Advancements in Artificial Hydraulic Lime Composites for Sustainable Restoration of Stone Cultural Heritage

Abstract

The restoration of stone cultural relics requires materials that align with the relics’ inherent characteristics and are economically viable. While natural hydraulic lime has historically been the preferred material for such restoration efforts, challenges such as limited availability and high costs have prompted the exploration of alternative solutions. In this study, three distinct formulations of artificial hydraulic lime (GL1, GL2, and GL3) were meticulously developed by combining hydraulic components, volcanic ash activators, heavy calcium powder, and slaked lime powder. Emphasizing compatibility with stone cultural relics, GL2 and GL3 were selected for the preparation of a stone cultural relic restoration mortar. Comprehensive testing, including fluidity, water absorption rate, strength, and drying shrinkage, was conducted. The restoration mortars demonstrated optimal fluidity between 170 and 180 mm, meeting stringent requirements for restoration applications. Notably, the water absorption rate, ranging from 13% to 15%, exceeded that of native rock, satisfying sacrificial protection criteria. After a 28-day carbonization period, the compressive strength of AL3 and BL3 samples surpassed 20 MPa, while AL2 and BL2 samples exhibited compressive strengths ranging from 16 to 19 MPa—well within the 20%-80% range of the native rock’s compressive strength. The pull-out bonding strength at 28 days was moderate for all four restoration mortar types, with no discernible irreversible damage to the underlying rock base. The adaptability of selecting restoration mortar based on the material strength of stone cultural relics was demonstrated. Finally, the successful application of the restoration mortar formulated with GL2 lime in restoring stone slabs at the Confucius Temple highlights the practical significance of the research findings, offering valuable insights for the sustainable preservation of architectural heritage.