Nailing of Layers: A Promising Way to Reinforce Concrete 3D Printing Structures

Abstract

Today, the extrusion-based 3D printing of concrete is a potential breakthrough technology for the construction industry. It is expected that 3D printing will reduce the cost of construction of civil engineering structures (removal of formwork) and lead to a significant reduction in time and improve working environment conditions. Following the use of this additive manufacturing layer-wise process, it is required to change the way concrete structures are designed and reinforced, especially for the parts of the structure under tension loads. Indeed, the extrusion-based concrete 3D printing process does not allow for the production of conventional reinforced concrete, and there is a need to develop other ways of compensating for the low mechanical performances of concrete, particularly in tension. In this study, the reinforcement of printed structures by using steel nails through the deposited layers of fresh concrete was investigated. Additionally, three-layer and 10-layer samples were reinforced with nails with varying inclination and spacing. The results show that inclined nails can be used to provide a flexural strengthening of the printing material in different directions.

Interlayer Reinforcement Combined with Fiber Reinforcement for Extruded Lightweight Mortar Elements

“…Another possibility is to use reinforcement perpendicular to the layers. This can be inserted into the deposited layers in predetermined intervals (see e.g., [25]) or build up simultaneously with the layers (see e.g., [9]). The combination of reinforcement built-up layer by layer with e.g., gas-metal arc welding and molded concrete showed comparable mechanical properties to common steel reinforcement and satisfying bonding between rebars and concrete [9].…”

“…This can be implemented by placing a textile with single vertical fibers between two layers [9] or by inserting individual elements as fibers, nails, screws or rebars. Recently, the nailing of the layers was described in literature [25]. Perrot et al [25] examine the insertion of straight steel nails through up to 10 freshly deposited mortar strands.…”

“…Recently, the nailing of the layers was described in literature [25]. Perrot et al [25] examine the insertion of straight steel nails through up to 10 freshly deposited mortar strands. Inclined nails led to an increase in flexural strength in the magnitude of 50%.…”

“…Inclined nails led to an increase in flexural strength in the magnitude of 50%. The surface properties of the nails (smooth or rusty) played only a minor role [25]. Furthermore, first studies about the insertion of screws have been conducted [27][28][29].…”

Buildability and Mechanical Properties of 3D Printed Concrete

“…Moreover, the printed structure may collapse suddenly by buckling during printing; the buckling behavior depends on the geometry and support conditions of the structure. Thus, lateral support or reinforcement is needed [23,24]. For example, steel wire mesh reinforcement improved the flexural strength of printed specimens [25], although there were obvious limitations in the printing process and the design of the nozzle for the reinforcement.…”