Influence of walls surface topography on water droplet damping and absorption for earthen constructions

Abstract

The use of raw earth as a building material is gaining interest, indeed raw earth has considerable environmental advantages. However, the correct use and development of such materials requires an accurate assessment of the water content within the walls during service life, since this latter strongly impacts both their mechanical and thermal properties. For that purpose, a good knowledge of water ingress mechanisms at the surface of earthen walls is essential, due to impacting rain for example. In this context, this paper aims at studying the impact of the compacted earth blocks surface topography on the absorption and damping of water droplet through two experimental devices. Surface topography of samples made with three different raw earths is determined using a new chromatic confocal sensor technique revealing the multi-scale roughness of this material through the waviness Wa and the roughness Ra. With the water damping experimental device can be followed the maximal height h(t) and the diameter D(t) of the impacting droplet along the time. Despite the quickness of the absorption (max 50 m s), two behaviors can be distinguished depending on the samples: oscillating or cushioned. The results show that the Dmax of the droplet increases with the Ra while the time of absorption drastically decreases until a threshold.