Processing methods for optimising 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, local characteristics and recyclability. However, the strength of this material fluctuates in reality due to the variability of soils and the different methods used in vernacular earth construction. The aim of this study was to identify the mechanisms that increase the strength of this material. Optimisation of the processing method of raw earth blocks was sought in order to obtain better strength for different sorts of soils systematically. Soils were extracted from the same region, Brittany, France, in order to keep the local character of this material. The soils were mixed with water only or water and a dispersant (sodium hexametaphosphate or tannins). The rheological behaviour of each soil changed with different processing methods. Thus, the processing method and the use of dispersant can be efficient ways to enhance the mechanical properties of the selected soils. This study highlights that some of these methods could be used in the near future at a semi-industrial scale to produce a structural material that can achieve compliance with modern standards without hydraulic binders.

Effect of bio-stabilizers on capillary absorption and water vapour transfer into raw earth

“…Three kinds of earth (K, R and S) representative of the variability of the local resources were studied. All of these resources have already been studied in previous works [13,14,46,47].…”

“…The use of a dispersant can be efficient to minimize and optimize the porosity of earthen materials, and thus help to increase their mechanical and water durability properties. In order to highlight the effect of an efficient dispersant on the water durability of earthen materials, Hexametaphosphate (HMP) was used as it has been used in previous studies [13,14,32,47]. Also, some of the bio-based additions could have a thickening effect on the rheological properties of the raw earth-based materials [13,47]: thus, the addition of an efficient dispersant in the mix design is important.…”

“…Compressive strengths at the dry state were also measured for all of the formulations. The compressive tests were carried out with a sample of an aspect ratio following the adopted procedure of previous studies [13,14,47].…”

“…However, even if raw-earth seems to be a promising building material, it also presents some disadvantages, such as its significant variability and durability issues that limits the democratization of its use [8,9]. Such a large variability of resources (using various processing routes) is also leading to unguaranteed minimal mechanical performances [10][11][12][13][14][15]. Furthermore, the water sensitivity of earth, in both liquid and vapour phases, is often quoted as its main weakness related to durability because it can alter the material and strongly reduce its mechanical properties.…”

“…Other options could have less impact on the environment. Thus, the optimization of the processing method could systematically improve the final mechanical properties of the material by increasing its dry density [14,[34][35][36][37]. In addition, to substitute the previously cited additions that increase the water durability and the mechanical properties of the material during its life, some bio-based additions could be used.…”