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• The coating method assists the CNTs for good dispersion and is strongly connected to the surface of fly ash. • The coating method allows CNTs to concentrate in the ITZ between fly ash and cement particles. • The coated CNTs generate nucleation and pore-infilling effects to strengthen the ITZ in cementitious composites. • The workability of the CNTs-coated fly ash-modified cementitious grouting can be significantly reinforced. Cementitious composites reinforced with carbon nanotubes (CNTs) offer notable benefits compared to conventional cement-based materials in terms of durability and strength. Despite these advantages, the widespread implementation of CNTs in cement-based grouting engineering has not been carried out due to the limitations of dispersion issues. In order to facilitate the progression of carbon nanotubes (CNTs) from laboratory experiments to engineering applications, we proposed a method of using amino-functionalised functional groups to coat CNTs on the fly ash (FA) particles' surfaces to assist the dispersion and prepare cost-effective, low-carbon emission, energy consumption-saving and high-performance cementitious slurry. The experimental results exhibit that compared with plain cement-based grouting materials, incorporating 0.023 wt% CNTs and 14.3 wt% FA can reinforce the compressive and tensile strength by 14.2–25.8% and improve the workability by about 21.0%. The application of coated CNTs induces nucleation and pore-infilling effects within the interfacial transition zone (ITZ) of the cementitious composites. This action leads to a reduction in ITZ width and a decrease in crack occurrence within the ITZ. Consequently, these effects contribute to an augmentation in the consolidation strength of the slurry. Acoustic emission and fracture surface fractal analysis further reveal that incorporating CNTs enhances the resist-loading ability of the cement matrix by increasing its energy absorption capability. The innovative coating method reported in this work is expected to facilitate the future application of CNTs in practical grouting engineering. [ABSTRACT FROM AUTHOR]

By virtue of its low cost, high workability, wide availability and suitability for large-volume fabrication, cement-based grouting is the most applied material in underground projects. However, due to the weak tensile strength and high-frequency impact dynamic load disturbance in underground engineering, cement-based grouting is vulnerable to tensile damage, seriously influencing the stability and safety of underground projects. Hence, in this work, the graphene oxide (GO) coated fly ash was adopted to reinforce the dynamic tensile behaviour of the cement-based matrixes to fabricate high-performance, cost-effective and environmentally friendly cementitious composites. The test results show that the GO-coated fly ash could significantly enhance the dynamic tensile performance of the cementitious composites. With only 0.08 wt% GO mixing, the dynamic tensile properties can be strengthened by 19.5–88.5%. After GO nanosheets accelerate the cement hydration process and improve the chemical composition of hydration products, GO nanosheets exhibit macroscopic nucleation and "crack-bridging" effects on the cement matrixes, and the cracks propagation of the hardened specimens would be suppressed under dynamic loading, thus enhancing the tensile resistance of the specimen. The fractal dimension calculation results prove that the GO-coated fly ash-modified cementitious composites have higher integrity after tensile impact, about 2.8–11.9% higher than plain cement-based slurry. Finally, the theoretical analysis reveals that GO nanosheets can enhance the tensile behaviours of the cement matrix by optimizing the dynamic load coefficient. Nevertheless, with the crack propagation, the reinforcing efficiency of GO would be gradually weakened. The findings of this study can promote an understanding of the enhancing mechanisms of GO on the dynamic tensile behaviour of cementitious composites and inspire the potential application of GO-coated fly ash to reduce cement usage in grouting engineering. ● GO-coated fly ash can significantly enhance the dynamic tensile performance of cementitious composites. ● GO nanosheets can suppress the cracks propagation of the cement under dynamic loading. ● The GO-coated fly ash-modified cementitious composites have high integrity after tensile impact. ● One theoretical model of GO in reinforcing cementitious composites under dynamic tensile loading was proposed. [ABSTRACT FROM AUTHOR]

• CWRB is an essential composite in supporting technology for safe and green production in mining. • GO is promising for CWRB composite reinforcement and solid waste recycling. • The reinforcing effects of GO on CWRB is more pronounced under the low Talbot index. • GO-FA hybrid assists CWRB in creating a high-performance material for backfill. Cemented waste rock backfill (CWRB) is an important composite in supporting technology for safe and green production in mining. However, the mechanical performance of CWRB is highly correlated to cement consumption. This study utilized industrial graphene oxide (GO) and fly ash (FA) to create a high-performance, low-cost, and environment-friendly material for backfill. The results show that the GO-FA hybrid improves the microstructural matrix of hydrated cement by generating nucleation effects that refine the microstructure to a denser state and promote pore-filling effects that form barriers at pore throat junctions. This significantly reinforced the compressive strength (up to 53.6%) of the CWRB specimens. The reinforcing efficiency is more pronounced when using fine particle size distributions due to the lack of skeleton effect of gangue aggregates. By monitoring the acoustic emission and analyzing fractal properties, it can be further revealed that GO improves the integrity of CWRB material during loading. Compared to traditional backfill materials, the study found that 0.008 wt% industrial GO can assist FA to lower the consumption of cement by over 20% and improve the engineering properties by 2.6–53.6% at the same time. This research further proves that GO is promising for CWRB composites reinforcement and solid waste recycling. [ABSTRACT FROM AUTHOR]

