Feasibility of using cellulose filaments as a viscosity modifying agent in self-consolidating concrete

Abstract

Nanomodification of concrete represents one of the phenomenal leaps in concrete technology providing innovative tools for engineering cement composites with improved performance. In self-consolidating concrete (SCC), for instance, designing flowable–yet stable and robust–SCC mixtures requires an optimum balance between flowability and stability. This is conventionally achieved by optimizing the dosage of high range water reducing admixtures (HRWRA) indispensable for flowability, while increasing the binder content or introducing viscosity modifying agents (VMA) necessary for stability. This study shows how cellulose filaments (CF)–a new type of nanocellulose materials–can be used as a novel tool for rheology modification and strength enhancement in SCC. CF were incorporated at concentrations ranging from 0.05 to 0.30% per weight of binder in cement pastes and SCC. Rheological and mechanical properties of CF systems were compared to those of plain systems and systems incorporating a commercially available VMA of welan gum type. Results showed that CF serve as a VMA due to the buildup of flexible nanoscale CF networks. As such, a geometry-based percolation model showed that at a concentration of 0.12 wt.%, a network of percolating CF was formed. Beyond this CF content, the yield stress, the plastic viscosity, as well as the HRWRA demand exhibited a substantial increase. CF networks increased mixture viscosity–essential for stability–at low shear rates. On the other hand, at high shear rates, CF networks led to lower apparent viscosity essential for improving pumpability; owing to the streamlining of the flexible nanocellulose fibrils in the direction of flow, thereby imparting a shear thinning behavior. Furthermore, CF imparted improvement in mechanical performance of 12–26% in compression, splitting-tension, and flexure. Research outcomes are expected to contribute towards offering an alternative VMA with strength improvement potential while contributing towards the implementation of sustainable materials for concrete technology.