No abstract

Earth-based mortars are commonly reinforced with bio-based materials such as straw or biopolymers. The aim of this work is to identify reinforcements that are able to improve the mechanical strengths and the ductility of an earth-based matrix. We have also attempted to describe the mechanisms of reinforcement involved in such materials. Firstly, a kaolinite-based clay soil was mixed with sand to achieve earth-based mortars with the highest density at the dry state. For this material (kaolinite-based mortar), we have shown that, at the same water content, the compressive strength at the dry state only depends on the dry density of the sample whatever the forming process. Various quantities of fibers, fabrics and alginate were then used to reinforce the studied mortars (a kaolinite based mortar and a natural soil containing swelling clay sieved at 4 mm). We found that these reinforcements significantly increase the compressive strength of all tested samples containing kaolinite. A comparison between the two materials helps us to understand the reinforcement mechanisms for various fibers; it also demonstrates that natural fibers and woven fabrics enhance the mechanical behavior of earth mortars notably under a compressive load.

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.

While raw earth can be used as a structural material, its water sensitivity limits its use in modern construction. Earth has a strong affinity with water. Both water imbibition and water vapour transfer have to be taken into consideration. This affinity can be a positive point to regulate indoor ambience, but it can also negatively affect earth's mechanical properties. To avoid this possible detrimental effect, bio-based additions are used all around the world to stabilize, protect from water and enhance the mechanical properties of earth-based building materials. Biobased stabilizers have to limit liquid water absorption and maintain mechanical properties without acting as a water vapour barrier that can lead to durability issues. In this article, capillary water absorption and water vapour permeability 3 measurements are performed for combinations of various earths and bio-based additions (linseed oil, xanthan gum, casein, alginate and tannins). Linseed oil and xanthan gum help to protect the earth-based samples from absorbing liquid water without affecting the water vapour transfer in these materials.