Computational Simulations Fresh-to-Solid Transition for Additive Manufacturing of Ultra-High-Performance Fiber Reinforced Concrete

Additive manufacturing of concrete is a topic of interest within the academia and industry. Simulating the printable concrete behavior from the fresh state to hardened state to long-term will provide the future engineers the ability to optimize the design and predict failure of structural elements. A key aspect for concrete additive manufacturing is the complexity of optimization which includes systems, schedule, and materials. Our research focus on the simulation fresh state, hardened behavior, and the transition from fluid-to-solid of nanoclay modified ERDC ultra-high-performance fiber reinforced concrete system. Discrete fresh concrete model (DFC) and Smooth Particle Hydrodynamics (SPH) model are studied to model the flow of fresh concrete from visco-elastic solid contact and non-Newtonian fluid perspectives. A new thixotropy model for the flow of 3D printed concrete is considered to model the rotational rheometer test, flow test, and direct shear test. DFC model flow is coupled with mathematical fiber orientation algorithm to generate fiber distribution and alignment according to the flow. Simulation of extrusion DFC particles from piston extruder and auger are performed to obtain extrusion shape and surface reconstruction was implemented. Lattice Discrete Particle Model (LDPM) using the 3D scan surface topography of 3D printed samples to study the effect of the surface features in the mechanical behavior of reinforced and unreinforced UHPC. Using data from Isothermal Calorimeter and Ultrasonic Pulse Velocity, a couple the DFC and LDPM model was developed which transitions the behavior between fluid to solid. This opens the pathway to optimize concrete 3D printing design.