THE EFFECT OF THERMAL SHOCK ON
CLAY BODIES
I. INTRODUCTION
1. Previous Data.-Prior to 1927, published data on the effect of
thermal shock on clay bodies were confined to the results of water and
air quenching tests in which the basis of comparison was the number
of quenchings required to produce failure.
Since that time data concerning thermal shock have been pub-
lished by Goodrich* with relation to the compressive strength of
firebrick; by Parmelee and Westmant with reference to the transverse
strength of firebrick; by Heindl and Mongt correlating transverse
strength and other physical properties with quenching tests on sagger
bodies; and by Heindl and Pendergast¶ correlating transverse
strength and other physical properties with quenching tests on
firebrick.
2. Purpose of Present Investigation.-The present study of ther-
mal shock has been made as part of a general investigation of the
physical properties of twenty commercial shale and fireclay bodies,
ranging in softening point from cone 7 to cone 30, corresponding
approximately to temperatures of 2280 and 3000 deg. F., respectively.
It was undertaken primarily for the purposes of developing a method
for making comparisons of the resistance of bodies to thermal shock
on a quantitative basis, and of establishing relations between physical
properties and resistance to thermal shock by means of which resist-
ant bodies could be designed and plant control of their manufacture
effected.
The purposes of this bulletin are:
(1) To describe the method briefly, presenting only sufficient data
to indicate the general relation between physical properties, and to
indicate, in part mathematically, the relation between these prop-
erties and resistance to thermal shock.
*H. R. Goodrich, "Spalling and Loss in Compressive Strength of Fire Brick," Jour. Amer. Cer.
Soc., 10, 784-94, 1927.
tC. W. Parmelee and A. E. R. Westman, "The Effect of Thermal Shock on the Transverse
Strength of Fireclay Brick," Jour. Amer. Cer. Soc., 11, 884-895, 1928.
$R. A. Heindl and L. E. Mong, "V. Progress Report on Investigation of Sagger Clays and Prep-
aration of Experimental Sagger Bodies According to Fundamental Properties," Jour. Amer. Cer. Soc.,
12, 457, 1929.
J¶R. A. Heindl and W. L. Pendergast, "VI. Progress Report on Investigation of Fireclay Brick
and the Clays Used in Their Preparation," Jour. Amer. Cer. Soc., 12, 640, 1929.
ILLINOIS ENGINEERING EXPERIMENT STATION
(2) To discuss the published data and conclusions of other inves-
tigators on the basis of the results obtained in the present investi-
gation.
3. Acknowledgment.-The data presented in this bulletin were ob-
tained in an investigation which was conducted by the Engineering
Experiment Station of the University of Illinois, of which M. S.
KETCHUJM, Dean of the College of Engineering, is director, in co6per-
ation with the Clay Products Association. The research was carried
out in the Department of Ceramic Engineering of which C. W.
PARMELEE, Professor of Ceramic Engineering, is the head, and of
which R. K. HURSH, Professor of Ceramic Engineering, has been the
acting head, during the completion of the work.
Acknowledgment is made to Professor PARMELEE for his co6per-
ation and assistance during the early part of the investigation; to
Professor HURSH for his interest and advice and especially for his
critical survey of the material during its preparation for publication;
and to Mr. G. H. DUNCOMBE, Jr., Ceramic Engineer for the Clay
Products Association, for his many helpful suggestions throughout
the progress of the work.
II. THERMAL SHOCK TESTS
4. Testing Procedure.-Twenty 1 in. x 1 in. x 6 in. test pieces of
each commercial body were burned in laboratory kilns to cone 04,
twenty to cone 2, and twenty to cone 6, approximately equivalent to
temperatures of 1925, 2075, and 2175 deg. F., respectively.
The average transverse strength or modulus of rupture for each
body was determined by breaking ten of the specimens in each sample
by application of a concentrated load at the center of a five-inch span.
The remaining ten specimens in each sample were subjected to ther-
mal shock before transverse strength determinations were made. The
per cent reduction in strength, based on initial strength, was then
calculated.
The thermal shock test was planned to be equivalent to the more
severe conditions to which the material might be subjected in service,
and, in addition, the test temperature selected was above the inver-
sion temperature of quartz.
Thermal shock was produced by heating the samples for fifteen
minutes entirely within a gas fired muffle furnace maintained at 1100
deg. F., and then removing them and cooling them for fifteen minutes
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
by an air blast applied to one face. The cycle was repeated eight
times.
The method was essentially that of Parmelee and Westman, but
differed in the size of the test pieces, the temperature of the furnace,
and the length and number of heating and cooling periods.
5. Experimental Data.-All modulus of rupture values, or initial
strengths, for the bodies were plotted against the corresponding per
cent reduction values, and a smooth curve was drawn showing the
general trend of the field (Fig. 1). Each point represents the average
results from ten specimens before thermal shock and ten specimens
after thermal shock. There are three such points for each material
tested. The values of modulus of rupture after thermal shock, or
final strengths, were also plotted against per cent reduction in strength
in Fig. 2. The curve in the figure was made to correspond to that of
Fig. 1 by calculating the final strength from values on the curve in
Fig. 1. The general relationship between final and initial strength
corresponding to the curve values of Figs. 1 and 2 is shown in the
curve of Fig. 3. The points representing the experimental data are
also plotted for comparison.
