Development and Application of Carbon Nanotubes in Cements: Sustainability and Nanotechnology

The cement industry is a major contributor to carbon dioxide (CO₂) emissions, accounting for a substantial share of global emissions [1]. In response to the need to mitigate the environmental impact of the construction sector, the integration of nanotechnology into cementitious matrices has emerged as a promising solution. Carbon Nanotubes (CNTs) possess remarkable physical and chemical properties, including high mechanical strength and thermal stability [2], making them excellent candidates for enhancing cementitious materials. The synthesis of CNTs directly onto cement grains is achieved through the dry impregnation of metallic catalysts, followed by Chemical Vapor Deposition (CVD), enabling the anchoring of transition metals such as Iron (Fe) and Cobalt (Co) onto pre-prepared alloys. This process results in a nano-structured cement known as nanocement [3]. Nanocement has the potential to replace up to 10% of conventional mortars and concretes by mass, promoting the development of cementitious matrices with superior mechanical properties, while also supporting the environmental sustainability of the construction industry [4,5].

Preparation of nanocement

The production process of nanocement starts with the preparation of metallic catalysts from transition metal salts, such as iron and cobalt, supported on magnesium oxide. These catalysts are dissolved in alcohol, heated to 550 °C for oxidation and the removal of volatiles, and then impregnated into materials such as sand, clay, or waste. Subsequently, the mixture is combined with Portland cement and reheated to 550°C to anchor the metals onto the cement grains. Following dry homogenization, the process facilitates the formation of carbon nanotubes directly on the cement grains, resulting in nanocement [6,7].

Chemical and microstructural properties

Through advanced characterization techniques, the efficient anchoring of Carbon Nanotubes (CNTs) directly onto cement grains was confirmed, resulting in significant chemical and microstructural modifications. Scanning Electron Microscopy (SEM) verifies this anchoring by revealing the homogeneous distribution of CNTs within the cement matrix. Additionally, Fourier- Transform Infrared Spectroscopy (FTIR) compares pure cement and nanocement, demonstrating the formation of chemical bonds between the CNTs and the cement compounds. X-ray Diffraction (XRD) further indicates that the developed catalysts exhibit phases of cement combined with metallic phases (Fe and Co), confirming the interaction between the components. These analyses validate the efficient synthesis of high-quality carbon nanotubes on cement grains. The process employs straightforward techniques, eliminating the need for sophisticated chemical processes or specialized labor, thus representing a significant advancement of nanotechnology in the field of civil engineering.

Improvements in mechanical properties

The incorporation of Carbon Nanotubes (CNTs) into cement has shown significant improvements in the material’s mechanical properties, as evidenced by tests conducted on nanocement. The compressive strength of mortar using 1g of nanocement to replace 40g of conventional cement (10%) showed a marked increase, with gains of up to 30%, compared to both materials, attributed to the formation of a denser cementitious matrix reinforced by CNTs. Flexural strength was also enhanced due to the homogeneous distribution of the nanotubes, which act as bridges between microscopic cracks, delaying their propagation and increasing structural integrity, achieving a 15% increase under the same conditions with the use of nanocement. Additionally, the reduction in permeability of nanocement, evidenced by water absorption tests, confirms the formation of a denser structure that minimizes the penetration of liquids and aggressive agents, resulting in greater durability [6]. These improvements not only enhance the material’s mechanical performance but also contribute to sustainability in the construction industry, allowing for partial replacement of conventional cement and reducing CO₂ emissions associated with its production, without compromising structural efficiency [8,9].

Environmental and sustainable benefits

The environmental impact of nanocement is associated with the reduction of CO₂ emissions and the sustainability of the cement industry. The partial replacement of conventional cement with nanocement reduces the need for clinker production, the main source of carbon emissions in the sector. Furthermore, the incorporation of Carbon Nanotubes (CNTs) improves the mechanical strength of cementitious composites, allowing for the use of smaller amounts of material without compromising structural performance [10]. The developed synthesis process uses dry impregnation and Chemical Vapor Deposition (CVD), eliminating the need for aggressive chemical reagents (acids), external agents such as additives, and specialized labor. Nanocement is mixed at ambient temperature through mechanical methods already known in the industry, making the developed technology viable for largescale application and potentially contributing to a more sustainable revolution in the construction industry.

The development of nanocement represents a significant advancement in the integration of nanotechnology and the construction industry. The dry impregnation technique allows for the formation of metallic catalysts directly on cement grains, promoting the efficient growth of CNTs via CVD. This process results in a material with enhanced mechanical properties, increased durability, and a lower environmental impact. The results obtained demonstrate that the partial replacement of conventional cement with nanocement can be an effective strategy to reduce raw material consumption and minimize CO₂ emissions associated with cement production. Moreover, the simplicity of the method and its economic viability indicate great potential for large-scale application in the construction industry.

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