ARTIGO CONCRETOS x TIJOLOS

Prévia do material em texto

Dr. Štefan Palčo is an independent consultant for 
refractories. He received his Ph.D. from the Slovak 
Academy of Sciences and worked as a researcher at the 
Refractories Research Institute in Bratislava, with Res-
co Products, USA, and at CIREP Ecole Polytechnique, 
University of Montreal, Canada.
E-Mail: stepal@gmail.com
020 01– 02|17
F. Tomšů, Š. Palčo
Refractory Monolithics versus Shaped Refractory Products
AUTHORS
ABSTRACT
Dr.-Ing. Frantisek Tomšů studied Silicate Technol-
ogy at the Technical University Prague and earned his 
Ph.D. from the Slovak Academy of Sciences in 1960. 
From 1953 till 2001 he worked as a researcher at the 
Refractories Research Institute in Bratislava, where he 
focused on the technology, application and testing of 
refractory materials. Since then he acts as an independent consultant for 
refractories technology. E-Mail: frtomsu@stonline.sk
The share of the world’s gross refractory production due to monolithics 
has progressively increased. This trend can be attributed primarily to im-
proved properties of new products and the introduction of new installa-
tion techniques. Development of advanced refractory castables is briefly 
described and the properties of monolithic refractories are compared 
with the properties of similar shaped products. The use of monolithics as 
a substitute for refractory bricks in different industrial high-temperature 
processes is discussed.
KEYWORDS: advanced monolithic refractories, shaped refractories, installation techniques, global trends 
 » Interceram 66 (2017) [1–2]
1. Global trends in the production of refrac-
tory materials
Global production of refractories is estimated to total approximately 
45 million t/a and is expected to reach 50 million t by 2020 [1, 2, 4]. Iron 
and steel will remain the main market for refractories and is expected 
to account for 71 % of the total quantity of refractory materials used 
by 2020. World production of crude steel doubled in the last 15 years, 
reaching 1623 million t in 2015 [3], approx. 50 % of which is China’s 
share. Growth in the production of cement, ceramics and other mineral 
products is expected to complement this growth trend in coming years. 
Furthermore, it is expected that the increase in the use of refractory ma-
terials for the production of metallic and non-metallic products will fur-
ther extend the prospects of market’s growth. In addition, an upsurge in 
the use of refractories for production of metal and non-metallic mineral 
products is expected to advance the prospect of wide market growth. On 
the other hand, specific consumption of refractories is permanently de-
creasing across all sectors. Since the late 1970s, utilisation of carbon has 
been a focus. Unburned carbon-containing bricks became widely used 
for steelmaking and steel-refining vessels to reduce refractory consump-
tion. Around the same time, low-cement castables began to replace 
most bricks, except for those containing carbon. Unshaped refractories, 
such as castables and gunning mixes, have been actively improved not 
only as materials but also in their installation methods. Monolithic lin-
ings can be installed more quickly than brick linings, reducing kiln or 
furnace downtime, which can result in considerable cost savings.
Monolithics now account for over 50 % of the global market. The 
growth prospects for monolithic refractories, especially for castables and 
preformed shapes, are very high. In Japan, considered a guide to global 
trends, unshaped refractories accounted for more than 70 % of all refrac-
F. Tomšů, Š. Palčo
Refractory Monolithics Versus Shaped Refractory Products
Dr.-Ing. Frantisek Tomšů studied Silicate Technology at the 
Technical University Prague and earned his Ph.D. from the 
Slovak Academy of Sciences in 1960. From 1953 till 2001 he
worked as a researcher at the Refractories Research Institute in 
Bratislava, where he focused on the technology, application and 
testing of refractory materials. Since then he acts as an
independent consultant for refractories technology.
E-Mail: frtomsu@stonline.sk
Dr. Štefan Palčo is an independent consultant for refractories. He 
received his Ph.D. from the Slovak Academy of Sciences and 
worked as a researcher at the Refractories Research Institute in 
Bratislava, with Resco Products, USA, and at CIREP Ecole 
Polytechnique, University of Montreal, Canada.
E-Mail: stepal@gmail.com
ABSTRACT
The share of the world’s gross refractory production due to 
monolithics has progressively increased. This trend can be 
attributed primarily to improved properties of new products and
the introduction of new installation techniques. Development of 
advanced refractory castables is briefly described and the 
properties of monolithic refractories are compared with the 
properties of similar shaped products. The use of monolithics as a 
substitute for refractory bricks in different industrial high-
temperature processes is discussed.
