A study on cob sample production and techniques

This paper deals with the validation of a 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, 0.75 and 1.00 m) and moulding water contents (25.7–39.7%) 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 contents. Based on the trial test results, the other two drop heights of 0.50 and 1.00 m were adopted for further validation. The effects of confinement, drop height and moulding water content on the compressive strength and density of cubes were studied. Test results show maximum compressive strengths and densities ranging from 1.22 to 1.31 MPa and 1.65 to 1.70 g/cm³, respectively, at a 33.7% water content and a 0.75 m drop height, with those for the confined specimen being the highest. The strength and density values obtained satisfy the guidelines prescribed by some standards. Thus, the proposed technique for cob production may be adopted to achieve desirable compressive strength and density for the particular soil used in the present study.