Rheological behaviour of concrete enriched with carbon nanofillers

Nanofillers can provide beneficial effects upon both mechanical and durability properties of hardened cementitious composites, but may adversely affect workability. The fluid properties and associated workability of fresh concrete mixes containing commercially-available and/or experimental carbon nanotube (CNT) admixtures, an experimental carbon nanofibre (CNF) admixture or a reference concrete were quantified using a commercial portable concrete rheometer and compared to results from slump tests. Bingham flow parameters of yield stress and plastic viscosity were derived from stress growth and flow curve tests, while thixotropic behaviour was quantified using two different methods. Parameters such as mixing time, resting time, ambient temperature, admixture type and dosage as well as water to binder ratio were altered to study their impact on the workability of the fresh concrete test mixes. Results indicated that increased mixing and resting time, lower temperature, larger nanofillers and reduced water to binder ratio generally deteriorated the workability of concrete. On the other hand, increased dosage of admixtures improved the fresh properties and workability of concrete. Strong linear relationships were observed between measured slump and calculated static yield stress values and between thixotropy values determined by the two different methods. In conclusion, the current study indicates that carbon nanofillers may result in enhanced structural performance of concrete without an associated reduction in workability.