Download files
Abstract
Surface treatment of steel fibres can greatly improve corrosion resistance and their propensity to bond with other materials. Surface treatment of carbon nanotubes (CNTs) can greatly improve their dispersion, but CNT reinforcement of concrete is new and not fully understood, particularly in terms of how the concrete is affected by the CNTs’ surface treatment. This study investigates the potential for different surface treatments to enhance the properties of steel fibre- and CNT-reinforced concrete.
The study showed that silane treatment increased the surface energy of steel fibres and led to stronger fibre/cement bonds, thereby producing fibre-reinforced mortar with smaller cracks, a lower volume of permeable voids and superior mechanical performance. Similar benefits were found in the case of oxygen/argon plasma treatment of steel fibres, mostly to a greater extent than silane. Nitrogen plasma also improved the fibre/cement bond, but not as much as the other two treatments. All three can easily be performed on an industrial scale.
Since CNTs are the subject of human health concerns, the risk of releasing CNTs into the atmosphere and water was also studied. Different treatment methods and concentrations of single- and multi-walled CNTs were considered. Multi-walled CNTs (MWCNTs) were found to be more likely than single-walled CNTs (SWCNTs) to remain attached to the cement matrix during casting and demolition; safety was improved further still by treatment of the CNTs, particularly with potassium persulfate (KPS) treatment.
MWCNTs were best dispersed in a cementitious matrix after application of a sodium dodecylbenzenesulfonate (SDBS) coating, but this noticeably delayed the cement hydration reaction. Acid functionalisation and ultraviolet-ozone (UVO) treatment of CNTs both allowed CNTs to be similarly well dispersed in cement and accelerated the cement hydration reaction, although UVO was slightly better, thereby making it the best of the tested alternatives for CNT treatment.
The study concluded that surface treatments of steel fibres and CNTs are a viable technology for improving fibre-reinforced concrete’s performance, as well as durability.