ACI 547R-79
Refractory Concrete: Abstract of State-of-the-Art Report
(Revised 1983)
(Reapproved 1997)
Reported by ACI Committee 547
Refractory concretes are currently used in a wide variety of
industrial applications where pyreprocessing and/or thermal containment is required. The service
demands of these applications are
becoming increasingly severe and
this, combined with the constant
demand for refractories with enhanced service life and more efficient means of installation, has
resulted in an ever expanding refractory concrete technology. ACI
Committee 547 has prepared this
state-of-the-art report in order to
meet the need for a better understanding of this relatively new
technology.
The report presents background information and perspective on the history and current status of the technology.
Composition and proportioning
methods are discussed together
with a detailed review of the constituent ingredients. Emphasis is
placed on proper procedures for
the installation, curing, drying,
and firing. The physical and engineering properties of both normal
weight and light weight refractory
concretes are reported, as are
state-of-the-art construction details and repair/maintenance techniques. Also included is an indepth review of a wide variety of
applications together with the
committee‘s assessment of future
needs and developments.
Keywords: abrasion; accelerating agents;
admixtures; aggregates; aluminate cement
and concretes; anchorage (structural); cement-aggregate reactions; chemical analysis; construction; corrosion: curing; drying;
failure mechanisms; formwork (construction); hydration; insulating concretes; kilns;
lightweight concreetes; mechanical properties; mix proportioning; packaged concrete;
physical properties; placing; pumped concrete; quality control; refractories; refractory concretes; reinforcing materials: repairs; research; shotcrete; spalling;
structural analysis; temperature; thermal
properties; water; welded wire fabric.
This abstract first appeared in Concrete International: Design & Construction, V. 1, No. 5, May 1979, pp. 62-77. The full report is available as a
separate publication in 81/4 x 11 in., paper cover format, consisting of 224
pages. Contents listed on this page represent only tbe sections of the report
covered in this abstract.
Contents of summary
Chapter 1 -Introduction, p.
547R-2
Chapter 7 -Properties of
normal weight refractory
concretes, p. 547R-10
7.1 - Introduction
1.1 - Objective of report
1.2 - Scope of report
1.3 - Nomenclature
1.6 - Non-hydraulic setting refractories
7.2 - Maximum service temperature
7.4 - Shrinkage and expansion
7.5 - Strength
7.6 - Thermal conductivity
7.10 - Specific heat
Chapter 2 -Criteria for refractory concrete selection, p.
547R-5
Chapter 8 -Properties of
lightweight refractory concretes, p. 547R-11
2.1 - Introduction
2.2 - Castables and field mixes
2.5 - Load bearing considerations
2.7 - Corrosion influences
2.10 - Abrasion and erosion resistance
8.1 - Introduction
8.4 - Shrinkage and expansion
8.5 - Strength
8.6 - Thermal conductivity
8.10 - Specific heat
Chapter 3 -Constituent ingredients, p. 547R-6
Chapter 9 -Construction details, p. 547R-12
3.2 - Binders
3.3 - Aggregates
3.4 -Effects of extraneous materials
9.1 - Introduction
9.2 - Support structure
9.3 - Forms
9.4 - Anchors
9.5 - Reinforcement and metal embedment
9.6 - Joints
Chapter 4 -Composition and
proportioning, p. 547R-7
4.1 - Introduction
4.3 - Field mixes
4.4 - Water content
Chapter 5 -Installation, p.
547R-8
5.1 - Introduction
5.2 - Casting
5.3 - Shotcreting
5.4 - Pumping and extruding
5.5 - Pneumatic gun casting
5.8 - Finishing
Chapter 6 -Curing, drying,
firing, p. 547R-9
6.1 - Introduction
6.2 - Bond mechanisms
6.3 - Curing
6.4 - Drying
6.5 - Firing
Copyright 0 1979, American Concrete Institute
All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device,
printed or written or oral, or recording for sound
or visual reproduction or for use in any knowledge or retrieval system or device, unless per-
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Chapter 10 -Repair, p. 547R-13
10.1 - Introduction
10.2 - Failure mechanisms
10.3 - Surface preparation
10.4 - Anchoring and bonding
10.5 - Repair materials
10.6 - Repair techniques
Chapter 11 -Applications, p.
547R-15
11.1 - Introduction
Chapter 12 - New developments and future use of refractory concrete, p. 547R-15
12.1 - Introduction
12.2 - New developments
12.3 - Research requirements
mission in writing is obtained from the copyright
proprietors.
Discussion of this committee report may be submitted in accordance with general requirements
of the ACI Publication Policy to ACI Headquarters, P.O. Box 19150. Detroit, Michigan 48219.
Closing date for submission of discussion is November 1, 1979.
547R-2
MANUAL OF CONCRETE PRACTICE
HEAT RESISTANT CONCRETE - Any concrete
Chapter 1 -Introduction
1.1 Objective of report
The objective of this report is to provide a source of
information on the many facets of refractory concrete technology. The report is intended as a unified
and objective source of information to aid the engineer or consumer in categorizing and evaluating
monolithic refractory concrete technology and the
many materials and processes available today. It is
not intended to be a specification or standard, and
should not be quoted or used for that purpose.
1.2 Scope of report
Refractory concrete is concrete suitable for use at
temperatures up to about 3400 F (1870 C). It consi
of a graded refractory aggregate bound by a suitable
cementing medium. This report is concerned with
refractory concrete in which the binding agent is a
hydraulic cement, and does not consider concretes
which use waterglass (sodium silicate), phosphoric
acid, or phosphates as a principal cementing agent.
It covers all facets of refractory concrete installation
and use, including the properties of individual ingredients and concretes, placing techniques, methods
of curing and firing, repair procedures, construction
details, and current and future applications.
1.3 Nomenclature
The following definitions
are used in this report:
ACID REFRACTORIES - Refractories containing a
substantial amount of silica that may react chemically with basic refractories, basic slags, or basic
fluxes at high temperatures.
APPARENT POROSITY (ASTM C20) - The relationship of the volume of the open pores in a refractory specimen to its exterior volume, expressed as a
percentage.
BASIC REFRACTORIES - Refractories whose major constituent is lime, magnesia, or both, and which
may react chemically with acid refractories, acid
slags, or acid fluxes at high temperatures. (Commercial use of this term also includes refractories
made of chrome ore or combinations of chrome ore
and dead burned magnesite).
CALCIUM ALUMINATE CEMENT - The product
obtained by pulverizing clinker which consists of hydraulic calcium aluminates formed by fusing or sintering a suitably proportioned mixture of aluminous
and calcareous materials.
CASTABLE REFRACTORY - A proprietary packaged dry mixture of hydraulic cement and specially
selected and proportioned refractory aggregates
which, when mixed with water, will produce refractory concrete or mortar.
CERAMIC BOND - The high strength bond which
is developed between materials, such as calcium
aluminate cement and refractory aggregates, as a result of thermochemical reactions which occur when
the materials are subjected to elevated temperature.
EXPLOSIVE SPALLING - A sudden spalling
which occurs as the result of a build-up of steam
pressure caused by too rapid heating on first firing.
GROG - Burned refractory material, usually calcined clay or crushed brick bats.
which will not disintegrate when exposed to constant or cyclical heating at any temperature below
which a ceramic bond is formed.
HIGH ALUMINA CEMENT - See calcium aluminate cement.
NEUTRAL REFRACTORIES - Refractories that
are resistant to chemical attack by both acid and basic slags, refractories, or fluxes at high temperatures.
REFRACTORY AGGREGATE - Materials having
refractory properties which form a refractory body
when bound into a conglomerate mass by a matrix.
REFRACTORY CONCRETE - Concrete which is
suitable for use at high temperatures and contains
hydraulic cement as the binding agent.
SOFTENING TEMPERATURE - The temperature
at which a refractory material begins to undergo
permanent deformation under specified conditions.
This term is more appropriately applied to glasses
than to refractory concretes.
THERMAL SHOCK - The exposure of a material
or body to a rapid change in temperature which may
have a deleterious effect.
1.6 Non-hydraulic setting re
The following discussion, while not pertinent to the
main theme of the report, will be of some interest
and use to the reader.
1.6.1 Refractory brick - High quality brick, known
as firebrick, with unique chemical and physical properties is obtained by blending different types of clay
and other ingredients and by varying both the
method of processing and the burning temperatures.
In addition to the many varieties of fireclay brick,
high alumina, insulating, silica, fused aggregate, and
basic firebrick have been developed. Refractory
brick remains a major construction material for applications in which heat containment and control is
necessary and in many instances, is the only satisfactory solution to a specific problem.
Brick has a number of disadvantages when compared to monolithic refractories. These disadvantages include multiple joints, complicated anchoring, higher placement costs, more difficult repair
procedures, the need to maintain expensive inventories of special or scarce items, a certain inflexibility
in structural design, and higher fuel requirements
during manufacture.
1.6.2 Plastics and ramming mixes - Plastic refractories and ramming mixes are refractories which are
tamped or rammed in place and are used for monolithic construction, for repair purposes, and for
molding special shapes. These materials find extensive use in industry. They usually employ a clay, alumina, magnesite, chrome, silicon carbide, or graphite
base, and are blended with a binder. Heat setting
mixes are likely to contain fireclay or phosphoric
acid as a binder. Air or cold-setting mixes generally
contain fireclay and sodium silicate as the binder.
