3D-printing could offer substantial benefits to the construction industry including the fabrication of customized/bespoke components, eliminating formwork, and reducing material waste. Despite these advantages, control of the pumpability, extrudability, and buildability of 3D-printed concrete (3DPC) remains challenging. This study demonstrates how the use of fly ash (FA) enables enhanced thermal stiffening, and rapid alkali-activation in the presence of portlandite (Ca(OH)2, CH). In general, blends of CH and FA exhibit less structural build-up at low temperatures, but upon reaching a trigger temperature of 75 °C, these blends achieve rapid stiffening, at rates of ∼800 Pa/s. The rapid stiffening arises from the flocculation of CH particles, and the onset of the pozzolanic/alkali-activation reactions between CH and FA, resulting in the formation of C-A-S-H and N-A-S-H during stiffening. Careful selection of the FA-CH blend ratio, which displays an optimum at ∼20 mass % CH, enables the composition of cement-free formulations for 3D-printing applications. The outcomes have important implications on alternate feedstock pathways to compose carbon-efficient formulations for construction.

中文翻译：

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热刺激的硬化和粉煤灰通过 Ca（OH）2 添加产生的碱性活化促进了 3D 打印


3D 打印可以为建筑行业带来巨大的好处，包括制造定制/定制组件、消除模板和减少材料浪费。尽管有这些优势，但控制 3D 打印混凝土 （3DPC） 的可泵送性、可挤出性和可建造性仍然具有挑战性。本研究展示了在硅酸盐 （Ca（OH）2， CH） 存在下，使用粉煤灰 （FA） 如何实现增强的热硬化和快速碱活化。一般来说，CH 和 FA 的共混物在低温下表现出较少的结构堆积，但在达到 75 °C 的触发温度时，这些共混物以 ∼800 Pa/s 的速率实现快速硬化。CH 颗粒的絮凝以及 CH 和 FA 之间火山灰/碱活化反应的开始导致了快速硬化，导致在硬化过程中形成 C-A-S-H 和 N-A-S-H。仔细选择 FA-CH 混合比例，在 ∼20 质量 % CH 时显示最佳比例，从而能够为 3D 打印应用配制无水泥配方。这些结果对构成建筑用碳高效配方的替代原料途径具有重要意义。