These are "average curves," and are intended to indicate only the
general trend of the data. The use of broken line curves indicates the
uncertainty of the trend in the region of the higher values of per cent
reduction, in Figs. 1 and 2, and of initial strength, in Fig. 3.
The method of plotting is shown in Fig. 4 for an individual body,
the data consisting of the three experimental points.
Individual curves, each based on three points and representing
one body, are shown in composite form in Fig. 5. The general form
of each curve is fixed to some extent by the three plotted points in
that they indicate the presence of a maximum value for final strength.
The curves in general have the same form as the average curve.
In order to secure a more positive indication of the trend of the
relation between initial and final strength, additional tests were made
on an individual body, covering a burning range from cone 09 to
cone 9 corresponding approximately to temperatures of from 1700 to
2300 deg. F. Initial strength ranged from approximately 800 to
3200 lb. per sq. in.
The data are plotted in Fig. 6, in which each point represents the
average results from ten test pieces before thermal shock and ten
test pieces after thermal shock.
The results show definitely the presence of a maximum value for
final strength, and indicate that the general form of the individual
ILLINOIS ENGINEERING EXPERIMENT STATION
(~)
(I
{J)
- 1 /9
Per Cent
FIG. 1. RELATION
~0 dO 4 ~,9 ?4 80 .~0 /00
Rea c//lo'O /12 Transverse Sfren2gfh, /P
After Ther,7a/ 2Shoca-
BETWEEN INITIAL STRENGTH AND PER CENT
REDUCTION IN STRENGTH
3rOO\ - - - - - - - - - - - * -
800o- o-Burned ato Cone 04
S-Burnea or7 Cone 2 06 i
* -Burned a' Cone 6 - a
2400 ----o
1800 ~ ~ -------- -a^'*'-I- -------------
/0 * a [
/6?00------- --- -- -- -- -
/200 --/-/ ----_____b lve-5q/7
800 - - y - - - - - - - - - -
f Aver'g'e Curie P/o/!ea'fo
4 A where / r ? 00 /bper sr./ :.
- ----were' /7 /s 2. --- - - -- -
Per Cent Reac/ic/on , Trhnsverse Stregfth, P,
Af/er T7erea'/ Shoc*
FIG. 2. RELATION BETWEEN FINAL STRENGTH AND PER CENT
REDUCTION IN STRENGTH
v
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
I I I I I I
- -Burne' at Cone
a- Burneo' ato' Co
~ *-Bt/r/neo a'^ Cone
' 000
e~z2y oo
.,00
goo
I I I I I I
.4'eroge Curp-e P/o/fed fri~',':
$ s,.f-4~J7
3»/?/^/1
400 500 /26)0 /66)6' z6)'o ~ao ~ ~
/ni//a/ TraTNsverse STtreE g/?, 5,, A / /7 pe-R s5. /n.
FIG. 3. RELATION BETWEEN INITIAL AND FINAL STRENGTH
/1000
(i 800
400
K
0
0 400 800 /200
X'n /.. pe qs. in.
Per Cet /?R ed'uction /7
T7ra-7sierse 53renqg1/7
After Th7ermroV ShocA-
FIG. 4. METHOD OF PLOTTING DATA FOR INDIVIDUAL BODIES
and average curves is correct. In addition it seems probable from
Fig. 6 that, with increased vitrification and high initial strength
development, final strength will decrease and finally approach zero.
6. Results of Tests.-The data indicate, for the burning range
studied, that:
(1) Per cent reduction in strength increases as initial strength
increases, i.e., the stronger bodies lose a greater percentage of their
strength than do the weaker ones.
I,
0 0
S!__ 0
_ - _o
/ _ _ -
6
K
-^ /200
K,
g800
400
..
I,
z
where M,'_ /5 2900 lb. pe1' 5'. q/
and n is 2.
0170' 17
- \
S\
S
6) 5. __---______
ri- * 3^-- ;* - -- - -
0 *^ - - - -__ __
*.s "
^
7
ILLINOIS ENGINEERING EXPERIMENT STATION
.4.'k
4~
(4)
KK
~z
SZ
Z000 - --- -7 - - - - -
800 ;100II
4° L/'e ?epreseni7ngi
/600' --------- - --7' - - -7TreoretA-/'cg/y--
/' ~Per fect Boady.
---T---o-- ----/ --
400--
^ \ A veroye' Curve-"\
0 400 300 /IOO /600 2000 2400 2800 3zoo
/n/i/al Transverse Strengqh // Ik /7 Zpr sq /1
FIG. 5. RELATION BETWEEN INITIAL AND FINAL STRENGTHS FOR ALL BODIES TESTED
/na'/ Tiransv-erse Strengt/7 i17 /z per s. //.
FIG. 6. RELATION BETWEEN INITIAL AND FINAL STRENGTH FOR AN INDIVIDUAL BODY
(2) Strength after thermal shock, or final strength, increases to a
maximum and then declines, as the strength before thermal shock, or
initial strength, increases.
If it is accepted that the average exponential curves of Figs. 1, 2,
and 3 correctly represent the test results, the properties of these
mathematical curves define the following relations between initial
strength, final strength, and per cent reduction in strength.
