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Fire Safety Journal 41 (2006) 155163
The effects of high temperature on compressive and flexural strengths
of ordinary and high-performance concrete
Metin Husem
Department of Civil Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey
Received 29 April 2004; received in revised form 10 October 2005; accepted 5 December 2005
Abstract
The variation of compressive and flexural strengths of ordinary and high-performance micro-concrete at high temperatures was
examined. Compressive and flexural strengths of ordinary and high-performance micro-concrete which were exposed to high
temperatures (200, 400, 600, 800 and 1000 1C) and cooled differently (in air and water) were obtained. Compressive and flexural strengths
of these concrete samples were compared with each other and then compared with the samples which had not been heated. On the other
hand, strength loss curves of these concrete samples were compared with the strength loss curves given in the codes. Experimental results
indicate that concrete strength decreases with increasing temperature, and the decrease in the strength of ordinary concrete is more than
that in high-performance concrete. The type of cooling affects the residual compressive and flexural strength, the effect being more
pronounced as the temperature increases. Strength loss curves obtained from this study agree with strength loss curves given in the
Finnish Code.
r 2006 Elsevier Ltd. All rights reserved.
Keywords: High-performance concrete; Ordinary concrete; High temperature; Compressive strength; Flexural strength; Loss of strength
1. Introduction
Concrete has been defined as a composite material
obtained using cement, aggregate, water and when
necessary chemical and/or mineral additives, placed into
moulds of various sizes and shapes and hardened under
convenient conditions [13]. Today concrete has been used
with an increased strength and durability in connection
with the developments in technology in pre-stressed
concrete, concrete and reinforced concrete structures.
Pre-stressed concrete, concrete and reinforced concretestructures are sometimes exposed to fires and many
structures become damaged and/or out of use [4]. As it is
known, high temperatures caused as a result of fire
decreases the concrete strength and durability of such
structures. Fire resistance of concrete is affected by factors
like the type of aggregate and cement used in its
composition, the temperature and duration of the fire,
sizes of structure members, and moisture content of
concrete [57]. Fire resistance of the aggregates is generally
high. However, having non-uniform high temperature
effect of aggregate or cooling the heated aggregate using
water spray may cause internal pressure in the aggregates.
This pressure may make the aggregate spall. Some of the
deformation in the concrete is due to the expansion of
cement in its composition. Hydrated Portland cement
contains a significant amount of free calcium hydroxide
and will decompose into calcium oxide due to loss of water
at 4004501
C . If this calcium oxide is wetted after beingcooled or is kept in a moist environment, it transforms into
calcium hydroxide again. The concrete may crumble as a
result of such changes in volume [2,3,8,9]. An increase in
the size of structural members increases fire resistance.
The effects of high temperature on the mechanical
properties of concrete have been investigated since the
1940s [8,1034]. These studies examined the behavior of
cement paste, mortar, concrete samples and reinforced
concrete members exposed to high temperature [14].
Results of these studies constituted the technical basis for
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the provisions and recommendations for determining
concrete strength of elevated temperature in many codes
[14]. For design purpose, mechanical properties of concrete
at elevated temperature may be obtained using design
curves prescribed in the codes [3338].
Many of these studies were realized for properties of
ordinary concrete exposed to high temperature. Fewerstudies have been carried out with high-performance
concrete than with ordinary concrete [23,2732].
Concrete structures are sometimes exposed to the effects
of fire. Although there are different ways to extinguish the
fire, it is generally done with water spray. This causes
different stresses in reinforced concrete members at high
temperature and the structural member can lose load
bearing capacity. In this study, the behavior of ordinary
and high-performance concretes exposed to high tempera-
tures is examined after cooling in air or water. In the tests,
temperatures of 23, 200, 400, 600, 800, and 1000 1C were
chosen for ease of observation of the test results. All series
were exposed to same temperatures.
To determine the resistance of concrete samples exposed
to high temperature, many test methods are used. Three
test methods are commonly referred in most experimental
programs on the fire performance of concretes [14]. These
are named as stressed, unstressed and unstressed residual
strength tests. In stressed tests, a preload (2040% of the
compressive strength at 23 1C) is applied to the specimen
prior to heating and is sustained during the heating period.
