Fabrication of Piezoresistive CNT/CNF Cementitious Composites with Superplasticizer as Dispersant

Dispersion of carbon nanotubes (CNTs)/carbon nanofibers (CNFs) in cement matrixes is one of the key problems for fabricating piezoresistive CNT/CNF cementitious composites. The use of existing dispersants such as sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (NaDDBS), and methylcellulose to disperse CNTs/CNFs has negative effects on the hydration of cement and will cause decreases in the mechanical properties of cementitious composites. In this study, a superplasticizer, a commonly used component in cementitious composites, is found to be capable of effectively dispersing CNTs and CNFs in a cement matrix. This eliminates the need for additional dispersants for fabricating piezoresistive CNT/CNF cementitious composites and avoids the impairment of composite properties by additional dispersants. The dispersion of CNTs/CNFs in cement matrix is evaluated by observing the dispersion of CNTs/CNFs in the superplasticizer aqueous solution, examining the morphology of composites, and analyzing the discreteness of resistance of composites. The piezoresistive responses of the composites with different types and concentrations of CNTs and CNFs are also investigated. Experimental results show that the fabricated CNT/CNF cementitious composites have strong piezoresistive responses, and the piezoresistive response sensitivity depends heavily on the types and concentrations of CNTs and CNFs. These findings indicate that piezoresistive CNT/CNF cementitious composites can be developed only by using a typical component of cementitious materials (i.e., superplasticizer) as dispersant and without adding any additional dispersants for CNTs/CNFs.