Rheology control is the most critical determinant of success in 3D concrete printing (3DCP), typically achieved through the hydration control of cement. However, this inevitably leads to overdesign of printed concrete featuring a low water-to-binder ratio (w/b), which is incompatible with its non-load bearing purpose and raises a series of environmental and durability problems, such as high carbon footprint and early-age shrinkage. Herein, we propose a novel rheology control strategy via in-situ polymerization, allowing the mix design of printed concrete with a high w/b ratio of 0.6. The proposed approach consists of two stages: 1) introducing monomers as retarders to extend the open time during pumping, and 2) incorporating initiators into the mixture to trigger polymerization, facilitating the structural build-up after deposition by forming polymer bridges between cement particles. We show that the addition of monomers significantly retards yield stress growth, while the following in-situ polymerization engenders a rapid strength development, satisfying the rheological requirements for 3DCP. Mechanistic experiments reveal that the retarding effect results from the complexation of monomers with aqueous species, such as Ca2+ ions, thereby hindering the nucleation of hydrates. As polymerization initiates, the impetus for the structural build-up of the cement pastes first originates from the proliferation of polymer bridges due to the gradual formation and adsorption of polymer, and then relies on the reinforcement of these polymer bridges through the formation of chemical bonds or crosslinks. On top of the environmental benefit, the proposed strategy holds the potential in avoiding admixtures conflict, mitigating early-age shrinkage, and improving mechanical properties. Our strategy opens possibilities for a novel technical route to achieve rheology control of 3DCP, and the discovery in this work will be a landmark for revealing the mechanism of 3DCP via in-situ polymerization.

中文翻译：

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用于 3D 打印应用的原位聚合对水泥浆体进行流变控制


流变控制是 3D 混凝土打印 （3DCP） 成功与否的最关键决定因素，通常通过水泥的水化控制来实现。然而，这不可避免地导致水料与粘合剂比 （w/b） 低的打印混凝土的过度设计，这与其非承载目的不相容，并引发了一系列环境和耐久性问题，例如高碳足迹和早期收缩。在此，我们提出了一种通过原位聚合的新型流变控制策略，允许打印混凝土的配合比为 0.6。所提出的方法包括两个阶段：1） 引入单体作为缓凝剂以延长泵送过程中的开放时间，以及 2） 将引发剂掺入混合物中以触发聚合，通过在水泥颗粒之间形成聚合物桥来促进沉积后的结构堆积。我们表明，单体的添加显着延缓了屈服应力的增长，而随后的原位聚合会产生快速的强度发展，满足 3DCP 的流变要求。机理实验表明，延迟效应是由于单体与水性物质（如 Ca2+ 离子）络合而产生的，从而阻碍了水合物的成核。随着聚合的开始，水泥浆结构堆积的动力首先来自聚合物逐渐形成和吸附导致的聚合物桥的增殖，然后依赖于通过形成化学键或交联来增强这些聚合物桥。除了环境效益之外，所提出的策略还具有避免外加剂冲突、减轻早期收缩和改善机械性能的潜力。 我们的策略为实现 3DCP 流变控制的新型技术路线开辟了可能性，这项工作中的发现将成为揭示通过原位聚合实现 3DCP 机制的里程碑。