Rheology and early-age structure development in binary and ternary blends modified with novel graphene types

Abstract

Interest in the use of graphene to enhance the properties of cementitious materials is growing, but major impediments in implementation are the cost of graphene and changes in binder rheology attributable to these nanomaterials. This study explores the influence of novel, cost-effective, environment-friendly, and mass-producible graphene on the rheology and early-age structure development of cementitious binders. Two novel graphene types—fractal graphene (FG) and reactive graphene (RG)—are used in plain cement mixtures as well as those containing 30 % (by mass) of fly ash and/or limestone powder, at low dosages of ≤0.02 % by mass of binder. The early- and later-age compressive strengths are higher (by ∼5–35 %) for the graphene-modified mixtures, and they more-than-compensate for early strength reduction induced by higher cement replacement levels. Yield stress, plastic viscosity, storage modulus, and short-term thixotropy are found to be significantly higher (up to 2 times or more for yield stress, plastic viscosity, and storage modulus, and up to 3 times for short-term thixotropy) for the FG- and RG-modified pastes, with a dominant enhancement noted for the RG-modified pastes. Time-dependent storage modulus evolution using small amplitude oscillatory shear tests, supplemented with associated models indicate faster structural buildup for the FG- and RG-modified pastes due to the contributions of FG and RG to inter-particle interactions and hydration. Storage modulus evolution beyond the onset of acceleration is found to be well-related to adjusted cumulative heat of hydration and electrical conductivity values, providing rapid and inexpensive means of reliably estimating early-age structure development in cementitious systems. It is determined that ultra-low dosages (≤0.02 % by mass of binder) of FG and RG can aid in tuning the rheological and structure-development parameters, which will be beneficial towards unique applications such as 3D concrete printing and ultra-high performance concretes.