Compared to ramming mixes, plastic refractories
have higher moisture contents and therefore, higher
plasticity.
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TABLE 2.1a - Characteristics of normal weight refractory concretes
TABULAR A1203
HIGH PURITY BINDER
HIGH
STRENGTH
PRODUCT
DESCRIPTION
Recommended Service
Temperature max., Deg. F
ASTM Class (C-401)
Water Required for Mixinq,
Percent by Weight
Material Required (1)
lbs. per cu. ft., lbs. per bag
_
Method of Application
(2)
Bulk Density,
220 F
1000 F
Heated toI
temperature of:
1500 F
then cooled
2000 F
pcf
2550 F
2732 F
3000 F
Total Linear Change % Heated
to temp. of: then cooled
(Note: Linear change
figures are "TOTAL"
in all cases and include
percent of drying
shrinkage occurring
in conversion from
wet "as cast"
to "as dried" state)
220
1000
1500
2000
2550
2732
3000
F
F
F
F
F
F
F
Cold Crushing Strength,
psi
Heated to
temperature of:
then cooled
220
1000
1500
2000
2550
2732
3000
F
F
F
F
F
F
F
Thermal Conductivity
Btu/in/hr-sq.ft.-Deq F
at Mean
Temperature of:
Chemical Analysis percent
S102
A1 2 0 3 , T 1 0 2
Fe 2 03 , Fe0
500
1000
1500
2000
F
F
F
F
Ca0, Mg0
Alkalies
Ignition Loss
3000E
3400
G
3000
8-11
8-12
160-165
C -T-S
165
159
161
161
165
160
165
0.0
-0.1
-0.1
-0.1
-0.4
-0.7
178
169
174
174
176
169
167
to -0.5
to -0.5
to -0.5
to -0.3
to -1.3
to -1.4
E
HIGH
STRENGTH
2800 F GUN
2800
2800
10-12
140-145
139
138
138
137
139
138
136
-0.1
-0.1
-0.2
-0.2
-0.5
-0.2
to
to
to
to
to
to
147
146
146
146
150
146
149
-0.6
-0.6
-0.6
-0.7
-1.1
+0.3
+0.1 to +0.7
1600
1820
1450
930
1280
1290
750
5180
8170
7280
3036
6180
4330
3320
450
350
290
340
820
1260
1685
1030
1070
950
980
3280
4280
5870
- 840
- 570
- 580
- 590
- 2050
- 2400
- 4620
- 2160
- 2250
- 2250
- 2050
- 4640
- 5620
-10000
131
128
128
130
123
123
130
127
126
127
127
128
-0.l to -0.4
-0.2 to -0.3
-0.1 to -0.5
-0.3 to -0.7
-0.8 to +1.3
-0.5 to +1.0
-0.2
-0.2
-0.1
-0.1
-0.5
-0.8
to
to
to
to
to
to
10-13
125-130
136
133
133
133
130
135
135
129
129
127
-0.6
-0.5
-0.5
-0.9
+0.2
+0.8
0.2
02
0.2
0.1
to
to
to
to
260 - 2000
945 - 1240
020 - 1865
- 1385
1420
1490
1110
1330
3200
5280
- 3780
- 2950
- 2770
- 2920
- 7930
-12100
1190
1400
1690
1160
4250
7140
- 2620
- 3000
- 3340
- 3105
-11390
-13175
510 -
7910
810 - 6480
410 - 7110
620 - 5375
137-142
126-130
C
445
175
145
145
1245
2095
4280
645
540
560
3021
to
to
to
to
to
to
-0.4
-0.4
-0.4
-0.5
+2.2
+2.4
745
310
295
270
- 2605
- 2930
112
108
108
108
111
-0.1
-0. 1
-0.2
-0.4
-1.2
310
200
150
130
820
121
117
114
115
114
to
to
to
to
to
-0.5
-0.6
-0.5
-0.8
+0.3
126
120
120
120
-0.1
-0.2
-0.1
-0.1
- 520
- 270
- 200
240
- 1780
820
300
300
300
- 1570
- 1030
- 840
- 850
- 5490
2410
470
530
450
to
to
to
to
133
125
122
123
131
126
124
124
-0.5
-0.5
-0.7
-0.9
-0.1
-0.3
-0.4
-0.3
- 1170
590
- 560
- 460
975
535
400
405
C
133
129
129
128
to
to
to
to
-0.5
-0.6
-0.6
-0.5
- 1030
710
560
- 465
-
3145
1400
1260
915
3765
990
685
630
640
3200
-
3800
2210
2090
2070
3450
1800
1775
1480
-
3870
229
2325
2225
C-T-S-E
144
146
138
140
133
140
141
138
0.0 to
0.0 to
-0.1 to
-0.1 to
/
’
i
i
-0.3
-0.3
-0.5
+1.7
810 - 1015
300 - 415
310 - 395
520 - 910
-
2150 --450 -050 -470 --
3580
1590
1340
2280
124
122
121
120
121
-0.2
-0.4
-0.4
-0.5
-0.1
1020
395
370
385
370
131
124
122
121
123
to
to
to
to
to
-0.4
-0.5
-0.5
-0.7
+0.5
- 1250
- 440
- 570
- 605
- 2390
3075 299552425 1500 3735 -
5470
3795
2845
2105
6970
-
9.87
9.46
9.36
9.57
6.47
6.15
5.80
5.72
5.35
5.35
5.40
5.65
4.60
5.00
5.40
5.80
5.24
5.10
5.10
5.18
0.03
93.65
29.73
65.16
47.58
48.31
47.31
46.73
32.06
59.23
0.27
5.52
1.15
2.48
1.47
1.47
1.37
3.25
0.11
0.30
0.39
0.66
0.82
0.15
0.84
0.47
0.91
6.89
0.59
-
46.70
3.05
6.09
0.69
Trace
All measurements except thermal conductivity
taken at room temperature.
SI conversion factors
Deg F = 1.8 C + 32
1 pcf = 16. 02 kg/m3
1 lb = 0.4536 kg
1 psi = 0.006895 MPa
1 Btu-in./hr-sq ft - deg F
14-16
118-120
120-124
-0.3
-0.3
-0.2
-0.2
+1.7
+1.3
- 840
- 680
- 840
- 970
- 3030
- 3740
3.5-11
C-T-S-E
-0.7
-0.6
-0.6
-0.6
400
320
530
500
1300
2290
11-14
C-T-E
136
144
133
133
133
132
138
2600
c
2600
C
108-114
134
132
130
130
124
128
- 800
- 650
- 680
- 780
- 2450
- 2260
14.0-15.5
LOW IRON
HIGH
STR EN GTH
2350
B
C-E
143
134
134
135
360
370
230
390
1000
1110
15-21
COARSE
HIGH
STRENGTH
2600 F
COARSE
HIGH
STR EN G TH
2350 F
125-131
C -T-S
S
138
134
132
135
128
127
STANDARD
HIGH
STRENGTH
2500
C
10-12.5
129-133
C-T
2800 F
STEEL MILL
2400
B
(3 )
129-133
C _T_S_E
EROSION/
ABRASION
RESISTANT
-
-
-0.6 to -1.1
- 2590
- 2320
- 2120
- 1400
- 2615
- 2707
- 1280
- 10230
- 9160
- 9395
-10000
- 11000
- 10115
- 5325
GENERAL
PURPOSE
2800F
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4.10
4.48
4.85
5.19
4.48
4.85
5.30
5.73
7.25
7.40
7.65
7.85
4.60
5.00
5.40
5.80
44.35
38.68
4.78
34.64
4.18
46.08
40.03
4.22
9.03
1.22
1.14
11.31
0.74
0.11
MANUAL OF CONCRETE PRACTICE
547R-4
TABLE 2.1b- Characteristics of lightweight insulating refractory concretes
HIGH
ALUMINA
LOW IRON
COMMERCIAL
PRODUCT
DESCRIPTION
Recommended Service
Temp. max., Deg. F
ASTM Class (C 401)
Water Required for Mixing,
Percent by Weight
Materials Required,
lbs. per cu. ft.