• A novel anti-icing coating with low-cost and high-performance was developed. • The coating exhibited satisfactory anti-icing ability and easy deicing performance. • The performance relied on the developed admixture and micro/nano binary structure. • A novel theoretical contact angle model was established. Large icing areas on the tunnel-lining surface can affect safe operation of roads and railways in cold regions. However, traditional deicing technologies (i.e., thermal and manual deicing) have problems, such as high-energy consumption, high cost, and low-deicing efficiency. To effectively solve the problem of "easy freezing and slow deicing", we prepared an anti-icing concrete coating material using cement and fly ash, which exhibits cost-effectiveness and high anti-icing efficiency. The high performance of the coating material mainly relied on the developed low-cost and high-efficiency emulsion-type hydrophobic admixture and the micro-/nanobinary rough structure resulting from the recycled nylon mesh and metakaolin nanoparticles. Based on the systematic surface properties and freeze–thaw (F-T) and ice adhesion tests, we found that this material exhibited satisfactory anti-icing ability, easy deicing performance, and remarkable F-T durability. In addition, the superhydrophobicity mechanism and easy deicing property were studied via X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Finally, we established a novel contact angle (CA) model considering the micro-/nano binary structure of the concrete surface and a theoretical model of ice adhesion. Based on this, the influence of surface CA and ice adhesion was theoretically analyzed. This research provides important guidance for solving the anti-icing problem of the tunnel-lining surface in cold regions and can realize the transition from "passive deicing" to "active anti-icing". [ABSTRACT FROM AUTHOR]

• CNTs assist fly ash for cement reduction in cement-based grouting materials. • Fly ash improves the workability of cement-based grouting materials. • CNTs promote the hydration reaction of cementitious composites. • Crack-bridging and pulled-out CNTs form a net-like distribution in the matrix. Cement-based grouting is the most used method to strengthen the fractured rock mass and reinforce the mechanical properties and impermeability of the surrounding rock. The balance among the strength, durability, workability and cost of the grout has always been the key to grouting engineering. In this study, we use carbon nanotubes (CNTs) as the nano-additive to assist fly ash in preparing high-performance cement-based grouting materials. The results show that CNTs can generate nucleation effects and pore-filling effects in cementitious composites to promote the hydration reaction of the grouting materials and optimize the pore structure of the hardened slurry. Two reinforcing roles, bridging and pulled-out role of CNTs, act in the hardened cement matrix, where the former can improve the mechanical properties of grouting materials through micro-friction toughening, and the latter can form a net-like distribution in cement matrix together to enhance the impermeability. More importantly, we found that 0.08 wt% CNTs combined with 20 wt% fly ash can be a good substitute for cement with a moderate proportion of grouting materials. Compared with plain cement slurry, the mechanical properties are basically unchanged, while the workability can be increased by about 5%, and the impermeability can be reinforced by 6%. The discovery of this research provides an excellent chance for utilizing the superior properties of CNTs to fabricate high-performance, cost-effective and environment-friendly grouting materials. [ABSTRACT FROM AUTHOR]

• CWRB plays a central role in mining reinforcement projects and waste recycling. • IGO reinforces the CWRB microstructure via nucleation and pore-filling effects. • Optimized W/C ratio is significant for the modification effects of the IGO-FA hybrid on CWRB. • IGO enhances the integrity and toughness of the CWRB specimens. • IGO-FA hybrid can replace 20% cement in CWRB without affecting its consolidation properties. Cemented waste rock backfills (CWRB) play an essential role in mining safety engineering, waste reduction and harm resource recycling. However, the mechanical and permeability-related properties of the CWRB are limited by cement consumption and cost. This study adopted the industrial graphene oxide-fly ash (IGO-FA) hybrid to produce high-performance, cost-saving, and environment-friendly mine backfill materials. The IGO-FA hybrid exhibited the optimal reinforcing efficiency under a 0.5 water-to-cement ratio, where the CWRBs' mechanical properties and impermeability were enhanced by 5.1%-16.9% and 32.7%-38.9%, respectively, with only 0.007 wt% IGO dosage. Compared with the traditional backfill materials, cement consumption can be reduced by up to 20 wt%. This work not only enhanced the understanding of GO in reinforcing cementitious composites but could also provide an affordable alternative to GO-related composites. [ABSTRACT FROM AUTHOR]