Impact of Carbon Nanotubes on Concrete: A Systematic Review

Concrete, as one of the most used construction material, has some limitations when it comes to strength and durability. In recent years, use of different advanced nanomaterials has found to improve the property of concrete. Among these nanomaterials carbon nanotubes (CNTs) has gained huge popularity. Carbon nanotube, which is simply a rolled graphene nanosheet with sp2-bonded carbon atoms, is a one-dimensional tube or cylindrical nanocarbon and Depending upon the numbers of rolled overlapping cylinders, carbon nanotube can be named as single-walled carbon nanotube (SWCNT), double-walled carbon nanotube, and multi-walled nanotube (MWCNT) (Kausar, 2023). According to the systematic review by Dias Reis the number of research studies on the incorporation of carbon nanotubes in concrete has been increasing each year (Elvys Dias Reis, 2023).

Traditional concrete may no longer handle the growing demands placed on it and therefore it is important to use less cement while improving concrete’s strength as to make structures more affordable and environmentally friendly by reducing CO2 emissions (Khitab A., 2017). The use of CNTs in concrete reinforcement aims to achieve properties such as compressive strength, flexural strength, and resistance to cracking, while also enhancing the material’s durability under various environmental conditions (Borges, 2019). Despite the benefits, there are challenges in uniformly dispersing CNTs within the concrete mix, and further research is needed to optimize this process (Fávero, 2016).

This review aims to explore the current state of research on CNT reinforcement in concrete, evaluating the methods of CNT incorporation, the effects on concrete's mechanical and durability properties, and the challenges that still need to be addressed for widespread practical application. Through a comprehensive analysis of recent studies, this paper seeks to provide a clearer understanding of the potential and limitations of CNT-enhanced concrete, as well as identify promising directions for future research in this rapidly evolving field

Introduction

In this review, a comprehensive and structured approach was adopted to collect and analyze relevant studies related to the incorporation of carbon nanotubes (CNTs) in concrete. The primary objective was to evaluate the effects of CNTs on the mechanical and durability properties of concrete, as well as to identify challenges and gaps in the existing literature.

A systematic literature search was conducted in major academic databases, including Google Scholar, Scopus, Web of Science, and ScienceDirect, using a combination of the following keywords:

• "Carbon Nanotubes"

• "Concrete Reinforcement"

• "CNTs in Concrete"

• "Mechanical Properties of Concrete with CNTs"

• "Durability of Concrete with CNTs"

• "Nanotechnology in Concrete"

The search was limited to peer-reviewed journal articles, conference papers, theses, and reports published from 2010 to 2024. Only the articles focusing on the use of carbon nanotubes in concrete were included in the study. The types of carbon nanotubes (CNTs) used in the studies, including single-walled CNTs and multi-walled CNTs, were noted, as these variants may influence the performance of concrete. The concentration and dosage of CNTs incorporated into the concrete mix were also extracted, as varying amounts of CNTs can have different effects on the material’s properties. Additionally, the methods of CNT incorporation, such as dispersion techniques and mixing methods, were analyzed to understand how CNTs were integrated into the concrete matrix. The studies assessed several mechanical properties, including compressive strength, flexural strength, and tensile strength, to evaluate the impact of CNTs on the material’s structural performance. Finally, the key findings and conclusions of each study were summarized to identify trends, benefits, and challenges associated with CNT reinforcement in concrete.

Methodology

Carbon nanotubes (CNTs) can be simply defined as cylindrical-shaped materials composed of hexagonally arranged hybridized carbon atoms (Arash Yahyazadeh, 2024). These materials are the strongest and stiffest discovered to date in terms of elastic modulus and tensile strength, surpassing steel in strength while having only a quarter of its density and rigidity is comparable to that of diamond. Due to the strong covalent bonds between carbon atoms, they possess an exceptionally high melting point. They are highly resistant to corrosion, as their chemical stability—similar to graphite—enables them to withstand most chemical reactions, unless exposed to high temperatures and oxygen (Raut, 2003).

Literature Review

There are essentially two types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs), which differ in the arrangement of their graphene cylinders. Nanotubes with one wall are mostly curved and are narrower in diameter than the nanotubes with multiple walls (Khurana, 2022).

Synthesis

The synthesis of carbon nanotubes (CNTs) involves several methods, each with its own advantages and challenges. Here are the most common methods (M. S. Dresselhaus, 2001):

1. Arc Discharge:

This method involves creating an arc between two carbon electrodes in an inert gas atmosphere. The high temperatures generated cause the carbon atoms to form CNTs. It's one of the earliest methods used for CNT synthesis. This method has some challenges, including issues related to the scalability of the process, the uniformity of CNTs produced, and the need for further optimization to improve yield and quality (Neha Arora, 2014).

2. Laser Ablation:

In this method, a high-powered laser is used to vaporize a carbon target in a high-temperature reactor. The carbon vapor then condenses to form CNTs. This method produces high-quality CNTs but is not suitable for large-scale production. The choice of laser wavelength significantly affects the yield and properties of CNTs, with UV lasers requiring more precise control over laser fluence for optimal results (Stobinski, 2015).