Heat is applied at a constant rate until a target temperature
is reached, and is maintained for a time until a thermal
steady state is achieved. Stress or strain is then increased at
a prescribed rate until the specimen fails. In the unstressedtest, the specimen is heated, without preload, at a constant
rate to the target temperature, which is maintained until a
thermal steady state is achieved. Stress or strain is then
applied at a prescribed rate until failure occurs. In
unstressed residual strength test, the specimen is heated
without preload at a prescribed rate to the target
temperature, which is maintained until a thermal steady
state is reached within the specimen. The specimen is then
allowed to cool, following a prescribed rate, to room
temperature. Load or strain is applied at room temperature
until the specimen fails. In this study, unstressed residual
strength test is used to obtain the effects of high
temperature on compressive and flexural strengths of
ordinary and high-performance concrete.
Research has indicated that [20,28,29] strength loss and
explosive spalling occur in the concrete exposed to high
temperatures. High-performance concrete has been found
to have greater strength loss in the intermediate tempera-
ture range than ordinary concrete when exposed to the
same heating condition. High-performance concrete speci-
mens are prone to explosive spalling, even when heated at a
relatively slow heating rate (p5 C/min). According to the
test results obtained from this study, strength loss of high-
performance micro-concrete is more than that of ordinarymicro-concrete. But explosive spalling in high-performance
micro-concrete does not occur in ordinary micro-concrete.
2. The aim of study
The main objective of this research is to examine the
variation according to cooling type of compressive and
flexural strength of high-performance micro-concrete and
ordinary micro-concrete at high temperatures. Compres-
sive and flexural strengths of ordinary and high-perfor-
mance micro-concrete exposed to high temperatures (200,
400, 600, 800, and 10001
C) and cooled in variousenvironments (in air and water) were obtained and the
results compared. Tests were also carried out on samples
which had not been exposed to high temperatures. The
study also examines the effects of minerals and chemical
additives used in the production of high-performance
concrete, on the mechanical properties of concrete exposed
to high temperature.
3. Experimental study
3.1. Materials
Because it is commonly used in concrete production in
the region, the limestone aggregate was used in ordinary
and high-performance concrete production. The maximum
aggregate size used was 16 mm. The physical properties of
this aggregate are given in Table 1. The petrographic
structure of ordinary aggregate includes only opaque
minerals o1% and micritic cemented limestone compris-
ing partially old microfossils.
In the production of high-performance concrete and
micro-concrete, PC 42.5 Portland cement was used. The
number 42.5 denotes its characteristic compressive strength
in MPa. In the production of ordinary concrete and micro-
concrete, PC 32.5 Portland cement was used. Some
properties of these cements are given in Tables 2 and 3,
respectively.
In the production of high-performance concrete
and micro-concrete, silica fume and superplasticizer
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Table 1
The physical properties of aggregate
Aggregate size Loose density (kg=m3) Dry density(kg=m3) Saturated density (kg=m3) Water absorption (%)
Course(44 mm) 1445 2706 2720 0.43
Fine(o4 mm) 1485 2675 2682 0.50
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(ASTM C-494 F type) admixture were used. Chemical
properties of silica fume are given in Table 4.In the examination of the effects of high temperatures on
the compressive and flexural strengths of high performance
and ordinary concrete, micro-concrete samples were used.
High performance and ordinary concrete were produced
first and their compressive strengths were determined.
Micro-concrete having the same properties with the mortar
phase in the concrete was then produced. Micro-concrete is
used in the study of the effect of high temperature on
flexural and compressive strength.
3.2. Mixture and production of concrete
The gradations of aggregate used in the high perfor-
mance and ordinary concrete were the same. The aggregate
proportion is given in Table 5. In the mixture proportion-
ing of high performance and ordinary concrete, water to
cement ratios of 0.30 and 0.50 were used, respectively. The
mixture proportions of concretes are given in Table 6. In
the production of high-performance concrete, silica fume
was added (10% of weight of cement) and superplasticizer
admixture was used (2% of total weight of cement and
silica fume).