Method of Application*
Bulk Density,
220 F
lbs. per cu. ft.,
Heated to
1500 F
Temp. of:
2000 F
then cooled
2250 F
2550 F
2910 F
Total Linear
Percent,
Heated to
Temp. of:
then cooled
Change,
220
1500
2000
2250
2550
2910
F
F
F
F
F
F
3000
-
GENERAL
PURPOSE
-
LIGHTWEIGHT
1800 F
LIGHTWEIGHT
2250 F
1600
**1800
2250
2500
VERMICULITE
BASE VERY
LIGHTWEIGHT
Q
Q
24-27.5
38-47
40-47
46-55
176
87-92
80-85
48-50
46-48
24
C-T-S-E
C-S-E
51-53
47-48
48-49
47-49
48-54
47-54
46-52
C-S-E
C-T-S-E
92-96
90-91
89-92
90-91
86-92
88-93
-0.2
-0.4
-0.6
-0.4
-0.6
-0.2
to
to
to
to
to
to
86-90
80-83
80-84
80-82
Special
N
P&O
_
C-T-E
21-25
20-25
-0.3
-0.7
-0.8
-0.6
+0.8
+0.2
-0.2
-0.4
-0.3
-0.2
to
to
to
to
-0.6
-0.8
-0.8
-1.4
-0.3
-0.3
-0.3
-0.4
to
to
to
to
-0.4
-0.9
-1.1
-1.4
-0.1 to -0.4
-1.7 to -2.0
-0.8 to -1.3
Modulus of Rupture,
220 F
psi
Heated to
1500 F
Temp. of:
2000 F
then cooled
2250 F
2550 F
2910 F
265-360
205-225
280-315
625-640
950-955
1755-1835
190-350
140-230
120-250
155-315
100-150
70-90
75-115
160-170
200-420
105-140
100-205
Cold Crushing Strength,
220 F
psi
Heated to
1500 F
Temp. of:
2000 F
then cooled
2250 F
2550 F
2910 F
615-685
550-610
450-545
800-880
265-1415
3535-4100
560-1040
830-710
460-800
500-810
290-450
160-290
130-220
270-330
390-750
295-405
200-285
37.38
34.79
6.63
17.68
43.17
17.68
3.11
31.34
2.05
2.40
30-70
20-80
I
Chemical Analysis, percent
Si0 2
A1 2 0 3 , Ti0 2
Fe 2 0 3 , Fe0
CaO, MgO
Alkalies
Ignition Loss
36.52
54.63
1.38
4.56
1.11
1.90
40.08
38.13
5.31
13.53
1.66
1.20
1.88
1.45
2.58
2.86
3.14
3.42
1.66
1.98
2.31
2.63
SO3
Thermal Conductivity (k),
Btu/Hr./Sq. Ft./F./In,
At Mean
Temp. of:
500 F
1000 F
1500 F
2000 F
*C-Casting;
T-Troweling;
2.88
3.19
3.50
3.82
S-Shotcretinq; E-Extruding.
1.40
1.71
2.01
0.87
1.15
1.43
All measurements except thermal conductivity taken
at room temperature.
**2000 F (For back-up material)
SI conversion factors
DegF = 1.8 C + 32
1 pcf = 16.02 kg/m'
1 lb = 0.4536 kg
1 psi = 0.006895 MPa
1 Btu-in./hr-sq ft - deg F
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REFRACTORY CONCRETE
Plastics are generally placed without use of forms.
With the exception of some specialized tabular alumina castables, plastics have a somewhat higher service limit than castable refractories. Their main disadvantages are greater shrinkage and crack
development. Except for phosphate bonded materials cured above 600 F (315 C), plastics generally
have lower cold and hot strengths than refractory
concretes. In addition, plastics tend to have a relatively low strength zone on the cool side of the lining.
Ramming mixes usually have higher density and
less shrinkage than plastic refractories. With their
low water content, they must be forced into place
and require strong well-braced forms. Some of the
dryer medium grind ramming mixes are suitable for
gunning, and are used for patching and maintenance
materials.
1.6.4 Gunning mixes other than refractory concretes12,13 - As used in this section, the term “gunning mixes” does not refer to refractory concrete
and should not be confused with gunned refractory
materials which produce refractory concrete. Gunning mixes are mixtures of non-hydraulic setting ingredients which are installed hot or cold, usually by
the shotcrete method.
Gunning mixes generally have low rebound loss,
are predominately used for patching or resurfacing
brick or other refractories, have a strong internal
bond, and exhibit excellent adhesion or bond to the
existing refractory lining. They find extensive use in
basic oxygen, electric arc and open hearth furnaces,
among other applications.
Chapter 2 - Criteria for refractory concrete
selection
2.1 Introduction
Refractory concrete is usually made with high alumina cement. It is not generally used as a structural
material and its primary purpose is as a protective
lining for steel, concrete or brick structures. It is
considered a consumable material requiring replacement after an appropriate service life.
Some of the destructive forces that refractory concretes withstand are abrasion, erosion, physical
abuse, high temperatures, thermal shock, hot and
molten metals, clinker, slag, alkalies, mild acid or
acid fumes, expansion, contraction, carbon monoxide,
and flame impingement.
Refractory concretes are categorized as either normal weight or lightweight. The former are also referred to as “heavy refractory concretes” and the
latter are often called “insulating refractory concretes.” Table 2.la shows the characteristics of a
typical range of normal weight refractory concretes;
Table 2.lb shows the characteristics of lightweight
refractory concretes.
2.2 Castables and field mixes
Refractory concretes are usually prepared at the job
site from materials supplied to the user in either of
two ways: (1) prepackaged so-called “refractory castables;” (2) field mixes.
547R-5
Refractory castables are plant packaged mixes
composed of ingredients that are weighed, blended
and usually bagged in convenient sizes for shipping
and handling. They require only mixing with water
on the job to produce refractory concrete. Field
mixes are made from material components which are
proportioned and mixed on the site just prior to the
addition of water.
2.5 Load bearing considerations
Most application designs of refractory concrete consider that there is a thermal gradient through the
material with heat conducted from the hot face to
the cold face. A cross section of the refractory will
usually have a layer at the hot face that has a ceramic bond, an intermediate section with a weaker
combination of ceramic and a partial hydraulic bond,
and a cold face section that retains most of its hydraulic bond. Refractory concrete linings in this type
of situation are usually well anchored and self-supporting.
Castables containing high proportions of coarse aggregates produce refractory concrete with good load
bearing characteristics. Certain types of refractory
concrete tend to have low strengths in the intermediate temperature zones [1500-2250 F (820-1230 C)]
and should not be subjected to excessive mechanical
abuse or dead load. Generally, lightweight concretes
designed for insulating purposes should not be subjected to impact, heavy loads, abrasion, erosion or
other physical abuse. Normally, both the strength
and the resistance to destructive forces decline as
the bulk density of the refractory concrete decreases.
There are a number of special refractory castables
available which have better than average load-bearing capabilities and withstand abrasion or erosion
much better than the standard types.
2.7 Corrosion influences
High temperature in combination with a corrosive
environment can have a serious deleterious effect on
both the concrete and the backup steel structure.
Generally, the higher density, higher purity refractory concretes have better corrosion resistance than
the lower density, lower purity types.
Alkalies can effect the service life of refractory
concretes. The furnace charge can give off both alkalies (K2O) and the fuel sulfur compounds (SO2) as vapors. These can penetrate into the pores of the refractory concrete and react; their reaction products
cool, solidify, and expand, sometimes causing the hot
face of the refractory to peel or shear away.
In certain applications, the refractory concrete is
subjected to highly reducing conditions. Low-iron
refractory concretes should be used for this type of
application.
2.10 Abrasion and erosion resistance
Abrasion and erosion begin with the wearing away
of the weakest matrix constituent, binder, leaving
the coarse or hard aggregate to eventually fall away.
A hard aggregate, a high modulus of rupture, and
high compressive strength at the hot face are necessary for good abrasion and erosion resistance in refractory concretes.
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MANUAL OF CONCRETE PRACTIC
IE
547R-6
Chapter 3 - Constituent ingredients
3.2 Binders
The binders principally used in refractory concretes
are calcium aluminate cements. However, ASTMtype portland cements can be used in some refractory applications up to an approximate maximum of
2000 F (1090 C) with selected aggregates, if special
precautions are taken to ensure a sound refractory
concrete. Cyclic heating and cooling tends to disrupt
portland cement concretes and adding a fine siliceous material to react with the calcium hydroxide,
formed during hydration, is helpful in alleviating the
problem.
Calcium aluminate (high alumina) cements are
commercially available hydraulic binders. They are
TABLE 3.3a- Maximum service temperature of selected aggregates mixed with calcium aluminate cements
under optimum conditions
Maximum
temperature
Aggregate
Alumina, tabular
Dolomitic limestone
(gravel)
Fireclay, expanded
Fireclay brick,
crushed
Flint fireclay,
calcined
Kaolin, calcined
Remarks
_
Refractory, abrasion
resistant
Abrasion and corrosion
resistant
Insulating, abrasion and
corrosion resistant
Abrasion and corrosion
resistant
Mullite
Perlite
Sand
Slag, blast furnace
(air cooled)
Slag, blast furnace
(granulated)
Trap rock, diabase
Vermiculite
Deg C
Deg F
1870
3400
500
930
1640
1600
1650
Abrasion and corrosion
resistant
Insulating
(Silica content less
than 90 percent not recommended)
Abrasion and corrosion
resistant
Abrasion resistant
Insulating, abrasion and
corrosion resistant
(Basic Igneous RockMinimal Quartz) Abrasion
and corrosion resistant
Insulating
TABLE 3.3b- Aggregate grading
Maximum size aggregate (except for gun placement)
Maximum size aggregate for normal gun placement
Maximum size insulating crushed firebrick
Maximum size expanded shales and clays
Maximum size, with the above exceptions, should
not be greater than 20-25 percent of the
concrete minimum dimension.
Aggregate of V2 in. (1.27 cm) or larger size:
Retained on No. 8 Sieve = 50 percent
Passing No. 100 Sieve
= 10-15 percent
Aggregate of less than l/2 in. (1.27 cm) maximum size:
Retained on No. 50 Sieve = 75 percent
Passing No. 100 Sieve
= 10-15 percent
*In special cases larger sizes have been used successfully.
