Fabric formwork also gives the finished concrete a level of strength not given by other formwork due to the filtering that occurs through the fabric. The porosity of the fabric allows air bubbles and extra mix water to filter through the formwork membrane. The formwork itself is also very lightweight, inexpensive, and, due to its flexibility, reusable for multiple castings.
Aside from the efficiencies that can be produced in structural concrete members, fabric concrete also provides flexibility in design for architects, allowing them to create a variety of forms otherwise impossible with more orthogonal formwork types. The shapes created by fabric are tensile geometries, something that would be hard to obtain in concrete, a naturally compressive material.
One of the main architects exploring the possibilities of fabric formwork is Kenzo Unno, who uses fabric formwork to obtain both an efficient use of material and certain aesthetic desires in his work. In his research, Kenzo Unno was able to create a “zero waste” wall assembly into which the concrete is poured and the only piece that is then removed is the fabric formwork, which can then be reused for another casting or as an earth stabilizer. A diagram of the wall assembly can be seen at the right. The linear wood pieces on the exterior become battens onto which the exterior cladding is applied. These wall assembly pieces can easily be constructed off-site, and then dropped into place on the construction site.
Aesthetically, Kenzo Unno has done a lot of cast-in-place walls in fabric formwork, giving walls a soft, pillow-like surface, and again reducing the amount of material wasted during construction. His cast-in-place walls have come in two forms, one known as the frame method, the other as the quilt-point method. The frame method uses a series of vertical restraints in between which the fabric is stretched and the concrete poured. The quilt-point method uses a series of ties in the walls between which the fabric is stretched and the concrete poured. The concrete is vibrated externally by poking the wet concrete contained by the fabric with a stick and, as in the case of the quilt-point method, the fabric being stretched by the concrete forms into its natural tension geometries, allowing it to be entirely self-sufficient structurally.
Fabric formwork has also been used to create precast concrete panels in a variety of forms. The method for producing these forms is simple-first a rectangular frame of the dimensions of the final panel is laid down inside of which intermediate supports are placed (these supports will retain the fabric at these points and the fabric will in turn bow between them). Next, a pre-tensioned fabric membrane is placed over this frame, on top of which an upper frame that will contain the wet concrete is placed. This frame will determine the edge thickness of the panel and inside of it any reinforcement can be placed. When wet concrete is poured into this assembly, it causes the fabric to deflect downward creating three-dimensional tension curves between the designated support points of the base frame. The castings created from this method can then in turn be used to create inverse castings by pouring a new casting along its surface on top of a layer of fabric.
The implications that this research has on the future of concrete as a building material are huge. Not only is it efficient in how it uses materials in construction and creates a strong product through the filtering process, but it provides an aesthetic to concrete previously unavailable. I like that the fabric formwork uses the properties of wet concrete to create its form. Instead of trying to contain the wet concrete, it works with what it naturally wants to do unlike many other types of formwork, allowing what is seen as a “difficult” property of the material to become its driving force. The next step will be to test some of these processes myself-specifically the precast panel construction method-on a smaller scale.
What aspects of this research will translate into the warming hut is yet to be seen. I definitely like the idea that using this formwork will allow for less waste as our hut is located at the top of a very steep mountain side and so to have a lot of waste due to construction would be very inefficient indeed. I also think the efficiently shaped beams that give a very natural form to the architecture is something I think I’d like to apply to the warming hut. Let’s see what the castings help me discover.
"CAST :: Fabric Formwork." University of Manitoba. Web. 23 Jan. 2011. http://www.umanitboa.ca/cast_building/research/fabric_formwork/index.html
Miller, Anne. "Concrete Dreams." Canadian Architect (2008): 71-73. Print.
West, Mark. Kenzo Unno Fabric Formed Walls. PDF.
West, Mark. Prestressed Fabric Formworks For Precast Concrete Panels. Centre for Architectural Structures and Technology. PDF.
West, Mark. "True to Form." Canadian Architect: 54-56. Print.