Exploring scalable fabrication of self-sensing cementitious composites with graphene nanoplatelets

Abstract

Graphene nanoplatelets (GNPs) have the same chemical structures as carbon nanotubes but their internal structure consists of multiple layers of graphene with thicknesses of only a few nanometers. Compared to carbon nanotubes, GNPs are less prone to agglomeration and entanglement when they are used as nanofillers in composite materials. This paper investigates the development of self-sensing cement composites using a simple fabrication method that does not require special preparation procedures such as ultrasonication and chemical (covalent) preparation for the dispersion of GNPs. Three fabrication methods were evaluated, two of which used variations of polycarboxylate-based superplasticizer and mechanical mixing to disperse GNPs into mortar matrix while the third served as a benchmark and relied on ultrasonication for the dispersion of nanomaterials. Standard prismatic mortar specimens containing different GNP concentrations were prepared to evaluate bulk resistivity at different curing ages and piezoresistive characteristics of the developed composites. Cyclic compressive tests were conducted to assess the relationship between the fractional change in electrical resistivity and applied load or strain. Scanning electron microscopy was employed to study the microstructure of the mortar composites and dispersion of GNPs. In addition, the effect of various factors on the electrical properties of the composites cast using the most promising fabrication method was evaluated. Results indicate that mechanically mixing GNPs first with water and superplasticizer, and then mixing the suspension with dry materials can lead to the development effective self-sensing mortar composites when the GNP concentration is at least 7.5% by weight of the cement (1.1% by volume). The incorporation of silica fume into GNP-reinforced mortar composites enhanced the piezoresistive characteristics of the composite. It was also shown that the piezoresistive behavior of GNP mortar composites are highly affected by the composition of the composition of superplasticizer.