Understanding the role of unzipped carbon nanotubes in cement pastes

Carbon nanotubes (CNTs) and graphene oxide (GO) are the most studied carbon-based materials for the modification of cementitious materials. Prior studies have shown that CNTs (due to high bending stiffness) can improve flexural strength more efficiently than GO, whereas GO (due to active surface groups) performs better in improving the compressive strength of cementitious composites. This laboratory study investigates the role of unzipped CNTs (UCNTs) in cement pates. All three types of UCNTs have a similar C/O atomic ratio as GO, without any wrinkles to be observed under transmission electron microscope. The UNCTs admixed at 0.1% by weight of cement improved the compressive and flexural strengths of a cement paste (w/c of 0.38) by 22% and 51%, respectively, greatly outperforming CNTs and GO, respectively. Such outstanding reinforcement efficiency of UCNTs resulted from their abundant surface chemistry (similar to GO) as well as one-dimensionality and bending stiffness (similar to pristine CNTs).