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
7. Relation between Initial Strength and Per Cent Reduction in
Strength.-All values of per cent reduction will lie between 0 and 100
and can be expressed as some fractional part of 100, while the relation
between initial strength and the strength corresponding to 100 per
cent reduction can also be expressed as a ratio. It is evident that this
ratio and the per cent reduction are dependent variables which will
change as the initial strength changes.
While any particular equation selected may not completely satisfy
all conditions, it will offer a means of systematic variation of the rela-
tion between strength before and after thermal shock and per cent
reduction, from which a helpful analysis of the problem can be made.
Such a relationship, which fits the test data fairly well, can be ex-
pressed by the equation:
P = 100 (1)
Where P = per cent reduction in strength.
Si = initial strength, modulus of rupture in lb. per sq. in.,
corresponding to per cent reduction P.
Mioo = initial strength, modulus of rupture in lb. per sq. in.,
corresponding to 100 per cent reduction.
n = a variable exponent.
In more convenient form Equation (1) becomes
S, = M,0o (0 (2)
8. Relation between Final Strength and Per Cent Reduction in
Strength.-The relation between final strength and per cent reduction
in strength can be obtained readily from Equation (2), since the final
strength is always equal to the initial strength multiplied by the factor
1 - P-) where P is the per cent reduction.
100
Let Sf = strength after thermal shock, or final strength, modulus
of rupture in lb. per sq. in., corresponding to per cent reduction P.
Then Sf = Si 1 - - (3)
but Si = M100o - (2)
/ \1 / D\
so that Sf = M1oo (I- 1 1 - -1 -
\IUU/ \ IUIJ/
ILLINOIS ENGINEERING EXPERIMENT STATION
From Equation (4), Sf will be zero when P is 0 and when P is 100.
Placing the first derivative of Sf with respect to P equal to zero,
Sf becomes a maximum when
(n + 1)P = 100 (5)
For any positive value of n, S1 will have a maximum value, i.e.,
strength after thermal shock will increase to a maximum and then
decline.
9. Discussion of Mathematical Relationships.-
When M100 is Variable and n is Constant
The solid line curves in Fig. 7 are plotted from Equation (2),
where n is 2 and Mo10 is 1200, 1600, 2000, and 2400 lb. per sq. in.,
respectively. They represent the relation between initial strength
and per cent reduction.
The broken line curves represent the corresponding relation be-
tween strength after thermal shock and per cent reduction, and are
plotted from Equation (4).
When n is kept constant and M1io varied, the per cent reduction
corresponding to maximum strength after thermal shock remains
fixed, for S. is a maximum when (n + 1)P = 100. A group of curves
for a different value of n will have a fixed but different value for the
per cent reduction corresponding to maximum strength after thermal
shock.
When n is Variable and M100 is Constant
In Fig. 8 the light solid lines are plotted from the same general
Equation (2), but in this case M1oo is kept constant at 2000 lb. per
sq. in., and n is allowed to vary. When n = 1, the equation repre-
sents a straight line.
For values of n greater than one, a series of curves can be plotted
which will rise more or less sharply from the origin, will be concave
downward, and will approach M1io with gradually decreasing slope.
For values of n less than one, the curves will rise very slowly at
first, will be concave upward, and will approach M0io with increasing
slope.
7 The broken line curves again represent the corresponding relations
between strength after thermal shock and per cent reduction. They
are plotted from Equation (4).
As the relationship between transverse strength and per cent
reduction changes from that represented by a straight line, when
9 = 1, to relationships represented by curves which are concave
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
Per Ce -X eC1d/0'oer? /7 - Transverse 1 5-re7g17'
After T77erm'a// 51oc/ e
FIG. 7. GRAPHIC RELATIONSHIP BETWEEN INITIAL AND FINAL STRENGTHS AND
PER CENT REDUCTION BASED ON MATHEMATICAL DERIVATION
downward when n is greater than 1, the point of maximum strength
after thermal shock changes from 50 per cent reduction to lesser
values as n increases, i.e., the more abruptly the curve representing
the relation between transverse strength before thermal shock and
per cent reduction rises from the origin, the lower will be the per cent
reduction at which the body will attain its maximum strength after
thermal shock.
The heavy solid line curve represents the maximum strength after
thermal shock corresponding to different values of n.
Relation between Initial and Final Strength
The direct relation between initial and final strength is obtained
by combining Equations (1) and (4) and eliminating P.
Thus Sf = Si 1_ -(W)1 (6)
\ Mlm
ILLINOIS ENGINEERING EXPERIMENT STATION
N 86
246
206?(
N
/66L
S86.
(I
^4
Per Cent AReacI/o /n T47 i'V'erse Stre6-1gt2
After T17errn7/ S5o'acl
FIG. 8. GRAPHIC RELATIONSHIP BETWEEN INITIAL AND FINAL STRENGTHS AND
PER CENT REDUCTION BASED ON MATHEMATICAL DERIVATION
from which it follows that Sf will be zero when Si is equal to zero
and M0oo.
Placing the first derivative of Sf with respect to Si equal to zero,
Sf becomes a maximum when
S--M100 (7)
(n + 1)»
The direct relation between initial and final strength is shown
graphically in Fig. 9, having been plotted from Equation (6). The
curves indicate that, for a fixed value of Mioo, resistance to thermal
shock increases with increase in value of the exponent n, and that the
higher the value of n, the more abruptly the resistance falls off after
the maximum point is reached.
