Abstract: Hollows in the secondary lining vault often leads to the failure of tunnel lining, posing a serious threat to driving safety. Current grouting materials fail to adequately adapt to the characteristics of mold grouting construction, thereby limiting the effectiveness and the further promotion of this technique. This study aims to address the limitations of traditional grouting materials, such as high water leakage, low solid setting rate, and poor bonding with the secondary lining concrete. To this end, micro-expansion materials were tested and investigated for use in mold grouting construction. On the basis of commonly used ratios in grouting engineering, the optimal mechanical properties of mortar were explored by varying the ratios of sulphoaluminate cement (SAC) and ordinary Portland cement (OPC) and water-binder ratios. The dosage of admixtures was then adjusted to improve working performance, and the influence of air-entraining agent dosage on mechanical properties and frost resistance was studied. Experimental results indicate that an OPC∶SAC ratio of 91∶9 and a water-binder ratio of 0.30 enable the best early and late strength development of mortar. Meanwhile, the optimal dosages of water reducing and thickening agents are found to be 0.4% and 0.34% of cementitious material, respectively, to achieve desirable working performance. In addition, the resulting grouting material exhibits good frost resistance, as well as maintained mechanical properties. Finally, the developed grouting material was applied to a mold grouting project, where its applicability and effectiveness were verified.

Key words: secondary lining grouting, workability, micro-expansion, mix proportion, water-reducing agent, frost resistance