1 l/z in. (3.81 cm)
I/4 in.* (0.64 cm)
1 in. (2.54 cm)
‘12 in. (1.27 cm)
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1650
3000
1650
1340
300
3000
2450
570
540
1000
1200
2190
1000
1830
1100
2010
specifically designed for use in monolithic refractory
concrete construction. They are generally classified
under three basic categories: Low Purity, Intermediate Purity, and High Purity. This is a relative
classification scheme and is based primarily on the
total iron content of the cement.
Binder selection is primarily based on the service
temperature desired for the refractory concrete.
Maximum service temperatures are extended with
increasing Al2O3 and decreasing iron contents.
Lower iron content binders are also beneficial in reducing carbon monoxide (CO) disintegration of concrete (Section 2.7).
3.3 Aggregates
The maximum service temperatures of selected ag
gregates mixed with appropriate calcium aluminate
cements are listed in Table 3.3a. These maximum
temperatures are based on optimum conditions of
binder and aggregate. Thermal properties of aggregates, such as volume change (expansion, shrinkage
or crystalline inversion) and decomposition, can affect these maximum temperatures, along with the
chemical composition of both aggregate and binder
and the reactivity between these mix constituents.
Temperature stability of the aggregate determines
the maximum service conditions below approximately 2400 F (1320 C). Therefore, any type of calcium aluminate cement can be used at these temperatures. For conditions above 2400 F (1320 C), binder
purity also becomes a design factor. Generally, the
low purity binder can be used with proper aggregates up to 2700 F (1480 C), intermediate purity to
3000 F (1650 C) and high purity to 3400 F (1870 C).
Aggregate gradation is an important consideration
in designing refractory concrete. Table 3.3b provides
suggested guidelines for nominal maximum size and
grading of refractory aggregates.
For refractory mix designs a 1:3 or 1:4 by bulk
volume dry basis cement: aggregate mix is generally
used to satisfy typical applications. In certain cases
the ratio may change from as low as 1:2 to as high
as 1:6, with the latter being used for lightweight
concretes. Within the range of normal usage, increasing the cement content will provide higher
strength development. However, increased cement
content may also result in increased shrinkage. A
higher aggregate content will increase insulating or
refractory properties, depending on the type of aggregate selected for the mix. Combinations of various aggregates can be made to secure the desirable
properties of each.
3.3.1 Lightweight aggregates - Perlite, expanded
shale, expanded fireclay, and bubble alumina are the
more commonly used lightweight aggregate for commercial insulating concretes.
3.4 Effects of extraneous materials
Extraneous materials commonly associated with
portland cements, either as admixtures or as contaminants from equipment or surrounding conditions, may behave differently when used with calcium aluminate cement mixes. Many castables
contain proprietary additions which may be adversely affected by field admixtures.
Chapter 4 - Composition and proportioning
4.1 Introduction
In designing mixes, refractory concretes are not only
defined by density but also by operating temperature. Refractory concretes fall into three subclasses
based on service temperature ranges. The first sub
class is “ceramically-bonded concrete,” defined as
concrete in which the cement binder and the fine aggregate particles react thermochemically to form a
bond. This bond is referred to as the ceramic bond
and may occur at temperatures as low as 1650 F
(900 C). The second subclass is “heat resistant concrete,” defined as concrete in which the cement has
dehydrated but has not formed a ceramic bond. The
third category is concrete which still has some hydraulic bond when heated but performs satisfactorily
under cyclic conditions.
4.3 Field mixes
4.3.1 Ceramically bonded concrete - The ceramic
bond can be formed at temperatures as low as
1650 F (900 C). To aid formation of the ceramic bond,
concretes operating above this temperature should
have 10-15 percent of the aggregate passing a No.
100 sieve.
Most field insulating concretes are made with presoaked aggregate. Since the specified proportions
are based on dry materials, the actual batch mixes
may require correction.
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MANUAL OF CONCRETE PRACTICE
4.3.2 Heat resistant concrete - This concrete is generally used in the range 930 F (500 C) to 1650 F (900
C). Many coarse aggregates are unsuitable for use as
refractory aggregates because they contain quartz,
which has a large volume change at 1065 F (575 C ) .
4.4 Water content
A majority of the aggregates used in refractory and
heat resistant concretes have high water absorbency. For this reason specific water/cement ratios
are generally not used in developing mix designs. Instead, water requirements are arrived at by periodically conducting a “ball-in-hand” test (ASTM C860).
This test is illustrated in Fig. 4.4. The correct water
content is that which will provide a placeable, rather
than a pourable, mix. When using well-soaked aggregates, it may be necessary to add little or no water
at the mixer. It is sometimes found that a mixture
which appears fairly stiff when discharged from the
mixer will yield excess water as the concrete is
placed.
Chapter 5 - Installation
5.1 Introduction
Regardless of the quality of the refractory cement,
aggregate, and/or castable, and regardless of the research devoted to the selection of correct materials
for a specific application, maximum service life will
not be obtained unless the refractory concrete is installed properly.
The most frequently used methods of installing refractory concretes are casting and shotcreting.
5.2 Casting
5.2.1 Mixing - Proper mixing of castables is of primary importance. Care should be taken to avoid
mixing previously hydrated material into fresh refractory concrete. Mixers, tools and transporting
equipment used previously with portland or other
type cement concretes must be cleaned prior to mix-
Deg c
60
80
h
0
Cured 24h
0 Drled 230 F - 24h (110 C)
0 Dried, Fast Fired 2012 F (11 00 C) (ASTM 268-70)
0
1
32
I
1
68
I
24h CURE
I
104
I
Temperature DEG F
>90% R . H .
I
140
I
1
176
Deg F
ing. Remains of lime, plaster, or portland cement
will induce flash set and will lower refractoriness.
Generally, paddle mixers are used for small to medium size jobs involving calcium aluminate cement
concretes. In a paddle mixer, normal weight refractory concretes should be mixed for about 2 to 4 min.
Refractory concretes of less than 60 lbs/cu ft (960
kg/m 3) density should be mixed no longer than necessary to insure thorough wetting. This precaution
is necessary because the lightweight aggregate may
break-up during the mixing action and reduce the effectiveness of the concrete as a heat insulator. Refractory concretes in the 75 to 90 lb/cu ft (1200-1400
kg/m3) range should be mixed for approximately 2
to 5 min. Because working time may be short, all
castables should be cast immediately after mixing.
5.2.3 Mixing and curing temperature - Mixing and
curing temperature can affect the type of hydrates
formed in set concrete. A castable develops its hydraulic bond because of chemical reactions between
the calcium aluminate cement and water. To get the
maximum benefits from these chemical reactions, it
is preferable to form the stable C3AH6 during the
initial curing period. The relative amount of C3AH6
formed versus metastable CAH10 and C2AH8 can be
directly related to the temperature at which the
chemical reactions take place.
Recent work illustrates the significant impact of
mixing and curing temperatures on strength properties. Fig. 5.2.3 34 shows the flexural strength of a
tabular alumina, high purity cement castable plotted
as a function of mixing and curing temperatures. It
can be seen that the strength developed after mixing and curing at 85 F (30 C) and drying at 230 F
(110 C) is nearly twice that of the concrete mixed
and cured at 60 F (15 C) and dried at 230 F.
Explosive spalling of high purity cement concretes
can occur when casting and curing temperatures below 70 F (21 C) are used. Thus, a refractory concrete
containing a high purity cement should be cast or
cured above 70 F (21 C). This spalling phenomenon is
less likely to occur with low or intermediate purity
cement binders.
5.2.4 Transporting - Other than shotcreting and
pumping, the techniques for transporting refractory
concretes are similar to those used for portland cement concrete. Some calcium aluminate cement binders have a shorter placing time available.
5.3 Shotcreting
Shotcreting of refractory concrete is particularly effective where, (1) forms are impractical, (2) access is
difficult, (3) thin layers and/or variable thicknesses
are required, or (4) normal casting techniques cannot
be employed.
5.3.1 Equipment - There are two basic types of
shotcrete methods: dry-mix and wet-mix. The drymix method conveys the aggregate and binder pneumatically to the nozzle in an essentially dry state
where water is added in a spray. The wet-mix
method conveys the aggregate, binder and a predetermined amount of water, either pneumatically or
under pressure, to the nozzle where compressed air
is used to increase the velocity of impact. The dry
method, though it produces greater rebound, is the
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Fig. 5.2.3 - Flexural strength of tabular alumina,
high purity cement castable (ASTM C268)
REFRACTORY CONCRETE
most suitable and recommended technique for shotcreting refractory concrete. An exception is the recommended use of a wet-mix gun for hot patching.
5.3.2 Installation - To ensure a uniform covering
free of laminations and with minimum rebound, the
nozzleman should move the nozzle in a small circular
orbit and where possible, maintain the flow from a 34 ft (0.9-1.2 m) distance at right angles to the receiving surface.35
5 The shotcrete should be left in its asplaced state. If for some reason scraping or finishing
is required, the absolute minimum should be done so
as to avoid breaking the bond or creating surface
cracks. Shotcreting of refractory concretes can increase the in-place density and result in other
changes in the physical properties. This effect is
more pronounced in lower density castables, and
must be taken into account when specifying thicknesses and material quantities for insulating applications. The user should be aware that certain aspects of portland cement concrete shotcrete practice
do not apply to refractory shotcrete.
