Fiber reinforced 3D printable cementitious composites

Abstract

Layer-by-layer extrusion of cementitious composites is a production method proposed for the 3D printing of concrete structures. Clay-based modifiers are commonly added to the cementitious mixture to adapt it to the extrusion process. However, these modifiers affect the mechanical properties as well. Therefore, it is essential to evaluate the buildability of the proposed composites mixtures. Hence the intended layer stability can be achieved during the extrusion process. This thesis investigates the early age mechanical behavior of twelve 3D printable cementitious composite mixtures. It links the early age mechanical behavior to the hardened state of the 3D printable cementitious composite alternatives. The effects of varying percentages of two clay types on the buildability, the early-age strength development, and the load-bearing capacity of 3D printable cementitious composites are in focus. For this purpose, twelve mix designs were proposed with varying combinations of two clay types and a viscosity modifying agent (VMA). Combinations of two clay alternatives and VMA with/without fly ash content were compared to predetermined test cases. In total, two control mixtures, four mixtures with nano-montmorillonite, four mixtures with sepiolite, and two mixtures with VMA were produced and characterized. To evaluate the fresh state properties, the green strength, and to evaluate the hardened state properties, the 3-point bending tests, and the compression test, were performed at 28 days. Furthermore, to improve mechanical properties and crack control of the predetermined mixes, 12 mm carbon fibers were included. Among twelve mixtures four representative mixtures were selected to include soft carbon fibers. All fresh and hardened state tests applied to fiber-reinforced cementitious composite mixtures.