The relation between initial and final strength for a fixed value of
n with Mioo variable is not shown. It is evident, however, that the
increase in maximum final strength is directly proportional to the
increase in the value of M1oo.
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
/7///7/a Trotnsverse S/-rel/i, 5,; i, /7. per sq. i?.
FIG. 9. THEORETICAL RELATIONSHIP BETWEEN INITIAL AND FINAL
STRENGTHS BASED ON MATHEMATICAL DERIVATION
Sf (max) in Terms of M100 and n, with Corresponding Values of Si and P
The direct relation between maximum final strength, initial
strength corresponding to 100 per cent reduction (M100) and n is
obtained by substitution in Equation (4) of the value of P corre-
sponding to maximum final strength, given in Equation (5); or by
substitution in Equation (6) of the value of Si corresponding to
maximum final strength, given in Equation (7).
In either case
Sf (max) = [n+ I M100 (8)
n(n+l) n
From Equations (7) and (8) it is seen that, in the limit, as n becomes
infinite, both S, (max) and the corresponding value of Si approach
Mioo; and as n approaches zero, Sf (max) approaches zero, and Si
approaches Mo0, where e is the base of Naperian logarithms.
e
ILLINOIS ENGINEERING EXPERIMENT STATION
&/00
80
60
4
t 40
N
S3
^ .,
~0
Va/&les of the Expone/nt 72?"
FIG. 10. RELATION BETWEEN MAXIMUM VALUES OF Sf AND CORRESPONDING
VALUES OF Si, P, AND n
Values of P corresponding to maximum values of Sf are given by
Equation (5)
(n + 1) P = 100
As n approaches zero, P approaches 100, and as n becomes infinite,
P approaches zero.
These general relationships are shown graphically in Fig. 10 for
values of n from 0 to 10.
It has been shown that, for a given characteristic relationship
between initial and final strengths, there is a corresponding value of n.
The curves indicate that, for any given value of n, the maximum final
strength and corresponding initial strength are fixed fractional parts
of M1oo. For any value of n there is also a fixed value of per cent
reduction corresponding to maximum final strength.
Relations When Initial Strength Approaches a Minimum Value Greater Than
Zero as Final Strength Approaches Zero
In the case in which the initial strength approaches a minimum
value greater than zero, as final strength approaches zero, the curve
representing the relationship may be considered to have been trans-
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
k/i/7a/ Transverse Streng/h, S,
0 80 40 60 8o /OO
Per Cenl/ £vl cA'/On 7i Transverse Streng'/h
FIGa. 11. RELATION BETWEEN INITIAL AND FINAL STRENGTH AND PER CENT
REDUCTION WHEN DECREASING INITIAL STRENGTH APPROACHES A
CONSTANT C, AS FINAL STRENGTH APPROACHES ZERO
lated parallel to the X axis a distance equal to the intercept C on the
X axis. Such a relationship is shown in Fig. 11. The range of values
for final strength remains unchanged, while each value of initial
strength is increased by amount C. Thus the relation between initial
and final strength becomes:
Sf = (Si - C) 1 - (Si - C
As initial strength increases from C to Mo0o, and the final strength
increases from zero to a maximum and then decreases to zero, the per
cent reduction decreases from 100 to a minimum value and increases
-again to 100.
The relationships, when n is 2, are shown graphically in Fig. 11.
ILLINOIS ENGINEERING EXPERIMENT STATION
10. Application to Experimental Data.-The characteristics of
individual bodies are shown by curves in Fig. 5. In form, these curves
closely resemble the "average curve" of Fig. 3 which is repeated for
comparison. In each case the final strength increases to a maximum
and then decreases with increasing initial strength. While the data
available are not sufficient for exact determinations of the constants
for the several bodies, the values of M00oo range from 1200 to 4000 lb.
per sq. in., and n is, in all cases, greater than 1.
Values for initial and final strength for all bodies below maximum
resistance to thermal shock lie in a comparatively narrow field slightly
below the 45 deg. line. It is evident, however, that each body has its
individual characteristics, for, as the maximum points are approached
and passed, the curves become widely divergent. In preliminary
experiments, only small differences were obtained in final strength
corresponding to quite large differences in initial strength. The
reason is now apparent, for, at the flat upper part of the average
curve (Fig. 5) representing maximum resistance, final strength appar-
ently remains unchanged at 1080 lb. per sq. in., while initial strength
changes from 1400 to 1940 lb. per sq. in.
This also may offer some explanation of the discrepancies between
service tests and laboratory thermal shock tests. Laboratory tests
usually are made on refractories which in their manufacture have
attained an initial strength considerably below that which would cor-
respond to 100 per cent reduction in strength in a properly designed
test. Most refractories tested would lie in the best range, below or
approaching maximum resistance. In severe service, however, at
least the exposed surface approaches complete vitrification, and at
this point the refractory is far beyond its maximum resistance.
Refractories which compare favorably at or below their maximum
resistance might be widely different under service conditions, as in-
dicated by the divergence of the curves representing the relation
between initial and final strength after they have passed their maxi-
mum value.
