ICME Overview of Carbon Nanotube Reinforced Concrete Fracture Analysis

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Background

In the construction industry, concrete is the most widely used material due to its resource efficiency, durability, thermal properties, and environmental impact in retaining storm water and minimizing waste in production. Despite these advantages, there is a limit to the amount of stress and abuse that it can withstand from both humanity and nature and with the increase in urbanization and human population to the work load that concrete must support, the life cycle of concrete has begun to reduce. The previous solution to these problems came in the form of rebar to increase the amount of tensile stress concrete can withstand and reduce the amount of cracking that occurs over time. Recently, new materials and techniques have been studied to improve or replace rebar. One such material implemented to combat the life cycle issue is carbon nanotubes.

Discovered in 1991, carbon nanotubes (CNT) made a huge impact in several different industries due to their physical properties and are recently being considered as replacements for traditional reinforcement fibers in upcoming high-performance nanocomposites. Some researchers believe that by adding carbon nanotubes to the cement paste not only increases the compressive strength, but also increases the fracture resistance properties. Additionally, the CNTs reduce the number of pores in the concrete and shrinkage post set. [1]

Adding CNTs to a paste mix uniformly is incredibly difficult as they tend to attract each other and mesh together. Several methods are available to integrate a homogenous mix, such as directly synthesizing the CNTs into the mix or combing them into carboxyl or hydroxyl groups on the carbon atoms.[1] The synthesizing method is one of the only methods where the distribution of CNT is uniform. Having a uniform distribution helps with the finite element analysis part of the multiscale study as it allows for a smoother analysis.

Multiscale Modeling Diagram Example for Carbon Nanotube Reinforced Concrete Fracture Analysis

Atomistic Scale

Crack analysis in concrete historically presents a challenge in computational mechanics. This proposal will implement an extended finite element method (XFEM) approach starting by downscaling from the nanoscale by identifying the properties of CNTs interfacial energy and elasticity. [1]

Nanoscale

Afterwards, the data collected will shifted upward into the next level of the nanoscale where the interaction of the hydrated and unhydrated molecules and how they affect the chemical make-up of the cement paste based on the mechanical properties of the CNTs will be placed in a Molecular Dynamics simulation. [1]

Microscale

A representative volume element will be constructed based on the hydration model undergoes FEA to collect the damage to the cement paste.[1]

Macroscale

Finally, the results will be upscaled to the macroscale for an extended finite element analysis to predict the damaged caused by several bending and torsion tests.[1]

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 Eftekhari, Mehdi, Saeed Hatefi Ardakani, and Soheil Mohammadi. "An XFEM multiscale approach for fracture analysis of carbon nanotube reinforced concrete." Theoretical and Applied Fracture Mechanics 72 (2014): 64-75. Web. 23 Jan. 2017.
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