Nanolime consolidation of the main building stone of the archaeological site of Volubilis (Morocco)

Abstract

Abstract Volubilis is the most important archaeological site in Morocco, considered as a UNESCO world heritage site since 1997. Unfortunately, the sustainability of the site is in danger by the many degradation patterns detected on the site. Urgent interventions are required in order to consolidate and restore the monuments of the site. In this paper, the efficiency of nanolime as a consolidation treatment for calcarenite stone, the main construction stone of the site, was assessed. To create degraded reference samples, calcarenite samples were subjected to two accelerated aging tests: a thermal shock test and a salt crystallization test. The two tests created damage quite similar to that of the site, namely cracking and surface degradation respectively. These samples were then treated with nanolime according to a protocol defined in relation to the stone properties and the concentration of the product used. After the application of nanolime, the samples were characterized using non-destructive tests (P-wave velocity, capillary absorption, surface hardness, and colorimetric tests) depending on the type of stone damage. On cracked samples, the treatment acted on the surface of the stone while cracks were still present in depth. On salt crystallized samples, the treatment was efficient as it helped recover the lost surface cohesion. Therefore, the nanolime treatment is efficient for stones that are degraded at the surface (sanding, alveolization, scaling) but less so for cracked stones of the Volubilis site.