Nanostructure and Fracture Behavior of Carbon Nanofiber-Reinforced Cement Using Nanoscale Depth-Sensing Methods

Area of Science:

• Materials Science
• Nanotechnology
• Civil Engineering

Background:

• Carbon nanofibers (CNF) are explored as reinforcements for cementitious composites, aiming for multifunctional materials.
• Understanding CNF interactions with cement hydration products is crucial for mechanical response and durability, but remains incomplete.

Purpose of the Study:

• To investigate the influence of CNF on the nanostructure of Portland cement paste.
• To analyze the distribution of hydration products within cement paste reinforced with CNF.

Main Methods:

• Portland cement paste specimens with varying CNF content (0.0, 0.1, 0.5 wt%) were prepared using a multi-step dispersion technique.
• High-resolution scanning electron microscopy (SEM) was used to analyze nanostructure.
• Grid nano-indentation, statistical deconvolution, scratch testing, and micromechanical modeling were employed to assess mechanical properties and porosity.

Main Results:

• CNF were observed to fill nanopores and connect calcium-silicate hydrate (C-S-H) grains, increasing the packing density of C-S-H.
• CNF addition led to a significant increase in high-density C-S-H fraction, increased C-S-H gel porosity, and decreased capillary and total porosity.
• Fracture toughness increased by up to 7.6%, and Young's modulus increased by up to 21.78% with CNF addition.

Conclusions:

• CNF effectively reinforce cement paste by modifying nanostructure and hydration product distribution.
• The enhanced nanostructure translates to significant improvements in mechanical properties, including fracture toughness and stiffness.
• CNF show promise for developing advanced cementitious composites with superior performance.