KEYWORDS
advanced monolithic refractories, shaped refractories, installation 
techniques, global trends
1. Global trends in the production of refractory 
materials
Global production of refractories is estimated to total 
approximately 45 million t/a and is expected to reach 50 million t 
by 2020 [1, 2, 4]. Iron and steel will remain the main market for 
refractories and is expected to account for 71 % of the total 
quantity of refractory materials used by 2020. World production 
of crude steel doubled in the last 15 years, reaching 1623 million t 
in 2015 [3], approx. 50 % of which is China’s share. Growth in 
the production of cement, ceramics and other mineral products is
expected to complement this growth trend in coming years. 
Furthermore, it is expected that the increase in the use of 
refractory materials for the production of metallic and non-
metallic products will further extend the prospects of market’s 
growth. In addition, an upsurge in the use of refractories for 
production of metal and non-metallic mineral products is expected 
to advance the prospect of wide market growth. On the other 
hand, specific consumption of refractories is permanently 
decreasing across all sectors. Since the late 1970s, utilisation of 
carbon has been a focus. Unburned carbon-containing bricks 
became widely used for steelmaking and steel-refining vessels to 
reduce refractory consumption. Around the same time, low-
cement castables began to replace most bricks, except for those 
containing carbon. Unshaped refractories, such as castables and 
gunning mixes, have been actively improved not only as materials 
but also in their installation methods. Monolithic linings can be 
installed more quickly than brick linings, reducing kiln or furnace 
downtime, which can result in considerable cost savings.
Monolithics now account for over 50 % of the global market. The 
growth prospects for monolithic refractories, especially for 
castables and preformed shapes, are very high. In Japan, 
considered a guide to global trends, unshaped refractories 
accounted for more than 70 % of all refractories produced in 
2012. The graph in Fig. 1 shows the growing share of monolithics 
in Japan since 1980 [4].
2. Development of advanced castables
A decisive breakthrough in the production and consumption of 
castables occurred with the development of castables that were 
suitable for use in corrosive environments (French patent 69 34 
405 in 1969).
A substantial increase in the quality of castables was achieved by 
introducing a new batch composition – a concept featuring
reduction of cement content, addition of micro-fillers and 
application of effective dispersants. It started an intensivephase of 
progress in the development of new varieties of monolithic 
refractory materials, oriented towards increasing quality 
parameters and facilitating product installation.
Hydraulic binders in refractory castables had primarily used
calcium aluminate cements (CAC) containing from 40 to 80 mass-
% Al2O3. However, 70 mass-% CAC became the dominant 
cement in castables development during the early 1970’s. The 
overall amount of cement has continually been reduced, from 15–
25 mass-% to much lower levels. New low-cement castables 
(LCC, 1–2.5 mass-% CaO), ultralow cement castables (ULCC,
0.2–1 mass-% CaO) and no-cement castables (NCC, <0.2 mass-%
F. Tomšů, Š. Palčo
Refractory Monolithics Versus Shaped Refractory Products
Dr.-Ing. Frantisek Tomšů studied Silicate Technology at the 
Technical University Prague and earned his Ph.D. from the 
Slovak Academy of Sciences in 1960. From 1953 till 2001 he
worked as a researcher at the Refractories Research Institute in 
Bratislava, where he focused on the technology, application and 
testing of refractory materials. Since then he acts as an
independent consultant for refractories technology.
E-Mail: frtomsu@stonline.sk
Dr. Štefan Palčo is an independent consultant for refractories. He 
received his Ph.D. from the Slovak Academy of Sciences and 
worked as a researcher at the Refractories Research Institute in 
Bratislava, with Resco Products, USA, and at CIREP Ecole 
Polytechnique, University of Montreal, Canada.
E-Mail: stepal@gmail.com
ABSTRACT
The share of the world’s gross refractory production due to 
monolithics has progressively increased. This trend can be 
attributed primarily to improved properties of new products and
the introduction of new installation techniques. Development of 
advanced refractory castables is briefly described and the 
properties of monolithic refractories are compared with the 
properties of similar shaped products. The use of monolithics as a 
substitute for refractory bricks in different industrial high-
temperature processes is discussed.
KEYWORDS
advanced monolithic refractories, shaped refractories, installation 
techniques, global trends
1. Global trends in the production of refractory 
materials
Global production of refractories is estimated to total 
approximately 45 million t/a and is expected to reach 50 million t 
by 2020 [1, 2, 4]. Iron and steel will remain the main market for 
refractories and is expected to account for 71 % of the total 
quantity of refractory materials used by 2020. World production 
of crude steel doubled in the last 15 years, reaching 1623 million t 
in 2015 [3], approx. 50 % of which is China’s share. Growth in 
the production of cement, ceramics and other mineral products is
expected to complement this growth trend in coming years. 
