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KnitCandela: a flexibly formed, thin concrete shell exhibited at MUAC, Mexico City

KnitCandela is a thin, sinuous concrete shell built on ultra-lightweight knitted formwork that was carried to Mexico from Switzerland in a suitcase.

Constructed at the Museo Universitario Arte Contemporáneo (MUAC) in Mexico City as part of Zaha Hadid Architects’ first exhibition in Latin America, KnitCandela is an experimental structure that pays homage to the Spanish-Mexican architect and engineer Félix Candela. KnitCandela reimagines his inventive concrete shell structures through the introduction of new computational design methods and innovative KnitCrete formwork technology.

The dynamic geometry of KnitCandela’s shell is inspired by the fluid forms of the colourful traditional dress of Jalisco, Mexico. While the structure’s local builders nicknamed the project 'sarape' (a striped scarf that originated in Mexico), KnitCandela’s form references his acclaimed restaurant at Xochimilco; a concept he further developed in several of his subsequent projects.

While Candela relied on combining hyperbolic paraboloid surfaces (“hypars”) to produce reusable formworks leading to a reduction of  construction waste, KnitCrete allows for the realisation of a much wider range of anticlastic geometries. With this cable-net and fabric formwork system, expressive, freeform concrete surfaces can now be constructed efficiently, without the need for complex moulds. KnitCandela’s thin, double-curved concrete shell with a surface area of almost 50 sq.m. and weighing more than 5 tonnes, was applied on a KnitCrete formwork of only 55 kg. The knitted fabric of the formwork system was carried to Mexico from Switzerland in a suitcase.

Designed and constructed by multiple teams in Europe and Mexico, the realisation of KnitCandela is the result of a collaborative effort that harnessed collective expertise in computational design, engineering and fabrication. The architectural design is the latest expression of the Zaha Hadid Architects’ computation and design research group (ZHCODE) for designs that utilise structural and constructional features to enhance the spatial experience of the user. For the realisation of this expression, Block Research Group (BRG) of ETH Zurich introduced the KnitCrete formwork technology and developed the structural design and construction system. Architecture Extrapolated (R-Ex) managed the execution of the project on site in Mexico City as part of its continued engagement in the digitisation of building trades in Mexico.

Designed to be constructed within a tight schedule, restricted space and minimal budget, KnitCandela demonstrates the rapid evolution and adaptation of digital design and fabrication to the challenges faced by the construction industry. This experimental structure also explores the possibilities of integrating digital fabrication with the skills of traditional craftsmanship and construction methods.

KnitCrete is an innovative material-saving, labour-reducing and cost-effective formwork system for the casting of doubly curved geometries in concrete. The KnitCrete technology is being developed at ETH Zurich by the Block Research Group in collaboration with the Chair for Physical Chemistry of Building Materials, as part of the Swiss National Centre of Competence in Research (NCCR) in Digital Fabrication.
KnitCrete formworks use a custom, 3D-knitted, technical textile as a lightweight, stay-in-place shuttering, coated with a special cement paste to create a rigid mould, and supported by additional falsework elements such as a tensioned cable-net or bending-active splines. Compared to conventional weaving, knitting minimises the need for cutting patterns to create spatial surfaces, allows for the directional variation of material properties, and simplifies the integration of channels and openings, for example, for the insertion of additional formwork elements, insulation, reinforcements, electrical components and technical systems for heating and cooling.
The hybrid and ultra-lightweight KnitCrete formworks are easily transportable, reduce the need for additional supporting structure and scaffolding, and simplify the logistics on the construction site.

The 50 sq.m. of textile shuttering of KnitCandela's formwork is comprised of four long strips ranging from 15 m to 26 m in length. Each of the four strips is a seamless, double-layered textile produced as a single piece. Two layers of textile fulfil different tasks. The visible inside is an aesthetic surface that displays a colourful pattern and reveals traces of the supporting cable-net falsework system. The exterior surface fulfils technical requirements by including features for inserting, guiding and controlling the position of additional formwork elements.

The pockets created between the two layers as part of the spatial knitting process are inflated using standard modeling balloons. These inflated pockets become cavities in the cast concrete, forming a structurally efficient waffle shell without the need for a complex, wasteful formwork. Pockets located on this exterior side of the textile have different knit densities to control the inflated shape and openings for the insertion of the balloons, enabling cavities of different dimensions to be created with one standard balloon size.
The soft, colourful textile interior of KnitCandela’s shell and its hard, concrete exterior is visible from all viewing angles. The textile’s striped pattern expresses the knitting fabrication process and the radial symmetry of the shape. This patterning, along with the simultaneous visibility of the soft interior and the hard exterior of the shell enhances the visitor’s spatial experience and the curvatures of the KnitCandela’s form.

Images, videos and animation for download

MUAC Website

Photograph by Juan Pablo Allegre