A STUDY OF THE HEAT RESISTANCE
OF LOW-CEMENT HIGH-TEMPERATURE CONCRETES
and I. Pundene
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp. 34 – 38, February, 2001.
The heat resistance of five batches of low-cement high-temperature concretes with fireclay fillers is investi
gated. The effect of microsilica in an amount ranging from 5 to 16% on the heat resistance of the concrete is
determined. The influence of primary heat treatment to 1300°C on the resistance of the material to abrupt heat
ing and cooling cycles is analyzed. The results of the observation of crack formation on the surface of concrete
specimens after the action of heat cycles correlate with the data on the heat resistance and the speed of propa
gation of ultrasonic pulses in them.
There are many methods for determining the heat resis-
tance of refractories that have a complete structure as a result
of high-temperature roasting in their production [1 – 4].
High-temperature concretes possess a primary structure that
changes in the first heating depending on the treatment tem-
perature due to the dehydration processes, solid-phase reac-
tions, polymorphic transformations, and crystallization of
amorphous phases. In the present work we used the method
of determining the relative heat resistance of high-tempera
ture concretes with a density exceeding 1500 kg/m
has been developed by the Heat Insulation Institute . In
this method, prismatic specimens are subjected to abrupt
thermal cycles with heating to 850°C and cooling on a wa
ter-cooled plate. After the chosen number of cycles the speci
mens are tested for bending strength. The relative heat resis
is evaluated by the formula
is the ultimate bending strength after gradual roast
ing at 850°C,
is the ultimate bending strength after three
heating – cooling cycles, and
is the ultimate bending
strength after seven heating – cooling cycles.
The aim of the work consisted in evaluating the effect of
the temperature of primary treatment of low-cement high-
temperature concretes with fireclay fillers on their capacity
to resist abrupt heat cycles. In addition, we studied the effect
of the content of microsilica in the composition of the con-
crete on its heat resistance and the effect of the amount of
microsilica and the treatment temperature of the concrete on
the appearance of cracks on the surface of the specimens.
We tested five compositions of low-cement concretes
that differed in the amount of microsilica (from 5 to 16%).
The content of high-alumina cement Gorkal-70, fireclay of
fractions 2.5 – 5.0, 1.25 – 2.5, 0.63 – 1.25, 0.315 – 0.63, and
0.14 – 0.315 mm, and deflocculant (sodium pyrophosphate)
was invariable. As the amount of microsilica was changed,
the content of milled fireclay (up to 0.14 mm) in the compo
sition was changed respectively so that their total content re
mained at a 40% level. The specimens were graded L-5, L-7,
L-10, L-13, and L-16 in accordance with the content of
microsilica in the composition.
We studied concrete specimens 40 ´ 40 ´ 160 mm in
size. Forty-five specimens of each composition were investi
gated. After three days of hardening the specimens of each
composition were divided into five batches with 9 specimens
in each batch. The specimens of the first batch were studied
without heat treatment, i.e., immediately after their harden
ing they were subjected to abrupt heating-cooling cycles.
The specimens of the second batch were dried at 105 – 110°C
to a constant mass and then subjected to thermocycling.
Dried specimens of the third, fourth, and fifth batches were
roasted to 850, 1100, and 1300°C, respectively. Thus, con
crete specimens of the same composition were studied after
Refractories and Industrial Ceramics Vol. 42, Nos.1–2, 2001
1083-4877/01/0102-0083$25.00 © 2001 Plenum Publishing Corporation
Heat Insulation Institute, Lithuania.