Fire Safety and Concrete Structures - Febelcem

expansion (%)
5
4
3
2
1
epsilon,cu1
epsilon,c1
epsilon,sy
expansion of the siliceous concrete
steel reinforcement expansion
specific heat (kJ/kg°C)
2,2
2
u=3%
1,8
u=1,5%
1,6
u=0%
1,4
1,2
1
0,8
0,6
0,4
0,2
0
0 200 400 600 800 1000 1200
temperature (°C)
0
0 200 400 600 800 1000 1200
temperature (°C)
Figure: Evolution of extensions of steel and concrete as a function of
temperature (source FEBELCEM)
The plastification of concrete is the key phenomenon to
understanding the reason for concrete’s resistance to the intense
compressive stresses created when the skin of the concrete heats
up and in general for any restrained concrete.
The thermal expansion of concrete
The thermal deformation εc(θ) of concrete as a function of
temperature is illustrated in the following figure.
thermal expansion
16,E-3
14,E-3
12,E-3
10,E-3
8,E-3
6,E-3
Figure: Thermal expansion of concrete as a function of temperature
[107]
The specific heat of concrete
The variation in the specific heat cp(θ) of concrete as a function of
temperature and water content is illustrated in the following
figure.
The peak observed between 100 and 200 °C corresponds to the
heat needed to evaporate the water contained in the concrete.
Figure: Specific heat of concrete, cp(θ ), as a function of temperature for
3 different water contents, u: 0 %, 1,5 % and 3 % of the weight of the
concrete [107]
The thermal conductivity of concrete
The variation in the upper and lower limits of the thermal
conductivity λc of concrete, as a function of temperature, is
illustrated in the following figure.
thermal conductivity
of concrete (W/m°C)
2,00
1,80
1,60
1,40
1,20
1,00
0,80
0,60
0,40
0,20
0,00
0 200 400 600 800 1000 1200
temperature (°C)
upper limit
lower limit
Figure: Variation in the upper and lower limits of the thermal
conductivity of normal concrete as a function of temperature [107]
The thermal conductivity value will be provided by the National
Appendix. This value will lie within the interval defined by the
upper and lower limits.
4,E-3
siliceous aggregates
2,E-3
calareous aggregates The lower limit of thermal conductivity was obtained from
000,E+0
comparisons with temperatures measures in fire tests on
0 200 400 600 800 1000 1200
different types of concrete structures. The lower limit gives
more realistic temperatures for concrete structures than the
Temperature (°C)
upper limit, which was obtained from tests on composite
steel/concrete structures.
At 20 °C, the thermal conductivity curves taken from
ENV 1992‐1‐2 produce a thermal conductivity for calcareous
concretes of around 20 % less than that of silica concretes.
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