Effect of Carbon Nanofiber Clustering on the Micromechanical Properties of a Cement Paste.

Lesa Brown,Paul G Allison,Florence Sanchez,Catherine S Stephens

doi:10.3390/nano12020223

Lesa Brown, Paul G Allison + Show 2 more

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https://doi.org/10.3390/nano12020223

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Abstract

The use of carbon nanofibers (CNFs) in cement systems has received significant interest over the last decade due to their nanoscale reinforcing potential. However, despite many reports on the formation of localized CNF clusters, their effect on the cement paste micromechanical properties and relation to the mechanical response at the macroscopic scale are still not fully understood. In this study, grid nanoindentation coupled with scanning electron microscopy and energy dispersive spectroscopy was used to determine the local elastic indentation modulus and hardness of a portland cement paste containing 0.2% CNFs with sub-micro and microscale CNF clusters. The presence of low stiffness and porous assemblage of phases (modulus of 15–25 GPa) was identified in the cement paste with CNFs and was attributed primarily to the interfacial zone surrounding the CNF clusters. The CNFs favored the formation of higher modulus C–S–H phases (>30 GPa) in the bulk paste at the expense of the lower stiffness C–S–H. Nanoindentation results combined with a microscale–macroscale upscaling homogenization method further revealed an elastic modulus of the CNF clusters in the range from 18 to 21 GPa, indicating that the CNF clusters acted as compliant inclusions relative to the cement paste.

Highlights

The clustering of Carbon nanofibers (CNFs) formed both microscale and sub-microscale CNF clusters
The difference in flaws/porosity was consistent with the overall more uniform distribution of indentation modulus and hardness seen in the contour maps of the cement paste with CNFs (Figure 7) and the results found in [25], which showed that the presence of CNFs provided for a pore refinement of the cement paste
Gaussian fitting with the presence of a low stiffness, porous assemblage of phases that were not found in the reference cement paste and was attributed primarily to the interfacial zone surrounding the CNF clusters

Summary

Introduction

Carbon nanofibers (CNFs) are excellent candidates for reinforcement of cementitious materials at the nanoscale due to their unique characteristics (high aspect ratio with nanoscale diameters, and lengths of a few hundred nm to a few hundred μm; high strength; low density; and corrosion resistance) [1,2,3]. In addition to enhancing the mechanical properties and durability of cement-based materials, CNFs can perform new functions, such as stress-sensing, temperature monitoring, and electromagnetic shielding [4,5,6,7,8,9,10,11,12]. Potential applications of CNFs in cement-based materials include infrastructure health monitoring, traffic monitoring, and where low density-high performance materials are important

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