3. Chemical Vapor Deposition (CVD):

This is the most widely used method for CNT synthesis. It involves decomposing a carbon-containing gas (like methane, ethylene, or acetylene) over a metal catalyst at high temperatures. The carbon atoms deposit on the catalyst and form CNTs. CVD is scalable and can produce large quantities of CNTs. However there are areas for future investigation, such as exploring new catalysts, refining deposition techniques, and developing scalable methods for industrial production (Hyo Chan Hong, 2023).

4. High-Pressure Carbon Monoxide (HiPco):

This method uses high-pressure carbon monoxide to grow CNTs on a metal catalyst. It's similar to CVD but uses CO as the carbon source. The HiPco method involves using metal carbonyls as catalysts, high temperatures (~1000°C), and high pressures (~100 atmospheres) to produce SWCNTs. This method is known for producing high-purity SWCNTs with small diameters (Varun Shenoy Gangoli, 2019).

5. Plasma Enhanced Chemical Vapor Deposition (PECVD):

This method is a variation of CVD that uses plasma to enhance the chemical reactions, allowing for lower synthesis temperatures and potentially better control over the CNT structure. However challenges still remain in PECVD, such as the need for further optimization of process parameters and the development of scalable methods for industrial production. There are areas for future research, including the exploration of new catalysts and precursor gases, as well as the refinement of deposition techniques (J. Zhang, 2022).

6. Electrochemical Synthesis:

This method involves using an electrolytic cell to deposit carbon atoms onto a substrate, forming CNTs. It's a relatively new method and offers the potential for low-cost production. However, there is the need for further research to optimize the electrochemical synthesis process, exploring new precursor materials, developing more efficient electrolytes, and refining electrode designs to enhance the quality and yield of carbon nanostructures (Authors: M. Revathi, 2024).

Each of these methods has its own set of parameters, such as temperature, pressure, catalyst type,

CNT Reinforcement in Concrete

CNTs can significantly enhance the mechanical properties of concrete, making them a promising material for improving the strength and durability of cementitious composites (Tupe Kiran, 2023). After conducting an extensive experimental program to evaluate the effects of CNTs on concrete's flexural, splitting tensile, and compressive strength, as well as ultrasonic pulse velocity, elastic modulus, and fracture toughness, it was found that The addition of 0.05–0.1% CNTs significantly improved the compressive, flexural, and splitting tensile strength of concrete. The fracture energy and elastic modulus also increased by up to 42% and 15%, respectively. Additionally, CNTs showed great potential in enhancing the crack resistance and fracture toughness of concrete, especially in the pre-peak performance stage (Tupe Kiran, Experimental Study on Mechanical Properties of CNT Reinforced Concrete, 2023). Because of the unique mechanical, electrical, thermal, and chemical properties of CNTs it make them suitable for enhancing the performance of cementitious materials. Also huge potential of CNTs in 3D printing concrete can be seen for future prospects in this area. This innovation aims to produce high-performance, customized building materials with enhanced mechanical properties and functionality (Kai Cui, 2022).

After conducting experiments to evaluate the effects of adding different percentages of CNTs (0.015%, 0.020%, 0.030%, and 0.040% by weight of cement) on the compressive strength, flexural strength, and split tensile strength of concrete. The addition of CNTs significantly improved the compressive, flexural, and split tensile strength of concrete. The highest improvement was observed at 0.030% CNT addition. The experiment concluded that CNTs could significantly enhance the mechanical properties of concrete, making them a promising material for improving the strength and durability of cementitious composites (Tupe Kiran, Experimental Study on Mechanical Properties of CNT Reinforced Concrete, 2023).

With the significant potential of CNMs in revolutionizing cementitious materials there is a need for continued research to optimize dispersion methods and characterization techniques for practical applications. As CNMs tend to agglomerate due to strong van der Waals forces, which hinders their effective integration into cementitious matrices. Therefore, proper dispersion is critical to maximize the benefits of CNMs, such as improved strength, conductivity, and crack resistance (Li Yuyang, 2024).

There are some dispersion techniques that includes physical methods like ultrasonication, which breaks up agglomerates but can damage CNTs if overused, and high-shear mixing, which effectively disperses CNTs in solutions. Chemical methods involve surfactants that reduce agglomeration by adsorbing onto CNT surfaces and surface functionalization (e.g., oxidation or covalent bonding) to improve dispersion and bonding with the cement matrix. Combined approaches, integrating both physical and chemical methods, often achieve the best dispersion results (Yibo Gao, 2023).

The incorporation of carbon nanotubes (CNTs) in concrete has been widely studied, with multiple research findings indicating significant improvements in mechanical properties such as compressive, tensile, and flexural strength. Despite the general agreement on the positive effects of CNTs, various challenges still exist, including proper dispersion of CNTs, leading to agglomeration and uneven distribution. Additionally, one of the primary challenges is achieving affordable and scalable production of CNTs in cementitious materials.

