Performance of alkaline activation for the consolidation of earthen architecture

Abstract Earth has been an important building material in many cultures over the course of history. However, it is quite fragile compared with other building materials, requiring permanent maintenance and frequently consolidation. Conventional consolidation treatments often had drawbacks due to limited penetration and long-term effectiveness. In order to improve the earthen structure´s water resistance and mechanical properties, an alternative consolidation treatment based on highly alkaline KOH solution has been evaluated on outdoor-exposed adobe walls and was compared to a standard ethyl silicate treatment. The KOH treatment showed superior penetration and long-term effectiveness, causing partial dissolution of soil minerals and the formation of an amorphous phase with cementing properties. These mineralogical changes reduced the soils swelling capacity and improved its weathering resistance and mechanical properties. The consolidation treatment did not induce the formation of harmful salts but caused important color changes. Results indicate that lower concentrated KOH solution could be used, which would reduce consolidation-induced color changes, potential salt crystallization, treatment costs, and environmental risks. Overall, alkaline consolidation appears to be a valid alternative to conventional treatments.