Rheology of low carbon fibre content reinforced cement mortar

It is recognised that the addition of carbon fibres to a brittle cement matrix results in a less dense composite with enhanced ductility, improved impact resistance and increased toughness. In addition, the reinforcing effect of fibres in the cement often produces superior flexural strength and marked improvements in post-cracking behaviour. Further, carbon fibres influence the electrical properties of the composite which could, potentially, make it a smart material, with a range of applications. Despite attention directed towards the mechanical and electrical properties of carbon fibre reinforced cement (CFRC), there is a dearth of information of the influence of fibre additions on the rheological properties of the resulting composite. To this end, this paper describes an investigation using the Viskomat NT into the influence of carbon fibre additions (fibre length in the range 3–12 mm and volume in the range 0–0.5%) on the rheological properties of CFRC. Within the limitations of the instrument and testing procedure it is shown that CFRC’s conform to the Bingham model: increasing fibre volume and fibre length increase both the yield stress and plastic viscosity.