III. MODULUS OF ELASTICITY AND POROSITY
11. Determination of Modulus of Elasticity.-Modulus of elasticity
was determined by loading the specimen as a cantilever beam with a
concentrated load of 2 pounds suspended 7 inches from the support.
Deflections were measured by an Ames dial graduated to 0.0001 in.
The breadth and depth of the specimens were measured to 0.01 in.
The values were calculated from the standard equation for modulus
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
/inf,"a/ Trnsiers6e Stre "te, fAverages) lb //l A/er . 1
FIG. 12. RELATION BETWEEN INITIAL STRENGTH AND MODULUS OF
ELAsTIcIr BASED ON AvERAGE VALUES FOR EACH BODY
Pl3
of elasticity, E - -, which for specimens of rectangular cross-
3AI
section becomes
E =4P13
Abd3
where
E = modulus of elasticity
P = load in pounds
I = length of span in inches
A = deflection in inches at point of application of the load
b = breadth of specimen in inches
d = depth of specimen in inches
The values determined for modulus of elasticity are not sufficiently
accurate for a determination of the absolute value of that elastic
constant, but are of sufficient accuracy for the determination of the
relation between modulus of elasticity, initial strength, and final
strength.
ILLINOIS ENGINEERING EXPERIMENT STATION
Per Cernt ea'dcc/o of Tr'asverse Stfre,/g'f
FIG. 13. RELATION BETWEEN MODULUS OF ELASTICITY AND PER CENT
REDUCTION BASED ON INDIVIDUAL VALUES FOR EACH BODY
BURNED AT THREE DIFFERENT TEMPERATURES
12. Results.-The modulus of elasticity increases with the initial
strength, as shown by average values of the several bodies plotted in
Fig. 12.
The relationship between the modulus of elasticity and the per
cent reduction in strength due to thermal shock is shown by the
"average curve," and by curves for three individual bodies in Fig. 13.
The linear relationship shown in Fig. 12 and the similarity of the
curves of Fig. 13 with that in Fig. 1 shows that the mathematical
relationship between the modulus of elasticity and the per cent re-
duction in strength due to thermal shock would take the same form as
the equation given.
13. Determination of Porosity.-Apparent porosity is the per cent,
by volume, of open pore space based on the bulk volume of the
test piece.
The test pieces were weighed dry and were then saturated by
immersing in kerosene under a 28-in. vacuum for twelve hours.
The saturated specimens were then weighed both in air and sus-
pended in kerosene.
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
FIG. 14. RELATION BETWEEN POROSITY AND PER CENT REDUCTION
BASED ON AVERAGE VALUES
35 -
0
30
00
" 0
5 0
/0-
^ _______^^ ^^ -^___ ___\
- ± - - .1 - I - L - .1 - L - .J - L - .1 - L - .I........A - .1 - .1 - J. - .1 - L - .1 - I
/0 wO 30 40 s0 60 70 80 90
Per Cen't Reduct'orn7 /?2 Transverse Streng/h
FIG. 15. RELATION BETWEEN POROSITY AND PER CENT REDUCTION
BASED ON INDIVIDUAL VALUES FOR EACH BODY BURNED AT
THREE DIFFERENT TEMPERATURES
K
ILLINOIS ENGINEERING EXPERIMENT STATION
30
;?o
t /
K
1<
S0 0 " .
/0 /000 -
W-W
where
, = weight suspended in kerosene
0 0 40 60 80 /00 ,0
in strength increase. Rur erse
FIG. 16. GENERAL RELATION BETWEEN INITIAL AND FINAL STRENGTH,
PER CENT REDUCTION, MODULUS OP ELASTICITY, AND POROSITY
The porosity was then calculated from the equation
p 100 (W- Wd
where
P = per cent apparent porosity
WyV = saturated or wet weight
Wd = dry weight
W, = weight suspended in kerosene
14. Results.-As the porosity of the body decreases (with greater
degree of vitrification) the initial strength and the per cent reduction
in strength increase.
The general relation between porosity* and strength is an estab-
lished fact and will not be discussed.
The relation between porosity and per cent reduction is shown in
Fig. 14 in which each point is the average of all values for each body.
*A. V. Bleininger: Trans. Amer. Cer. Soc., XII, 564, 1910.
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
60
z50
40
20
la
0
4000-
SN3000
/--5/7 Grog'
0 20 40 60 80 /00
Per Cent PReuki3 w in Trawsverse Strengh
FIG. 17. EFFECT OF GROG ON PHYSICAL PROPERTIES AND
RESISTANCE TO THERMAL SHOCK
All individual values are plotted in Fig. 15 and give a scattered
field because the data represent a comparison of bodies, of widely
different characteristics, which have been burned at different tem-
peratures.
The broken line curve shows a fairly definite lower limit in poros-
ity for corresponding values of per cent reduction.
The average values in Fig. 14 represent the same group of bodies,
each burned at the same temperature, and show the general trend
clearly.
15. General Relationships.-Initial strength, per cent reduction in
strength, and modulus of elasticity increase and porosity decreases
as strength after thermal shock increases to a maximum and then
declines.
The general relationships are shown graphically in Fig. 16.
ILLINOIS ENGINEERING EXPERIMENT STATION
IV. EFFECT OF ADDITION OF GROG
16. Effect of Grog on Resistance to Thermal Shock.-Grog ordina-
rily is considered to be any non-plastic and inert material used in
ceramic products for the purpose of altering the physical properties.
