Lack-of-fusion (LOF) in digital concrete fabrication is one of the paramount technical issues that must be elucidated before mass industry implementation of this emerging technology. This review paper initially accentuates the ramifications of poor interlayer bonding, which include impaired mechanical and thermo-mechanical performance in the hardened concrete state, durability issues pertaining to corrosion of reinforcing steel and the complexities associated with numerical modelling of 3D printed structures. Focus is then placed on the mechanisms that induce LOF, which constitute an intricate combination of mechanical interaction, chemical bonding and intermolecular forces between filaments. Comprehension of these mechanisms is required to develop appropriate solutions to this problem. The paper presents current interlayer bond strength (IBS) characterization tests and their associated (dis)advantages. Lastly, solutions employed in literature to reduce LOF are presented to give readers a holistic perspective of the current state-of-the-art surrounding LOF in 3D concrete printing.

数字混凝土制造中的融合不足（LOF）是最重要的技术问题之一，必须在大规模工业中实施这一新兴技术之前加以阐明。这篇评论文章最初强调了不良的层间粘合的后果，包括硬化混凝土状态下机械和热机械性能的降低，与钢筋腐蚀有关的耐久性问题以及与3D打印结构的数值建模相关的复杂性。然后将重点放在引起LOF的机制上，这些机制构成了细丝之间的机械相互作用，化学键合和分子间力的复杂结合。必须理解这些机制才能开发出针对此问题的适当解决方案。本文介绍了当前的层间粘结强度（IBS）表征测试及其相关（不利）优势。最后，介绍了文献中用于降低LOF的解决方案，以使读者全面了解3D混凝土打印中当前最先进的LOF。