An alternative to Portland cement concrete is metakaolin (MK)-based digitally fabricated geopolymer concrete. However, global adoption is sparse due to the prolonged setting time of a two-part geopolymer concrete (GPC) system and the uncertain long-term durability properties. The durability and pore structure of the MK-based 3DPGPC (M1) and slag-modified MK-based 3DPGPC (M2) are examined and juxtaposed with mould-cast specimens. Firstly, the fresh properties, rheological behaviour, compressive and flexural strength of 3DPGPC and cast specimens were characterised. Thereafter, the durability and pore structure are investigated by examining the drying shrinkage, water absorption, capillary and gel porosity, and oxygen permeability index (OPI) and X-ray computed tomography (X-CT) analysis. A 5% slag inclusion reduced workability and final setting time from 17 hours in M1 to 4 hours in M2. Also, slag inclusion increased the initial static and dynamic yield stresses by 0.1 and 2%, respectively, resulting in an increase in buildability from 27 of 42 layers. At the 28-day curing age, the average compressive strength of M2–3DPGPC is 11 and 21% higher than M1–3DPGPC in D1 and D3 specimens, while the flexural strength is 33 and 28% higher, respectively. Drying shrinkage and water absorption are mitigated with slag inclusion, and the OPI compares with OPC concrete. Specimens cored along the printing direction (D3) are less permeable compared to disc specimens’ core in the perpendicular to the printing direction (D1). The M1 and M2–3DPGPC specimens contain lower average CT scan macro pores of 2.98 and 1.81% in comparison to the mould-cast specimens having 4.48 and 4.07%. The porosity is position-dependent in 3DPGPC due to the presence of more voids at the interlayer region. 3DPGPC specimens depicted a more compact pore structure in the range of 0.1–1.7 mm, whereas pores in mould-cast are in the range of 0.1–2.5 mm. The durability index tests indicate that 3DPGPC is a potentially durable material.

中文翻译：

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偏高岭土基3D打印地质聚合物混凝土的耐久性和孔隙结构

波特兰水泥混凝土的替代品是基于偏高岭土 (MK) 的数字化制造的地质聚合物混凝土。然而，由于两部分地质聚合物混凝土（GPC）系统的凝结时间较长且长期耐久性能不确定，全球采用率很低。对 MK 基 3DPGPC (M1) 和矿渣改性 MK 基 3DPGPC (M2) 的耐久性和孔隙结构进行了检查，并与模铸样品并置。首先，对 3DPGPC 和铸造样品的新鲜性能、流变行为、压缩和弯曲强度进行了表征。此后，通过检查干燥收缩率、吸水率、毛细管和凝胶孔隙率、透氧指数 (OPI) 和 X 射线计算机断层扫描 (X-CT) 分析来研究耐久性和孔隙结构。 5% 的夹渣量降低了可加工性，最终凝固时间从 M1 中的 17 小时降低到 M2 中的 4 小时。此外，夹渣使初始静态和动态屈服应力分别增加了 0.1% 和 2%，从而使 42 层中的 27 层的可施工性提高。在 28 天养护龄期，D1 和 D3 试件中 M2-3DPGPC 的平均抗压强度比 M1-3DPGPC 高 11% 和 21%，而弯曲强度分别高 33% 和 28%。夹渣减轻了干燥收缩和吸水率，OPI 与 OPC 混凝土进行了比较。与沿垂直于打印方向 (D1) 的圆盘样本芯相比，沿打印方向 (D3) 取芯的样本的渗透性较低。与具有 4.48 和 4.07% 的模铸样品相比，M1 和 M2-3DPGPC 样品的平均 CT 扫描大孔含量较低，分别为 2.98 和 1.81%。由于层间区域存在更多空隙，3DPGPC 中的孔隙率取决于位置。 3DPGPC 样品呈现出更致密的孔隙结构，孔径范围为 0.1–1.7 毫米，而模铸中的孔径范围为 0.1–2.5 毫米。耐久性指数测试表明3DPGPC是一种潜在的耐用材料。