Environmentally friendly additives and vegetable fiber to improve the mechanical properties and durability of rammed earth constructions

Despite the awareness that earth cannot provide the same mechanical performances of other materials, it should be asserted that this natural material is sufficiently apt to certain types of constructions. With the ultimate aim to improve the carrying capacity of the earthen constructions, especially in the seismic areas of the world, an experimental campaign was carried out on specimens and structural elements made with stabilized and or reinforced rammed earth. These experimental studies were directed to search for fully biodegradable natural additive and reinforcement methods that could better durability and strength in order to achieve a standard of quality of the earth material. Among natural additives and fibres, gypsum powder and fiber of broom, hemp and jute were chosen. These additives and fibres have the immediate consequence of limiting shrinkage and, therefore, increasing mechanical properties, stability, durability and resistance to weathering. Compression tests, three point bending tests and durability tests on "ad hoc" specimens has been focused to assessing the effects that the addition of stabilizing substances and fiber reinforcement have on the physical and mechanical performances of rammed earth. The results obtained from tests on specimens made with thin fiber layers showed better mechanical characteristics and water resistance. Furthermore gypsum and vegetable fibers are natural materials fully biodegradable and gypsum is also used in agriculture as fertilizer. Finally, acting with appropriate correctives and reinforcements, rammed earth buildings are apt to resist to seismic actions guaranteeing acceptable safety margin