mechanical properties corresponded to the specifications of LST EN 1402. Drying and firing of
specimens was carried out in accordance with the instructions SN165–79. Changes in the structure of
hardening concrete were observed by measuring the ultrasound propagation velocity by means of
special equipment (Schleibinger Geräte GbH [13]) making it possible to record the change in
ultrasound velocity in a concrete mix immediately after mixing with water.
In order to reveal optimal composition of concrete for lining service of combustive aggregates for
medical waste and slug, formed during medical waste combustion, influence, investigations of slag
resistance of concrete with deflocculant FS-20, with hybrid deflocculant and traditional concrete
without deflocculant were carried out. The methods were following: in concrete samples, which were
fired at a temperature of 1100 °С (7х7х7cm), 2 cm diameter and 4 cm depth holes were drilled. Those
holes were filled consequently for three times (after they were filled totally): firstly 6 g (after that the
samples were held for 10 h at a temperature of 1200°С), then another 5 g, holding the samples for 5h
at 1200°С, and 3 g, firing the samples for 20h at 1200°С.
Performed investiogations of deflocculant type and quantity impact on cement paste dynamic
viscosity measures revealed, that (see Figure 2 and 3), minimal concentration of NT deflocculant
diminished cement paste viscosity significantly, compared to cement paste viscosity without NT
deflocculant, and further increase of it did not change viscosity significantly. However, 25-30 min
later, independently of deflocculant concentration, cement paste has viscosity of 5000-6000 MPа·s,
that shows, that paste is not suitable for laying. In case of deflocculant FS-20 initial measures of
cement paste viscosity are 1,5-2 fold lower than with NT and increase of FS-20 concentration
contributed to cement paste viscosity diminishing. Only in cement paste with 0,1% of FS-20 25-30
min later viscosity came up to 4500 MPа·s, varying from 500-2000 MPа·s in other samples.
Investigation of cement paste viscosity with hybrid deflocculant (FS-20 amount was constant (0,1%)),
showed, that increase of NT concentration contributed to increase of cement paste viscosity (see
Figure 4 and 5), which became obvious after 10-15 min, but all-in-all the viscosity was much lower,
than in cement paste with only NT supplement. In case of constant NT concentration (0,1%), similar
tendencies were observed (increase of FS-20 amount facilitated cement paste viscosity increase), but
viscosity measures were much lower, compared to viscosity measures of cement paste with only FS20 supplement and also to previous hybrid deflocculant (FS-20 concentration was constant (0,1%)). It
also can be concluded, that optimal concentrations of deflocculants in cement paste were following: in
case of NT – 0,1-0,2%, concentration of FS-20 may vary from 0,1 to 0,4%.
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
Figure 2. Changing the dynamic viscosity of cement paste for 30 minutes (with deflocculant NT).
Figure 3. Changing the dynamic viscosity of cement paste for 30 minutes (with deflocculant FS-20)
Figure 4. Changing the dynamic viscosity of cement
paste for 30 minutes (deflocculant FS-20 – const., NT
- concentration changes)
Figure 5. Changing the dynamic viscosity of cement
paste for 30 minutes (deflocculant NT – const., FS-20 concentration changes)
The impact of individual deflocculants (0-0,3%) and their compositions ((FS-20 was constant
(0,1%), while NT varied (0-0,3%) and NТ was constant (0,1%), while FS-20 varied (0-0,3%)) – on
concrete mix hydration process (composition shown in Table 1) was evaluated determining the time
and temperature for maximum exothermic reaction (EXO). It was revealed (see Figure 6), that
increase of NT to 0,1%, delayed concrete mix hydration process for 2h compared to deflocculant-free
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
concrete mix, further increase of NT amount only slightly diminished maximum EXO time compared
to deflocculant-free concrete mix.
However, increase of NT amount significantly diminished maximum EXO temperature (from 41°С
(without deflocculant) to 33°С (0,3% deflocculant). Increase of FS-20 concentration significantly
increased maximum EXO time (from 4h (without deflocculant) to 44h (0,3% deflocculant) ), and
maximum EXO temperature diminished to 28°С (0,3% deflocculant). Using hybrid deflocculant (see
Figure 7) with constant concentration of FS-20 ((FS-20 constant (0,1%), while NT varies (0-0,3%) it
is obvious, that increase of NT concentration facilitated diminishing of maximum EXO time (from 15
to 6h) and increase of maximum EXO temperature (from 31 to 35°С). Using hybrid deflocculant with
constant NT concentration (FS-20 varies (0-0,3%), maximum EXO time (as in case of individual
deflocculant FS-20) increased significantly (from 15 to 110h), while maximum EXO temperature
diminished significantly (from 31 to 23°С). It can be concluded, that using hybrid deflocculant
hydration characteristics of concrete mix can be regulated in required direction.
