Towards field-oriented tests to evaluate the workability and cohesion of earth slips for building applications

Abstract

Hemp-clay concrete for building thermal insulation can be made of earth available on-site, obtained from earthworks or ancient clay building deconstruction. Craftsmen evaluate qualitatively the slip binding capacity in order to optimize and control the formulation with simple field oriented tests. There is a need for scientific works to understand the rheological behavior of clay slips depending on all the parameters that can vary on-site, such as the water to clay ratio, the clay activity, the particle size distribution. This knowledge would allow to define quantitative field-oriented tests that can be used on-site by craftsmen.

In this study, the variability of 27 earths was first assessed through a simple qualitative test to identify their behavior at different water levels, and conventional geotechnical identification tests. Slips behave as non-Newtonian fluids, with an apparent yield stress  and a shear rate dependent viscosity. These two characteristics help to quantify the slip cohesion. Both yield stress and viscosity of slips with different earths were studied thanks to a vane-geometry rheometer and a simple test, developed for this study, which could be used on-site: the plate test. The results allow to assess the validity of this test to identify the yield stress level.