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.

中文翻译：

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用新型石墨烯类型改性的二元和三元共混物的流变学和早期结构开发


人们对使用石墨烯增强胶凝材料性能的兴趣日益浓厚，但实施的主要障碍是石墨烯的成本和这些纳米材料引起的粘合剂流变学变化。本研究探讨了新型、经济高效、环保且可大规模生产的石墨烯对胶凝基粘结剂流变学和早期结构发育的影响。两种新型石墨烯——分形石墨烯 （FG） 和活性石墨烯 （RG）——用于普通水泥混合物以及含有 30%（质量）粉煤灰和/或石灰石粉的混合物，粘合剂质量为 ≤0.02% 的低剂量。石墨烯改性混合物的早期和晚期抗压强度更高（约 5-35%），并且它们足以补偿由较高的水泥替代水平引起的早期强度降低。FG 和 RG 改性浆料的屈服应力、塑性粘度、储能模量和短期触变性明显更高（屈服应力、塑性粘度和存储模量高达 2 倍或更多，短期触变性高达 3 倍），RG 改性浆料的显著增强。使用小振幅振荡剪切测试并辅以相关模型的时间依赖性储能模量演变表明，由于 FG 和 RG 对颗粒间相互作用和水化的贡献，FG 和 RG 改性浆料的结构堆积更快。研究发现，加速开始后的储能模量演变与调整后的累积水化热和电导率值密切相关，为可靠地估计胶凝系统中的早期结构发展提供了快速且廉价的方法。经确定，超低剂量 （≤0.FG 和 RG 的 02 % 粘合剂质量）有助于调整流变和结构发育参数，这将有利于 3D 混凝土打印和超高性能混凝土等独特应用。