Electrochemical impedance interpretation for the fracture toughness of carbon nanotube/cement composites

Electrochemical impedance spectroscopy is a nondestructive testing method for explaining the feature of carbon nanotube or cement CNTs composite materials. Dr. Wei-wen Li and colleagues proposed to develop a non-destructive testing method for CNTs reinforced cement-based material. Their study was published in Construction and Building Materials. Prior to their research, the CNTs reinforced cement-based material were usually evaluated by comparing their fracture toughness and microstructural characterization. The method of comparing fracture toughness is a destructive type that involves destruction of large amount of samples to get the statistical data. Moreover, the development of mechanical strength cannot be obtained with this method.

Researchers introduced an electrochemical impedance spectroscopy method. This is an improved method used to study the electrical properties of fiber reinforced cement-based material. From literature, fiber perpendicular to the flexural plane pull out completely and provide the greatest toughening reinforcement and fibers parallel to the flexural plane provide the less toughening reinforcement. Therefore, the research team ensure the CNTs become perpendicular to achieve large amount of CNTs. The researcher carryout investigation about fracture roughness of CNTs or cement composites using EIS method. They added different CNTs content to cement paste. The EIS method characterized it and a novel equivalent circuit model was proposed to interpret the fracture behaviors of the cement composites.

 The team pointed that, multi-walled CNTs could cause a noticeable reduction in the high-frequency resistance compared with pure cement paste. The improvement of fracture toughness is attributed to the successful aqueous dispersion of multi-walled CNTs which caused the reduction of fiber area in the material.

The analytical results indicate the larger amount of multi-walled CNTs perpendicular to the cracks opening is reached due to the improvement of fracture toughness index. Based on the characteristic, it is feasible to assess the fracture toughness of CNTs/cement composites with different multi-walled CNTs content by means of electrochemical impedance method.

The newly developed electrochemical impedance spectroscopy has shown great improvement in interpreting fracture toughness of carbon nanotube/cement composites as it does not involve destruction samples to obtain statistical data. The EIS method therefore can be used as a reliable, convenient and non-destructive method to assess the fracture toughness of CNTs/cement composites.