An Experimental Study on the Consolidation of Earthen Surfaces Using Nanoparticle-Based Products

This paper presents the results of research conducted as part of a bilateral cooperation project between National Research Council (Italy) and Chinese Academy of Cultural Heritage (China) for the conservation of the earthen walls of Ancient Ulanbay City (Xinjiang, China). In 2007 and 2012, conservation interventions were carried out on the remains of the ancient walls, focusing on areas at risk of collapse. This involved the construction of new adobe masonry (sun-dried earthen bricks and mud mortar) to support the ancient rammed-earth walls, which required consolidation treatments due to their exposure to weathering. In order to support the site’s conservation efforts, several nanoproducts were selected for testing as consolidants for the adobe bricks. Nano-silica (NanoEstel) and nano-lime (Calosil E25), with and without ethyl silicate, and a nano-calcium oxalate-functionalized ethyl silicate (SurfaPore FX WB) were tested and compared with commonly used products for surface consolidation. Ethyl silicate was applied alone as a reference treatment. The mixtures tested in this research had not been previously explored, thus offering new opportunities to identify suitable solutions for the consolidation of earthen structures exposed to environmental conditions. In this study, adobe bricks were sampled from the archaeological site, and the effectiveness of each treatment was assessed based on changes in chromatic appearance, cohesion, and water behaviour. The results showed different behaviours of nanoproducts. Nano-silica, alone or especially in combination with ethyl silicate, is overall more effective than nano-lime for the consolidation of earthen materials, thanks to its greater compatibility with these materials.