Such material may be prepared from clay by burning to remove plas-
ticity and shrinkage. The resulting product is inert, and after grind-
ing and screening is used as grog.
To determine the general effect of additions of grog, the following
bodies were subjected to thermal shock:
(1) 100 per cent clay (through 100 mesh)
(2) 85 per cent clay, 15 per cent grog (through 8 on 14 mesh)
(3) 70 per cent clay, 30 per cent grog (through 8 on 14 mesh)
The results are plotted in Fig. 17 and indicate that, as the per-
centage of grog increases, initial strength and modulus of elasticity
decrease, while strength after thermal shock increases to a maximum
and then declines.
For the particular bodies tested, 15 per cent grog gave less than
maximum resistance to thermal shock, while 30 per cent carried the
body beyond maximum resistance. Examination of the curves
shows that 20 per cent grog would have given best resistance to
thermal shock for the bond clay and size of grog tested.
V. GENERAL DIscussION OF EFFECT OF THERMAL SHOCK
17. Tentative Definitions.-The American Society for Testing
Materials has tentatively defined "spalling,"* with reference to re-
fractories, as "Breaking or cracking of refractories to such an extent
that fragments are separated, presenting newly exposed surfaces of
the residual mass." Comparisons of resistance to spalling are usually
made by heating the specimens to a specified temperature, followed
by quenching in air or water. The relative number of cycles required
to spall off 20 per cent of each of the materials being compared indi-
cates their relative resistance to spalling.
Such a test does not consider the effect of repeated thermal shock
under test conditions which are not sufficiently severe to cause com-
plete failure.
In the present investigation, comparison of the resistance of clay
bodies to thermal shock has been made on the basis of the reduction in
transverse strength produced by thermal shock.
*"Tentative Standards," A.S.T.M., 1927.
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
The most resistant body is considered to be the one which has the
highest transverse strength after thermal shock.
18. Comparisons with Data of Other Investigators.-Goodrich com-
pared the resistance of various brands of firebrick to thermal shock by
determining their loss in compressive strength. He pointed out that a
vitrified or brittle structure was the worst handicap for good resist-
ance to thermal shock.
As pointed out by Parmelee and Westman, his correlation be-
tween initial and final strength is good, the probable error of the aver-
age percentage of the original strength which was retained being
±3.1. This was attributed to the fact that comparisons were made
between the two halves of the same brick. The small probable error
is quite large, however, when compared with the values of the per-
centage of strength retained, which vary from 68.0 per cent to 85.7
per cent, a range of only 17.7 per cent.
Parmelee and Westman were able to predict the per cent loss in
strength of firebrick after thermal shock, from the initial strength,
with a probable error of + 6.8, and measure the per cent loss in
strength with a probable error of about ± 3.1. Their values for per
cent loss in strength varied approximately from zero to 86 per cent.
They concluded that, "It is evident that the stronger brands lost
a greater proportion of their strength when subjected to thermal shock
than did the weaker brands, although their final strength was, in
general, higher than that of the weaker brands."
It seems probable that the accuracy of their predictions may be
attributed, partially at least, to the fact that, with two exceptions,
the bodies are below or near maximum resistance so that the values
for initial and final strength lie in a comparatively narrow field
below the 45 deg. line.
These particular conditions will not exist for all groups of bodies
which might be tested, and for this reason their assumption of a
straight line relationship will not have general application.
It is evident also from the mathematical relationships that, as
the strength of the brick increases, the final strength of the stronger
brands will not continue to be greater than the final strength of the
weaker brands.
Heindl and Mong in their work on sagger bodies concluded that
the resistance of saggers to thermal shock "decreases with increased
temperature of firing saggers" and that "there is a direct relation
between modulus of rupture and modulus of elasticity."
ILLINOIS ENGINEERING EXPERIMENT STATION
Obviously, these conclusions contradict their empirical formula
which states, in part, that resistance to thermal shock is directly
proportional to modulus of rupture and inversely proportional to
modulus of elasticity.
Heindl and Pendergast in their work on firebrick concluded
that "the modulus of elasticity and transverse strength increase as
the temperature of firing of the brick is increased" and that "resis-
tance of firebrick to spalling on an average decreased with increase
of modulus of elasticity... "
Again, the conclusions obviously contradict the empirical formula,
devised as a result of the study, which states, in part, that resistance
to thermal shock is directly proportional to modulus of rupture and
inversely proportional to modulus of elasticity.
19. Summary of Results of Other Investigators.-Goodrich con-
tended that high firing and the development of vitrification decreased
resistance to thermal shock, which agrees in general with the stated
conclusions of Heindl, Mong, and Pendergast, but contradicts the
mathematical expression of their results, which, of course, they
themselves contradict.
Parmelee and Westman contended that resistance to thermal
shock in general increased with increased initial strength which
contradicts the statements of other investigators.
It has been shown in the present investigation that as initial
strength increases, resistance to thermal shock increases to a maxi-
mum and then declines.
It is possible then that the disagreement in results may be ex-
plained by the nature of the materials studied in each investigation,
for it is evident that, for a limited field, resistance to thermal shock
might either increase or decrease as initial strength increases.
