RESUMO
Two tombs of the Southern Tang Dynasty (Qinling Tomb and Shunling Tomb), the most important cultural heritages in China, were built for emperors 1000 years ago and decorated with murals and stone sculptures. After their excavation in the 1950s, it was found that drastic fluctuations in the environment within the tombs had caused multiple diseases, such as salt efflorescence, powdering, and biodeterioration, which led to irreversible damage to the murals. This research comprised long-term (yearly) environmental monitoring and short-term (monthly) investigation into the distribution of salt crystallization and microbial growth within the two tombs. The objective was to unveil the relationship between the temporal and spatial distributions of the mural diseases and environmental characteristics while proposing a promising environmental regulation strategy for relic conservation. The results showed a gradual reduction in temperature fluctuation from the entrance to the back chamber and a distinct vertical stratification in relative humidity. The relative humidity in the upper areas of the tombs reached 100% during summer, while it averaged around 40-50% in the lower areas during winter. Consequently, significant condensation was observed on the ceiling in summer, whereas salt crystallization occurred on the murals in the lower space in winter. The distribution of these diseases was influenced by the airflow exchange between the interior and exterior. Furthermore, the structural disparities between the two tombs contributed to higher relative humidity and greater microorganism coverage in the Shunling Tomb compared to the Qinling Tomb. From the abovementioned findings, we suggest that microclimate control is essential for mitigating mural deterioration and should be paid more attention in the future.
RESUMO
The preservation and restoration of heritage sites have always been of key focus in the field of cultural relics. Current restoration methods mainly involve physical or chemical techniques, which are in many cases intrusive, destructive, and irreversible. Hereby, we introduce a novel biological strategy (microbial-induced carbonate precipitation (MICP)) to repair natural and simulated surface cracks on six hundred years' old wall bricks (part of the Nanjing City Min Dynasty ancient wall, China). X-ray micro computed tomography (X-ray micro-CT) was employed to non-destructively visualize the internal structure of the MICP-treated brick cubes. The results showed that MICP can effectively repair both natural and simulated cracks present on the brick's surface. The compressive strength of the MICP-treated brick cubes was significantly higher than that of the untreated control cubes (33.56 ± 9.07 vs. 19.00 ± 1.98 kN, respectively). MICP significantly increased the softening coefficient and decreased the water absorption rate (p < 0.05), indicating that the water resistance of the wall bricks can be improved after treatment. The 3D images from X-ray micro-CT, a method that could non-destructively assess the internals of such cultural structures, showed that MICP can effectively repair ancient relics, promoting durability and limiting degradation without affecting the structure. X-ray diffraction analyses showed that MICP generates the same calcite form as that of original bricks, indicating that MICP filler is compatible with the ancient city wall brick. These findings are in line with the concept of contemporary heritage preservation.