The Centre for Architectural Structures and Technology (CAST), where the Material Reduction: Efficient Fabric-Formed Concrete project was developed is an architectural research laboratory that embraces both the poetic and technical dimensions of design. Following on from winning the Holcim Awards Bronze for North America in 2005, Mark West and his team continue to explore mold technology that uses flat fabric sheets stretched over simple rigid frames to cast beautiful, efficient, lightweight, precast concrete structural elements including trusses. Cast concrete trusses offer significant savings in materials, dead weight, and embodied energy.

An efficiently-curved truss offers significant savings in material and dead weight compared to conventional uniform section beams. Fabric molds use less materials, are less complex and simpler to use than conventional mold making technologies using steel and wood. By creating a continuous mold surface from two flat sheets of inexpensive fabric, smooth curves are created by stretching the fabric over rigid frames. The most commonly used materials for fabric form work are inexpensive woven polyolefin which does not adhere to the concrete and thereby eliminates the need for release agents. Research has been conducted using the fabric mold wall at CAST and also at universities in the United Kingdom and Latin America.

CAST, in collaboration with the University of Edinburgh and University of Bath (UK) is conducting engineering research into the structural behavior of short-span bending moment-shaped concrete beams. Results show simplified force paths in these efficiently shaped beams reduce shear stresses (diagonal tension). After reinforcing is installed, the completed truss mold is filled with self-compacting concrete.

It’s “curtains” for basic block design

CAST has also continued research into the use of hanging fabric sheets as a mold to produce thin-shell wall panels. The panels which take on an organic form of flowing fabric are created using fiber-reinforced spray concrete. The double curvature provides stiffness and strength to a tin concrete shell panel, while random fiber reinforcing (typically recycled glass) adds significant flexural strength and ductility. The complex buckled shapes created are pure natural forms, serving as both sculpture and structure.

Fabric formwork “open source technology”

Fabric formwork for reinforced concrete construction and architecture is an emerging technology with the capacity to transform concrete architecture and reinforced concrete structures. The natural tension geometries given by flexible fabric membranes provide extraordinarily light and inexpensive formworks, some using hundreds of times less material than conventional formworks, and some providing zero-waste formwork systems. The flexibility of a fabric formwork makes it possible to produce a multitude of architectural and structural designs from a single, reusable mold. The use of a permeable formwork fabric produces improved surface finishes and higher strength concrete as a result of a filtering action that allows air bubbles and excess mix water to bleed through the formwork membrane.

A flexible fabric mold awakens concrete to its original wet, plastic nature by naturally producing concrete elements with complex sensual curvatures. The sculptural and architectural freedom offered by this method of construction is matched by new possibilities for efficiently curved structures. Research at CAST has produced simple methods for forming beautiful and efficient beams, trusses, panels, vaults, slabs, and columns.

CAST is fundamentally interested in finding simple ways to reduce the amount of material consumed in construction, while at the same time, making these constructions more beautiful. The center is committed to making these methods accessible to as many people as possible and offers detailed information on methods developed as “open source” technology, and encourages further advancement of applications either independently or in partnership with CAST.