Flexibly formed concrete

Abstract

To reduce the construction industry’s negative influence on global climate, emissions related to concrete consumption need to be addressed. This implies reducing the amount concrete used, by creating material-efficient structures. One of concrete’s main advantages is that it can be moulded into virtually any shape. Despite the fact that modern digital design tools enable the effortless design and calculation of lightweight and graceful structures, this potential often goes unrealised. This can be attributed to the challenges associated with constructing intricate and custom geometries using conventional formwork techniques that depend on single-use cut timber or milled foam. Not only do these methods make the construction of these types of structures labour and cost intensive, they also cause them to be wasteful.

KnitCrete, which uses knitted technical textiles as stay-in-place moulds for concrete structures, has proven to be a solution for building doubly curved structures, eliminating the need for time-consuming, costly, and wasteful moulds. However, due to its inherent high flexibility and the challenges of predicting and controlling the geometry during the casting process, the technology relies on coating procedures using high-strength cement paste coating to stiffen the geometry before concrete can be poured.

This research addresses both issues and proposes a design approach, which models the deformation behaviour of the uncoated knitted formwork under concrete pressure to determine the final geometry of flexibly formed concrete structures, hence gaining better understanding on the deformation behaviour of knitted textile formworks and bypassing the stiffening steps during fabrication.

Developing a method to predict the final geometry of flexibly formed concrete structures involves various research disciplines, including material science, and structural mechanics. The research approach is divided into three parts. The first part investigates the stress-strain relationship of various textiles with different knitting patterns, alongside the rheological and mechanical strength properties of different cementitious mixtures. The second stage focuses on developing (semi-)analytical models to predict the deflection behaviour of membranes subjected to varying boundaries, loads, and material properties. Finally, the accuracy of the models are validated by the construction of multiple prototypes.

In conclusion, this thesis introduces a fabrication system that exploits the deflection behaviour of flexible formworks to create funicular shell structures and lays the foundation for implementing (semi-)analytical approaches to model these deformations.