From Ancient Techniques to Modern Solutions: In Situ Synthesis of C-S-H for Sandstone Conservation

Hydraulic calcium-silicate-hydrate (C-S-H), a key binding agent in both ancient mortars and modern cement, holds significant promise for heritage conservation. Drawing inspiration from ancient Roman techniques, this study investigates the development of C-S-H-based grouting materials to address water-induced erosive damage in the Beishan Grottoes of the Dazu Rock Carvings. The interfacial interactions between C-S-H mortar and sandstone are analyzed using molecular dynamics simulations, revealing the crucial role of hydrogen bonding at the interface of C-S-H and mineral phases for adhesion. In the in situ synthesis of C-S-H with a reticulated structure from Ca(OH)2/silica fume mixtures under ambient conditions, this work systematically investigates the impact of varying calcium-to-silica (C/S) ratio and water-to-binder ratios on the mechanical properties and pore structure of C-S-H-based mortars. The optimal mechanical and physical properties are achieved with a C/S ratio of 0.8, water/binder ratio of 2.0, binder/aggregate ratio of 1:3, and 4 wt% polycarboxylate superplasticizer. Laboratory-scale experiments confirm its excellent compatibility with sandstone, offering a potential effective grouting solution for the Beishan Grottoes and emphasizing the importance of material compatibility in heritage conservation. This integrated approach encompassing materials design, synthesis, characterization, and interfacial analysis, presents a robust framework for developing tailored binding agents for various applications.