Furthermore, it is expected that the increase in the use of 
refractory materials for the production of metallic and non-
metallic products will further extend the prospects of market’s 
growth. In addition, an upsurge in the use of refractories for 
production of metal and non-metallic mineral products is expected 
to advance the prospect of wide market growth. On the other 
hand, specific consumption of refractories is permanently 
decreasing across all sectors. Since the late 1970s, utilisation of 
carbon has been a focus. Unburned carbon-containing bricks 
became widely used for steelmaking and steel-refining vessels to 
reduce refractory consumption. Around the same time, low-
cement castables began to replace most bricks, except for those 
containing carbon. Unshaped refractories, such as castables and 
gunning mixes, have been actively improved not only as materials 
but also in their installation methods. Monolithic linings can be 
installed more quickly than brick linings, reducing kiln or furnace 
downtime, which can result in considerable cost savings.
Monolithics now account for over 50 % of the global market. The 
growth prospects for monolithic refractories, especially for 
castables and preformed shapes, are very high. In Japan, 
considered a guide to global trends, unshaped refractories 
accounted for more than 70 % of all refractories produced in 
2012. The graph in Fig. 1 shows the growing share of monolithics 
in Japan since 1980 [4].
2. Development of advanced castables
A decisive breakthrough in the production and consumption of 
castables occurred with the development of castables that were 
suitable for use in corrosive environments (French patent 69 34 
405 in 1969).
A substantial increase in the quality of castables was achieved by 
introducing a new batch composition – a concept featuring
reduction of cement content, addition of micro-fillers and 
application of effective dispersants. It started an intensive phase of 
progress in the development of new varieties of monolithic 
refractory materials, oriented towards increasing quality 
parameters and facilitating product installation.
Hydraulic binders in refractory castables had primarily used
calcium aluminate cements (CAC) containing from 40 to 80 mass-
% Al2O3. However, 70 mass-% CAC became the dominant 
cement in castables development during the early 1970’s. The 
overall amount of cement has continually been reduced, from 15–
25 mass-% to much lower levels. New low-cement castables 
(LCC, 1–2.5 mass-% CaO), ultralow cement castables (ULCC,
0.2–1 mass-% CaO) and no-cement castables (NCC, <0.2 mass-%
tories produced in 2012. The graph in Fig. 1 shows the growing share of 
monolithics in Japan since 1980 [4].
2. Development of advanced castables
A decisive breakthrough in the production and consumption of castables 
occurred with the development of castables that were suitable for use in 
corrosive environments (French patent 69 34 405 in 1969).
A substantial increase in the quality of castables was achieved by in-
troducing a new batch composition – a concept featuring reduction of 
cement content, addition of micro-fillers and application of effective 
dispersants. It started an intensive phase of progress in the development 
of new varieties of monolithic refractory materials, oriented towards in-
creasing quality parameters and facilitating product installation.
Hydraulic binders in refractory castables had primarily used calci-
um aluminate cements (CAC) containing from 40 to 80 mass-% Al2O3. 
However, 70 mass-% CAC became the dominant cement in castables 
development during the early 1970’s. The overall amount of cement has 
continually been reduced, from 15–25 mass-% to much lower levels. 
New low-cement castables (LCC, 1–2.5 mass-% CaO), ultralow cement 
castables (ULCC, 0.2–1 mass-% CaO) and no-cement castables (NCC, 
<0.2 mass-% CaO) were developed [5]. This minimised the negative ef-
fects of CaO, which causes formation of anorthite and gehlenite in the 
ternary system CaO–Al2O3–SiO2.
A novel calcium magnesium aluminate (CMA) binder combines hy-
draulic calcium aluminates and a large quantity of MA spinel crystals 
of size very similar to those formed in A-M castables [6]. The binder is 
designed to allow reduction of both the amount of free magnesia and of 
silica fume in A-M castable applications. It enhances thermo-mechanical 
properties, penetration and corrosion resistance.
refractory monolithics based on microporous aggregates. 
Proceedings: UNITECR´99, Berlin (1999) 177–180
[23] Van Garsel, D., et al.: New insulating raw material for 
high-temperature refractories. Proceedings of the 13th 
Conference on refractory castables, Praha (1998) 24–32
[24] Routschka, G.: Refractory Materials – design, properties, 
testing. (2008)
[25] Yaxiong, Li, et al.: The relationship between the pore size 
distribution and the thermo-mechanical properties of high 
alumina refractory castables. Internat. J. of Materials 
Research 107 (2016) [3]
[26] Staroň, J., Tomšů, F.: Refractory materials – production, 
properties and application. Slovmag (2000) (in Slovak)
[27] Miyawaki, M., et al.: Effect of materials and pore diameter 
control on the Al-penetration resistanceof castables.
