3D concrete printing of self-supported filaments via entrained cables: constructing formwork-free spanning structures

3D concrete printing (3DCP) enhances design flexibility, reduces construction costs and lowers environmental impact. Traditionally used for wall fabrication, this study introduces a system for printing self-supporting spanning structures using reinforced concrete filaments with tensioned cables, eliminating the need for formwork. The research involved conceptual design and prototyping to integrate cables into the printing process, as well as structural testing of a small-scale model consisting of a reinforced filament. Numerical analysis using the concrete damage plasticity model (CDP) and the traction-separation model simulated the filament's non-linear behaviour and damage. Compared with experimental data, numerical analysis showed good accuracy. Reinforced filaments exhibited a significant increase in flexural strength, from 1.2 kgf·m to 5.0 kgf·m, compared to non-reinforced filaments. Results confirm the feasibility of the proposed method, though challenges remain in ensuring long-term functionality and scalability. Improving the bond between concrete and cables, refining printing parameters and exploring alternative materials are key aspects. While this study focuses on reinforced filaments as proof of concept, future work will address multifilament and multilayer elements like slabs. Highlights A process for 3D concrete printing spanning structures without formwork was developed. A custom device unwinds cables and prints the concrete filament on top, making it self-supported. Kevlar cables were shown to be compatible with the process, while basalt cables presented difficulties. The flexural strength of cable-entrained filaments improves significantly compared to those without cables.