In mixing concrete, a concrete mixer having 80 l capacity
and inclined axes was used. Each granulometric aggregate
was weighed and placed into the concrete mixer moistened in
advance and mixed for 3 min with the addition of saturation
water, for 3 min with the addition of cement (together with
silica fume, if any), and thereafter, mixed for another 3 min
without stopping to add the mixing water (together with the
superplasticizer admixture, if any). The resulting concrete was
placed in standard cylinder (150 mm 300mm) moulds at 3
stages and 12 samples were prepared in each production (12
samples for high-performance concrete and 12 samples for
ordinary concrete).
The samples, which were taken out the day after, were
kept in water at 22 2 C for 21 days. They were kept at
23 1C and 65% relative humidity until the time of the
experiment. The specimens were 28 days old at the time of
the tests.
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Table 2
Some properties of PC 42.5 cement
Physical properties Mechanical properties
Density (g=cm3) 3.10 Age (day) Flexural strength (MPa) Compressive strength (MPa)
Specific surface (Blaine) (cm2=g) 3680 2 5.75 29.05
Setting Initial (h) 2.10 7 7.55 43.65
time (vicat) Final (h) 4.15 28 8.75 52.97
Table 3
Some properties of PC 32.5 cement
Physical properties Mechanical properties
Density (g=cm3) 3.05 Age (day) Flexural strength (MPa) Compressive strength (MPa)
Specific surface (Blaine) (cm2=g) 3260 2 4.01 15.20
Setting time (vicat) Initial (h) 2.10 7 5.35 28.2
Final (h) 3.40 28 6.65 36.17
Table 4
Chemical compositions of silica fume
Component SiO2 Fe2O3 Al2O3 CaO3 MgO3 CrO3 Loss on ignition Free CaO
(%) 82 1.8 3.2 1.4 5 3 2.2 1.2
Table 5
The gradation of aggregate
Gradation class %, total weight
0 mm0.25 mm 4
0.25 mm0.50 mm 8
0.50 mm1.00 mm 8
1.00 mm2.00 mm 12
2.00 mm4.00 mm 21
4.00 mm8.00 mm 19
8.00 mm16.00 mm 28
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3.3. Mixture and production of micro-concrete
The mix proportions of micro-high performance
(HPMC) and ordinary micro-concrete (OMC) are given
in Table 7. The maximum aggregate size used was 4 mm.
The gradation of aggregate is given in Table 8. On
examining the effects of high temperature on the mechan-
ical properties of high performance and ordinary concrete,prismatic micro-concrete experimental samples with di-
mensions of 40 mm 40mm 160 mm were produced to
represent the mortar in the composition of such concrete.
Watercement ratios (in high-performance concrete it is
0.30, in ordinary concrete 0.50) and cementsand ratios
used in the production of concrete (in high-performance
concrete it is 0.620, in ordinary concrete 0.425) are the
same in order to obtain the mortars in high performance
and ordinary concrete in the production of such samples.
They are placed into prismatic moulds in three stages,
applying vibration for 15 s. The samples were taken out of
their moulds after 1 day and kept in water at 22 2 C for
21 days. Until the time of the experiment, they were kept at
23 1C, and 65% relative humidity. For each micro-concrete
type, 180 test samples were produced. The samples were
28 days old at the time of the experiment.
3.4. Test procedure
In this study, uniaxial compressive tests on high
performance and ordinary concrete samples (for each
concrete 12 samples) were performed with a constant
loading rate of 0.15MPa/s. The reason of choosing
0.15 MPa/s is to keep the loading rate to a minimum in
the comparison of test results.
In determining the effects of high temperature on the
compressive and flexural strength of HPMC and OMC, a
flexural test was done on the prismatic samples with
dimensions 40 mm 40mm 160 mm. Compressive tests
were done on the samples which had been broken before.
