A study on cob sample production and techniques

This paper deals with the validation of cob sample production technique that replicates the on-site wall construction method. Cob cubes were prepared under confined and unconfined conditions with varying drop heights (0.50 m, 0.75 m and 1.0 m) and moulding water content (25.7% to 39.7%) by mass of soil. Prior to mass production of samples, a trial test was performed at a constant drop height of 0.75 m and varying water content. Based on the trial test results, other two drop heights of 0.50 m and 1.0 m were adopted for further validation. The effect of confinement, drop heights and moulding water content on compressive strength and density of cubes were studied. Test result shows maximum compressive strength and density ranging from 1.22 MPa to 1.31 MPa and 1.65 g/cc to 1.70 g/cc respectively at 33.7% water content and 0.75 m drop height with confined specimen being the highest. The strength and density values obtained satisfy the guidelines prescribed by some of the standards. Thus, the proposed technique for cob production may be adopted to achieve the desirable compressive strength and density for the particular soil used in the present study.