Sustainability of Carbon Nanotube-Reinforced Concrete
Concrete, despite being one of the most produced materials in the world, still has weaknesses and drawbacks. Significant concern of the cementitious materials in structural applications is their quasi-brittle behavior, which causes the material to crack and lose its durability. One of the very recently proposed mitigations for this problem is the implementation of nanotechnology in the concrete mix by adding carbon nanotubes (CNTs) to it. CNTs can enhance the critical mechanical properties of concrete as a structural material. Thus, this paper demonstrates a state-of-the-art review of reinforcing concrete with CNTs, emphasizing on the structural performance. It also goes over the properties of CNTs alone, the present methods and costs associated with producing them, the possible special applications of concretes reinforced with CNTs, the key challenges and drawbacks that this new technology still encounters, and the most reliable practices and methodologies to produce CNT-reinforced concrete in the lab. This work has shown that the addition of CNTs to the concrete mix in percentages as low as 0.25% weight of cement could increase the flexural strength and toughness of concrete by more than 45% and 25%, respectively, and enhance other durability-related properties, given that an effective dispersion of CNTs in the cementitious mix is achieved. Since nano reinforcement for cementitious materials is a new technology, many challenges have to be tackled before it becomes practiced at the mass level.
 S. Sasmal, B. Bhuvaneshwari and N. R. Iyer, "Can Carbon Nanotubes Make Wonders in Civil/Structural Engineering?" Progress in Nanotechnology and Nanomaterials, vol. 2, no. 4, pp. 117-129, October 2013.
 B. M. Tyson, R. K. Abu Al-Rub, A. Yazdanbakhsh and Z. Grasley, "Carbon Nanotubes and Carbon Nanofibers for Enhancing the Mechanical Properties of Nanocomposite Cementitious Materials," Journal Of Materials In Civil Engineering, vol. 23, no. 7 , p. 1028–1035, 2011.
 B. Bhuvaneshwari, S. Sasmal and N. R. Iyer, "Nanoscience to Nanotechnology for Civil Engineering – Proof of Concepts," Recent Researches in Geography, Geology, Energy, Environment and Biomedicine, 2011.
 J. L. Fraga, J. M. D. Campo and J. Á. García, "Carbon Nanotube -Cement Composites in the Construction Industry: 19 52 -2014. A State State of the Art Review," 2nd International Conference on Emerging Trends in Engineering and Technology (ICETET'2014), pp. 137-144, 2014.
 G. Yakovlev, G. Pervushin, I. Maeva, J. Keriene, I. Pudov, A. Shaybadullina, A. Buryanov, A. Korzhenko and S. Senkov, "Modification of Construction Materials with Multi-Walled Carbon Nanotubes," Procedia Engineering, vol. 57 , p. 407 – 413, 2013.
 A. M. Hunashyal, S. V. Tippa, S. S. Quadri and N. R. Banapurmath, "Experimental Investigation on Effect of Carbon Nanotubes and Carbon Fibres on the Behavior of Plain CementMortar Composite Round Bars under Direct Tension," ISRN Nanotechnology, pp. 1-7, 2011.
 G. Ferro, J.-M. Tulliani and S. Musso, "Carbon nanotubes cement composites," 2011.
 P. W. Mast, G. E. Nash, J. Mchoulos, R. W. Thomas, R. Badaliance and I. Wolock, "Experimental Determination of Dissipated Energy Density as a Measure of Strain-Induced Damage in Composites," Mechanics of Materials Branch-Materials Science and Technology Division, 1992.
 T. Madhavi, Pavithra P., S. B. Singh, S. V. Raj and S. Paul, "Effect of Multiwalled Carbon Nanotubes," International Journal Of Scientific Research, 2013.
 S. Cha, C. Song, Y. Cho and S. Choi, "Piezoresistive properties of CNT reinforced cementitious composites," Materials Research Innovations, vol. 18, pp. 716 - 721, May 2014.
 H. M. Chenga, F. Li, G. Su, H. Y. Pan, L. L. He, X. Sun and M. S. Dresselhaus, "Large-Scale and Low-Cost Synthesis of Single-Walled Carbon Nanotubes by the Catalytic Pyrolysis of Hydrocarbons," Applied Physics Letters, vol. 72, no. 25, pp. 3282-3284, 22 June 1998.
 M. F. L. De Volder, S. H. Tawfick, R., H. Baughman and A. J. Hart, "Carbon Nanotubes: Present and Future Commercial Applications," SCIENCE, vol. 339, 1 February 2013.
 L. NaBond Technologies Co., "NaBond," (Online). Available: http://www.nabond.com/specification/CVD-751.pdf. (Accessed 2015).
 M. S. Konsta-Gdoutos and C. A. Aza, "Self sensing carbon nanotube (CNT) and nanofiber (CNF) cementitious composites for real time damage assessment in smart structures," Cement & Concrete Composites, vol. 53, p. 162–169, 2014.
 P. Jackson, N. R. Jacobsen, A. Baun, R. Birkedal, D. Kühnel, K. A. Jensen, U. Vogel and H. Wallin, "Bioaccumulation and ecotoxicity of carbon nanotubes," Jackson et al. Chemistry
 H. –. U. Technology, "Ultrasonic Dispersing of Carbon Nanotubes (CNT)," (Online). Available: http://www.hielscher.com/nano_03.htm. (Accessed 24 4 2015).