5.4 Pumping and extruding
Certain refractory concretes can be installed with
positive displacement pumps in conjunction with
rigid or flexible pipelines. The design of the mix is
critical, and special attention must be given to the
absorptive characteristics and sizing of the aggregate.
Some applicators use the term “extruding” to describe the conveying and placing of refractory concrete at velocities that are very low or close to zero
on exit from the pipeline. When extruding, mixing of
the refractory castable and water can be done internally or externally depending on type of extruding
device.
5.5 Pneumatic gun casting
Pneumatic gun casting, or gun casting, is a relatively new technique for casting concrete and is finding increased uses for refractory concrete. Conventional dry shotcrete equipment and procedures
are utilized with the exception that an energy reducing device is attached to the nozzle body in place of
the standard shotcrete nozzle tip.
5.8 Finishing
Surface finishing or rubbing of refractory concretes
should be kept at a minimum. Use of a steel trowel
should be avoided, and the final surface can be
lightly screeded to grade but should not be worked
in any manner.
Chapter 6 - Curing, drying, firing8,16,17,18
6.1 Introduction
Refractory concrete should be properly cured for at
least the first 24 hr. Following this curing it should
be dried at 220 F (105 C), and then heated slowly until the combined water has been removed before
heating at a more rapid rate.
6.2 Bond mechanisms
Calcium aluminate cements have anhydrous mineral
phases which react with water to form alumina gel
547R-9
CA
+
)
>
F (35 C)
I\
Reaction Products of CA
a)
CA
CA2
+
95
H 10 + A H 3
H
Reaction
Products
of CA 2
The cement chemistry abbreviations:
C = CaO
A = Al2O3
H = H2O
Fig. 6.2 - Hydration reaction products of calcium
aluminates 195
and crystalline compounds which function as a
binder for the concrete. 20,21 The hydration of these
cements (Fig. 6.2) is exothermic. The rate of the
chemical reaction is relatively fast.22 For all practical
purposes, calcium aluminate concretes will develop
full strength within 24 hr of mixing.
The total drying shrinkage of calcium aluminate
cement concretes in air, is comparable to that of
portland cement concrete. In order to provide for
complete hydration, and to control drying shrinkage,
special attention must be given to the curing of refractory concretes.
6.3 Curing
The temperature of hardening calcium cement rises
rapidly. If the exposed surfaces are not kept damp,
the cement on the surface may dry out before it can
be properly hydrated. The application of curing water prevents the surface from becoming dry and furnishes water for hydration. In addition, the evaporation has a cooling effect which helps to dissipate
the heat of hydration.
Conversion of the high alumina cement hydrates,
which occurs if the cement is allowed to develop excessive heat, does not present the same problem in
refractory concretes that it does in high alumina cement concretes used for structural purposes. It has
been shown that if refractory concrete is fully converted by allowing it to harden in hot water and
then heated to 2500 F (1370 C), the fired strength is
equal to that obtained for well cured concrete. When
possible, however, refractory concrete should be
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MANUAL OF CONCRETE PRACTICE
kept cool by appropriate curing under 210 F (99 C)
for two reasons:
l The entire refractory concrete structure does not
usually reach the maximum service temperature,
and the higher cold strengths obtained by good curing may be useful in the cooler portions of the refractory.
l If the temperature within the concrete reaches a
high level during hardening, the thermal stresses
produced during cooling may be sufficient to cause
cracking.
Curing should start as soon as the surface is firm.
Under normal atmospheric temperatures, this will
occur within 4 to 10 hr after mixing the concrete.
The concrete should be kept moist for 24 hr by covering with wet burlap, by fine spraying or by using
a curing membrane. Alternate wetting and drying
can be detrimental to the cure of the concrete.
When using a curing membrane, the compound
should contain a resin and not a wax base, and
should be applied to the surface as soon as possible
after placing and screeding. The reason for discouraging the use of wax is that a hot surface will
melt the wax, causing it to be absorbed into the concrete, breaking the membrane.
6.4 Drying
The large amount of free water in the refractory
concrete necessitates a drying period before exposure to operating temperatures. Otherwise, the formation of steam may lead to explosive spalling during firing.
6.5 Firing
Following drying of the refractory concrete, the first
heat-up should be at a reasonably slow rate. A typical firing schedule, for a 9 in. (22.9 cm) thick lining,
consists of applying a slow heat by gradually bringing the temperature up to 220 F (105 C), and holding
for at least 6 hr. The temperature is then raised at a
rate of 50-100 F (10-40 C) per hr up to 1000 F
(540 C) and again held for at least 6 hr. The first
hold is to allow remaining free water to evaporate,
and the second hold is to eliminate the combined water without danger of spalling.
Beyond 1900 F (540 C), the temperature of the refractory concrete can be raised more rapidly. Calcining of the green concrete into a refractory structure
will take place between 1600 F (820 C) and 2500 F
(1370 C). Wall thickness and mix variations may require somewhat different rates of heating, but the
hold temperatures should remain at least 6 hr.
If steam is observed during heat-up, the temperature should be held until steam is no longer visible.
Cbapter 7 - Properties of Normal Weight
Refractory Concretes
7.1 Introduction
There are various physical properties and tests
which are standard in the refractory industry and
these are usually provided in the material specifications. Table 2.la is an example of typical data for
normal weight refractory concrete.
7.2 Maximum service temperature
The recommended maximum service temperature
will normally assume that the castable will be used
in a clean, oxidizing atmosphere, such as is present
when firing with natural gas. The maximum service
temperature is usually determined as the point
above which excessive shrinkage will take place. It
is about 150-200 F (70-90 C) below the actual softening point of the concrete.
If a fuel has solid impurities, such as in coals or
heavy fuel oils, or if the solids or dust in the process
contact the refractory, the maximum permissible
service temperature will usually be considerably reduced. Solid impurities can react with the concrete
and produce compounds of lower melting point
which melt and run. This is generally referred to as
slagging. The lower softening point thus represents
a limit for the operating temperature. Slag forming
reactions usually do not occur below about 2500 F
(1320 C) except in the presence of alkalies where reactions can occur in the 1900-2000 F (1040-1090 C)
range.
A reducing atmosphere can lower the melting
point and hence the maximum operating temperature by 100-200 F (40-90 C) if sufficient quantities of
iron compounds are present in the refractory.3
7.4 Shrinkage and expansion
In discussing shrinkage and expansion of a refractory concrete, it is important to define the distinction between the independent effects of permanent shrinkage or expansion and reversible
thermal expansion. Permanent change is determined
by measuring a specimen at room temperature, heating it to a specified temperature, cooling to room
temperature, and remeasuring it. The difference between the two measurements is the permanent
change, which occurs during the first heating cycle.
Subsequent heating to the same or lower temperature will have little or no additional effect on the
permanent change. Heating to a higher temperature
may cause some additional permanent change.
Reversible thermal expansion of a specimen which
has been previously stabilized against further permanent change, is the dimensional change as a specimen is heated. Upon cooling, the specimen contracts
to its original size.
At any given temperature, the net dimensional
change of a refractory concrete is the sum of the reversible expansion and the permanent shrinkage corresponding to the highest temperature to which the
castable has been heated.
7.4.1 Permanent shrinkage and expansion - The initial heating of a refractory concrete usually causes
shrinkage. At higher temperatures permanent expansion can occur. This effect, which varies with the
maximum temperature attained, must be considered
with reversible thermal expansion when calculating
the net expansion (or shrinkage) at service temperature. The ASTM rating of castables is based on no
more than 1.5 percent permanent linear shrinkage
occurring at prescribed temperatures (ASTM C64
and C401). Most normal weight refractory concretes
will have less than 0.5 percent permanent linear
shrinkage after firing at 2000 F (1090 C).
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REFRACTORY CONCRETE
The permanent change appears as cracks after the
first firing. These cracks will generally be about 2-3
ft (0.6-0.9 m) on centers, and may vary, depending
on the concrete thickness and the anchor spacing.
Usually, the width of the cracks at room temperature is partly dependent on the permanent shrinkage. Normally, the cracks will be tightly closed at
operating temperatures. Such cracking, which may
start during drying, is to be expected and will not
adversely affect the service performance of the refractory.
7.4.2 Reversible thermal expansion - The reversible
thermal expansion of most refractory concretes is
approximately 3 x 10-6 in./in./F (5 x 10-6 cm/cm/CL
However, the expansion coefficient may be as high
as 4 x 10-6 in./in./F (7 x 10-6 cm/cm/C) for high alumina concretes and to 5 x 10-6 in./in. /F (9 x 10-6
cm/cm/C) for chrome castables. Fig. 7.4.2 shows
typical length changes due to permanent shrinkage
and reversible expansion.
7.5 Strength
7.5.1 Modulus of rupture - Modulus of rupture is
measured by means of a flexure test and is considered as a measure of tensile strength (ASTM C268).
The extreme fiber tensile strength calculated from
this test will be 50 to 100 percent higher than the
tensile strength derived from a straight pull test.
Typical modulus of rupture values are 300 to 1500
psi (2.07-10.4 MPa). Shotcreting can increase modulus of rupture values by up to 50 percent.
Fig. 7.5 shows typical trends of modulus of rupture strength versus temperature.
