Recent innovations in energy efficiencies and assembly techniques for precast concrete building envelopes open the door to unimagined architectural and sustainable designs.
By Matt Roper, M.Arch., LEED AP BD+C
The influence of concrete on the modern world cannot be understated. It has formed, shaped and progressed our built environment. Its solidity, strength and durability have advanced its prevalence in the building sector.
Precast concrete in particular has advanced modern civil, structural and architectural design. It has been used in some of the world’s most iconic structures, borne of advancements and refinements in material properties and assembly techniques.
While precast concrete has afforded our society functional advancements, its primary use has often been underappreciated as the foundations of our cities’ hidden infrastructure networks and buildings, structural systems. However, what was once viewed as a mundane industrial material is now developed and refined to reflect a sustainable, flexible and responsive product demanded by today’s economies, societies and environment.
Now more than ever, construction projects are demanding efficiencies in both invested time and materials. Precast concrete innovations offer economic, environmental and aesthetic solutions. Advancements in admixtures, panel system assemblies and formwork techniques have all contributed to the revival of architectural precast in modern building design. In many cases, these advancements were explored, refined and reinvented in the form of both conventionally and prototypically built projects.
Superior sustainability with insulated precast panels
Insulated precast panels have presented designers with integrated building envelope and cladding systems that offer advantages in continuous air/vapor barriers, superior lifespan and reduced construction schedules. The article “Precast Insulated Wall Panels: Get the Whole Package!” (Summer 2012 Precast Solutions) offered a holistic overview of product configurations and their benefits, and nowhere have the advantages of this method of construction been pushed further than the Habitat for Humanity Net-Zero Prototype in Edmonton, Alberta (see “Precast Concrete Can Be Habitat Forming,” Fall 2012 Precast Solutions).
High-performance insulated precast concrete panels were used to construct the exterior envelope, which when fully assembled created a superior level of thermal performance. The 8-in. layer of expanded polystyrene between the interior and exterior precast concrete wythes produced a continuous insulation barrier with an exceptional R-Value of 40.
The inherent strength and thermal mass of the precast concrete structure has lent itself to the integration of numerous other sustainable initiatives that will ultimately allow the home to achieve its net-zero status (net-zero is defined in this application as having a balanced energy usage/production over the course of a full year). For example, the high insulating value and thermal capacity of the panels help normalize the fluctuations of warm and cool cycles, while a geothermal system that feeds hydronic heating and cooling through the structure’s interior can minimize or even offset any heating and cooling requirements.
The hollowcore roof structure also provided opportunities for the mounting of photovoltaic cells as well as vegetation to further contribute to the home’s sustainable features. The solar cells feed into the home, or back into the electrical grid if surplus energy is produced while surplus rainwater is collected and fed through additional planters incorporated in the exterior panels, allowing the ground nativescaping to climb up the structure to form exterior green walls.
Precast insulated panels provided the vehicle in which the Habitat for Humanity net-zero prototype was explored, with intentions of supplying a social, innovative and affordable housing option for both new and in-fill developments. While the system proved to offer incredible benefits in achieving the sustainable goals, additional work is required to economize the panels. In order to enhance the affordability of future structures, it became apparent that the number of unique panel types would either have to be reduced or, like childhood Erector and Lego sets, have to be assembled in multiple variations for various housing forms.
Methods of achieving this flexibility and adaptability while maintaining simple and efficient formwork may lie in the formwork itself.
Fabric formwork: fluid poetic potential
Concrete is a remarkably fluid material that can pick up detailed textures and impressions from its casting. In addition to the moldability of concrete, a variety of aggregates, concrete surface retarders and sandblasting techniques can achieve additional transformations of this highly adaptable material. Nowhere is this fluid nature of concrete being pushed more than at The Centre for Architectural Structures and Technology (CAST) at the University of Manitoba.
Using fabric formwork methods of casting, CAST and its founding director, Mark West, have made prototypes of precast concrete panels and other precast structural members including columns, beams and thin-shell vaults. Commonality in the work that has been produced at CAST includes “using simple construction methods and common building materials, new technologies become accessible to both high- and low-capital building cultures and economies.”
Fabric formwork allows for a much more dynamic and reactive resistance to the weight, shape and structural forces of the object being created. For the production of precast panels, rectangular polyethylene or polypropylene fabric sections are stretched or suspended from the panel framework, and are allowed to deflect under the weight of the concrete they contain.
Intermediate supports are then positioned under the suspended framework, which, when built-up layers of glass fiber-reinforced concrete are applied to the flexible fabric, will interact with the flexible surface producing a dynamic ”direct-cast” mold for casting future panels. This efficiency in form means a significant reduction of material, time and labor in each element produced, as the casts are “defined by three-dimensional tension curves rather than planar surfaces” (West, 2011). While the forms generated from these studies often hold extraordinary creative potential, the structural possibilities are just as great.
Further prototyping of this method of precast fabrication will continue to prove its value for greater integration into the construction industry. While standardization is often seen as the path to finding project economies, fabric formwork may serve as the basis for standard yet easily customized molds for structural and architectural precast panels.
Casting innovations: unlimited architectural possibilities
The ability to shape concrete as desired, supplemented by the economies, versatility and durability of precast panels, make it the preferred building material of today.
Both academic and industry innovations in precast concrete have revealed the potential and benefits this method of construction has to offer. An efficient building system must be multifaceted and the sustainability, durability and flexibility offered by precast panel systems are lending themselves to ever more economic and aesthetic solutions. The prototyping described demonstrates leading-edge research with the intention of learning through construction. As more data are collected and additional structures are monitored and measured, we will continue to see rapid and progressive refinement of this product.
Matt Roper, M.Arch., LEED AP BD+C, is an intern architect at Stantec Architecture Ltd. in Edmonton, Alberta. He has worked in development of the Edmonton Habitat Net-Zero Prototype, and has advanced his firm’s portfolio through modular and prefabricated research and development initiatives. Contact him at Matt.Roper@stantec.com.