Studies on the behaviour of the fibre reinforced cement stabilised rammed earth

Abstract

Cement stabilised rammed earth (CSRE) is a monolithic construction used for the loadbearing walls in the buildings and other structures. The soil, fine aggregates and cement form the basic materials for the CSRE construction. The partially saturated processed materials are compacted in layers in a rigid formwork, to construct the CSRE structural elements such as walls. The CSRE walls in a building can experience compression, tension, and shear. The literature review on the mechanical behaviour of the CSRE walls reveals that the CSRE wall elements undergo sudden catastrophic shear failures under compression, and shear loading, and under out of plane bending exhibit brittle flexure failures. Generally, the brittle and catastrophic failures are avoided in the structural elements. The short randomly oriented fibres in the brittle matrices can help promoting ductile failures by bridging the cracks and inhibiting the crack propagation. The limited R&D on the fibre reinforced CSRE reveal that the fibre inclusion can enhance the tensile strength, energy absorption capacity and the post peak response of the CSRE. However, the behaviour of the fibre reinforced CSRE is a scantily explored area. The present thesis is focused on investigating the mechanical behaviour of the coir fibre reinforced CSRE. The investigations were focused on (a) characterising the physical, chemical and mechanical properties of coir fibre and assessing the fibre durability, (b) examining the bond strength of coir fibres in the CSRE matrix and assessing the influence of fibre embedment length, matrix’s dry density, cement percentage and moisture at test, (c) determining the influence of fibre volume fraction (VF) on the compressive strength and stress-strain characteristics of coir fibre reinforced CSRE composite and finding the optimum fibre volume fraction, (d) establishing the shear strength and shear stress-shear strain relationships and understanding the flexure strength and flexure behaviour of the composite, (e) assessing the durability characteristics of the coir fibre reinforced CSRE when exposed to cyclic wet and dry cycles, and (f) exploring the novel concept of the shear studs across the rammed earth layers on the flexure, shear and compression. The major conclusions of investigations are (a) coir fibres show high tensile strength (~100 MPa) and large failure strain (23%), (b) the critical fibre embedment length yielding maximum pull-out resistance was 25 mm, (c) coir fibre addition eliminated the sudden shear failures in the CSRE under compression and improved the energy absorption capacity and post peak response, (d) the optimum fibre volume fraction yielding the maximum compressive strength was 1%, (e) the coir fibre inclusion significantly improved (30 – 40%) the split tensile strength of the CSRE and there was marginal improvement in the shear strength but significant enhancement in the post peak response, (f) improved the straining capacity of CSRE in the direction when flexure tension is parallel to the compacted layers and (g) the coir fibre reinforced CSRE is durable when exposed to cyclic wet and dry cycles. The last part of the thesis work was devoted to developing a novel concept of using shear studs across the compacted layers of the CSRE for the first time. The steel studs embedded CSRE specimens were tested under compression, diagonal tension (shear) and four-point bending. The introduction of steel studs across the compacted layers enhanced the shear strength of CSRE by 50%. The steel studs embedded CSRE showed extremely ductile failures under flexure. The thesis ends with highlighting major scientific contributions to the domain knowledge and scope for future work.