Parmelee and Westman studied carburetor brick of compara-
tively low strength, while Heindl, Mong, and Pendergast studied
sagger bodies and firebrick which either developed higher strength
normally, or were preheated at high temperatures before testing. It
seems probable that the carburetor brick in the first instance all
were below or near maximum resistance, while the sagger bodies and
firebrick in the other instances were beyond maximum resistance.
20. Improvement of Test.-The progressive effect of repeated
thermal shock must be determined before a comparison of bodies of
different types can be made safely on the basis of a limited number
of thermal shocks. It is possible that a body of low initial and final
strength with low per cent reduction in a standard test might have
THE EFFECT OF THERMAL SHOCK ON CLAY BODIES
a higher final strength than a body having high initial and final
strength with a high per cent reduction in a standard test, if com-
pared after a large number of thermal shocks.
Since vitrification is known to decrease resistance to thermal
shock it is important to know how a body would behave when
vitrified to a degree corresponding to that which would be produced
by service conditions.
The greatest difference between bodies, as determined in a ther-
mal shock test which does not affect their vitrification, appears after
they have passed their maximum resistance and are approaching
vitrification. For this reason it is probable that comparisons of
bodies could best be made by determining their resistance through-
out the range of burning from a very soft to a vitrified structure.
VI. SUMMARY
21. Summary.-Previously published conclusions of other in-
vestigators are contradictory because they apply only to limited
fields in each case.
The results of the present investigation indicate that:
(1) In general, initial strength, modulus of elasticity, and per
cent reduction in strength increase and porosity decreases as strength
after thermal shock increases to a maximum and then declines.
(2) As grog is added to a clay body the initial strength and mod-
ulus of elasticity decrease, while strength after thermal shock in-
creases to a maximum, and then declines.

RECENT PUBLICATIONS OF
THE ENGINEERING EXPERIMENT STATIONt
Bulletin No. 183. Tests of the Fatigue Strength of Steam Turbine Blade Shapes,
by Herbert F. Moore, Stuart W. Lyon, and Norville J. Alleman. 1928. Twenty-five
cents.
Bulletin No. 184. The Measurement of Air Quantities and Energy Losses in
Mine Entries. Part III, by Alfred C. Callen and Cloyde M. Smith. 1928. Thirty-five
cents.
Bulletin No. 185. A Study of the Failure of Concrete under Combined Com-
pressive Stresses, by Frank E. Richart, Anton Brandtzaeg, and Rex L. Brown. 1928.
Fifty-five cents.
*Bulletin No. 186. Heat Transfer in Ammonia Condensers. Part II, by Alonzo
P. Kratz, Horace J. Macintire, and Richard E. Gould. 1928. Twenty cents.
*Bulletin No. 187. The Surface Tension of Molten Metals. Part II, by Earl E.
Libman. 1928. Fifteen cents.
Bulletin No. 188. Investigation of Warm-Air Furnaces and Heating Systems.
Part III, by Arthur C. Willard, Alonzo P. Kratz, and Vincent S. Day. 1928. Forty-
five cents.
Bulletin No. 189. Investigation of Warm-Air Furnaces and Heating Systems.
Part IV, by Arthur C. Willard, Alonzo P. Kratz, and Vincent S. Day. 1929. Sixty
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Bulletin No. 190. The Failure of Plain and Spirally Reinforced Concrete in
Compression, by Frank E. Richart, Anton Brandtzaeg, and Rex L. Brown. 1929.
Forty cents.
Bulletin No. 191. Rolling Tests of Plates, by Wilbur M. Wilson. 1929. Thirty
cents.
Bulletin No. 192. Investigation of Heating Rooms with Direct Steam Radiators
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Maurice K. Fahnestock, and Seichi Konzo. 1929. Forty cents.
Bulletin No. 193. An X-Ray Study of Firebrick, by Albert E. R. Westman.
1929. Fifteen cents.
*Bulletin No. 194. Tuning of Oscillating Circuits by Plate Current Variations,
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Bulletin No. 195. The Plaster-Model Method of Determining Stresses Applied
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*Bulletin No. 196. An Investigation of the Friability of Different Coals, by Cloyde
M. Smith. 1929. Thirty cents.
*Circular No. 18. The Construction, Rehabilitation, and Maintenance of Gravel
Roads Suitable for Moderate Traffic, by Carroll C. Wiley. 1929. Thirty cents.
Bulletin No. 197. A Study of Fatigue Cracks in Car Axles. Part II, by Herbert
F. Moore, Stuart W. Lyon, and Norville J. Alleman. 1929. Twenty cents.
*Bulletin No. 198. Results of Tests on Sewage Treatment, by Harold E. Babbitt
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*Bulletin No. 199. The Measurement of Air Quantities and Energy Losses in
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*Bulletin No. 200. Investigation of Endurance of Bond Strength of Various Clays
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*Circular No. 19. Equipment for Gas-Liquid Reactions, by Donald B. Keyes.
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Bulletin No. 201. Acid Resisting Cover Enamels for Sheet Iron, by Andrew I.
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Bulletin No. 202. Laboratory Tests of Reinforced Concrete Arch Ribs, by
Wilbur M. Wilson. 1929. Fifty-five cents.
