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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

M. Husem / Fire Safety Journal 41 (2006) 155163156


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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

M. Husem / Fire Safety Journal 41 (2006) 155163 157


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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

ARTICLE IN PRESS

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

ARTICLE IN PRESS

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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0

0.2

0.4

0.6

0.8

1

1.2

0 200 400 600 800 1000 1200 1400

Temperature (C)

fc/f'c(23)

Eurocode Desing Curve (Siliceous aggregate)

Eurocode Design Curve (Calcareous aggregate)

CEB Desing Curve

Finnish Design Curve (rakMK B4 K70-K100)

OMC (Cooling in air)

OMC (Cooling in water)

HPMC (Cooling in air)

HPMC (Cooling in water)

Fig. 6. Comparison of design curves and experimental loss of strength curves.



9/9

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