For each micro-concrete, 36 samples were used at each test
temperature. The tests were performed at five different
temperatures (200, 400, 600, 800 and 1000 1C) in order to
have practical measurements. Twelve of these samples were
kept at 23 1C and the other 24 samples were put in theoven. They were removed 1 h after the desired temperature
was reached. Twelve of these samples were cooled in water
and the other 12 were cooled in air (at room temperature)
until they were at 23 1C. The flexural and compressive tests
were performed on the cooled samples and 12 others which
were kept at 23 1C.
4. Results and discussion
Compressive strength tests are done on the concrete and
micro-concrete samples. Twelve samples were used for each
series of experiments. The average compressive strengths
and standard deviations are given in Table 9.
In this study, ordinary concrete with an average
compressive strength of 34 MPa and high-performance
concrete with an average compressive strength of 71 MPa
have been produced using the composition ratios in Table
6. Micro-concrete samples are produced to represent the
mortar phase of the produced ordinary and high-perfor-
mance concrete.
The samples produced for the examination of the
behavior of HPMC and OMC exposed to high temperature
are placed into an oven with a heating capacity of 1200 1C.
The variation of the oven temperature as a function of time
is given in Fig. 1. As it is seen in the figure, the rate of
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Table 6
Mix design of high performance and ordinary concrete
Concretes W/C Cement kg=m3 Water kg=m3 Total aggregate kg=m3 Absorbed water kg=m3 Admixtures
SP kg=m3 SF kg=m3
HPC 0.30 500 150 1789 9.5 22 50
OC 0.50 350 175 1829 11.70
HPC, high-performance concrete; SP, superplasticizer admixture; OC, ordinary concrete; and SF, silica fume.
Table 7
Mix design of micro-high performance and ordinary micro-concrete
Components Micro-high-
performance
concrete kg=m3
Micro-ordinary
concrete kg=m3
Cement 786 572
Water 236 286
Sand 1286 1345Silica fume 78.6
Superplasticizer 25.9
Table 8
The gradation of aggregate for micro-concrete
Gradation class %, total weight
0 mm0.25 mm 7
0.25 mm0.50 mm 15
0.50 mm1.00 mm 15
1.00 mm2.00 mm 23
2.00 mm4.00 mm 40
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achieving an oven temperature of 1000 1C is 6.67 1C/min in
OMC and 5.5 1C/min in HPMC. The slope of time
temperature curve is higher for HPMC than for OMC.
Because HPMC has a structure with fewer pores than
OMC, therefore thermal conductivity of HPMC is higher
than that of OMC.
Twenty-eight days after their production, experimentalsamples were kept in the oven until the temperature is 200,
400, 600, 800, and 1000 1C, respectively. Then, they were
taken out of the oven and some of them were left to cool in
air and some of them in water till they reached 231C.
Cooled in air or water, samples were first exposed to
flexural and then to compressive experimentation on
broken pieces. The flexural test was carried out on 12
samples for each series, but the compressive strength test
was performed on 24 samples for each series. The
compressive and flexural strengths obtained in this way
are given in Table 10.
Change with temperature of flexural strength of HPMC
and OMC concrete is given in Fig. 2, and change with
temperature of compressive strength of micro-concretes is
given Fig. 3. In these figures, ordinary micro-concrete isdenoted as OMC, high-performance micro-concrete as
HPMC, air cooling as AC, and water cooling as WC.
The flexural strength of OMC cooled in air after being
exposed to the effect of different temperatures is lower than
that of the reference samples: 21% for 200 1C, 33% for
400 1C, 58% for 600 1C, 63% for 800 1C. Flexural strength
of OMC cooled in water after being exposed to the effect of
different temperature is also lower than that of reference
samples: 22% for 200 1C, 36% for 400 1C, 68% for 600 1C,
84% for 800 1C. The compressive strength of OMC cooled
in air is less than that of the reference samples: 7% for
200 1C, 12% for 400 1C, 27% for 600 1C, 47% for 800 1C.