Figure 6. The influence of deflocculant to time (columns) and temperature (lines) of EXO maximum reaction.
Figure 7. The influence of hybrid deflocculant to time (columns) and temperature (lines) of EXO maximum
reaction.
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
Changes in structure formation in early hydration period were fixed measuring ultrasound
propagation velocity in freshly prepared concrete samples. As may be seen in Figure 8, formation of a
concrete structure with addition of NT (composition Nr. 1) occurs in two stages. During the first stage
ultrasound propagation velocity reaches about 2500 m/s, during the second stage – 5000 m/s. Initial
structure formation with addition of FS-20 deflocculant (соmposition Nr. 2), occurs in three stages.
During the first stage ultrasound propagation velocity reaches about 1000 m/s, during the second stage
– 2500 m/s, during the third stage – 5000 m/s. In case of hybrid deflocculant (composition Nr. 3) three
stages of structure formation remain, but during the second stage ultrasound propagation velocity in
the sample increases to about 3500 m/s.
Figure 8. Change in
ultrasound propagation
velocity in the initial
period of hardening
concrete for
composition Nr. 1-3.
Comparing the effect of a different type of deflocculant on the change in concrete structure during
the initial period of its formation, it may be noted that the main difference is the rate of structure
formation and the level of structure development in the second stage. With NT deflocculant the
structure forms more rapidly (stage 2) than with FS-20 (stage 3), and the ultrasound velocity in the
second stage of concrete structure development with a composite deflocculant is considerably higher
than for concrete of compositions 1 and 2.
Comparing data for studies of ultrasound and measuring the temperature of the exothermic reaction
in concrete mixes it is not possible to note that development of the initial structure coincides in time
with exothermic reactions. However, no temperature changes are observed during the first stage
recorded by studies of ultrasound in specimens with deflocculant FS-20.
Comparison of values of ultimate strength in compression σco for medium-cement refractory
concrete with deflocculants NT, FS-20 and a composite after three days of hardening showed (see
Figure 9) that specimens with deflocculants NT and FS-20 (compositions Nr. 1 and 2) differ markedly
with respect to values of σco (45 – 53 MPa), whereas for specimens with a composite deflocculant
(composition Nr. 3) σco reaches 65 MPa. After drying at 100°C and firing at 800 – 1100°C values of
σco with the composite deflocculant are almost twice as high as for concrete with deflocculants NT and
FS-20.
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
Figure 9. Values of ultimate
strength in compression σco
(columns) and ultrasound
velocity (lines) in concrete
specimens in relation to
treatment temperature.
Values of ultrasound velocity in specimens of concrete after three days of hardening confirm the
strength properties: ultrasound velocity in all concretes is approximately the same (see Figure 9). After
drying the main difference is observed in the structure of concretes, i.e. in specimens with
deflocculants NT and FS-20 the ultrasound velocity is reduced, but in a specimen with a composite
deflocculant it increases markedly, which is in good agreement with strength properties. After firing at
800°C the ultrasound velocity decreases in all concrete compositions, although the difference between
the ultrasound velocity for concrete with individual deflocculants and a composite deflocculant is
about 1000 m/sec. After firing at 1100°C ultrasound velocity in all concretes increases, but the
difference is retained.
In our opinion, a possible reason for this strong difference in structure formation and strength
properties after drying and firing of concrete with a composite deflocculant from concretes with
deflocculants NT and FS-20 is the initially formed structure in the second stage of hardening in the
aluminate cement – microsilica – deflocculant system. In this stage hydrated amorphous and
crystalline phases form, some of which are nanostructures. During hydration the effect of the nature of
the deflocculant, about which it is possible to judge from the differences in pH and electrical
conductivity in aqueous solution. Composite deflocculant apparently stimulates formation of nanostructures (the recorded ultrasound propagation velocity is the highest). After drying these structures
are compacted significantly, whereas the skeleton of crystal hydrates is subject to transformation, and
in the temperature range 100 – 400°C it is broken. Therefore the strength of concrete before the start
of sintering (>800°C) may be markedly affected by the quality of the skeleton formed from nanostructures.
Observed differences in structure formation and strength properties of concrete with hybrid
deflocculant were also confirmed by tests for slug resistance. Those tests were carried out with
traditional concrete, medium-cement concrete with deflocculant FS-20 and medium-cement concrete
with composed deflocculant (see Figure 10- 12). Pictures below represent, that slug penetration into
traditional concrete structure was the highest – the depth of slug penetration into the sample was 1,5
cm. Slug penetration into the sample of concrete with deflocculant FS-20 was 0,5-0,7cm and in case of
the sample of concrete with hybrid deflocculant – 0,1-0,2 cm. The use of hybrid deflocculant allows to
get even more dense and resistant concrete structure, preventing slug penetration.