Taikabutsu Overseas 20 (2000) [2] 115–120
[28] Tomšů F., Adamovič, A.: Comportement 
thermoméchanique des matériaux réfractaires pour 
revêtments monolithiques. Bull. Soc. Franç. Céram. (1973) 
98
[29] Czech Silicate Society: Refractory materials, Part 8:
Application of refractory materials. (in Czech), Czech 
Silicate Society (2016)
Received: 05.02.2017
Captions
Fig. 1 Share of monolithics in Japan
Bitte korrigieren Sie in Fig. 1:
Vertikale Achse: Share of monolithics / %
Horizontale Achse: Year
Fig. 2 Pore size distribution in castables (C) and bricks (B):
corundum C (d50 = 0.7 µm), corundum B (d50 = 18 µm), fireclay C (d50
= 1.2 µm), fireclay B (d50 = 2.5 µm)
Bitte korrigieren Sie in Fig. 2:
Vertikale Achse: Total share (absolute) / %
Horizontale Achse: Porediameter / μm
Auf der horizontalen Achse bitte die Kommas zu Punkten wandeln
Fig. 3 Thermal conductivity of refractory materials (apparent porosity,
ca. 20 %); HA - high alumina (B brick, C castable), FC - fireclay (B 
brick, C castable)
Bitte korrigieren Sie in Fig. 3:
Vertikale Achse: Thermal conductivity / W/m·K
Horizontale Achse: Porediameter / μm
Fig. 4 Stress/strain curves for various refractory materials (bending 
test at 1000 ° C)
Bitte korrigieren Sie in Fig. 4:
Vertikale Achse: Stress / MPa
Horizontale Achse: Strain / mm
Fig. 1
Fig. 2
 
year
sh
ar
e
of
 m
on
ol
ith
ic
s, 
%
 
0
5
10
15
20
25
0,01 0,1 1 10 100
to
ta
ls
ha
re
 %
(a
bs
ol
ut
e)
 
 
fireclay 
corundum 
C B C B 
Sh
ar
e 
of
 m
on
ol
ith
ic
s 
/ %
Year
021REFRACTORIES
For no-cement castables, a new hydraulic binder was developed – hy-
dratable alumina (ρ-Al2O3) [7, 8]. It reacts with water to form a gel of 
aluminium hydrates.
For basic castables, a forsterite bond formed by the reaction of MgO 
with microsilica in the presence of water proved to be suitable [9].
Another type of bond that is often used in refractory castables is phos-
phate binding. A system that contains aluminium oxide or aluminium 
hydroxide, after reaction with phosphoric acid or phosphates will pro-
duce a refractory AlPO4 [10]. Another type of bond that is also suitable 
for non-oxide systems (e.g. those based on SiC) is formed through sol-gel 
processing [11–12]. Application of colloidal SiO2 and Al2O3 in castables 
has gained more attention in connection with trends of using nano-tech-
nology in the formulation and manufacture of refractory materials [13].
The formation of nano-matrix brings a new dimension to the properties 
of refractory materials because it shifts pore sizes into the nanometre 
range. It is reflected particularly in improved resistance to melt pene-
tration and in better mechanical and thermomechanical properties, par-
ticularly toughness and resistance to mechanical and thermal shock. For 
application in castables, substitution of a sol of SiO2 for hydraulic binder 
has a noticeable positive effect, resulting in accelerated drying and heat-
ing of newly installed refractory lining. In gelation of SiO2 sol no water is 
chemically bonded. The water is released and can therefore be removed 
at temperatures below 100 °C.
It is crucial to optimise the matrix composition for castable quality. 
It must be designed for dense filling of space down to the submicron 
particle size range. The chemical composition of the matrix is critical for 
minimising the content of compounds forming eutectics with low melt-
ing points.
The rheological behaviour of refractory castables is primarily influ-
enced by submicron particles. The discovery that addition of highly reac-
tive silica fume dramatically changed the physical properties of mixtures 
resulted in a new family of castables [14]. For alumina-based mixes, 
containing calcium aluminate cement (CAC), is necessary to minimize 
the content of SiO2 (castables without microsilica), because the presence 
of even small amounts of SiO2 deteriorates significantly the thermome-
chanical behavior of castables [15]. Replacement of microsilica, which 
constitutes the finest matrix fraction, was possible using reactive alumi-
nas, which are now available as monodisperse and polydisperse powders 
even in the submicron particle size range [16].