Compressive strength of OMC cooled in water is also less
than that of reference samples: 27% for 200 1C, 29% for
400 1C, 44% for 600 1C. Because the samples disintegrated
in water, compressive tests on samples could not be
completed for 800 and 1000 1C.
The flexural strength of HPMC cooled in air after being
exposed to the effect of different temperature is lower than
that of reference samples: 36% for 200 1C, 27% for 400 1C,
36% for 600 1C, 60% for 800 1C, 71% for 1000 1C. The
flexural strength of HPMC cooled in water after being
exposed to the effect of different temperature is also lower
than that of reference samples: 30% for 200 1C, 28% for
400 1C, 45% for 600 1C, 70% for 800 1C. Because thesamples disintegrated in water, flexural tests on samples
could not be completed for 1000 1C. Compressive strength
of HPMC cooled in air is smaller than that of reference
samples: 32% for 200 1C, 23% for 400 1C, 26% for 600 1C,
51% for 800 1C and 75% for 1000 1C. Compressive
strength of HPMC cooled in water is also less than that
of the reference samples: 33% for 200 1C, 29% for 400 1C,
34% for 600 1C, 56% for 800 1C. Because the samples
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Table 9
The mechanical properties of concretes
Concretes Average compressive
strength (MPa)
Standard division(MPa)
HPC 71 1.3
OC 34 0.8
0
200
400
600
800
1000
1200
0 50 100 150
Time (minute)
Tempera
ture(C)
HPMC
OMC
Fig. 1. Variation of oven temperature by time.
Table 10
The mechanical properties of micro-concrete in different temperatures
Temperature
(C)
Ordinary micro-concrete High-performance micro-concrete
Flexural strength (MPa) Compressive strength (MPa) Flexural strength (MPa) Compressive strength (MPa)
Type of cooling
in air in water in air in water in air in water in air in water
23 9.1 59.4 9.7 85.1
200 7.2 7.1 55 43.2 6.2 6.8 58 57.1
400 6.1 5.8 52.2 42.1 7.1 7.0 65.4 60.1
600 3.8 2.9 43.4 33.0 6.2 5.3 62.9 56.2
800 3.4 1.5 31.5 0 3.9 2.9 41.3 37.6
1000 0.7 0.2 6.5 0 2.8 0 21 0
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disintegrated in water, compressive test on samples could
not be completed for 1000 1C.
As one will see from these figures, flexural and
compressive strength of high-performance concrete cooled
in air and water after being exposed to the effect of hightemperature decrease up to 200 1C compared to the flexural
and compressive strengths of the reference samples and the
strength rapidly decreases after showing a certain increase
at 200400 1C. This decrease is more in those samples
cooled in water. Decrease in flexural and compressive
strength of ordinary concrete is much more compared to
that of high-performance concrete. And this shows that
high-performance concrete is more resistant to the effect of
high temperature. However, above 600 1C, decrease in the
strength of both concretes rapidly increases. The reason for
this is that there is no significant change in concretes up to
a temperature of 300 1C in aggregate and mortar phases,
and that there are significant changes in aggregate and
mortar phases after this temperature. These results are in
harmony with the results of various research studies
[17,18,22].
Flexural and compressive strengths of OMC and HPMC
exposed to a high temperature, then cooled in water are less
than those cooled in air. It is apparent that strength losses
of OMC cooled in water compared to OMC cooled in air is
more than the losses of HPMC (see Table 10).
In the former studies, it is stated that, when ordinary
concrete is heated to 300 1C, strength loss changes by
1020% and up to 600 1C it changes by 6070%. In
addition, high-performance concrete heated over 450 1C
has a 40% strength loss [14,28]. In this study, test results
show that compressive strength loss of OMC heated to
400 1C and cooled in air is 12%, in water is 29%.
Compressive strength loss of samples heated up to 600 1C
and cooled in air is 27%, in water is 44%. Compressive
strength loss of HPMC heated to 400 1C and cooled in air
is 23%, in water is 29%. Compressive strength loss of sameconcrete heated to 600 1C and cooled in air is 26%, in water
is 34%.
