KnitCrete: Stay-in-place knitted formworks for complex concrete structures

Abstract

To address the increasingly urgent requirement of decreasing embodied energy and waste in construction, this dissertation presents a novel type of flexible and cost-effective formwork for casting concrete using 3D weft-knitted textiles as mould. Designing structures that intelligently include structural performance and architectural geometry leads to beautiful, economical and structurally optimised systems that use very little material. Concrete, specifically, is a favourite material for these structures, as it can be moulded into almost any shape desired. However, their expressive, intricate and bespoke geometries can be challenging to build with traditional formwork methods that rely on single-use cut timber or milled foam. These custom constructions account for approximately one-half to as much as two-thirds of a structure’s cost. To harness the full potential of non-standard and non-repetitive efficient concrete structures, the formwork systems used for construction need to be rethought. Using knitted technical textiles as stay-in-place moulds for concrete structures can be a solution for building without the need for expensive, wasteful and time-consuming moulds. In contrast to the traditionally used woven textiles, knitted materials can be tailored to doubly curved and spatially complex 3D shapes, allowing for the integration of features and the design of very specific properties without the need for glueing, welding or stitching several parts together. Knitted textiles can be easily prefabricated by programming industrial knitting machines. A computational pipeline consisting of algorithms and design tools is developed for translating any given 3D geometry into a knitting pattern in an automated way. With this pipeline, commonly available CNC knitting machines produce intricately knitted textiles, that are light, compact and can be effortlessly transported to the construction site. Through tensioning the custom-tailored textile is formed into the desired shape and coated with a special cement-paste to obtain the mould, which becomes a basis for efficient, lightweight structures. The feasibility of the system is demonstrated with a series of prototypes from component to architectural scale. They show that the super-lightweight moulds drastically reduce the need for additional support and scaffolding, simplify logistics on site and have the potential to increase efficiency throughout the complete design-to-production chain.