This study investigates salt weathering in the indoor, humid environment of China's Jinsha earthen site. Methods such as digital microscope, scanning electron microscopy (SEM), ion chromatography (IC), energy dispersive spectroscopy (EDS), and laser particle size analysis were employed to collect and analyze samples from four heavily weathered walls. The sampling approach took into account differences in depth and height and prioritized the extraction from various weathering layers to unveil the attributes, causes, and mechanisms of salt weathering. The findings indicate that the Jinsha site's eastern segment suffered salt-induced damage, such as powdering, salt crusts, and blistering, due to the presence of gypsum and magnesium sulfate. These salts were primarily sourced from groundwater. Groundwater ions ascended to the site's surface via capillary action, instigating various forms of salt damage. Salt damage severity has a direct link to salt and moisture content. The degradation patterns can be categorized into powder and multi-layered composite deterioration, both seems related to soil particle composition. Powder deterioration tends to occur when the sand content exceeds 40%. This research proposes preservation strategies that focus on managing groundwater and conducting environmental surveillance. These measures are designed to effectively address and mitigate the risks associated with salt damage.

The reinforcement and repair materials for earthen sites have high requirements for strength, resistance to deterioration, and aesthetic coordination. In this study, the enzyme-induced carbonate precipitation (EICP) and the microbially induced carbonate precipitation (MICP) techniques were used to reinforce the earthen site soil. The applicability of EICP and MICP for stabilizing earthen sites soil was investigated through static contact angle tests, disintegration tests and colorimetry tests. In addition, the improvement of mechanical properties of biotreated earthen sites soil was examined by unconfined compression strength tests. The tests results show that MICP and EICP techniques could improve the mechanical characteristics and water-stability properties of the earthen sites soil. With the increase in cementing solution concentration, the effectiveness of EICP was enhanced, while the water-stability and hydrophobicity of MICP-treated soils increased first and then decreased due to the influences of organic matter and soluble salts. EICP and MICP techniques showed different performance in reinforcing effects on calcium carbonate content, shear wave velocity, unconfined compressive peak strength, total disintegration time, and static contact angle. This study is expected to contribute valuable insights to the conservation of earthen heritage site using bio-based methods.

The recurrent crystallization and subsequent volumetric expansion of soluble salts pose significant risks to earthen sites, particularly those with archaeological remains on their surfaces. Therefore, timing interventions based on salt content is crucial. This study focuses on the effects of soluble salt content on the earthen site within the burial pits of the Qin Mausoleum, with a particular emphasis on defining safe salinity levels. A mixture of Na2SO4/NaCl salts in a 1:1 mass ratio was added to remodelled soil cakes, which were then aged in a climate chamber for several months. The area of salt expansion on the soil cakes' surfaces was measured using a deep-focus microscope to assess damage. The results indicate a sudden increase in salt expansion when salinity exceeded 0.1%. Additionally, re-evaluations of these soil cakes years later allowed for the exploration of mechanisms and the feasibility of assessing soil surface expansion and friability at different stages of the earthen site's lifecycle, including excavation and display. These findings provide preliminary scientific bases and novel methodologies for the further preventive conservation of heritage earthen sites.

As an important part of human cultural heritage, earthen sites are subject to damage caused by a variety of environmental factors, such as cracking, weathering, and flooding. Due to the low mechanical strength of earthen site materials, especially in humid environments, they are susceptible to hazards like moisture penetration, freeze-thaw cycles, and biological invasion. Superhydrophobic coatings show promising potential in the protection of earthen sites, with key properties that include waterproof performance, breathability, robustness, and transparency. By exploring various material systems and preparation methods, the current state of research on the protection of building materials with superhydrophobic materials has been demonstrated, highlighting advantages in the corrosion resistance, self-cleaning, frost prevention, anti-scaling, and other aspects. At the same time, it also points out the challenges faced in the practical application of earthen site protection and the prospects for future research. These include enhancing the bonding strength between the coating and soil particles, improving durability and breathability, and developing large-scale, low-cost, and efficient coating construction techniques.

Dry cracking and salt enrichment are common deterioration of earthen sites being exposed to soil- air coupled environments. The deterioration of earthen sites cannot be completely prevented by simply maintaining a high relative humidity (RH) of air environment, especially in the absence of supplemental liquid water, because of one-way migration of moisture from earthen sites to air environment. In the current work, a protection strategy of constructing a mist atmosphere over the surface of earthen sites, of which near-saturated air with micron-sized moisture droplets by an ultrasonic water atomization, was proposed to enhance the back diffusion of liquid moisture into earthen sites, and thereby inhibit the deterioration of earthen sites. The experimental moisturizing system with an ultrasonic atomization unit was built in an analogous earthen site exhibition hall in the field of Han Yangling Museum of Xi'an City, China. A series of tests were conducted to evaluate the feasibility and safety of the moisturizing system for earthen sites. The results showed that the moisture content of earthen site topsoil after moisturizing can be recovered to a level close to that prior to excavation of earthen sites, and the fractures once occurring on the surface of earthen site was effectively inhibited; The soluble salt content of earthen site topsoil was significantly reduced, and no salt damage occurred. It is anticipated that this study has a great potential for application to resist the one-way migration of moisture from earthen sites to air environment, and the salt damage and fracture of earthen sites. (c) 2023 Consiglio Nazionale delle Ricerche (CNR). Published by Elsevier Masson SAS. All rights reserved.