This paper aimed to explore the mechanical properties of a cement-based material with carbon nanotube (CNT) under drying and freeze-thaw environments. Mercury Intrusion Porosimetry and Scanning Electron Microscopy were used to analyze the pore structure and microstructure of CNT/cement composite, respectively. The experimental results showed that multi-walled CNT (MWCNT) could improve to different degrees the mechanical properties (compressive and flexural strengths) and physical performances (shrinkage and water loss) of cement-based materials under drying and freeze-thaw conditions. This paper also demonstrated that MWCNT could interconnect hydration products to enhance the performance of anti-microcracks for cement-based materials, as well as the density of materials due to CNT’s filling action.

Carbonation induced corrosion is one of the major durability issues for reinforced concrete structures. To address this issue, it is essential to understand the underlying mechanism of carbonation by detecting the ingress of the CO₂ and carbonation depth quantitatively. This paper demonstrates the potential of Raman spectroscopy, as a powerful technique, to implement quantification analysis of cement paste carbonation. In present work, the correlation between the content of the CO₃²⁻ and the Raman peak intensity was initially established by using several standard specimens premixed with certain amount of CO₃²⁻. The established correlation was then used to investigate the carbonation of the cement paste in a CO₂ diffusion scenario, and the results show a good agreement with that obtained by thermogravimetry measurements. Therefore, the feasibility of the Raman spectroscopy to quantify the carbonation degree of the cement paste can be demonstrated.

Carbon nanotubes (CNTs) have shown promise for improving the mechanical performance of cement composites through crack-bridging and frictional pull-out. The interactive behaviors between CNTs and cement matrix act are crucial in optimizing the reinforcement of CNTs in cement composites. This study investigates the effects of nano-silica (NS) sol-gel on the interactive behaviors of CNTs and the cement matrix through a series of experiments and analyses. UV-visible spectrometer results show that CNTs are well-dispersed in suspension and the addition of NS has a negligible effect on the stability of CNT dispersion. Calorimetry tests and dynamic mechanical analysis demonstrate the nucleation and frictional performance of CNTs in cement matrix, respectively. The paper shows that the physical adsorption of NS on the CNT surface could result in the acceleration of cement hydration. Morphology observation confirms that a denser interface between CNTs and cement hydrates is formed. Finally, the improved interaction between CNTs and cement hydrates leads to a substantial increase in friction between CNTs and the cement matrix under periodic loading. NS may act as an ideal admixture for improving both the interactive behaviors between CNTs and cement matrix and the damping properties of cement composite.

With the development of nanotechnology, reduced graphene oxide (rGO) has been used to improve the flexural strength of geopolymers. However, the reinforcing mechanism of rGO nanosheets on the flexural strength of geopolymers remains unclear. Here, this reinforcing mechanism was investigated from the perspectives of hydration and chemical composition. The effect of the reduction degree on rGO-reinforced geopolymers was also studied using isothermal calorimetry (IC), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) tests. Results show that the hydration degree and flexural strength of geopolymers effectively increase due to rGO addition. After alkali reduction at a temperature of 60 °C, rGO nanosheets have maximum reinforcement on the flexural strength of geopolymers with an increment of 51.2%. It is attributed to the promotion of slag hydration, as well as the simultaneous formation of calcium silicate hydrate with low Ca/Si ratio (C-S-H(I)) and calcium aluminosilicate hydrate (C-A-S-H) phases due to the inhibiting effect of rGO nanosheets on Al substitution on the end-of-chain silicates of C-S-H and C-A-S-H gels. In addition, different reduction degrees have almost no effect on the chemical composition of rGO-reinforced geopolymers, while excessive reduction impairs the improving effect of rGO nanosheets on the hydration process and flexural strength of geopolymers due to significant structural defects.

As a kind of coating material, the inorganic coating of alkali-activated metakaolin geopolymer cured at high temperature has been studied a lot for special applications. To our best knowledge, however, not much attention has been given to investigate the influence of SiO₂/Na₂O molar ratio on property of the geopolymer coating. This paper is, thus, dedicated to investigate the role of SiO₂/Na₂O molar ratio on property and microstructure of metakaolin-based geopolymer coating at ambient temperature. The effects on setting behavior, adhesive strength, shrinkage deformation and permeability are discussed. Multiple experiments were used to reveal microstructure changes of the geopolymer coating with different ratios of SiO₂/Na₂O, including Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results indicated that the optimal ratio of SiO₂/Na₂O was 1.0 for good properties of adhesive strength, shrinkage and impermeability. In addition, it has been found that the setting time of geopolymer coating increased with SiO₂/Na₂O ratio which increased from 0.8 to 1.5. That agrees well with the other property and results of exothermal rate of alkali-activated metakaolin. As for the microstructural changes, the SiO₂/Na₂O ratio of 1.0 reduced pore size and porosity of the geopolymer coating and particularly increased volume percentage of pores with a size lower than 20 nm. Besides, FTIR results suggested that geopolymer prepared by the ratio of 1.0 was likely to produce more heterogeneous geopolymer due to a greater silicate structural reorganization.