SHCC Reinforced 3D Printed Concrete

The paper presents a reinforcement strategy for 3D printed concrete by a thin, bonded strain-hardening cement-based composite (SHCC) overlay. Concrete structures additively manufactured through extrusion-based 3D concrete printing (3DCP) present orthotropic mechanical behaviour. Tensile strength and ductility across layers are a fraction of those in the extruded direction, i.e. parallel to the layers, due to reduced interfacial bond between printed layers. In addition, structural application of 3DCP may require reinforcement to enhance limited tensile capacity of printed concrete. Strategies for automated 3DCP reinforcement are sought that retain the benefits of 3DCP technology. Here, a thin, bonded SHCC reinforcing overlay is proposed. Automation is envisaged by integration of either spraying technology, or multiple nozzle technology for new, composite structural elements. For retrofitting of existing 3DCP, shotcrete or plaster application is appropriate. For the proof of concept here, thin SHCC overlays were simply plastered onto 3DCP elements. Characterising tensile tests are performed on SHCC dumbbells, and SHCC-3DCP interfacial tensile (pull-off) and shearing adhesive (triplet) tests. From these results composite 3DCP-SHCC specimens were designed to exhibit ductile behaviour by multiple cracking of the SHCC overlay, as opposed to abrupt, brittle delamination of the SHCC overlay from 3DCP substrate. Subsequently, reference 3DCP beams and SHCC reinforced 3DCP beams were prepared and subjected to in-plane and out-of-plane actions. The results validate thin bonded SHCC overlay as an appropriate reinforcement strategy for significantly increased resistance and ductility.