Surface-modified graphite nanomaterials for improved reinforcement efficiency in cementitious paste

Graphite nanomaterials can play multi-faceted roles towards enhancing the mechanical, physical and functional attributes of cementitious materials. Graphite nanoplatelets and carbon nanofibers, when compared with carbon nanotubes, offer desired mechanical and physical characteristics at reduced cost. However thorough dispersion of nanomaterials in the cementitious matrix is critical for effective use of their distinct geometric and engineering properties towards development of higher-performance cementitious nanocomposites. The dispersion and interfacial interaction of nanomaterials in the aqueous medium of cementitious matrix can benefit from proper surface treatment of nanomaterials. The surface modification techniques employed in this study emphasize introduction of hydrophilic groups on graphite nanomaterials to facilitate their dispersion in aqueous media. These include: (i) polymer wrapping of oxidized carbon nanofiber; and (ii) covalent attachment of functional groups. The effects of these surface modifications on the performance characteristics of cementitious nanocomposite were evaluated. It was found that wrapping of oxidized graphite nanomaterials with PAA, at polymer-to-nanofiber weight ratio of 10%, was particularly beneficial. With the addition of 0.13 wt.% (0.81 vol.%) of nanomaterials (with respect to anhydrous cementitious materials), up to 73% gain in the flexural strength of cementitious matrix was realized. Test results also indicated that oxidized of graphite nanoplatelets markedly lowered (by up to 50%) the moisture sorptivity.