Panagiotis A. Danoglidis

MWCNT and CNF Cementitious Nanocomposites for Enhanced Strength and Toughness

Cementitious nanocomposites reinforced with carbon fibers at the nanoscale were fabricated and tested, exhibiting remarkably improved mechanical and fracture properties. The cementitious nanocomposites were reinforced with well dispersed multiwall carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs). A dispersion method involving the application of ultrasonic energy and the use of a superplasticizer was employed to prepare the nanoscale fiber suspensions. Flexural strength and Young’s modulus were experimentally investigated and compared with similarly processed reference cement based mixes without the nano-reinforcement. The nanocomposites’ fracture properties were also determined using the two parameter fracture model (TPFM). The excellent reinforcing capability of MWCNTs and CNFs is demonstrated by a significant improvement in flexural strength (87 % for MWCNTs and 106 % for CNFs reinforcement), Young’s modulus (100 %), and fracture toughness (86 % for MWCNTs and 119 % for CNFs reinforcement).

Measurement and Modeling of the Elastic Modulus of Advanced Cement Based Nanocomposites

Carbon nanotubes and carbon nanofibers exhibit several distinct advantages as a reinforcing material for cementitious composites, as compared to more traditional fibers. They exhibit significant greater strength and stiffness, which greatly improve the composites’ mechanical behavior. In this research, an experimental study of the mechanical characterization of cement based nanocomposite materials reinforced with carbon nanotubes is presented. The classic micromechanical approach for fiber reinforced composites was employed to develop predictive models for the modulus of elasticity of the nanocomposites. Results reveal a good agreement between the experimental and predicted values, when using the Benveniste model with disk like inclusions.

Self Sensing Capability of Multifunctional Cementitious Nanocomposites

Carbon nanotubes (CNTs) exhibit excellent electrical properties and can be used to produce multifunctional nanocomposite cement based materials with exceptional self sensing capabilities. The self sensing behavior of cementitious nanocomposite materials, their ability to sense strain, stress and cracking, while achieving superior mechanical properties, can be closely related to the electrical and piezoresistive properties of the material. In this research, the piezoresistive behavior of novel multifunctional cementitious nanocomposites was investigated in order to determine the carbon nanotube electrical percolation threshold. Carbon nanotube cement composites with different percentages of CNTs for w/c = 0.485 were prepared. The electrical resistance was initially measured using direct current (DC), followed by piezoresistivity measurements under cyclic compressive loading. The 4-pole method was employed for both conductivity and piezoresistivity measurements. Results demonstrate that carbon nanotubes can be used to successfully create a conductive network for stress/damage detection in advanced, multifunctional cement based nanocomposites.

Flexural Strength Optimization in CNF Cement Based Nanocomposites with Tailored Electrochemical Impedance Properties

To unlock the efficiency of carbon nanofibers (CNFs) in potential applications, it is necessary to take into consideration their distribution in cement-based materials. In this work, it is observed that the relationship between flexural strength and electrochemical impedance properties such as capacitance and resistivity may provide valuable information on the actual CNF dispersion state in the matrix and a method to optimize flexural strength in reinforced mortars.

Enhanced Young’s Modulus in Percolative Cementitious Composites Reinforced with Carbon Nanotubes

The modulus of elasticity, resistivity and capacitive reactance were determined for carbon nanotube reinforced mortars, near percolation. It is shown that the abrupt decrease of the resistivity values observed at the CNT content of 0.1 wt% is associated with the onset of percolation. Mortars reinforced with 0.1 wt% CNTs exhibit an 89% increase in Young’s modulus. Values of resistivity and capacitance are 27% and 90% lower than that of the plain mortar, respectively. After the conductive network is formed, resistivity values show a little dependence on the CNT content, reaching a plateau. Capacitance on the other hand was increased by an order of magnitude, showing an amplified energy storage ability, probably due to the existence of small CNT agglomerates. The observed relationship between capacitance values and modulus of elasticity may provide valuable information on the actual CNT dispersion state in the matrix.