The emerging concept of 3D concrete printing (3DCP) by the laminate stacking of layers without formwork has major issues of poor interlayer bond adhesion and inadequate buildability of printed layers. This paper explores microwave heating technique as a set-on-demand method to increase the structuration rate of geopolymer concrete for 3DCP applications. The microwave heating was applied just before the placement of layers (i.e. at the nozzle head) and the effect of heating duration on the interlayer bond strength and buildability were assessed. Moreover, the loss of surface and bulk moisture and the bond strength enhancing mechanism were also investigated. The results demonstrated that the optimum microwaving duration of 10 s has increased the interlayer bond strength by 132%. The interlayer temperature and surface moisture loss has shown an increasing trend with the heating duration. Despite the increased surface moisture loss with microwave heating, the observed increment in interlayer bond strength (for up to 10 s of heating) was due to the acceleration in polycondensation reaction between the filaments having adequate stiffness for maximum mechanical interlocking with minimum deformation after stacking. On the other hand, the buildability of printed filaments, as measured from the rate of particle re-flocculation and structuration, has showed a major improvement. Findings from this study propose incorporating “set-on demand” technique using electromagnetic radiations in construction 3D printing. This initiates a new era of print heads, designed to solve problems faced by current concrete printing industry.

通过不带模板的层的层压堆叠而出现的3D混凝土印刷（3DCP）的新概念存在主要问题，即层间粘结粘合性差和印刷层的可构建性不足。本文将微波加热技术作为一种按需设置的方法进行研究，以提高用于3DCP应用的土聚合物混凝土的结构化速率。就在放置层之前（即在喷嘴头处）进行微波加热，并评估加热持续时间对层间粘结强度和可建性的影响。此外，还研究了表面和主体水分的损失以及粘结强度的增强机理。结果表明，最佳的微波持续时间为10 s，层间粘结强度提高了132％。夹层温度和表面水分损失随着加热时间的增加而显示出增加的趋势。尽管微波加热增加了表面水分的损失，但是观察到的层间粘结强度的增加（加热时间长达10 s）是由于长丝之间的缩聚反应加速所产生的，该长丝具有足够的刚度，可以最大程度地实现机械互锁，并且在堆叠后变形最小。另一方面，从颗粒再絮凝和结构化的速度来衡量，印花长丝的可建造性已显示出重大改进。这项研究的发现建议在建筑3D打印中使用电磁辐射结合“按需设置”技术。这开创了打印头的新时代，旨在解决当前混凝土印刷行业面临的问题。