Design of a soil concrete as a new building material – Effect of clay and hemp proportions

Abstract

This study aims to optimize the composition of new ecological concrete constituted of upgraded excavated soil. The novelty of this study is the fact that earth concrete is poured with classical vibration as ordinary concrete. Several soil concrete mixtures, composed of different proportions of clayey soil, sandy soil and small amounts of cement, lime and hemp fibers have been tested. The mineralogical composition of clayey soil was studied by X-ray diffraction (XRD) analysis The chemical composition was established by Environmental Scanning Electron Microscopy (ESEM) coupled with the X-Ray Energy Dispersive Spectrometry (EDS). Casting of concrete mixtures has been realized by vibration, as ordinary concrete, to obtain the required workability on construction sites. Compressive tests have been carried out on samples at different curing times. Ultrasonic non-destructive technique has been used to monitor the hardening of soil concrete. As this concrete presents important volumetric changes that can cause the infiltration of water and impact their durability, an experimental investigation on autogenous and drying shrinkage is reported. Water porosity and water absorption tests have been also carried out to evaluate the transfer property of this porous material. The results show that the compressive strength of soil concrete is greater than 1 MPa, which is sufficient for filling application (wall of a frame building) and increases to 5 MPa after 6 months. Compressive strength, density, and workability of the tested concrete mixtures decrease with increasing clayey soil and hemp fibers. Desiccation shrinkage increases with the volume fraction of clayey soil and hemp fibers.