A procedure to measure the in-situ hygrothermal behavior of unstabilised rammed earth walls

Rammed earth is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities and its mechanical behavior. Both of them are known to strongly depend on the amount of water contained in material pores and its evolution. Then the aim of this paper is to present a procedure to measure this key parameter in rammed earth walls by using two types of probes operating on the Time Domain Reflectometry (TDR) principle. A calibration procedure for the probes requiring solely four parameters is described. This calibration procedure is then used to monitor the hygrothermal behavior of a rammed earth wall (1.5 × 1 × 0.5 m), instrumented by five probes during its manufacturing, and submitted to insulated, natural convection and forced convection conditions. These measurements underline the robustness of the calibration procedure for a large range of water content, even if the wall is submitted to quite important temperature variations. They also emphasize the importance of gravity on water content heterogeneity when the degree of saturation is high, and the role of liquid-to-vapor phase change on the thermal behavior.