*Bulletin No. 203. Dependability of the Theory of Concrete Arches, by Hardy
Cross. 1929. Twenty cents.
tCopies of the complete list of publications can be obtained without charge by addressing the
Engineering Experiment Station, Urbana, Ill.
*A limited number of copies of the bulletins starred are available for free distribution.
30 ILLINOIS ENGINEERING EXPERIMENT STATION
*Bulletin No. 204. The Hydroxylation of Double Bonds, by Sherlock Swann, Jr.
1930. Ten cents.
Bulletin No. 205. A Study of the Ikeda (Electrical Resistance) Short-Time Test
for Fatigue Strength of Metals, by Herbert F. Moore and Seichi Konzo. 1930.
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*Bulletin No. 206. Studies in the Electrodeposition of Metals, by Donald B.
Keyes and Sherlock Swann, Jr. 1930. Ten cents.
*Bulletin No. 207. The Flow of Air Through Circular Orifices with Rounded
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Thirty cents.
*Circular No. 20. An Electrical Method for the Determination of the Dew-Point
of Flue Gases, by Henry Fraser Johnstone. 1929. Fifteen cents.
Bulletin No. 208. A Study of Slip Lines, Strain Lines, and Cracks in Metals
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Bulletin No. 209. Heat Transfer in Ammonia Condensers. Part III, by Alonzo
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Bulletin No. 210. Tension Tests of Rivets, by Wilbur M. Wilson and William A.
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Bulletin No. 211. The Torsional Effect of Transverse Bending Loads on Channel
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Bulletin No. 212. Stresses Due to the Pressure of One Elastic Solid upon
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Bulletin No. 213. Combustion Tests with Illinois Coals, by Alonzo P. Kratz
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*Bulletin No. 214. The Effect of Furnace Gases on the Quality of Enamels for
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Bulletin No. 215. The Column Analogy, by Hardy Cross. 1930. Forty cents.
Bulletin No. 216. Embrittlement in Boilers, by Frederick G. Straub. 1930.
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Bulletin No. 217. Washability Tests of Illinois Coals, by Alfred C. Callen and
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Bulletin No. 218. The Friability of Illinois Coals, by Cloyde M. Smith. 1930.
Fifteen cents.
Bulletin No. 219. Treatment of Water for Ice Manufacture, by Dana Burks, Jr.
1930. Sixty cents.
*Bulletin No. 220. Tests of a Mikado-Type Locomotive Equipped with Nichol-
son Thermic Syphons, by Edward C. Schmidt, Everett G. Young, and Herman J.
Schrader. 1930. Fifty-five cents.
*Bulletin No. 221. An Investigation of Core Oils, by Carl H. Casberg and Carl E.
Schubert. 1931. Fifteen cents.
*Bulletin No. 222. Flow of Liquids in Pipes of Circular and Annular Cross-
Sections, by Alonzo P. Kratz, Horace J. Macintire, and Richard E. Gould. 1931.
Fifteen cents.
*Bulletin No. 223. Investigation of Various Factors Affecting the Heating of
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*Bulletin No. 224. The Effect of Smelter Atmospheres on the Quality of Enamels
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*Buletin No. 225. The Microstructure of Some Porcelain Glazes, by Clyde L.
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*Bulletin No. 226. Laboratory Tests of Reinforced Concrete Arches with Decks,
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*Bulletin No. 227. The Effect of Smelter Atmospheres on the Quality of Dry
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*Circular No. 21. Tests of Welds, by Wilbur M. Wilson. 1931. Twenty cents.
*Bulletin No. 228. The Corrosion of Power Plant Equipment by Flue Gases, by
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*Bulletin No. 229. The Effect of Thermal Shock on Clay Bodies, by William R.
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*A limited number of copies of bulletins starred are available for free distribution.

UNIVERSITY OF ILLINOIS
THE STATE UNIVERSITY
URBANA
HARRY WOODBURN CHASE, Ph.D., LL.D., President
The University includes the following departments:
The Graduate School
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in the Humanities and the Sciences; Chemistry and Chemical Engi-
neering; Pre-legal, Pre-medical, and Pre-dental; Pre-journalism, Home
Economics, Economic Entomology, and Applied Optics)
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eral Business, Banking and Finance, Insurance, Accountancy, Railway
Administration, Railway Transportation, Industrial Administration,
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tural, Ceramic, Civil, Electrical, Gas, General, Mechanical, Mining, and
Railway Engineering; Engineering Physics)
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Home Economics; Landscape Architecture; Smith-Hughes-in con-
junction with the College of Education)
The College of Education (Curricula: Two year, prescribing junior stand-
ing for admission - General Education, Smith-Hughes Agriculture,
Smith-Hughes Home Economics, Public School Music; Four year, ad-
mitting from the high school-Industrial Education, Athletic Coaching,
Physical Education. The University High School is the practice school
of the College of Education)
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three years of college work at the University of Illinois)
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college work)
The College of Medicine (in Chicago)
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Experiment Stations and Scientific Bureaus: U. S. Agricultural Experiment
Station; Engineering Experiment Station; State Natural History Sur-
vey; State Water Survey; State Geological Survey; Bureau of Educa-
tional Research.
The Library collections contain (May 1, 1930) 836,496 volumes and 221,800
pamphlets.
For catalogs and information address
THE REGISTRAR
Urbana, Illinois
I