Amendment of Cement Paste with Low Concentrations of Well-Dispersed Partially Unzipped Carbon

Presented by Shohana Iffat, University of South Carolina

Title: Amendment of Cement Paste with Low Concentrations of Well-Dispersed Partially Unzipped Carbon Nanotubes

This presentation introduces partially unzipped carbon nanotubes (PUCNTs) as nano-amendments for cement composites. Oxidized PUCNTs are of interest because they combine the aspect ratio and mechanical strength of multiwalled carbon nanotubes (MWCNTs), and the high graphene edge content and dispersibility of graphene nanoplatelets. In addition, PUCNTs offer a greater specific surface area than MWCNTs, which makes them suitable for exploring reduced concentrations. Cement paste samples were manufactured with oxidized PUCNT concentrations of 0, 0.001, 0.005 and 0.05 in weight of cement (wt%). Through dynamic light scattering analysis, a stable dispersion in aqueous solution was verified for equivalent concentrations of 0.001 and 0.005 wt%; instead, unstable suspensions were obtained for 0.05 wt%, which is often used as a lower-bound concentration for MWCNTs. Potential implications on strength and dispersibility in cement paste were investigated through uniaxial compression tests on 25 × 25 × 76 mm prism specimens, which were moist-cured for 28 days, and visual inspection of scanning electron microscopy (SEM) micrographs. Compared to plain cement paste, the incorporation of 0.001, 0.005 and 0.05 wt% of PUCNTs resulted in an average increase in compressive strength of 10%, 29%, and 14% respectively. These results were supported by SEM micrographs, which showed PUCNT agglomerates for a concentration of 0.05 wt%; instead, for 0.001 and 0.005 wt%, well-dispersed PUCNTs were noted together with a preferential formation of cement hydrates.