Bioconsolidation of construction materials – Effect on the durability of an eco-efficient earthen plaster

Abstract

Bioconsolidation is a relatively novel technique used for consolidation, repair, protection and improvement of construction materials. This biotechnology is based on the precipitation of chemical compounds produced by microbial metabolism. It can be used for treatment or formulation. Although recently applied in several construction materials, such as earth blocks or cement-based materials, bioconsolidation has been unexplored on earth-based plastering mortars. Although the use of earth mortars for earth plasters has been growing on recent years for its eco-efficiency, they are less resistant to damage by contact with water. Therefore, the use of a bioproduct may have a great potential for the improvement of earth mortars´ weaknesses. In the present thesis, two types of bioconsolidation techniques have been studied on earth mortars: as a biotreatment for the improvement of surface properties; and as a component for earth mortars’ formulation (bioformulation) for the improvement of the whole material. The bioproducts used are based on microbial iron mineralization using Escherichia coli cells, since iron compounds are present in earth materials, are non-toxic, easy to handle and are not expensive. Several experimental conditions have been studied leading to the proposal that iron concentration is a key parameter. Tested biotreatments show promising results, producing a slight consolidative effect and significant increasing of water absorption resistance of earth mortars. Bioformulated mortars present a very distinct macrostructure, with a great decrease on mechanical properties. Nevertheless, they achieve a considerable improvement on resistance towards water and a lower thermal conductivity. The results show the interest on further studies on the use of iron-based bioproducts on earth mortars.