7.5.2 Cold compressive strength (crushing) - The
test is ordinarily run on 9 x 41/2 x 21/2 in. (22.9 x 11.4
x 6.4 cm) specimens 9 in. (22.9 cm) straights in brick
terminology with pressure applied to the smallest.
surface (ASTM C133). Failure in this test is generally due to shear.
Crushing strengths vary from 1000 to 8000 psi (6.9
to 55.2 MPa). Typically, compressive strengths are
three to four times greater than modulus of rupture
values.
7.6 Thermal conductivity
For normal weight refractory concretes, thermal
conductivity tends to vary with density. Typical values (k factors) range from about 5 Btu-in./sq ft -hr-F
(72 W -cm/m 2-C) for 120 pcf (1920 kg/m 3) material to
about 10 Btu-in./sq ft -hr -F (144 W-cm/m2-C) for
160 pcf (2560 kg/m 3 ) material. There is usually an increase in thermal conductivity with temperature.
547-11
Deg C
4;.
_____
260
540
820
1090
|
|
|
|
INITIAL COOLING AND
SUBSEQUENT CYCLING
-0.2
00
500
1000
1500
2000
Temperature Deg F
Fig. 7.4.2 - Net thermal expansion of a typical refractory concrete
100 pcf (320 to 1600 kg/m3) and can be formulated to
have high maximum service temperatures and relatively high strengths. This often allows the use of
these materials as single component, exposed service
linings.
Table 2.lb shows physical property values for typical lightweight refractory concretes.
8.4 Shrinkage and expansion
The reversible thermal expansion of lightweight concretes will vary from 2.5 x 10-6 to 3.5 x 1O -6 in./in./F
(4.5 x l0 -6cm/cm/C) Because of compensating permanent shrinkage, the thermal expansion of lightweight refractory concrete is normally insignificant
and is usually ignored in the design of lightweight
refractory concrete systems.
8.5 Strength
Strengths of lightweight refractory concrete are
measured by both a modulus of rupture and a crushing test.
8.5.1 Modulus of rupture - Typical values range
from approximately 50 (0.3 MPa) to 400 psi (2.8
MPa).
100
260
540
820
500
1000
1500
1090
Deg C
1370
-1” ---I----w
7.10 Specific beat
The specific heat of a refractory concrete increases
with temperature from about 0.20 Btu/lb/F (837 J/
kg-C) at 100 F (40 C) to about 0.29 Btu/lb/F (1210 J/
kg-C) at 2500 F (1370 C). This can vary plus or minus
0.025 units, depending on the aggregate.
Chapter 8 - Properties of lightweight
refractory concretes
8.1 Introduction
Refractory concretes are widely used as insulating
materials. They have a wide range of densities (20 to
212
2000
2500
Temperature Deg F
Fig. 7.5 - Effect of temperature on modulus of rupture
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MANUAL OF CONCRETE PRACTICE
TABLE 8.5.1 - Hot and cold modulus of rupture of a 2800F (1538C) lightweight refractory
concrete containing expanded fireclay aggregate
Modulus of rupture, psi (MPa)
(Hot tested
at temperature)
230F (110C)
1 0 0 0 F (538C)
1500F (816C)
2000F (1093C)
2500F (1371C)
2700F (1482C)
-___-----
350 (2.4)
300 (2.1)
250 (1.7)
210 (1.4)
240 (1.7)
90 (0.6)
(Cold tested after
firing and cooling)
350 (2.4)
N.D.*
250 (1.7)
225 (1.6)
470 (3.2)
800 (5.5)
*N.D. = Not Determined
Table 8.5.1 shows the difference between the cold
and hot modulus of rupture for a typical 2800 F
(1540 C) lightweight refractory concrete.
8.3 Forms
Both metal and wood forms are used for refractory
concrete.
8.6.2 Cold compressive strength (crushing) - Cold
crushing strengths vary from 200-500 psi (1.4-3.5
MPa) for lightweight refractory concretes with densities up to 50 pcf (800 kg/m3). For materials having
densities in the 75-100 pcf (1200-1600 kg/m3) range,
the cold crushing strength varies from 1000-2500 psi
(6.9-17-3 MPa).
9.4 Anchors41,44,45,46
8.6 Thermal conductivity
Thermal conductivity is one of the most important
physical properties of a lightweight refractory concrete and is controlled primarily by the density of
the concrete. For hydraulically bonded, alumina-silica concretes, a usable correlation exists between
concrete density [after drying at 230 F (110 C)] and
the thermal conductivity (k factor). Typically, the
thermal conductivity for insulating concretes ranges
from 1 to 4 Btu-in./sq ft-hr-F (0.1 to 0.6 W/M2-C).
8.10 Specific Heat
The specific heat of a lightweight refractory concrete is approximately the same as that of normal
weight concrete. The range is from 0.2 Btu/lb/F
(837 J/kg-Cl at 100 F (40 C) to approximately 0.3
Btu/lb/F (1255 J/kg-C) at 2500 F (1370 C).
Chapter 9 - Construction details
8.1 Introduction
Construction details are an important ingredient in
the successful application of refractory concrete.
Proper design details and careful implementation are
essential, and parameters such as support structure
integrity, forms, anchors, and construction joints
have a major influence on the overall quality and
performance of refractory concrete installations.
8.2 Support structure
Normally, refractory concrete is permanently supported by a back-up structure. The support material
is usually bolted or welded steel which, prior to installation of the refractory concrete, should be
checked to ensure that there is no warpage and that
all joints are structurally sound and tight.
An anchor is a device used to hold refractory concrete in a stable position while counteracting the effects of dead loads, thermal stressing and cycling,
and mechanical vibration. Anchors and anchoring
systems are not designed to function as reinforcement.
Anchors are produced as alloy steel rods or castings, and prefired refractory ceramic shapes. The requirements of a particular installation will determine
the type and positioning of anchors. Typical factors
to be considered are: unit size, wall thickness, number of refractory concrete components, area of application, and service temperature.
9.4.1 Metal anchors - The most frequently used
metal anchors are V-clips, studs, and castings. However, in special applications, welded wire fabric, hex
steel and chain link fencing are used. Generally,
metal anchors are extended from the cold face for
2/3 to 3/4 of the lining thickness and are staggered
to avoid formation of planes of weakness.
Metal V-clips, stud anchors and castings are available in carbon steel, Type 304 stainless alloy, Type
310 stainless alloy, and other suitable alloys. The
choice of material depends on the temperature to
which the anchors will be exposed. Carbon steel can
be used for anchor temperatures of up to 1000 F
(540 C). Type 304 stainless is suitable for anchor
temperatures of up to 1800 F (980 C) and Type 310
stainless is adequate up to 2000 F (1095 C). Depending on the grade of alloy, alloy steel castings can
sustain a maximum temperature of between 1500 F
(815 C) and 2000 F (1095 C).
9.4.2 Pre-fired refractory anchors (ceramic anchors)
- The principal use of ceramic anchors is to anchor
refractory plastic, rather than refractory concrete.
However, ceramic anchors are used in areas where
refractory concrete is subjected to high service temperature. In addition, they are sometimes used as a
substitute for metal anchors where concrete thicknesses are 9 in. (230 mm), or greater.
Ceramic anchors usually are composed of refractory aggregates, clays, and binders. They are me-
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REFRACTORY CONCRETE
chanically pressed into shapes which provide for attachment to either the wall or roof and are ribbed to
aid in securing the refractory concrete. Ceramic anchors are pre-fired at elevated temperature to provide a strong, dense structure. Depending on the
composition, service conditions, and other factors,
ceramic anchors are available with maximum service
temperature ratings of up to 3200 F (1760 C).
Ceramic anchors are attached to structural wall or
roof supports by bolts and/or metal support castings. In order to minimize the tendency of the refractory concrete to sheet spall, the hot face of the
ceramic anchor should extend to the hot face of the
refractory concrete.
9.4.6.1 Thin single component linings. Plain metal
chain link fencing is often used to anchor single component linings, less than 2 in. (50 mm) thick, composed of lightweight or medium weight refractory
concrete and exposed to low to moderate mechanical
stresses and/or service temperatures.
9.4.5.2 Single component linings up to 9 in. (230 mm)
thick. Normally, single component linings 2 in.
(50 mm) to 9 in. (230 mm) thick, composed entirely of
lightweight, medium weight or normal weight refractory concrete, and exposed to moderate stresses
and service temperatures use metal anchors.
9.4.5.3 Single component linings greater than 9 in.
(230 mm) thick. Normal weight refractory concrete
linings, greater than 9 in. (230 mm) thick, utilize either ceramic or metal anchors. The type of anchor
chosen will depend on the operating parameters.
9.4.5.4 Roofs. Two types of anchor systems, internal
and external, are used for single component roofs.
The choice depends on roof thickness and on construction and design preferences.
9.4.5.5 Multicomponent linings. Multicomponent linings of 9 in. (230 mm) or less in thickness which are
subjected to moderate service temperatures and mechanical stresses should employ metal anchors.
Multicomponent linings of 9 in. (230 mm) or
greater thickness, composed of a combination of
lightweight or medium weight refractory concrete as
back-up in conjunction with a normal weight refractory concrete, can use a combination of ceramic and
metal anchors.
