Regulation of oxidation degree for graphene oxide on hydration process and engineering properties of natural hydraulic lime pastes for grout strengthening of stone cultural relics

The stone cultural relics represented by grottoes carry precious historical and cultural information and are important representations of the mutual learning of civilizations. Fissures are the main threat to stone cultural relics. The development of grout strengthening materials for fissure repair is of great significance to restrain or delay other threats, such as instability, water seepage, and surface weathering. In this work, based on the improved Hummers’ method, graphene oxide (GO) with different oxidation degrees was prepared by adjusting the amount of added KMnO4, which was then added to natural hydraulic lime (NHL2) pastes to explore the effect of the GO oxidation degree on the hydration process and engineering properties of NHL2 pastes. The results indicated that the addition of GO significantly promoted the hydration rate of the NHL2 pastes and resulted in the formation of more regular and ordered flower-like hydration products and aggregates. Compared with the reference sample, the engineering properties of the modified NHL2 pastes, including the mechanical properties and the autogenous shrinkage behavior, were significantly improved. The simulated grouting experiment also indicated that NHL2 pastes had good groutability and interface combination statuses. In the hydration process of NHL2, GO provided nucleation sites. The hydration reactions were preferentially carried out on the GO sheets, and regular aggregates formed to fill the cracks and holes in the NHL2 pastes, which improved the mechanical properties of the strengthened material. This work provides an effective strategy for the grout strengthening of stone cultural relics fissures.