| By virtue of the mechanical reinforcement and anti-seepage,grouting technology is widely applied in different engineering projects such as transportation,tunnels,mines,slopes,foundation reinforcement,new energy mining,nuclear waste disposal,etc.and solved many engineering problems.However,the abundant water,gas and harmful liquid environment always corrode the grouting materials,affecting their durability and service life.Hence,it is of great theoretical and engineering significance to effectively improve the impermeability properties of cement-based materials.To this end,carbon nanotubes and graphene oxide were selected as hybrid composites to modify the cementitious pastes in this study to fabricate the high-impermeability and high-durability underground engineering grouting materials.Combining various advanced technical methods such as the nano-characterization and molecular dynamics simulations,the reinforcing mechanisms of carbon nanomaterials on the impermeability of cement-based pastes was revealed from both macro-and micro-perspective.With funding from the National Natural Science Foundation of China(51734009,52074259),the main results are as follows.(1)In terms of the penetration test,a nano additive has been developed using carbon nanotubes-graphene oxide hybrid composites modification technology,which is suitable for enhancing the impermeability of cement-based grouting materials under a high water-to-cement ratio in underground engineering.The reinforcing mechanisms of the hybrid composites on the impermeability of cementitious pastes were revealed.The mixing of graphene oxide-carbon nanotube composites can improve the impermeability of the grouting materials by about 55.3%.The effects of different water-to-cement ratios,mixing ratios,and the influence of the methylcellulose on the impermeability reinforcement of cementitious grouting composites are illustrated.The findings solve the difficulty of the traditional pastes that are hard to balance strength,impermeability,durability and injectability,fluidity,and cost.(2)In terms of the theory analysis,based on the multifractal and the general effective media theory,the hydration enhancement and microstructure optimization of carbon nanomaterials on cementitious pastes were successfully integrated into the optimized permeation theoretical model.A new cement-based material permeation theoretical model was constructed,considering the nucleation effects and the "bridging" optimization effects of carbon nanomaterials.The calculation result of the theoretical model shows that,compared with the classical general effective media theory,the maximum error of theoretical calculation is reduced from 67.8% to 9.7% against experimental results,and the accuracy is increased by more than six times.The revised model makes up for the traditional cement-based permeability theory that is difficult to quantitatively describe the enhancement effects of micro-and nano-additives,and provides a new method for predicting and evaluating the permeability of nano-reinforced cementitious pastes.(3)In terms of nanomaterials optimization,a kirigami structure of the carbon nanomaterials with ultra-efficient selective separation performance was established via molecular dynamics simulation.Furthermore,a new method called “selective tearing” was proposed to generate the graphene kirigami structure.The simulation results show that compared with the single-layer nanoporous graphene structure,which is the highest theoretical separation efficiency proposed in the world,the separation efficiency of the graphene kirigami can be increased by 1.5 to 3.4 times.More importantly,the process of laboratory fabricating the graphene kirigami is realized via molecular dynamics simulation,which provides new ideas for the controllable molecular and ion separation in underground engineering and the preparation of high-quality carbon nanocomposite grouting materials in the future.This paper has 63 figures,30 tables and 267 references. |
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