Flexural Behavior of Stay-in-Place Load-Bearing 3D-Printed Concrete Formwork for Ribbed Slabs (2025-05)¶

Conventional timber formworks for concrete slabs are generally less suitable for complex geometries and are more cost-effective for flat, planar designs. Moreover, conventional formworks are temporary, non-load-bearing structures that require additional shoring elements to support the weight of wet concrete and live loads during onsite casting, resulting in significant labor work and costs. To address these challenges, the current study presents a novel approach for concrete slab construction using 3D-printed concrete (3DPC) formwork integrated with the post-tensioning system. The proposed formwork serves as both a stay-in-place, load-bearing component of the slab system and an effective fabrication method for complex slab geometries. It overcomes the current limitation of 3DPC formworks, which are typically used as non-load-bearing, sacrificial components due to the lack of a feasible method for integrating reinforcement in 3DPC without interfering with the printing process. In this fabrication method, lightweight 3DPC formwork is first printed, then post-tensioned using unbonded tendons, and subsequently filled with cast concrete. Post-tensioning enhances the formwork’s structural capacity, enabling it to support wet concrete and live loads without temporary shoring or with minimal shoring requirements for long spans. To assess the feasibility of the proposed approach, two distinct ribbed slab formwork designs were developed, printed, post-tensioned, and experimentally examined under large-scale four-point bending loading. The experimental results demonstrated that the designed post-tensioned 3DPC formworks exhibited sufficient cracking moment capacity to resist factored dead and live loads during construction for free spans up to 5 m, without the need for temporary support. Furthermore, with a single temporary support for the formwork during construction, the span length of the slab can be extended to 10 m.