Future research should focus on optimizing CNT dispersion methods to ensure uniformity and maximize the reinforcing potential of CNTs in concrete. Additionally, large-scale field trials and long-term durability studies should be conducted to evaluate CNT-reinforced concrete under real-world conditions, including exposure to varying environmental stresses. Research should also assess the economic and environmental viability of CNT applications in construction, addressing concerns related to cost, sustainability, and potential health risks associated with CNT production and handling. By addressing these research gaps and expanding on current knowledge, CNT-reinforced concrete can move closer to becoming a viable and widely adopted material in the construction industry.

Discussion

Incorporating carbon nanotubes (CNTs) into concrete has shown significant potential to enhance the mechanical and durability properties of cementitious materials. Research has demonstrated that CNTs can improve the compressive, flexural, and tensile strength of concrete, as well as its fracture toughness and crack resistance. These enhancements make CNT-reinforced concrete a promising material for advancing construction practices, offering stronger, more durable, and environmentally friendly alternatives to traditional concrete. However, challenges such as achieving uniform dispersion of CNTs, optimizing production techniques, and ensuring cost-effectiveness remain. Addressing these challenges is critical for the widespread adoption of CNTs in concrete. Future research should focus on improving dispersion methods, evaluating long-term durability under real-world conditions, and assessing the scalability and economic viability of CNT-enhanced concrete. By overcoming these hurdles, CNTs have the potential to revolutionize the construction industry, offering a pathway to more sustainable and resilient building materials.

Conclusion

Arash Yahyazadeh, S. N. (2024). Carbon Nanotubes: A Review of Synthesis Methods and Applications. Reactions.

Authors: M. Revathi, A. K. (2024). Electrochemical Synthesis of Carbon Nanostructures.

Borges, L. A. (2019). Performance of Concretes Produced with Carbon Nanotubes Synthesized Directly on Clinker. Federal University of Minas Gerais.

Elvys Dias Reis, L. A. (2023). A Systematic Review on the Engineering Properties of Concrete with Carbon Nanotubes. HAL open science.

Fávero, R. B. (2016). Mechanical Characterization of Advanced Cementitious Composite Material Based on Reactive Powders. Federal University of Rio Grande do Sul.

Hyo Chan Hong, J. I. (2023). Recent Understanding in the Chemical Vapor Deposition of Multilayer Graphene: Controlling Uniformity, Thickness, and Stacking Configuration. Nanomaterials.

J. Zhang, X. W. (2022). Plasma Enhanced Chemical Vapor Deposition (PECVD) of Carbon Nanotubes: A Review. Materials Science and Engineering: R: Reports.

Kai Cui, J. C. (2022). Developments and Applications of Carbon Nanotube Reinforced Cement-Based Composites as Functional Building Materials. Frontiers in Materials.

Kausar, A. (2023). Carbonaceous Nanofillers in Polymer Matrix. Elsevier.

Khitab A., A. S. (2017). Fracture Toughness and Failure Mechanism of High Performance Concrete Incorporating Carbon Nanotubes. Frattura Ed Integrità Strutturale.

Khurana, A. (2022). Carbon Nanotubes: Structure, Properties, Synthesis and Potential Applications. International Journal of Scientific Research (IJSR).

Li Yuyang, Z. L. (2024). Research Progress in Dispersion Technology and Characterization Methods of Carbon Nanomaterials in Cementitious Materials. Bulletin of the Chinese Ceramic Society.

M. S. Dresselhaus, G. D. (2001). Carbon Nanotubes: Synthesis, Structure, Properties, and Applications. Springer-Verlag.

Neha Arora, N. S. (2014). Arc discharge synthesis of carbon nanotubes: Comprehensive review. Diamond and Related Materials.

Raut, B. (2003). Carbon Nanotubes: Definition, Properties, Types, and 10 Reliable Applications. Chemist Notes.

Stobinski, L. (2015). Synthesis of Carbon Nanotubes by the Laser Ablation Method: Effect of Laser Wavelength. Physica Status Solidi B - Basic Solid State Physics.

Tupe Kiran, P. S. (2023). Experimental Study on Mechanical Properties of CNT Reinforced Concrete. International Journal of Advanced Research in Engineering and Technology (IJARIIE).

Tupe Kiran, P. S. (2023). Experimental Study on Mechanical Properties of CNT Reinforced Concrete. International Journal of Advanced Research in Engineering and Technology (IJARIIE).

Tupe Kiran, P. S. (2023). Experimental Study on Mechanical Properties of CNT Reinforced Concrete. International Journal of Advanced Research in Engineering and Technology (IJARIIE).

Varun Shenoy Gangoli, M. A. (2019). The State of HiPco Single-Walled Carbon Nanotubes. Carbon.

Yibo Gao, J. L. (2023). Dispersion of Carbon Nanotubes in Aqueous Cementitious Materials: A Review. Nanotechnology Reviews.

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