Imaging the water content of rammed earth materials with induced polarization

Abstract

Rammed earth is a traditional building material characterized by its low environmental impact. The variation of the moisture content of rammed earth can affect its mechanical properties. Therefore, the non-intrusive evaluation of the water content and its distribution inside rammed earth structures is of high interest to anticipate the risk of failure. A non-destructive geophysical method called induced polarization is used to evaluate its sensitivity to the water content distribution. Measurements are first performed on small cylindrical core samples of rammed earth in order to test a physical model developed to connect induced polarization properties to saturation. Then, the model is used to estimate the water content at 3 distinct heights in 3 cylindrical core samples undergoing capillarity rise. Finally, these samples were cut and their water contents were independently determined and compared to that estimated from induced polarization measurements. A good correlation between the two estimates was obtained. In the second part of this study, induced polarization is used to image the water content distribution and its evolution over time in a rammed earth structural element undergoing desiccation. The monitoring is done for a period of 25 days starting from saturated conditions. We assess the evolution of the 3D distribution of the water content and we demonstrate that the water content obtained through induced polarization tomography is in agreement with independent data from a Time Domain Reflectometry (TDR) probe. Such a probe provides a local measurement of the water content thanks to the measurement of the dielectric constant of the material.