The raw earth brick: a building material to meet the needs of local populations

This study tests the ways of improving compressed earth bricks by the addition of sugar cane bagasse, alluvial sand and fine aggregates. The objective is to contribute to the valorization of clay resources, with the aim of developing the production of sustainable, local and energy-saving building materials, particularly in the peri-urban areas of Kinshasa in D.R.Congo. Two raw clays were characterized and then mixed with the different additives to obtain raw earth bricks. Those bricks were then submitted to flexural and compression tests to evaluate their mechanical properties. The addition of 0 to 7.5% bagasse increases the flexural strength from 0.66 to 0.99MPa and the compressive strength from 2.54 to 3.14 MPa. The addition of 0 to 50% sand increases the flexural strength from 0.56 to 0.71 MPa and the compressive strength from 2.28 to 3.09 MPa. The addition of 0 to 35% of fine aggregate does not affect the flexural strength, but increases the compressive strength from 2.28 to 3,10MPa. Stabilization with sugarcane bagasse, sand or aggregates is an interesting prospect to improve by a factor of the order of 1/3 the mechanical properties of raw earth bricks. In addition the mechanical properties are also affected by environmental variation in humidity. The durability of the bricks (i.e., its resistance to water) was therefore evaluated by “the wetting drying test” after an addition of cement. The compressive strength after six cycles of wetting-drying decreases by 25% for the bagasse mixture, 6% for the sand mixture and 2% for the aggregate mixture. Likely an addition of cement allows to significantly increase the durability.