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
Figure 10. Slug resistance investigation (traditional
concrete)
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
Figure 11. Slug resistance investigation (mediumcement concrete with deflocculant FS-20)
Figure 12. Slug resistance investigation (medium-cement concrete with hybrid deflocculant)
4. Conclusions
1.
It has been found out, that minimal concentration of different type deflocculants influence on
dynamic viscosity of concrete mix was different – in case of deflocculant FS-20 it was 1,5-2 fold
lower, than in case of deflocculant NT. During further increase of FS-20 concentration, the viscosity
of cement paste decreased, while increase in NT concentration had no significant impact on cement
paste viscosity changes. 25-30 min later cement paste viscosity independently of deflocculant NT
concentration, reaches 5000-6000 MPа s, while the viscosity of cement paste with FS-20 varied from
500 to 4500 MPа s. The investigations of cement paste with hybrid deflocculant have revealed, that
the lowest viscosity values were reached in case, when NT:FS-20 ratio in hybrid deflocculant was 1:2.
2.
The investigations of individual deflocculants and their compositions influence on concrete
mix hydration process have shown, that the increase in NT concentration slightly accelerated
hydration processes, moreover, EXO maximum temperature decreased from 41°С (without
deflocculant) to 33°С (0,3% deflocculant). The increase of FS-20 concentration significantly slowed
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5th Baltic Conference on Silicate Materials
IOP Conf. Series: Materials Science and Engineering 25 (2011) 012001
IOP Publishing
doi:10.1088/1757-899X/25/1/012001
down hydration processes, the time of EXO maximum increased from 4h (without deflocculant) to
44h (0,3% deflocculant), while the temperature of EXO maximum decreased to 28°С. In case of NT
predomination in hybrid deflocculant the time of EXO maximum decreased (from 15 to 6 h), while the
temperature increased. In case of FS-20 predomination in hybrid deflocculant the time of EXO
maximum increased (from 15 to 110h), while the temperature decreased (from 31 to 23°С). Using
hybrid deflocculant allows regulating hydration characteristics of concrete mix in fairly wide time and
temperature range.
3.
It has been established that different types of deflocculant have a different effect on the
structure formation of medium-cement refractory concrete based on mullite filler during hardening. In
concrete with sodium triplyphosphate there are two stages of structure formation: first, when the
ultrasound pulse velocity reaches 2500 m/sec, and the second at 5000 m/sec. In concrete with
deflocculant of polycarboxylate ester Castament FS-20, there are three stages, within the ultrasound
pulse velocity is about 1000, 2500, and 5000 m/sec respectively. In concrete with a hybrid
deflocculant there are also three stages of structure formation, but the ultrasound pulse velocity during
the second stage exceeds 3500 m/sec. It is proposed that in this stage a nanostructure forms whose
effect on the concrete structure with the composite deflocculant is the greatest.
4.
The ultimate strength in compression of concrete with a hybrid deflocculantafter hardening
is 65 MPa and differs slightly from that of concrete with sodium triplyphosphate or polycarboxylate
ester Castament FS-20 additive (about 50 – 55 MPa). After drying at 110°C and firing at 800, 1100,
and 1200°C , the ultimate strength in compression of concrete with a hybrid deflocculant is higher up
to two times (150 – 180 MPa) than that of concrete with only sodium triplyphosphate or
polycarboxylate ester Castament FS-20 additive (80 – 100 MPa).
5.
It has been established, that the denser structure of concrete with hybrid deflocculant
prevented the penetration of slug into the sample.
References
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[2] Wutz K and Hommer H 2005 9th Biennial Worldwide Congress on Refractories (Orlando FL
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[3] Von Seyerl J 2005 Inteceram, Refractories Manual 3-4 46
[4] Vasilik P 2003 New Refractories 8 28 (in Russian)
[5] Goberis S, Pundiene I, Stonys R, and V.Antonovic 2005 XV conference on refractory castables
Prague 2005 p 86.
[6] Goberis S, Pundiene I and Antonovich V 2005 Refract. Industr. Ceram. 46 6 403
[7] Antonovich V, Goberis S, Pundienė I and Stonys R 2006 Refract. Industr. Ceram. 47 3 178
[8] Heikal M, Saad Morsy M and Aiad I 2006 Ceramics-Silikaty 50 1 5
[9] Otroj S, Nilforoshan M, Daghighi A and Marzban R 2010 Ceram. Internat. 54 3 284
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[11] Otroj S, Nilforoshan M andMarzban R 2009 Ceram. Internat. 53, 1 42
[12] Heikal M and Aiad I 2008 Ceramics-Silikaty. 52 1 8
[13] www. schleibinger.com
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