Effective dispersants are another very important component of refrac-
2
Fig. 1 • Share of monolithics in Japan
Fig. 2 • Pore size distribution in castables (C) and bricks (B): corundum C (d50 = 
0.7 µm), corundum B (d50 = 18 µm), fireclay C (d50 = 1.2 µm), fireclay B (d50 = 
2.5 µm)
refractory monolithics based on microporous aggregates. 
Proceedings: UNITECR´99, Berlin (1999) 177–180
[23] Van Garsel, D., et al.: New insulating raw material for 
high-temperature refractories. Proceedings of the 13th 
Conference on refractory castables, Praha (1998) 24–32
[24] Routschka, G.: Refractory Materials – design, properties, 
testing. (2008)
[25] Yaxiong, Li, et al.: The relationship between the pore size 
distribution and the thermo-mechanical properties of high 
alumina refractory castables. Internat. J. of Materials 
Research 107 (2016) [3]
[26] Staroň, J., Tomšů, F.: Refractory materials – production, 
properties and application. Slovmag (2000) (in Slovak)
[27] Miyawaki, M., et al.: Effect of materials and pore diameter 
control on the Al-penetration resistance of castables.
Taikabutsu Overseas 20 (2000) [2] 115–120
[28] Tomšů F., Adamovič, A.: Comportement 
thermoméchanique des matériaux réfractaires pour 
revêtments monolithiques. Bull. Soc. Franç. Céram. (1973) 
98
[29] Czech Silicate Society: Refractory materials, Part 8:
Application of refractory materials. (in Czech), Czech 
Silicate Society (2016)
Received: 05.02.2017
Captions
Fig. 1 Share of monolithics in Japan
Bitte korrigieren Sie in Fig. 1:
Vertikale Achse: Share of monolithics / %
Horizontale Achse: Year
Fig. 2 Pore size distribution in castables (C) and bricks (B):
corundum C (d50 = 0.7 µm), corundum B (d50 = 18 µm), fireclay C (d50
= 1.2 µm), fireclay B (d50 = 2.5 µm)
Bitte korrigieren Sie in Fig. 2:
Vertikale Achse: Total share (absolute) / %
Horizontale Achse: Porediameter / μm
Auf der horizontalen Achse bitte die Kommas zu Punkten wandeln
Fig. 3 Thermal conductivity of refractory materials (apparent porosity,
ca. 20 %); HA - high alumina (B brick, C castable), FC - fireclay (B 
brick, C castable)
Bitte korrigieren Sie in Fig. 3:
Vertikale Achse: Thermal conductivity / W/m·K
Horizontale Achse: Porediameter / μm
Fig. 4 Stress/strain curves for various refractory materials (bending 
test at 1000 ° C)
Bitte korrigieren Sie in Fig. 4:
Vertikale Achse: Stress / MPa
Horizontale Achse: Strain / mm
Fig. 1
Fig. 2
 
year
sh
ar
e
of
 m
on
ol
ith
ic
s, 
%
 
0
5
10
15
20
25
0,01 0,1 1 10 100
to
ta
ls
ha
re
 %
(a
bs
ol
ut
e)
 
 
fireclay 
corundum 
C B C B 
To
ta
l s
ha
re
 (
ab
so
lu
te
) 
/ %
Porediameter / μm
0
5
10
15
20
25
0,01 0,1 1 10 100
tory castables. Their application improves flowability and reduces the 
amount of mixing water, thereby increasing the density, strength and 
slag penetration resistance of castables. High mix flowability with very 
low water content can be achieved using active dispersants – organic 
polymers such as polyacrylates, polyglycols, polycarboxyethers and poly-
glycol ethers. Well-dispersed mixtures with controlled grain sizing up to 
submicron ranges (characterised by exponent q from 0.20 to 0.25) can 
be processed with about 4 mass-% water content. The resulting mixtures 
are pumpable and can be installed by shotcreting [17–18].
Addition of setting agents allows mix processing across a relative-
ly wide temperature range, from approx. 5 to 30 °C. For adjustment of 
working and setting times, setting accelerators (above all, lithium salts) 
are used at lower temperatures and setting retarders (alkaline citrates, 
tartrates or gluconates) are used at higher temperatures.
In order to facilitate dosage of small amounts of dispersants and set-
ting agents (typically in hundredths of a percent), additives combiningboth components together with active alumina are available. They are 
known as premixed dispersing aluminas, which allow easy dosage and 
homogenisation [19].
To reduce the sensitivity of monolithic installations on drying proce-
dures, organic fibres, usually of polypropylene, can be admixed in mix-
tures at a ratio of about 0.05 mass-%. The fibres facilitate capillary rise of 
water to the surface and accelerate its evaporation. Addition of fibres can 
reduce the risk of explosive spalling and accelerate drying and heating of 
monolithic linings [20].
