Characterization of a Humid Concrete by Study of Thermal Impedance

Abstract

In the paper the thermal characteristics evolution of a humid concrete with water content is determined by study of the relation between the thermal effusivity of concrete and the thermal impedance. At first, the theoretical impedance related the effusivity of material measured is expressed. In certain frequency band, a sample with its enough big thickness can be considered as a semi-infinite system for facilitating determination of the effusivity of material. In the experiment, a sensor which is consist of a plane fluxmeter for measuring the thermal flux and a thermocouple implanted in the fluxmeter for measuring the temperature is disposed below a surface of a humid concrete sample, while a plane electrical resistance for exciting heat signal is disposed below the fluxmeter. The relation of temperature and thermal flux in time is considered a linear system during each test. The experimental impedance is determined by measuring the flux and temperature as the input and output signals of a system. The results of evolution of effusivity with water content are obtained by optimization of parameters in the theoretical impedance while comparing between the theoretical impedance and the experimental impedance. The results of the study show that there is a strong sensibility of the concrete effusivity to water content. This remark allows envisioning the thermal impedance as a possible measure technique of water content. The water content in a humid concrete relates to the porosity of concrete. This thermal characterization method can allow detecting an eventual abnormality in concrete, for example degradation.