Hydraulic properties of single fractures grouted by different types of carbon nanomaterial-based cement composites.

In underground projects such as nuclear waste disposal facilities, the requirement of controlling the permeability is very important, and common grouting materials are not suitable. Therefore, creating a composite material to be used for the grouting in engineering projects is essential. The present study characterizes the efficiency of several kinds of carbon grouting composites based on nanomaterials, in terms of the hydraulic properties of single fractures in granites using a rock permeability test system. The pore structure and distribution of the carbon nanomaterials in the grouting pastes were investigated using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The results reveal that the hydraulic properties of grouting samples can be well described by linear Darcy's law. These grouting composites can decrease the equivalent permeability (K_g) by 31.8–81.0% in different confining pressures. The enhancing effect of the graphene oxide (GO)/multi-walled carbon nanotube (MWCNT)–based ordinary Portland cement (OPC) grouted sample is the best, improving the permeability resistance by 240.3–315.0%. The MIP test proves that mixing carbon nanomaterials will improve the pore characteristics. The GO/MWCNT-OPC grouting presents the optimal decrease in all total intruded volume, average pore diameter and porosity, dropping by 33.8, 40.7 and 22.9%, respectively. Both the average pore diameter and porosity of grouting pastes have zero-intercept linear correlations with the equivalent permeability and can predicate permeability-related properties with considerable accuracy. The SEM images further confirmed that carbon nanomaterials can not only refine the pore structure of grouting materials through the superior properties of the MWCNTs to bridge micro-sized cracks and the interfacial adhesion of GO but also reinforce the flow resistance of the interface between the grouting material and the granite. The findings of this study can help guide the implementation of carbon nanomaterial-OPC grouting in engineering projects. [ABSTRACT FROM AUTHOR]