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Inspired by ancient Roman concrete techniques, a team led by Prof. Ma Xiao from the University of Science and Technology of China (USTC) developed a novel low-cost, highly durable calcium-silicate-hydrate-based grouting material for grotto conservation. Their research is in Advanced Science.

Rock relics serve as vital archives of human history. China's grotto temples, such as the Mogao Caves in Dunhuang and the Beishan Grottoes of the Dazu Rock Carvings, integrate architecture, sculpture, and mural art into grand-scale treasures of Chinese civilization. However, centuries of natural erosion have left many grottoes vulnerable to various damage, such as wall cracking and water infiltration.

In southern China, the hot and humid climate exacerbates water seepage through cracks, which not only compromises the structural stability of the grottoes but also triggers compounded deterioration including surface weathering, salt crystallization, and biological erosion.

One of the key challenges in addressing water seepage in grottoes lies in using grouting materials to seal cracks. Ideal grouting materials must possess appropriate mechanical strength, good vapor permeability, and high durability. Conventional materials such as organic resins and cement-based compounds often fail to meet the special needs of cultural relic preservation due to insufficient compatibility or risks of secondary damage.

To search for ideal grouting material, the team combined experiments with molecular dynamics simulations and investigated how calcium–silicate–hydrate (C–S–H) interacts with key minerals (such as quartz, albite, and calcite) in the Beishan sandstone at the Dazu Rock Carvings. Their work revealed the critical role of hydrogen bonding in interfacial adhesion and the synergy of mechanical interlocking and chemical bonding, providing a theoretical basis for material optimization.

Building on this discovery, the team synthesized a network-structured C–S–H gel at room temperature. Through optimization of parameters such as Ca/Si ratio, water-to-binder ratio, binder-to-aggregate ratio, and polycarboxylate superplasticizer dosage, they significantly enhanced the overall performance of the grouting material. This optimized formulation now stands as an ideal candidate for addressing water seepage issues in the Dazu Rock Carvings.

Through an integrated method encompassing material design, synthesis, characterization and interface analysis, this work has developed a targeted research framework for protective materials and established a paradigm for the conservation of grotto temples and other stone cultural heritage.