Concrete casting, a cornerstone of construction, relies on formwork to shape structures and has been used to create topology-optimized lightweight designs. The interplay between cast structures and formwork necessitates balancing casting constraints, particularly filling efficiency in topological channels, to avoid defects that compromise performance. However, filling efficiency is often empirically addressed, limiting optimization potential. Traditional methods require extensive post-processing to improve filling efficiency, increasing costs and design time. This work introduces a process simulation-informed reverse topology optimization framework, integrating casting constraints into the design process. The framework combines topology optimization, Discrete Element Method (DEM) simulation, and filling ratio identification. Its effectiveness is demonstrated through 2D numerical examples, experimental validation, and a preliminary 3D extension. Results show that the optimized structures improve filling efficiency and allow customizable casting positions. This approach offers a novel strategy for formwork optimization, enhancing efficiency and reducing costs in the building industry.

Additive manufacturing (AM) facilitates the production of complex structures. It is often combined with structural design by topology optimization to create lightweight structures with minimal material and maximum stiffness. In this paper, we consider the design of lightweight structures to be created by casting in formwork that is produced by additive manufacturing. This problem, arising from the building industry, relates to but differs from prior work on topology optimization for structures that are directly produced by additive manufacturing. Specifically, formwork is not permitted to contain extra supports in casting space since otherwise it results in casting blockages. Moreover, topological structures with cavities cannot be produced through casting. This work presents a topology optimization method for designing structures to be cast in AM-produced formwork. This approach addresses these two key challenges: (i) ensuring the formwork is self-supporting during printing to eliminate the need for additional supports, and (ii) designing the structure to be free of internal enclosed cavities, which would otherwise lead to disconnected or floating parts in the formwork. The effectiveness of the proposed method was demonstrated through several numerical examples and experimental evaluations. Results show that the formwork can be printed without extra supports, and internal enclosed cavities in optimized structures can be fully eliminated. The findings provide a new strategy to produce the lightweight structure and corresponding structural formwork.