Physical and mechanical properties of clay–sand mixes to assess the performance of earth construction materials

Abstract

The reduction of CO2 emissions has become an important parameter in the choice of construction materials. Earth guarantees a low environment impact due to the reduced need of energy for its processing and transportation and also provides natural hygrothermal comfort. To facilitate the design of earthen constructions, the development of models is necessary. This paper aims to provide a database of experimental results that could be easily used for developing models based on the competition between positive effect of capillary pressure on material cohesion and negative effect induced by matrix shrinkage restrained by aggregates. Mechanical and thermal tests were carried out on three reconstituted soils composed of pure kaolinite and three contents of fine sand (0, 30 and 60%), as well as different water content configurations (fabrication water content and after drying at 50% RH). The thermal properties analyzed included thermal conductivity and specific heat capacity. The mechanical properties studied encompassed the tensile (three-point bending test) and compressive strengths, Young's modulus and Poisson's ratio (using video correlation). Moreover, an original test was developed for measuring sample shrinkage during drying. Specifically, the results clearly showed that while shrinkage is divided by 5 for the maximal sand content, tensile strength is reduced by half. Therefore, these results allow to assess the balance between benefices and disadvantages of capillary pressure induced by clay drying on earth construction materials, which is of first interest to assess cracking risk in a structure.