Effect of Nitrogen-Doped Graphene on the Hydration, Mechanical, and Microstructural Properties of Cement Pastes

Abstract

Graphene-engineered cementitious composites are gaining worldwide attention because of their higher strength, durability, and much improved conductivity. Current research is focused on developing multifunctional cementitious composites with graphene-related material as functional fillers, but there is not much information on the engineering of such composites with nitrogen-doped graphene (NG), which has shown fascinating benefits in the electrochemistry field. This study initiated research on NG-modified cement matrix and attempted to compare its mechanical and microstructural properties with cement pastes modified with graphene oxide (GO) and few-layer graphene (FLG), respectively. Such properties were assessed by performing calorimetry, mini-slump, shrinkage, nanoindentation, scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), thermogravimetric (TG)-derivative thermogravimetric (DTG), and mechanical tests on well-cured specimens. Incorporation of NG reduced cement flow, as did GO and FLG, but its presence altered the morphology of calcium silicate hydrate and decreased the formation of capillary pores in a cement matrix to almost half. FLG synthesis is more environmentally friendly, but its inclusion in a high-dose cement matrix led to the development of a porous microstructure. Both GO and NG were highly dispersible in water, and their incorporations up to 0.06% by weight densified the cement microstructure and also improved compressive and flexural strengths. Fillers that enable multifunctional properties should be evenly dispersed in a cement matrix to form an extensive conductive network within the cementitious composite. The research results indicate that the NG-modified cement mix may exhibit a strong self-sensing character because of the presence of NG, which is an excellent semiconductor. Therefore, a potential new route to develop novel structural materials that are applicable to smart infrastructure was identified through this investigation.