Optimization of microfine-cement-based slurry containing microfine fly ash and nano-CaCO_3 for microfracture grouting

摘要

Grouting technique is an important method for the prevention of water seepage and reinforcement of fractured rock mass in underground engineering. This study aims to investigate the rheological and mechanical properties of microfine-cement-based grouting material containing microfine cement (MC), nano-CaCO3 (NC), microfine fly ash (MFA), and polycarboxylate superplasticizer (SP) based on orthogonal tests, and optimize the slurry mix ratio. To better verify the results of orthogonal tests and understand the flow characteristics of the MC-based slurry when grouting in microfracture, laboratory grouting tests were carried out under triaxial stress state. The experimental results showed that the incorporation of NC could improve the compressive strength and shorten the setting time of the slurry. The results of MIP tests showed that the incorporation of NC significantly reduced the harmful pores and total porosity of the hardened slurry in the long term. The chloride diffusion coefficient of the slurry also decreased due to the incorporation of NC at early and later ages. The results of grouting tests indicated that the flow velocity of the slurry increased with increasing grouting pressure, while decreased with increasing confining pressure. The optimal ratio of the MC-based slurry was NC content of 1%, MFA content of 40%, SP content of 0.4%, and W/S ratio of 1.0.