Microstructural, physical, and mechanical characteristics of adobes amended with cement-metakaolin mixtures

The objective of this study was to improve the physical and mechanical properties of adobes reinforced by cement-metakaolin mixtures. For this purpose, a raw clayey material from Burkina Faso consisting of kaolinite (62 wt%), quartz (30 wt%), and goethite (6 wt%) and belonging to the category of sandy-silty soils with medium plasticity has been used for adobe manufacturing. Metakaolin was produced by thermal activation of a local raw clayey material at 680 degrees C for 2 h. Adobes were first formulated with cement up to 12 wt%. It appears from this formulation that 10 and 12 wt% cement offer good mechanical strength elaborated adobes. Taking into account the high cost of cement in Burkina Faso, 10 wt% of cement was retained to be replaced by 2, 4, 6, 8, and 10 wt% metakaolin. The microstructural (by SEM-EDS), physical (apparent density, porosity, linear shrinkage, water absorption test by capillarity, spray test), and mechanical (compressive and flexural strengths) characteristics of formulated adobes were evaluated. The obtained results showed that this substitution improved adobe microstructure with pores reduction leading to composite densification. The presence of metakaolin slows down the phenomenon of capillary rise of water in adobes. Also, the metakaolin presence within the cementitious matrix improves the mechanical behavior and reduces rain erosion effect. The improvement of different properties was mainly due to formation of calcium silicate hydrates (CSH) resulting by cement hydration and metakaolin's pozzolanic reaction. Adobes reinforced with 6 wt% cement and 4 wt% metakaolin have suitable technological characteristics to be used as building materials for developing countries.