Traditional cob wall: response to flooding

The influence of flood conditions upon traditional cob construction is little understood. This paper aims to investigate the ability of cob materials to resist flood situations and documents basic failure mechanisms. This work also seeks to investigate the wettability characteristics of cob materials utilising environmental scanning electron microscopy.

This paper takes the form of a literature review and case study underpinning laboratory experiments.

Cob walls that are suitably compacted, straw reinforced and are composed and manufactured of the correct materials appear to have the ability to resist total failure when subjected to initial flood conditions, however, the duration to which these structures will remain intact has still to be ascertained, and testing is ongoing. A correlation appears to exist between the rate of cob material's compaction and the duration to which the structural integrity of the walls was retained when the samples were submerged in water. In addition, the use of straw reinforcing increased the duration to which the wall could be submerged before failure. Un‐reinforced cob walls that were submerged in simulated floodwaters, exhibited an undercutting pattern of deterioration prior to failure. The materials for cob construction exhibited both hydrophobic and hydrophilic characteristics. This would have an influence on the material's ability to saturate and dehydrate, and also have an impact on moisture transfer mechanisms. Unsaturated cob wall/samples developed surface tension between hydrophilic surfaces and this is believed by the authors to increase inter‐particle bond strength within the material by the suction effect.

This paper is believed to be the first preliminary investigation into the effect of flooding on cob structures. Additionally, it utilises environmental scanning electron microscopy to reveal information about the surface characteristics of the materials and uses wettability studies to assess the hydrophilic and hydrophobic nature of the aforementioned.