Cast, compaction, vibro-compaction or extrusion: processing methods for optimizing the mechanical strength of raw earth-based materials

Abstract

In the last few years, raw earth construction has recovered much consideration due to its low environmental impact, its local character and its recyclability. However the strength of this material is really fluctuating as a consequence of soil’s variability and the different methods that are used in vernacular earth construction. The aim of this study is to identify the mechanisms that increase the strength of this material. The optimization of the processing method of raw earth’s blocks is sought in order to get better strengths systematically for different sorts of soils. All of these soils are extracted from the same region, Brittany, in order to insist on the local character of this material.

For three sorts of soils from Brittany this study will focus on four different processing methods: casting, compaction, vibro-compaction and extrusion. These soils will be mixed with water only or water and Sodium-hexametaphosphate which acts as a dispersant. The rheological behaviour of each soil will be adapted to the different processing methods. The fact that, for earth-based materials, the compressive strength at the dry state depends on its dry density will be shown. Thus it will be displayed that the processing method, and the use of dispersant that allows to reduce the water content during the processing, can be efficient to enhance the dry density and consequently the compressive strength of all of the selected soils. Those strategies are also efficient to improve the process robustness for ensuring high levels of compressive strength and dry density for raw earth construction.

This study highlights that some of these methods could be used soon at a semi-industrial scale, to produce a structural material that needs to achieve compliance with modern standards without hydraulic binders.