Characteristic Properties of Unstabilized, Stabilized and Fibre-Reinforced Cob Blocks

This paper presents the results of an experimental programme designed to assess the characteristic properties of cob blocks. Coconut coir, paddy straw and cement were mixed with soil in varying proportions (0-10% by mass of dry soil) before the addition of water. Test blocks were prepared at a consistent drop height of 0.75 m with 33.7% moulding water content. Properties of blocks were studied in terms of density, strength, failure pattern, shrinkage and durability. The results show that higher compressive strength and density were achieved for cement-stabilized blocks, and higher tensile strength was achieved for blocks reinforced with coconut fibre. An hourglass type of failure pattern was observed under compression. The addition of fibres to the soil matrix reduced the shrinkage cracks. Unstabilized and fibre-reinforced samples failed to attain suitable durability criteria. Cement-stabilized blocks satisfied the suitability criteria recommended by some researchers. Finally, 5% fibre by mass of soil was found to be the optimum content of fibre, and a 0.75 m drop height resulted in higher strength compared to the inconsistent drop heights adopted in the literature.