Flax fibers and dolomitic lime effects on mineralogical, microstructural and physico-mechanical properties of adobes

Adobes commonly used in Burkina Faso for habitats building are not durable due to their poor water resistance. This study so aims to stabilise adobes using dolomitic lime and flax fibers. A low-plasticity clay-sandy soil containing 20wt% fines and composed of kaolinite (49wt%), quartz (37wt%) and goethite (10wt%) was used to formulate adobes. Flax fibers (74wt% cellulose, 12% hemicelluloses, 11wt% pectin, 2wt% lignin, tensile strength of 700 MPa) and dolomitic lime were used as stabilisers. Compressive strength of adobes stabilised with up to 10wt% dolomitic lime was evaluated. Lime content of 4wt% was the minimum required to achieve a compressive strength of at least 2 MPa recommended for earth construction. Next, flax fibers (1.5 and 3 cm in length) were added to clay-lime mixtures up to 1wt%. Microstructural and physico-mechanical properties of adobes were evaluated. Above obtained results are better than adobes amended with dolomitic lime (42% reduction in thermal conductivity, 127 and 105% increase in flexural and compressive strength respectively for best AL4-F0.6 composite, low erodibility and ductile behaviour of adobes). These improvements are due to the formation of CSH and MSH from pozzolanic reactions involving finely ground quartz and/or kaolinite, which make composites microstructure homogeneous through bonds between soil particles. They are also due to good adhesion of flax fibers (with high tensile strength) to clay matrix and also to cellulose high presence in flax fibers, which helps to reduce thermal conductivity of adobes while improving its ductility. AL4-F0.6 composite is suitable for building houses in Sahelian climate.