Thermal conductivity measurement in clay dominant consolidated material by Transient Hot-Wire method.

¹ Laboratoire d'Etudes Thermiques, UMR CNRS 6608, Université de Poitiers - ESIP, 40, Avenue du Recteur Pineau, 86022 Poitiers, France.
² Laboratoire HYDRASA, Université de Poitiers, UMR 6269, Université de Poitiers – ESIP 40, Avenue du Recteur Pineau, 86022 Poitiers, France.
³ Communauté de Commune du Lezayen, 79120 Lezay.

^a e-mail: jean.philippe.garnier@univ-poitiers.fr

Abstract

The transient hot-wire (THW) technique is widely used for measurements of the thermal-conductivity of most fluids and some attempts have also been carried out for simultaneous measurements of the thermal-diffusivity with the same hot wire. This technique was also tried to determine thermal properties of soils by the mean of probes which can be considered as wire with some assumptions. The purpose of this paper is to validate the thermal conductivity measurement by the THW technique in geomaterials, composed of compacted sand + clay mineral that can be used for earth construction (Compacted Earth Brick). The thermal transfer behaviors are mainly governed by the texture and moisture of the geomaterials. Thus the investigations were performed (1) in media made of glass beads of different diameters in dry and saturated state in order to observe the role of grain sizes and saturation state on the wire temperature (Δt) measurements and (2) in the compacted clay-geomaterial at different moisture states. The Δt / ln(t) diagrams allow the calculation of two thermal conductivities. The first one, measured in the short time acquisition (< 1s), characterizes the microtexture of the material and its hydrated state. The second one, measured for longer time acquisitions, characterizes the mean thermal conductivity of the material.