Abstract
Earth has been used as construction material since prehistoric times, and it is still utilized nowadays in both developed and developing countries. Heritage conservation purposes and its intrinsic environmental benefits have led researchers to investigate the mechanical behaviour of this material. However, while a lot of works concern with rammed earth, CEB, and adobe techniques, very few studies are directed towards cob, which is an alternative to the more diffused rammed earth and adobe in specific geographic conditions. Due to this lack, this paper presents an experimental program aimed at assessing the failure mode and the main mechanical properties of cob earth walls (compressive strength, Young’s modulus, and Poisson’s ratio) through monotonic axial compression tests. Results show that, if compared with CEB, adobe, and rammed earth, cob has the lowest compressive strength, the lowest modulus of elasticity, and Poisson’s ratio. Differences are also found by comparing results with those obtained for other cob techniques, underlining both the high regional variability of cob and the need of performing more research on this topic. A strong dependence of material properties on loading rate and water content seems to exist too. Finally, the ability of a common analytical method used for masonry structures (an FEM macromodelling with a total strain rotating crack model) to represent the mechanical behaviour of cob walls is showed.
Highlights
Raw earth buildings constitute a considerable part of world cultural heritage
Damage to earthen structures can be caused by several environmental factors, mainly due to rainfall in combination with other factors or abandonment state [9,10,11,12,13]. ese buildings are characterized by a very low resistance against seismic lateral forces due to the low tensile and shear strengths of soil that in the past caused losses and casualties [3,4,5, 14,15,16,17,18]. en, it is important to deepen the study on their mechanical performance, without which it is impossible to provide adequate retrofit interventions [19, 20]
Builders, thanks to their experience and to the legacy orally transmitted by previous builders [39,40,41], had a specific knowledge on how to choose earth material for cob constructions. is knowledge is today partially lost in West countries, but it is still possible to learn from historic earthen buildings by means of geotechnical analyses [13, 30]
Summary
Raw earth buildings constitute a considerable part of world cultural heritage. About 15% of UNESCO heritage sites are built from raw earth [6], and it is estimated that about 30–40% of the world’s population lives and works today in earthen architecture [7], owing to their qualities such as low cost, better thermal insulation, and use of local material. In the Marche region (Italy), about 245 earthen buildings are still present according to a recent census [8]. As these buildings are part of our cultural and architectural heritage and a testimony of low-environmental impact constructions, it is needed to preserve them from ruin and deterioration. Damage to earthen structures can be caused by several environmental factors, mainly due to rainfall in combination with other factors or abandonment state [9,10,11,12,13]. ese buildings are characterized by a very low resistance against seismic lateral forces due to the low tensile and shear strengths of soil that in the past caused losses and casualties [3,4,5, 14,15,16,17,18]. en, it is important to deepen the study on their mechanical performance, without which it is impossible to provide adequate retrofit interventions [19, 20]
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