Self-dispersing Silica Fume Nanoparticles: A Valuable Admixture for Ultra High-Performance Concrete

Proper dispersion of silica fume (SF) plays a crucial role for the optimisation of low water-to-binder concrete mixtures like High and Ultra High-performance concretes (HPC and UHPC). At high concentrations (& GE; 10 wt%), dispersing SF can prove to be extremely challenging with conventional plasticizer. In this work, we evaluate the production of UHPC with SF@PEG which are SF particles with a small layer of polyethylene glycol (PEG) covalently grafted at the surface of SF. UHPC was used in this case as a good example of very low water-to-binder concrete with high volume silica fume. Remarkably, UHPCs made with all SF@PEG samples showed lower viscosity, longer workability and lower mixing power requirements compared to UHPC made with SF. The use of SF@PEG also allows to drastically reduce the amount of polycarboxylate superplasticizer needed to ensure a workable dispersion. Furthermore, the UHPC prepared with SF@PEG (2.5 wt% of PEG) exhibit a 14% increase in compressive strength compared to the UHPC prepared with SF. Finally, scanning electron microscopy of the UHPC containing SF@PEG particles clearly indicate that the SF@PEG is much better dispersed in comparison to UHPC containing SF particles. Due to their lower viscosity, longer workability, lower mixing energy requirements and higher compressive strengths, we envision that SF@PEG could significantly impact the manufacturing of HPC or UHPC.