Influence of built-in thermocouples on temperature field in cement composites exposed to high temperatures

Determination of thermal conductivity of porous building materials at high temperatures is of a great importance of today's materials engineering as it offers wide opportunities for practical applications. There are several methods to perform this measurement. An inverse analysis of an experimentally obtained temperature field in a one-sided heated sample seems to be the most promising technique as it enables to express the thermal conductivity as a function of temperature. The experimental monitoring of the temperature field is usually conducted by means of inbuilt thermocouples that are composed of various metal wires, depending on the temperature range applied. Anyway, metals in general have several times higher thermal conductivity than porous materials which leads to deformation of temperature field measured. Such a deformation may be then reflected in the following data processing and thus may load the results by systematic errors. This paper quantifies the influence of the thermocouple presence on the temperature field deformation as the first step towards the systematic errors elimination. It was revealed, that depending on the time of heating and thermocouple position, the temperature field deformation may reach up to 55 °C. These results were obtained using a three-dimensional computational modelling of heat transfer, in which the temperature fields of a simple specimen and a specimen with an inbuilt thermocouple were compared.