Case Studies in Construction Materials (Jul 2024)
Bio-stabilising earthen houses with tannins from locally available resources
Abstract
This study presents the first-ever comparative evaluation of traditional biostabilisation practices for housing employed in Northern Ghana. Such a comparative evaluation is crucial in understanding and addressing the increased risk of flooding in the region due to a combination of climate change and land use changes. Given the environmental conditions and material availability that shape construction techniques in this area, it is imperative to assess the effectiveness of these practices in mitigating flood risks. The investigation focuses on readily available resources from the Wa and Tamale regions, specifically dawadawa (D), beini (B), and rice husk (R). These biostabilisers were subjected to rigorous testing to assess their efficacy. Earth mortar samples were created using sieved plain local soil (P) with or without the addition of rice husk, which is a local practice, and dawadawa and beini solutions were tested as a water replacement (+ wD or + wB, added during material manufacture) or as a surface cover (+ coverD or + coverB). The effects are examined in terms of microstructure modifications detected through tannins type and presence, SEM/EDS, water absorption via capillary uptake, and compressive and flexural strength for two different types of application: embedded in the mixture or covering the surface. Overall, solutions containing dawadawa were superior to those containing beini for the tested soil. Both coverD and + coverB decreased the water absorption capacity of the earth mortars and provided almost complete protection for 15 min. After three days, all mortars mixed with the dawadawa or beini solutions (P + wD, PR + wD and PR + wB) displayed lower absorption than the P material. Condensed tannins were identified in dawadawa, but only small precipitation in beini and no precipitation in the rice husk. This indicates that dawadawa has a greater degree of polymerisation (compared to rice and beini), developing a polymerisation tannin-iron complex in contact with oxygen from the air, which explains the macrostructure results. SEM/EDS results indicated polymeric condensed tannins and hydrolysable tannins and that complex accumulation and subsequent oxidation are the main reasons for improving water resistance. The laboratory tests, therefore, support the traditional methods of using dawadawa, beini, and, to a lesser extent, rice husk to improve the resilience of earthen houses and structures to water damage and can be used to encourage agro-industry in Northern Ghana to preserve and promote dawadawa and beini resources.