With multicomponent shotcrete linings, the backup component is applied directly to the shell and
provisions must be made either to protect the anchor (metal or ceramic) from rebound build-up, or to
clean the anchor after placing of the back-up layer.
Rebound build-up can destroy the grip between the
heavy weight refractory concrete and the ceramic
anchor.
9.5 Reinforcement and metal embedment
The use of steel as a reinforcement should be
avoided. In general, the metal will cause cracking
due to the differential expansion, caused by temperature or oxidation, between the metal and concrete.
For the same reason heavy metal objects such as
bolts, pipes, etc. should never be embedded in refractory concrete.
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8.6 Joints37,48
In cast installations, construction joints occur at the
junction of walls and roofs or where large placements are broken into separate sections. Cold joints
of this type will not bond and should be avoided
where it is necessary to contain liquid or gases.
It is often necessary to include a provision for expansion. Expansion joints can be formed by inserting
materials such as wood, cardboard, expanded polystyrene or ceramic fiber in the appropriate location.
Shotcrete installations require construction joints
at transitions between materials, or when application must be curtailed due to shift changes or material supply. In these cases, the in situ refractory
concrete should be trimmed back to produce a clean
edge perpendicular to the shell. Expansion compensating materials are not generally inserted into
this type of joint. If a joint edge is allowed to stand
for a prolonged period of time (more than 4 hr), it
should be thoroughly moistened before any new material is applied.
Chapter 10 - Repair
10.1 Introduction
Repair of refractory concrete should be considered
only when economics dictate that cost and downtime
do not justify complete replacement. Before undertaking a repair, an effort should be made to determine the cause of the previous failure. If possible,
the design and/or construction details should be
modified to reduce the possibility of a recurrence of
failure and to prolong service life between repairs.
Hot repair techniques are valuable for minimizing
downtime and for extending an operating run until a
scheduled shutdown. Hot repairs are especially suitable for temporary repairs of localized failures and
hot spots.
10.2 Failure mechanisms
Some of the phenomena that can cause failure are:
(1) Thermal stress and thermal shock; (2) Exposure
to excessive temperatures; (3) Mechanical loading;
(4) Erosion and abrasion: (5) Corrosive environments;
(6) Anchorage failures and (7) Operational problems
or upsets.
10.3 Surface preparation
When the installation to be repaired is made of mortar or concrete, it is important to prepare the surface of the old material so that a mechanical bond
will be formed between it and the new refractory
concrete. No significant chemical bond will be
formed, and adhesion of the repair material must depend primarily on the mechanical bond. Preparation
of the surface requires removal of all deteriorated or
spalled materials and roughening of the exposed
sound surface of the old concrete. In all cases, the
chipping of old material must leave a flat base, and
square shoulders approximately perpendicular to the
hot face, completely around the perimeter of the repair section. If this is done properly, there is no
need to chamfer the edges or provide fillets to walls
and floors. Once initial removal of loose concrete has
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been completed, the old refractory should be
sounded with bars or hammers to make certain only
sound material remains.
Areas that were not chipped should be thoroughly
sandblasted to remove any traces of soot, grease, oil
or other substances that could interfere with the
bond. Excess sand and loose debris must then be
blown from the surface with compressed air. Particular care must be taken to remove any debris
from around the anchors.
10.4 Anchoring and bonding
If possible, patches should be anchored with a minimum of two anchors which should be solidly attached to the shell. In cases where this is impossible,
anchors should be solidly embedded in the old refractory. Ceramic anchors should extend to the hot
face of the new refractory concrete. Otherwise,
sheet spalling may occur. If metal anchors are used,
they should be brought as close as possible to the
hot face. The distance will depend on the metallurgy of the anchors and the thermal conductivity of
the concrete.
Where anchors are not practical, or repairs are
shallow, mechanical bonding will be aided by cutting
chases or keyways in a waffle pattern across the entire surface of the repair section and by slightly undercutting the existing refractory.
In certain limited applications, where other means
are not available, the bond may be improved by precoating the surface to be repaired with a bonding
agent. When repairing refractory concrete with a
similar cast-in-place material pre-wetting is required,
and use of a neat calcium aluminate cement slurry
may improve bonding.
10.5 Repair materials
A wide range of repair products is available for repairing refractory concrete. However, it is usually
best to use a material similar to that being repaired.
Refractory concrete is frequently used as a repair
material and performs satisfactorily in many situations. Among the other available repair materials
are the following:
1. Air setting mortars;
2. Phosphate-bonded and clay-based heat-setting
mortars;
3. Steel-fiber reinforced refractory concrete;
(Steel-fiber reinforced refractory concrete will generally exhibit superior resistance to cracking and abrasion. However, the fibers will not perform well if the
temperatures to which they are exposed induce oxidation. If the conditions are such that the fiber-reinforced system is above the oxidizing, but below the
melting temperature of the particular fibers being
used, it is possible that they may still be utilized, depending on the temperature gradient through the
concrete, the furnace atmosphere, the permeability
of the concrete, the severity and frequency of temperature cycles, the exposure time at maximum temperature, and the mechanical loading.)
4. Plastic refractories and ramming mixes; and
5. Hot repair materials. Some of the repair materials used for hot patching contain calcium aluminate
cement as the principal binder, however, most do
not. The latter utilize non-hydraulic and chemical
binders (see Section 1.6.4). Since these materials are
intended for temporary repairs, they may not have
service life or properties equivalent to those in the
original lining.
While field mixes can be used for hot gunning,
most applications use proprietary (prepackaged) materials which are specially designed for specific conditions of installation. Some manufacturers have designed special spray or gunning equipment and
maintenance programs to install their hot repair materials on a planned basis.
10.6 Repair techniques
10.6.2 Refractory concrete - When a refractory concrete is selected to effect repairs, the type of placement procedure must insure that the full thickness
of the repair section is installed in as short a time as
possible, preferably in a single lift.
When refractory concrete is placed by the shotcrete method, certain precautions must be followed.35 The area being repaired must be delineated
in advance so that the concrete can be shot to the
full section depth or thickness before any layer develops an initial set.
It is important that the refractory concrete be
cured properly during the 24-hr period following
placement (see Section 6.3). After the concrete has
been moist-cured for 24 hr, drying and firing can be
initiated (see Sections 6.4 and 6.5). Speeding up the
moist-curing, drying and firing can result in a
marked reduction in the physical properties and life
of the repair.
10.6.3 Plastic and ramming mixes - A refractory
mortar coating may be used to improve bonding
when repairing refractory concrete with a plastic or
ramming mix. In order to achieve high density and
prevent laminations, it is recommended that plastic
refractories be installed by the pneumatic ramming
method using a steel wedge-type head. The basic
pattern of ramming should be to build up layers of
plastic on top of the backing wall. The plastic is
placed in strips and laid at right angles to the forms.
It is important to angle the pneumatic rammer so
that the strips are driven against the form, and sideways against the previously installed material. The
repaired area should be trimmed to a rough surface
for more uniform drying.
Moisture escape holes should be made by inserting
a 1/8 in. (3 mm) diameter pointed rod, approximately two-thirds of the depth of the material, on
approximately 6 in. (150 mm) centers. In order to
prevent formation of an outer skin, which can seal in
moisture, a short period of forced drying of air-setting plastic refractories is desirable. Excessive temperature or direct flame impingement, which will
seal the surface and prevent escape of moisture,
must be avoided.
The following heat-curing procedure has been
found to give good results with plastic and ramming
mixes: Remove all free moisture at a temperature of
not over 250 F (120 C). Following removal of free
and absorbed moisture, raise the temperature at a
rate of 75-100 F (42-56 C) /hr until the desired oper-
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ating temperature is reached. If steam is observed
during heat-up, hold the present temperature until it
stops.
Whenever possible, repairs using plastic mixes
should be carried out immediately prior to heat-up.
A properly burned-in plastic will exhibit less cracking than a plastic exposed to lengthy air drying.
10.6.4 Steel-fiber reinforced refractory concrete
10.6.4.1 Cast-in-place mixes. A problem with steel fibers is their tendency to “ball-up”. Clusters of fibers
can be broken up by hand feeding or shaking of the
sieve before addition to the concrete mix. In some
cases, vibration will tighten up the fiber clusters and
it is not a recommended method of fiber dispersal.
The addition of steel fibers tends to reduce the
workability of the mix. Normally, this can be overcome by internal or external vibration. Use of additional water is not recommended since this will degrade cured strength and increase the porosity.
10.6.4.2 Shotcrete mixes. Steel fiber reinforced refractory concretes can be shot into place by either
the wet or dry process. Fiber lengths approaching
the internal diameter of the material hose or nozzle
can be shot successfully. Because rebound of the fibers can be dangerous, the nozzleman and support
crew should wear protective clothing when dry
shooting with steel fibers.
10.6.5 Hot repair procedures - Hot repair procedures are based on standard shotcreting technology. However, because of the high temperatures,
certain differences are necessary. Compared to normal shotcreting, the high temperatures require a
specially designed nozzle and an excessive amount of
water in the mix in order to insure proper delivery,
impingement, compaction, and material retention.
Hot shotcreting requires that the nozzleman and a
helper stand outside the furnace and manually or
mechanically manipulate an extended nozzle or
“lance” within the furnace. Special ports or openings
must be provided in the furnace for proper access.
The length, size, and design of the nozzle depends on
the furnace configuration, temperature, and type of
application.
