Flexural and compressive strengths of carbon nanotube reinforced cementitious composites as a function of curing time

Electrical Resistivity and Compressive Strength of Cement Mortar Based on Green Magnetite Nanoparticles and Wastes from Steel Industry

As concrete is one of the most used construction materials, lowering its environmental impacts is crucial for a more sustainable built environment. The incorporation of nanomaterials in concrete is a fast-growing field of research because a small amount of nano-compounds can significantly improve some of its properties. Few works have assessed the trade-offs between concrete properties improvement and environmental impacts. This paper reviews the main nanomaterial applications in concrete over the last decade with a focus on their environmental implications. Attention is given to nanotechnology applications boosting innovative properties (i.e., self-compacting, self-cleaning, self-healing, and self-sensing) and green concrete blends incorporating residues, identifying the underlined potential environmental impacts of these applications. Finally, some research gaps and future research directions are identified. The literature analysis showed that some nanomaterials can improve the mechanical properties of concrete, increase durability, and effectively promote the reduction of cement content, which results in a decrease of CO2 emissions. To allow the comparability of studies and relate carbon emissions with mechanical properties, a carbon intensity index is suggested. Despite different environmental impacts may be reduced in nano-enabled blends, cradle-to-gate life cycle assessment studies showed an increase in other impact categories. Nanomaterial production is often highly energy-intensive, not fully optimized, and still performed at the lab scale. Despite nanomaterial incorporation in concrete is increasing, studies regarding its environmental impacts or its potential ecotoxicity and toxicity (e.g., from a safe and sustainable-by-design perspective) are still scarce and require further investigation. 

Advancements in nano-enabled cement and concrete: Innovative properties and environmental implications

Many studies have been conducted using carbon-based nanomaterials (CBNs) for improving the electrical conductivity and mechanical properties of cementitious composites, but their practical use is yet to be achieved. Several methods have been attempted to secure the dispersibility in the cementitious composite matrix of CBNs, such as multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs). In this study, MWCNTs and GNPs were noncovalently functionalized using melamine, a low-cost chemical, and ball milling, a simple process commonly used in industrial fields. Additionally, MWCNTs and GNPs having one- and two-dimensional shapes were mixed with the cement paste to examine their effect on electrical conductivity and compressive strength. Following the experiment, it was shown that the electrical conductivity was improved via the noncovalent functionalization of MWCNT and GNP. The compressive strength increased up to approximately 0.30–0.60% of the CBNs content; however, for CBN content higher than 0.60%, the compressive strength decreased. The hybrid MWCNT and GNP mixture had a negligible effect on the electrical conductivity and compressive strength.

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Electrical Conductivity and Compressive Strength of Cement Paste with Multiwalled Carbon Nanotubes and Graphene Nanoplatelets

In this study, CNTs and graphite have been incorporated to provide electrical conductivity and self-heating capacity by Joule effect to an epoxy matrix. Additionally, both types of fillers, with different morphology, surface area and aspect ratio, were simultaneously incorporated (hybrid CNTs and graphite addition) into the same epoxy matrix to evaluate the effect of the self-heating capacity of carbon materials-based resins on de-icing and ice-prevention capacity. The self-heating capacity by Joule effect and the thermal conductivity of the differently filled epoxy resin were evaluated for heating applications at room temperature and at low temperatures for de-icing and ice-prevention applications. The results show that the higher aspect ratio of the CNTs determined the higher electrical conductivity of the epoxy resin compared to that of the epoxy resin filled with graphite, but the 2D morphology of graphite produced the higher thermal conductivity of the filled epoxy resin. The presence of graphite enhanced the thermal stability of the filled epoxy resin, helping avoid its deformation produced by the softening of the epoxy resin (the higher the thermal conductivity, the higher the heat dissipation), but did not contribute to the self-heating by Joule effect. On the other hand, the feasibility of electrically conductive epoxy resins for de-icing and ice-prevention applications by Joule effect was demonstrated.

Ice-Prevention and De-Icing Capacity of Epoxy Resin Filled with Hybrid Carbon-Nanostructured Forms: Self-Heating by Joule Effect.

The authors would like to acknowledge financial support received from European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 760940 and from the Generalitat Valenciana (Spain) (AICO/2019/050).

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Papers

Heating and de-icing function in conductive concrete and cement paste with the hybrid addition of carbon nanotubes and graphite products