The thermal shock resistance of monoliths can be improved by addition 
of steel fibres. This increases tensile strength and thus also resistance to 
catastrophic fracture. However, addition of steel fibres induces tempera-
ture and time limitations because of steel oxidation at high temperature 
in oxidising atmospheres [21].
Refractory aggregates constitute the “skeleton” of the castable. A wide 
variety of refractory aggregates is available and castables can be formu-
lated based on one or a combination of types of aggregates to achieve 
desired chemical, mineralogical and physical properties. The variety of 
available aggregates has considerably expanded. Besides aluminos-
ilicates and alumina, also spinel (MgO•Al2O3), magnesia (sintered or 
fused), cordierite, silicon carbide, fused silica, SiAlON, and more recently, 
calcium hexaaluminate in dense form as well as lightweight aggregates 
for insulation refractory concrete, are now frequently used [22–23].
1
St
re
ss
 / 
M
Pa
Strain / mm
Fig. 3
Fig. 4
 
HA-B
HA-C
FC- B
FC- C
th
er
m
al
 c
on
du
ct
iv
ity
,
W
/m
K
temperature, oC
 
strain, mm
st
re
ss
 ,
M
Pa
Th
er
m
al
 c
on
du
ct
iv
ity
 / 
W
/m
• K
Porediameter / μm
Fig. 3
Fig. 4
 
HA-B
HA-C
FC- B
FC- C
th
er
m
al
 c
on
du
ct
iv
ity
,
W
/m
K
temperature, oC
 
strain, mm
st
re
ss
 ,
M
Pa
022 01– 02|17
3 4
Fig. 3 • Thermal conductivity of refractory materials (apparent porosity, ca. 
 20 %); HA - high alumina (B brick, C castable), FC - fireclay (B brick, C castable)
Fig. 4 • Stress/strain curves for various refractory materials (bending test at 
1000 ° C)
3. Comparison of properties of monolithics 
and fired shaped refractory products
When choosing optimal technological processes, it is possible to achieve 
similar densities with either monolithic or shaped refractory products. 
However, the products differ in their structure. In castables, the empha-
sis is to control rheology of mixtures and that is why precisely controlled 
grain size distribution and use of ultrafine, even nano-sized particles is 
customary. Microporous structure is therefore typical for monolithics. 
In dense fired bricks, the pore sizes reach typically 20–25 microns, with 
special products up to 5 µm; in castables even after firing the medium 
pore diameter usually do not exceed 1–2 µm. The pore size distribution 
of two types of refractory castables and bricks (fireclay and high alumi-
na) are compared in Fig. 2 [24].
These structural differences are reflected in other properties. Micropo-
rous structures lead to significant growth in the strength and thermal 
shock resistance of castables [25]. This is manifested by increased resis-
tance to both formation and expansion of cracks under sudden tempera-
ture changes. 
Microporous structure also results in lower radiation heat transfer at 
higher temperatures. Castables have 20 to 30 % lower thermal conduc-
tivity compared to fired shaped products of similar composition and the 
same porosity (Fig. 3) [26].
The microporous structure of castables helps hinder slag penetration 
from contact with corrosive environments and improves corrosion resis-
tance against melts, particularly slags and metals [27].
Unlike fired shaped refractory products, castables have excellent de-
formability, i.e. they are capable of releasing the stress in refractory lin-
ing by their own deformation without allowing destruction of refractory 
material. In this respect, phosphate-bonded castables particularly excel 
(Fig. 4) [28].
When using monolithic linings some problems may arise that would be 
unlikely to occur if shaped refractory products are used.
It is necessary to take into account that manufacturers supply monolithic 
materials as semi-finished products (e.g. as a dry mix) that must be fur-
ther processed at the installation location to form a monolithic lining. 
This may cause problems due to non-compliance with manufacturer pre-
scribed instructions for mixing, moistening the mixture and using proper 
installation procedures.
When installing a monolithic lining, it is important to respect its longer 
heating and drying period and use temperatures high enough for com-
plete dehydration of binder.
When using conventional castables with hydraulic bonding, a possi-
ble drop in strength at intermediate temperatures must be taken into 
account. In the range of intermediate temperatures (250–600 °C), hy-
draulic bonds will gradually decompose while ceramic bonds have not 
started to develop. Similarly, less dimensional stability of monolithics at 
high temperatures is expected due to matrix shrinkage. 
