New Generation Graphenes in Cement-Based Materials: Production, Property Enhancement, and Life Cycle Analysis

Abstract

Several studies have explored the use of graphene to improve the properties of cement-based materials. However, most commercially available graphenes are expensive, not amenable to mass production, and have high embodied energy and emissions, making their use in concrete less attractive, despite the beneficial mechanical property attributes. This paper discusses the use of two novel graphene types, fractal graphene (FG) and reactive graphene (RG), obtained through a cost-effective and scalable detonation synthesis, in cement-based materials. FG and RG are sheets containing 6–10 layers, with lateral dimensions of 20–50 nm and a z-axis thickness of <5 nm. RG is functionalized with carboxylic groups. An ultrasonication process is employed to ensure dispersion of graphene particles in aqueous solutions. Both FG and RG, when added at very small dosages (≤0.04% by mass of cement), enhance the compressive strength of cement mortars by >70% at early ages and up to 20% at later ages. The beneficial effect of functionalization results in better performance for RG-modified mixtures, even at dosages as low as 0.02%. Concomitant enhancements in heat of hydration, hydrate formation, and rheological response are observed. A significant reduction in porosity and critical pore size (by 50% or more) promises significantly improved concrete durability, and thus reduced life-cycle costs. A comparative life cycle analysis (LCA) is used to show that FG- and RG-modified mortars have normalized (by the 28 d strength) energy demand and global warming potential (GWP) that is up to 15% lower than those of conventional mortars. Overall, this study shows that FG and RG, manufactured through a scalable, cost-, energy-, and CO2-efficient detonation synthesis, can beneficially impact the engineering and environmental performance of concretes.