Effect of the type of clay earthen materials and substitution materials on the physico-mechanical properties and durability of compressed earth blocks

Clay earthen materials are the most common building materials used all over the world for sustainable constructions. Today, the drastic increase of population and urbanization, especially in developing world, calls for better knowledge of earthen materials in the contemporary construction. The present thesis aimed to characterize the suitability of clay materials from four sites in the vicinity of Ouagadougou, Burkina Faso: Kamboinse, Pabre, Kossodo and Saaba for the production of stabilized compressed earth blocks (CEBs). The study also characterized by products of industry: calcium carbide residue (CCR) from Kossodo and agriculture: rice husk ash (RHA) from Bagré and Okra plant fibers from Kaya for the stabilization of CEBs. The characterizations were carried out on physico textural and chemico mineral properties. The study additionally tested the physico mechanical, hygro thermal and durability performances of CEBs stabilized with the by products for applications in building construction, specifically in the Sahelian climatic context. Mixtures were produced by addition of 0 25 wt% CCR, 10-25 wt% CCR:RHA (various ratios) and 0.2 1.2 wt% fibers to the earthen materials. The mixtures were used to produce the mix solutions and mold stabilized CEBs (295x140x95 mm3) by static compression (~35 bars), and cured in various conditions for 0 to 90 days. The results show that the clay materials from Pabre and Kossodo respectively contain the highest fraction of clay particles (20-30%) and gravel (40%). Saaba and Pabre respectively contain the highest fraction of kaolinite clay mineral (60 80%) and quartz (40 60%). Kamboinse contains the highest amount of exploitable deposit (700 000 m3), 10 25% clay particles and 40 75% kaolinite, while Kossodo contains medium fraction of kaolinite (35-50%). The CCR mainly contains portlandite (40 50 % hydrated lime: Ca(OH)2). The RHA is mainly amorphous, with pozzolanic reactivity. Saaba and Kossodo recorded the highest rate of pozzolanic reactivity with CCR, related to the high content and degree of poorly ordered kaolinite. Pabre and Kamboinse recorded the lowest rate of reactivity. With respect to unstabilized CEBs (0 % CCR), the compressive strength of CEBs stabilized with 20% CCR cured at 40±2°C for 45 days produced with the clay material from Saaba improved tenfold (0.8 to 8.3 MPa) compared to Kamboinse (1.1 to 4.7 MPa), Pabre (2 to 7.1 MPa) and Kossodo (1.4 to 6.4 MPa). All clay materials are suitable for the production of stabilized CEBs with compressive strength of 4 MPa. Furthermore, the stabilization of the earthen material from Kamboinse using by product binders improved the structural efficiency of CEBs cured in ambient conditions of the lab (35±5°C): increase of compressive strength and decrease of bulk density. It also improved the hygro thermal efficiency: decrease of thermal effusivity, conductivity and diffusivity and increase of thermal specific capacity and water vapor sorption. The CEBs stabilized with at least 10 % CCR or 18-2 to 16:4 % CCR:RHA satisfy engineering requirements and durability for the construction of two or three storey buildings. Therefore, the selection of earthen materials should take into account the reactivity with the stabilizer.