Evaluation of Cement-Based Grout for Reinforcing Unsafe Rocks of Stone Carvings at Hangzhou Klippe in China

Cement-based grouting materials can be applied to reinforce unsafe rocks of stone carvings that are attached to or carved out of cliffs. However, studies on the evaluation, that is, the pros and cons of the applied grouting materials, are relatively scarce. In this study, five grouts prepared with different binders [ordinary portland cement (OPC), superfine cement, $\mathrm{OPC}+$ metakaolin] and additives (water glass and organosilicone) were assessed through both laboratory tests and on-site operation. The results revealed that the use of superfine cement instead of ordinary portland cement could result in a more waterproof and durable mortar, at the same time having better injectability and less subsidence as a grouting material. The addition of organosilicone in cement-based grouts could improve waterproofness, greatly increase freeze-thaw resistance, and give better injectability. The incorporation of water glass could greatly increase freeze-thaw resistance. The use of metakaolin in cement grouts could reduce the dissolution of ${\mathrm{OH}}^{-}$ and ${\mathrm{Ca}}^{2+}$ and result in a more even distribution of the mortar components in the hardened grout, yet at the same time inducing higher porosity and lower mechanical strength and significantly promoting ${\mathrm{SO}}_4^{2-}$ precipitation of the mortar.