Auxetic Cementitious Composites by 3D Printing

Concrete is inherently brittle. This is a problem because important structures such as nuclear power plants need ductility to remain functional after earthquakes and impacts. ACC-3D aims at creating novel, ductile cementitious composites by using local reinforcement with an unusual quality, negative Poisson's ratio, known as auxetics. Currently, steel rebars or fibers are used to make concrete ductile. Such reinforcement is only active once the concrete has cracked: it prevents existing cracks from growing. Cracking might leave structures unfunctional or vulnerable to repeated events and aftershocks. Can we make reinforcement actively work with concrete already before cracking by making it auxetic? This has never been attempted before. Emerging auxetics with complex architectures fabricated by 3D printing offer excellent energy absorption capacity. However, they have low stiffness which makes them unsuitable for structural applications. I believe that using auxetics as reinforcement in cementitious composites will result in energy absorption at least 2 times higher than current approaches without impairing the stiffness. Through a preliminary study I discovered that auxetics can outperform conventional reinforcement in cementitious composites in terms of flexural strength and energy absorption. However, the mechanism of interaction between deformable auxetic reinforcement and the stiff cementitious matrix is unknown. In ACC-3D I aim to fundamentally understand and fully exploit the potential of auxetic cementitious composites by combining design, experiments, and numerical modelling. This will allow me to create innovative cementitious composites with high ductility and energy absorption capacity. The approach developed in ACC-3D will open possibilities for development of designer construction materials, allowing mechanical response of building materials to be tuned through purposefully adjusting their material architecture.