In the test results it is seen that compressive strength of
OMC under the effect of high temperature and cooled in
air and water has a decreasing trend when the temperature
increases. Strength loss curves obtained from this study for
the ordinary concrete have the same trendbut different
changing ratioobtained from Abrams [33], Morita et al.
[34], and Furumura et al. [39] and from studies in NIST
[14,29]. In the present study, it is seen that the strength of
high-performance concrete exposed to high temperature
and cooled in air and water decreases until 200 1C, an
increase between 200 and 400 1C and a continuous decrease
after 4001C (see in Fig. 3 and Table 10). The strength
increase at 200400 1C in the samples cooled in air is more
than for those cooled in water. These results have a similar
trend to those of Khoury [22] and Hammer [40,41] and to
the studies at NIST [14,24,27,29]. However, in Khourys
study, strength decreases until 100 1C, increases between
100 and 400 1C and decreases continuously above 400 1C.
In the studies performed at NIST, strength in high-
performance concrete decreased until 1001C, increased
between 100 and 200 1C for some concrete mixtures and
decreased rapidly after 2001C. In Hammers study, the
strength decreased until 300 1C (except the concreteproduced without silica fume), increased from 300 to
450 1C and decreased rapidly after 450 1C.
According to the results obtained from the tests, when
the temperature is increased from 23 to 200 1C, compres-
sive strength loss of HPMC is 32% for the specimens which
were cooled in air and 33% for the specimens which were
cooled in water. When the temperature is 400 1C,
compressive strength loss is 23% for cooling in air and
29% for cooling in water. As it can be seen in Fig. 3, when
the temperature is increased from 200 to 400 1C, compres-
sive strength gain is 13% for the specimens cooling in air
and 5% for those cooled in water. The former studies
indicated that the increase is caused by evaporation of free
water and removal of water of crystallization from the
cement paste [42]. This result is supported by the
experiments in that the specimens cooled in air have more
strength gain than the specimens cooled in water because
while they were being cooled in water some of the
evaporated water is regained.
It was reported that when explosive spalling occurs, the
temperature range is between 300 and 650 1C [14,25,27,29].
Many factors were identified as affecting explosive spalling.
These factors include age, moisture content, type of gravel
and sand used, curing method, rate of heating [15]. In this
study, it has been observed that when the temperature is
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0
20
40
60
80
100
0 200 400 600 800 1000 1200
Temperature
Compressivestrength(MPa)
OMC-AC
OMC-WC
HPMC-AC
HPMC-WC
Fig. 3. Variation of compressive strength with temperature.
0
2
4
6
8
10
12
0 200 400 600 800 1000 1200
Temperature
Flexturalstrength(MPa)
OMC-AC
OMC-WC
HPMC-AC
HPMC-WC
Fig. 2. Variation of flexural strength with temperature.
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400500 1C, approximately 30% of samples produced from
HPMC spalled in the experiment. To examine the effect of
admixed material used in concrete producing the explosive
spalling, micro-concrete was first produced without using
the superplasticizer admixture (which is used for theproduction of HPMC), and then without using silica fume
(Table 11). These concretes were exposed to a heat process
of 400 and 600 1C and cooled in air. The results are given in
Fig. 4.
As seen in the figure, flexural strength of micro-concrete
produced using superplasticizer admixture is 1% less than
the flexural strength of HPMC for 23 1C, 20% more for
400 1C, and 34% more for 600 1C. As for flexural strength
of micro-concrete produced using silica fume (without
using superplasticizer admixture), it is 41%, 4% and 10%
less than that of HPMC for 23, 400 and 600 1C,
respectively. Likewise, the compressive strength of micro-
concrete produced using superplasticizer admixture (with-
out using silica fume) is 25% less than the compressive
strength of HPMC for 23 1C, and 1% more for 400 1C, 6%
more for 600 1C. Compressive strength of micro-concrete
produced using silica fume is less than the compressive
strength of HPMC by 44% for 23 1C, 35% for 400 1C and
35% for 600 1C. And this shows that the decrease in the
flexural and compressive strength of micro-concrete
produced using only silica fume is more than that of
micro-concrete produced using only superplasticizer ad-
mixture and that the concrete produced using silica fume is
affected more from high temperature. According to the
results of experimentation conducted, it is considered that
the burst in HPMC is caused by the expansion of silica
fume (Fig. 5).
