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In recent years, many researchers have worked on the development of cementitious composites as self-heating components. To meet the requirements of self-heating composites, carbon-based nanomaterials have been considered as an electrically conductive filler in the cementitious matrix because of their excellent electrical and thermal characteristics. Most researches have focused on the heating performances of the CNT-incorporated hybrid cementitious composites, while fewer efforts were given to observe heat-dependent electrical characteristics of the modified cementitious composites under self-heating condition. In this regard, this paper summarizes recent studies in literature conducted to investigate heat-dependent electrical characteristics of cementitious composites with carbon-based nanomaterials.

The conductive polymeric composites (CPCs) have been highlighted due to their various applications. However, their electrical impedances are sensitive to the external factors such as tunneling-induction, frequency-dependence, and applied mechanical strain amplitudes. Herein, the carbon nanotube (CNTs) and carbonyl iron powder (CIP)-embedded CPCs were fabricated, and their tunneling-induced and frequency-dependent electrical impedance values were investigated considering the different input voltages and frequencies, and mechanical strain amplitudes. Moreover, the machine learning-based artificial neural network (ANN) model was adopted to predict the electrical impedances of the fabricated CPCs, and the predicted values were compared to the experimental results, showing the high accuracy with R-square values of 0.9081.

This study characterizes reactive MgO-modified calcium sulfoaluminate (CSA) cement upon carbonation. Paste samples were fabricated by replacing CSA cement with reactive MgO at levels of 0, 5, 10, and 20 wt%. The samples were cured for 56 days and further cured at a CO2 concentration of 3% for 28 days. MgO incorporation into the CSA cement favored the formation of monosulfate over ettringite. Externally supplied MgO in the CSA cement reduced Al uptake in C-A-S-H and formed hydrotalcite as a secondary phase, which is associated with a reduction in the carbonation degree. In addition, the incorporated MgO inhibited the carbonation of ettringite and monosulfate, while more C-A-S-H and aluminum hydroxide were formed in neat CSA cement upon carbonation, showing the nearly full decomposition of ettringite and monosulfate. The tetrahedral Al network of the MgO-modified sample was not altered upon carbonation, indicating that MgO modified the route of carbonation.

In the present study, CNT-embedded electric heating composites were fabricated and the effects of silica aerogel addition on the electric heating capabilities and heat-induced electrical stability were examined. Silica aerogel at levels of 0%, 0.5%, and 1.0% by mass of polymer were incorporated into the polymeric composites incorporating 4% CNT. The fabrication details, tunneling-induced electrical characteristics, and electric heating capabilities during cyclic and long-term heating conditions were reported. The electric heating test results were discussed in terms of the SEM observations, thermal images taken during the heating process, and schematic descriptions of the heating process. The test results showed that the incorporating silica aerogel could reduce the redistribution of the individual CNT particles, improving the electric heating capabilities including the heat generation stability and the heat-induced electrical stability during the heating process. Moreover, incorporating silica aerogel increased the cooling time, and improving the heat-storage capability related to the heating efficiency. Thus, it can be concluded that the silica aerogel addition has clear potential to improve the electric heating capability and heat-induced electrical stability of CNT-embedded electric heating composites.

The present study proposes a micromechanical model composed of a two-level homogenization process for predicting the electrical conductivity of polymeric composites incorporating carbon nanotube (CNT) and carbon fiber (CF). The curviness of the CNT and the interfacial resistivity between the polymer matrix and the CNT are considered in the micromechanical model. A series of numerical studies with model parameters are carried out, after which a genetic algorithm is applied to determine the optimized model parameters. The electrical and morphological properties of the composites are experimentally evaluated according to the content of CNT and CF. To verify the predictive capability of the proposed model, the present prediction is compared with that obtained from experiments. The proposed model combined with the genetic algorithm is found to closely simulate the effective electrical conductivity of the composites, as evidenced by the credible accuracy to the experimentally measured values.

A novel physicomechanical technique for the dispersion of carbon nanotube particles was proposed to fabricate the electrically conductive polymer composites in this study. The combination of dispersion agents such as superplasticizer and silica fume, ultrasonication, and melting processing method utilizing a solvent in the proposed technique was applied to improve the dispersion of carbon nanotube particles. Polypropylene and xylene were used as a binder material and as a solvent, respectively. The dispersion state of carbon nanotube particles in the xylene solution was estimated by the sedimentation and zeta potential tests, while that of carbon nanotube particles in polypropylene composites was evaluated by the electrical resistivity of the composites, Raman spectrum, and field-emission scanning electron microscopy images. The test results showed that the proposed technique significantly improved the dispersion of carbon nanotube particles in xylene solution, synergistically generating a physical shock to carbon nanotube agglomerates by the combination of silica fume and ultrasonication. The mechanism of the proposed technique for the dispersion of carbon nanotube particles was discussed. Furthermore, the electrical resistivity of polypropylene composites utilizing the proposed technique was significantly lower than that of polypropylene composites with carbon nanotubes measured in previous studies.