Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
In the study of the mechanical behaviour of building
materials in presence of fire, the knowledge of the correlation
of the thermal conductivity and of the specific heat with
temperature is of fundamental importance. The numerical
verifications of fire resistance of structures are often carried out
using computer codes that solve differential equations of
thermal exchanges. For the correct prediction of the evolution
with the temperature, the knowledge of the above thermal
properties as a function of temperature is required.
The measurement of thermal conductivity and thermal
diffusivity has been made with the Hot Disk Thermal Constants
Analyser equipment. This apparatus, that operates in variable
speed, generates a thermal constant power in a nickel sensor
placed in contact with two specimens of the same material. It
allows the detection of temperature increase on the surfaces of
these specimens.
Assuming as infinite the specimens size, the solution of the
general equation of the heat conduction allows to express the
temperature increase in of the specimen as a linear
dimensionless time function; the simultaneous determination of
thermal diffusivity and conductivity of the test material
becomes easy.
The experimental environment suitable to achieve high
temperatures consists of a special controlled temperature oven
in which measurements are made with sensors enclosed in two
layers of refractory material (mica) suitable for working with
acceptable accuracy in a range of temperatures between 500-
1000 K.
This paper presents the results of experimental measurements
of thermal conductivity and of volumetric specific heat, r cp,
carried out at high temperature on autoclaved aerated concrete
(AAC) specimens at different densities.
The results are also compared with the directions on the
material provided by national and international standards.
