Reinforcing rammed earth with plant fibers: A case study

This paper is about an experimental study on the mechanical behavior of rammed earth under compression and indirect tensile stresses. Local raw earth and sand are the base materials used. As stabilizers, cement, lime, barley straw and date palm fibers were used to manufacture the specimens tested. In all, five different mixtures were prepared and tested. The cylindrical specimens used were prepared under optimum compaction references using the Proctor test procedures. Two types of mechanical tests were performed: the uniaxial compression test and the splitting tensile strength test. For each compression test, four parameters were determined: the compressive strength, the initial tangent modulus, the secant modulus at maximum stress and the peak axial strain corresponding to the maximum compressive stress. The results obtained show that, plant fibers (barley straw or date palm fibers) can provide improvements in rammed earth strengths such as those that cement or lime can provide, especially in tensile strength. The results also show that plant fibers decrease the stiffness of rammed earth while cement and lime increase it. Nevertheless, a coefficient of proportionality of about 0.6 was observed between the secant modulus and the initial tangent modulus for all the mixtures tested. In addition, a linear correlation between tensile strength and compressive strength has been established in the cases of both unstabilized and cement-or-lime-stabilized rammed earth. However, no similar correlation has been found when considering fiber-reinforced rammed earth, because the adhesion of the fibers used to the sand-earth matrix has more effect on tensile strength than on compressive strength.