In general, the best bonds are achieved when the
vessel interior is a red or orange color (1500-1700 F
(815-925 C)]. The refractory concrete repair must be
allowed to heat-cure prior to placing the unit back in
service. The length of time to accomplish this, although usually brief, will depend on the temperature
at the time of repair, the type of material used for
the repair, and the thickness of the installed material.
Chapter 11- Applications
11.1 Introduction
Refractory concretes are currently used in a wide
variety of industrial applications where pyroprocessing or thermal containment is required. Because
there are literally hundreds of refractory concretes
available, it is impossible to discuss every composition and its application. Accordingly, only the more
important applications, where refractory concretes
have been used successfully, are reviewed. Included
in the review are the following industries:
(a) Iron and steel
(b)lNon-ferrous metal
(c)lPetrochemical
(d)lCeramic processing
(e)lGlass
(f) Steam power generation
(g) Aerospace
(h)lNuclear
(i) Gas production
(j) MHD power generation
(k) Lightweight aggregate
(l) Incinerator
(m) Cement and lime
Chapter 12 -New development and future use
of refractory concrete
12.1 Introduction
Traditionally, developments in the refractories industry have been closely related to the process industries, the primary customers for the product.
In recent years, there have been marked changes
in the production and use of refractories. A number
of factors have contributed to these changes including:
(a) development of new and improved industrial
processes,
(b) demand for higher temperatures and increased
production rates associated with the above developments,
(c) improvement in the quality of refractory products and increased use of different types of refractories, especially the monolithic castables and,
(d) increased technical knowledge of the service
behavior of refractory materials.
With these technological advancements, investigations into the use of refractory concretes for
special applications is increasing. Typical of these
new and proposed applications are incinerators, coal
gasification plants, chemical process plants, steel
plants, and foundries.
12.2 New developments
12.2.1 Steel fibers187,188,189,191 - The following potential advantages are offered by the use of steel-fiber
reinforcement in monolithic construction:
(a) improved flexural strength at ambient and elevated temperatures,
(b) improved thermal and mechanical stress resistance,
(c) improved thermal shock resistance,
(d) improved spall resistance, and
(e) improved load-carrying ability.
However, degradation of the steel fibers at high
temperature can occur under service conditions and,
therefore, limit the full potential of these materials.
Note: See References 197 through 205.
12.2.2 Shotcrete - The use of shotcrete for new refractory construction and for repairs is a rapidly
growing field and successful results have been
achieved in many applications.
12.2.3 Precast shapes - Increasingly, precast shapes
are being used for special conditions and this trend
will continue.
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MANUAL OF CONCRETE PRACTICE
12.3 Research requirements
Unfortunately, selection and use of refractory concretes is still considered an art and, with a few exceptions, the properties of refractory concretes are
not utilized in rational design schemes. In many instances, the wrong properties are being measured or
the available data are not being used correctly.
Future research efforts should be directed towards obtaining a better understanding of the behavior of refractory concretes under service conditions. Increased emphasis will be placed on elevated
temperature properties and how they are influenced
by such factors as proportioning, grading and compo
sition.
Areas of needed research include the following:
(a) Dimensional stability
(b) Chemical attack
(c) Mechanical properties
(d) Property measurements and tests
(e) Process conditions
(f) Rational design procedures
References
1. ACI Committee 116, Cement and Concrete Terminology, SP-19, American Concrete Institute, Detroit, 1967,
146 pp.
2. Van Schoeck, Emily C., Editor, Ceramic Glossary,
American Ceramic Society, Columbus, 1963.
3. Norton, F. H., Refractories, 4th Edition, McGraw-Hill
Book Company, New York, 1968, 782 pp.
5. Robson, T. D., High Alumina Cements and Concretes,
John Wiley and Sons, New York, 1962, 263 pp.
20. Chatterji, S., and Jeffry, J. W., “Microstructure of
Set High-Alumina Cement Pastes,” Transactions, British
Ceramic Society (London), V. 67, May 1968, pp. 171-183.
21. Midgley, H. G., “The Mineralogy of Set High-Alumina Cement,” Transactions, British Ceramic Society (London), 1966, pp. 161-187.
22. Wygant, J. F., “Cementitious Bonding in Ceramic
Fabrication,” Ceramic Fabrication Processes, W. D. King
ery, Editor, John Wiley and Sons, New York, 1958, pp.
171-198.
34. Givan, G. V.; Hart, L. D.; Heilich, R. P.; and MacZura, G., “Curing and Firing High Purity Calcium Aluminate Bonded Tabular Alumina Castables,” American Ceramic Society Bulletin, V. 54, No. 8, 1975, pp. 710-713.
35. Shotcreting, SP-14, American Concrete Institute, Detroit, 1966, 223 pp.
41. Wygant, J. F., and Crowley, M. S., “Designing Monolithic Refractory Vessel Linings,” American Ceramic Society Bulletin, V. 3, No. 3, 1964, pp. 173-182.
44. Crowley, M. S., “Failure Mechanism of Two-Component Lining for Flue-Gas Dust,” American Ceramic Society Bulletin, V. 47, No. 5, 1968, pp. 481-483.
45. Crowley, M. S., “Metal Anchors for Refractory Concretes,” American Ceramic Society Bulletin, V. 45, No. 7,
1966, pp. 650-652.
46. Vaughn, S. H., Jr., “Guidelines for Selection of Monolithic Refractory Anchoring Systems,” Iron and Steel Engineer, May 1972, p. 64.
187. Lankard, D. R., and Sheets, H. D., “Use of Steel
Wire Fibers in Refractory Castables,” American Ceramic
Society Bulletin, V. 50, No. 5, 1971, pp. 497500.
188. Lankard, D. R.; Bundy, G. B.; and Sheets, H. D.,
“Strengthening Refractory Concrete,” Industrial Process
Heating (London), V. 13, No. 3, Mar. 1973. pp. 34-47.
189. Lankard, D. R., “Steel Fiber Reinforced Refractory
Concrete,” Refractory Concrete, SP-57, American Concrete
Institute, Detroit, 1978, pp. 241-263.
191. Fowler, T. J., “Lessons Learned from Refractory
Concrete Failures,” Refractory Concrete, SP-57, American
Concrete Institute, Detroit, 1978, pp. 283-303.
195. Tseung, A. L. L., and Carruthers, T. G., ‘Refractory Concretes Based on Pure Calcium Aluminate Cements,” Transactions, British Ceramic Society (London), V.
62, 1963, pp. 305-321.
197. Peterson, J. R., and Vaughan, F. H., “Metal Fiber
Reinforced Refractory for Petroleum Refinery Applications,” Paper No. 51, Presented at Corrosion/80, National
Association of Corrosion Engineers, Pittsburgh, 1980.
198. Crowley, M. S., “Steel Fiber in Refractory Applications,” Paper No. MC-81-5. National Petroleum Refiners
Association Refinery and Petrochemical Maintenance Conference, Pittsburgh, 1981.
199. Venable, C. R., Jr., “Refractory Requirements for
Ammonia Plants,” American Ceramic Society Bulletin, V.
48, No. 12, 1969, pp 1114-1117.
200. Farris, R. E., “Refractory Concrete: Installation
Problems and Their Identification,” 18th Annual Symposium on Refractories-Changes in Refractory Technology-In Place Forming, American Ceramic Society, St.
Louis Section, The Engineers Club, Mar. 12, 1982.
201. MacZura, G.; Hart, L. D.; Heilich, R. P.; and Kopanda, J. E., “Refractory Cements,” Ceramic Engineers
and Science Proc.-Raw Materials for Refractories Conference, (4) 1-2, 1983, pp. 46-67.
202. “Standard Recommended Practices for Determining Consistency of Refractory Concretes,” (ASTM C 86077), 1982 Annual Book of ASTM Standards, Part 17.
American Society for Testing and Materials, Philadelphia,
pp. 932-937.
203. “Standard Recommended Practice for Preparing
Refractory Concrete Specimens by Casting, (ASTM C 86277), 1982 Annual Book of ASTM Standards, Part 17,
American Society for Testing and Materials, Philadelphia,
pp. 940-946.
204. “Standard Recommended Practice for Firing Refractory Concrete Specimens,” (ASTM C 865-77) 1982 Annual Book of ASTM Standards, Part 17, American Society
for Testing and Materials, Philadelphia, pp. 949-951.
205. “Standard Practice for Preparing Refractory Concrete Specimens by Cold Gunning,” (ASTM C 903-79) 1982
Annual Book of ASTM Standards, Part 17, American Society for Testing and Materials, Philadelphia, pp. 978-979.
The complete report was submitted to letter ballot of the committee which consisted of 16 members; 16 members returned affirmative ballots.
The preceding report was a summary. The complete report will
be available in May as a separate publication.
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REFRACTORY CONCRETE
ACI Committee 547
Refractory Concrete
I. Leon Glassgold
Chairman
Henry E. Anthonis
Seymour A. Bortz
William E. Boyd
Khushi R. Chugh
Timothy J. Fowler
Editor
Sidney Diamond
William A. Drudy
Joseph E. Kopanda
Svein Kopfelt
David R. Lankard
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Joseph Heneghan
Secretary
William S. Netter
Richard C. Olson
William C. Raisbeck
Richard L. Shultz