4. Refractory monolithics vs. shaped products 
– applications
The share of monolithic refractory materials is constantly increasing 
across all types of applications. Nevertheless, there are some appli-
cations which remain the domain of shaped materials. The so-called 
functional refractory materials are typical examples of shaped refractory 
materials that still dominate. Functional refractories are used, for exam-
ple, in continuous casting of steel to control steel flow. In other appli-
cation situations, high quality monolithic materials have not yet been 
developed, and therefore shaped articles are still preferred. In most cas-
es where basic refractory linings are used (dolomia, magnesia, MgO-C, 
magnesia-chrome), shaped refractories prevail. Here belong refractory 
linings of converters, slag lines of steel casting ladles, walls of electric arc 
furnaces, linings of sintering and transition zones of cement rotary kilns, 
furnaces for production of non-ferrous metals (Cu, Pb, Zn, ...), etc. Often, 
tradition plays a decisive role, which explains why shaped products are 
still used in linings constructed according to old designs.
Unshaped refractory materials have recently been used not only to 
manufacture new monolithic linings, but also as mixtures in large quan-
tities for repair and maintenance of in-service refractory linings. Several 
methods are available for installation of unshaped refractory materials, 
including casting with or without vibration (self-flow), gunning, spray-
ing, shotcreting, ramming and injecting. Some applications have been, 
and continue to be, the domain of monolithic refractories. Traditionally, 
monolithic refractories are used for the bottom of conventional electric 
arc furnaces (basic refractory materials), taphole clay, blast furnace run-
ners and a variety of repair and maintenance materials, just to name 
a few applications. In some cases, complex formations of brick are re-
placed by monoliths, thus creating combined linings. As an example, we 
can mention waste incinerators.
Monolithic refractories are used to form virtually joint-free linings and 
are only given shape upon application. A typical example of the extend-
ed application of castables is the evolution of refractory linings for steel 
casting ladles. In principle [28], ladle linings can be divided into those 
that are monolithic or brick, and are high alumina (neutral) or basic. 
Whilst monolithic linings with castables are restricted mainly to high 
023REFRACTORIES
alumina-based material systems, brick linings can be built with neutral 
as well as basic materials. Numerous efforts have been made to develop 
basic castables, but no really successful application of basic castables in 
steel ladles has been reported so far. The fundamental problems arethe 
susceptibility of magnesia to hydration and selection of an appropriate 
binder. With shaped refractory materials, addition of carbon compen-
sates for some of the negative properties of magnesia refractories like 
high thermal expansion and low resistance against slag infiltration. 
Effective addition of carbon to magnesia-based castables has not yet 
been successfully achieved and is a limiting factor in wide and success-
ful application of MgO-C castables. With the development of high-per-
formance low- and ultra-low cement castables, however, monolithic 
ladle linings have gained an increasingly important status for steel la-
dles. Alumina-based castables combined with new relining techniques 
is now a widespread technology. After the first ladle campaign with a 
new castable lining, the lining surface is mechanically cleaned. A new 
layer is cast on top of the worn surface. This procedure can be repeated 
several times. The material consumption for relining the ladle side wall 
is about 40–50 % of the initial complete new lining, which means that 
50–60 % of the original lining material is saved by this technology. The 
advantages of castables over brick linings can be summarised as follows: 
reduced manpower and time for lining, increased ladle availability – and 
therefore possible reduction of ladle fleet in service, and lower specific 
refractory consumption and cost.
Monolithic refractories are of major importance in the maintenance of 
furnaces because substantial repairs can be made with minimum down-
time and in some cases can even be performed during operations. Sys-
tematic maintenance of linings allows the campaign life of furnaces to 
be extended. Maintenance of basic linings (MgO-C) of oxygen converters 
can be mentioned as an example. Regular gunning applying basic mixes, 
together with precise control of the slag regime and the practice of slag 
splashing can extend the lifetime of linings to over 20000 heats, with 
the result that consumption of refractory material drops below one kg 
per ton of steel.
Quick installation (via new binders) and shortening of drying and heat-
up time are advantages that can play an important role when choosing 
between a monolithic lining and a classical brick lining. Raw materials 
in many cases represent the greatest portion of the price of finished 
products (up to 60 %), ruling out the possibility of a cheaper alternative 
because the raw materials have a substantial effect on the properties of 
the product. From this perspective, application of unshaped materials in 
which the raw materials are the main item in the total price of the prod-
uct has an undeniable economic effect. Constantly improving the qual-
ity and enabling simple and fast application ultimately result in better 
economy of use [29]. One can assume that the proportion of unshaped 
and shaped products in different applications will continue to grow. Fur-
ther development of new monolithic refractories and innovative installa-
tion and prefabrication techniques should maintain this trend.