Strength loss curves of micro-concrete used in this study
are given in Fig. 6 with the design curves given in Codes[3538]. As it is seen in this figure, the Finnish Code is more
suitable than the other Codes for high-performance
concrete (except cooled in water) until 4001C. CEB [35]
and the Finnish Code [38] are more suitable than Eurocode
[36,37] for ordinary and high-performance concrete be-
tween 400 and 600 1C. After 600 1C, Eurocode design
curves are the most suitable ones except for ordinary
concrete cooled in water.
5. Conclusions
The conclusions drawn from the results obtained in this
study are as follows:
Ordinary concrete with an average compressive strengthof 34 MPa and high-performance concrete with an
average compressive strength of 71 MPa have been
produced. In order to represent their mortars micro-
concrete samples have been prepared.
In ordinary and HPMC exposed to high temperature,flexural and compressive strength decreases with the
increase of temperature. Such decrease is greater in
those cooled in water.
The compressive strength of HPMC cooled in air and water
decreased up to 200 1C. The compressive strength of
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Table 11
The mechanical properties of micro concrete with silica fume or superplasticizer admixture
Temp. C Micro-concrete with superplasticizer
(without silica fume)
Micro-concrete with silica fume (without
superplasticizer)
High-performance micro-concrete (in
Table 10)
Flexural strength
(MPa)
Compr. strength
(MPa)
Flexural strength
(MPa)
Compr.
strength(MPa)
Flexural
strength(MPa)
Compr.
strength(MPa)
23 9.6 63.4 5.7 47.8 9.7 85.1
400 8.5 66.0 6.8 42.3 7.1 65.4
600 8.3 66.7 5.6 41 6.2 62.9
0
2
4
6
8
10
12
0 200 400 600 800Temperature
Flex
turalstrength(MPa)
SPMC SFMC HPMC HPMC-WC
Fig. 4. Variation of flexural strength of high-performance micro-concrete
with temperature.
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800
Temperature
Compressivestrength(MPa)
SPMC SFMC HPMC HPMC-WC
Fig. 5. Variation of compressive strength of high-performance micro-
concrete with temperature.
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HPMC was increased between 200 and 400 1C. The
compressive strength of OMC was decreased continuously.
The compressive strength gain was 13% for specimenscooling in air. For the specimens cooling in water the
strength gain was 5%.
The compressive test was not done for OMC in thetemperature above 600 1C, because of concrete samples
disintegrated. For HPMC, the compressive test was not
done at temperatures above 800 1C. It has been observed that some samples produced from
HPMC spall explosively at temperatures between 400
and 500 1C and it has been seen that the cause for such
explosive spalling in high-performance concrete is
expansion of silica fume used in the production of such
concretes. The explosive spalling was not observed for
OMC specimens.
Experimental studies indicated that OMC and HPMCproduced using limestone aggregate caused loss of
strength in high percentages in those cooled in water
after being exposed to high temperature.
Studies show that experimental samples have been
damaged to a great extent and they have lost their
compressive strengths if high-performance concrete is
cooled in water after being exposed to the temperature
of 800 1C, and ordinary concrete is cooled in water after
being exposed to the temperature of 600 1C.
The concrete may completely lose its strength as a resultof the immediate expansions that will form during the
expansion of mineral admixture used in the production
of high-performance concretes in high temperature and/
or water spray-cooling of a reinforced concrete building
element exposed to high temperature as a result of a fire.
The CEN Eurocode and the CEBs design curves for
properties of fire-exposed concrete are not applicable to
high strength micro-concrete. Finnish Code is more
suitable for high-performance concrete especially until
400 1C temperature. These codes are not applicable to
OMC and HPMC cooled in water.
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