[4]
[5]
[6]
[7]
[8] 
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23] 
[24]
[25]
[26]
[27]
[28]
[29]
References
[1]
[2] 
[3]
Roberts, J.: Outlook for refractory end-user markets to 2020. Proceedings: 57th Inter-
nat. Colloq. on Refractories, Aachen (2014) 228–230
Gerotte, M.V., et al.: Zero-cement high alumina castables. Amer. Ceram. Soc. Bull. 
79 (2000) [9] 75–83
Wöhrmeyer, C., et al.: Novel Calcium Magnesium Aluminate Bonded Castables For Steel 
And Foundry Ladles. Proceedings UNITECR 2013, Victoria, Canada (2013) 1031–1036
Hongo, Y.: ρ-Alumina bonded castable refractories. Taikabutsu Overseas 9 (1989) [1] 
35–38
Racher, R.P., et al.: Improvements in workability behaviour of calcia-free hydratable 
alumina binders. Proceedings: UNITECR´05, Orlando (2005)
Myhre, B., et al.: Castables with MgO-SiO2-Al2O3 as bond phase. IRMA Journal (2001) 
[4] 67–72
Luz, A.P., et al.: High-alumina phosphate bonded refractory castables: Al(OH)3 sourc-
es and their effects. Ceramics Internat. 41 (2015) [7] 9041–9050
Ghosh, S.: Microstructures of refractory castables prepared with sol-gel additives. 
Ceramics Internat. 24 (2003) 671–677
Ulbricht, J., Tomšů, F.: Bonding systems for SiC-containing refractory castables. Pro-
ceedings of the 15th Conference on refractory castables. Praha (2005) 51–58
Ismael, M.R., et al.: Colloidal Silica Nanostructured as a Binder for Refractory 
Castables. Refractories Applications and News 11 (2006) [4] 16–20
Shicano, H., et al.: Roll of silica flour in low cement castable. Taikabutsu Overseas 
10 (1990) [1] 17–22
Kriechbaum, G.W., et al.: The influence of SiO2 and spinel on the hot properties of 
high-alumina low-cement castables. Proceedings: 37. Intern. Colloq. on Refractories, 
Aachen (1994) 150–159
Almatis: Alcoa Product Data, Refractory Matrix Brochure (2004)
Evangelista, P.C., et al.: Control of formulation and optimization of self-flow 
castables based on pure calcium aluminates. Refractories Application (2002) [2] 14–18
Büchel, G., et al.: E-SY Pump – The new solution for pumpability of silica free high 
performance tabular alumina and spinel castables. Proceedings: 47th Intern. Colloq. on 
Refractories, Aachen (2004) 87–90
ALCOA Product Data: Dispersing Aluminas (2004)
Kobayashi, T., et al.: Optimization of PVA fiber explosion control of refractory 
castables. Proceedings UNITECR 2009, Sao Paulo, Doc. 127
Cutard, T., et al.: Thermomechanical behavior of fiber reinforced refractory castables. 
Proceedings UNITECR 2OO9, Sao Paulo, Doc. 045
Web-Janich, M., et al.: High temperature insulating refractory monolithics based on 
microporous aggregates. Proceedings: UNITECR´99, Berlin (1999) 177–180
Van Garsel, D., et al.: New insulating raw material for high-temperature refractories. 
Proceedings of the 13th Conference on refractory castables, Praha (1998) 24–32
Routschka, G.: Refractory Materials – design, properties, testing. (2008)
Yaxiong, Li, et al.: The relationship between the pore size distribution and the ther-
mo-mechanical properties of high alumina refractory castables. Internat. J. of Materi-
als Research 107 (2016) [3]
Staroň, J., Tomšů, F.: Refractory materials – production, properties and application. 
Slovmag (2000) (in Slovak)
Miyawaki, M., et al.: Effect of materials and pore diameter control on the Al-penetra-
tion resistance of castables. Taikabutsu Overseas 20 (2000) [2] 115–120
Tomšů F., Adamovič, A.: Comportement thermoméchanique des matériaux réfrac-
taires pour revêtments monolithiques. Bull. Soc. Franç. Céram. (1973) 98
Czech Silicate Society: Refractory materials, Part 8: Application of refractory materi-
als. (in Czech), Czech Silicate Society (2016) 
http://www.researchandmarkets.com: Global Refractories Market – Segmented 
by Product Type, End-User Industry, and Geography – Trends and Forecasts (2015–
2020).
FREEDONIA report 2013: World Refractories to 2016 – Industry Market Research, 
Market Share, Market Size, Sales, Demand Forecast, Market Leaders, Company Profiles, 
Industry Trends.
World Steel Association – statistics. Received: 05.02.2017