Style and Sustainability of Precast Concrete

New Perot Museum is both aesthetically intriguing and efficient

December 2013
Sponsored by Holcim (US) Inc.

Continuing Education

Use the following learning objectives to focus your study while reading this month’s Continuing Education article.

Learning Objectives - After reading this article, you will be able to:

  1. Describe the use of precast concrete in terms of building performance, sustainability, and construction benefits.
  2. Explain how precast concrete solved numerous design and sustainability considerations for the case study subject, the Perot Museum in Dallas.
  3. Discuss the effect of precast concrete on green building certifications and ratings.
  4. List the general attributes of cements and concrete mixes, and the selection criteria used for the case study project.

Precast concrete façade cladding systems have been used for significant works of architecture, and a contemporary example is reviewed in this continuing education article. The case study—the Perot Museum of Nature and Science in Dallas—is examined in detail to show how its precast concrete panels can contribute to design excellence, including sustainability, high performance, efficient construction, and advantages for occupant health and safety. Examples of the benefits of precast concrete include durability, low maintenance costs, good life-cycle performance, high thermal mass, acoustical isolation, and resistance to air infiltration and weather.

Choice of cements, aggregates, coloration, and other additives for both performance and aesthetic characteristics is an important part of developing any architectural solution. General guidelines are presented for determining the concrete mix, with attention to the specifications for the new museum.

In many projects utilizing precast, as was the case at the Perot Museum in Dallas, an important attribute of a precast panel mix is to minimize panel or unit weight without compromising the durability and sustainability of the cladding. The resulting mix may be compared to ordinary portland cement concrete to determine weight and material savings. This simple consideration will impact the building's green attributes, construction cost, and other variables.

A number of aesthetic benefits are possible with the use of precast concrete façades. Among the visual considerations outlined is the use of integral color throughout the precast slabs. In many typical applications, the use of pigmentation is isolated to an exterior portion and sandwiched against the uncolored grey cement, which typically comprises the interior. Integral color affords some advantages in design expression.

The precast concrete façade cladding on the new Perot Museum of Nature and Science in Dallas is used to aesthetic advantage by Morphosis Architects, with Pritzker Prize-winning architect Thom Mayne.

Photo courtesy of Holcim (US) Inc.

There are other advantages to using precast, according to the architects, engineers, precasters, and concrete manufacturers involved with the Perot Museum project. For example, the opaque concrete shell contributes to a more stable and comfortable indoor environment while also protecting the occupants. It is a fire-resistant enclosure that is also inherently strong and resilient when it comes to hurricanes, tornados, hail and wind-blown projectiles. In general, precast concrete is a good choice for public health, safety, and welfare (HSW) as well as security and life safety, according to PCI, Precast Prestressed Concrete Institute.

Recent developments in concrete technology have improved the material's suitability for green building. Portland cement, a key ingredient in concrete, whether precast or ready mixed, is a significant factor in concrete's environmental footprint. The cement industry as a whole has made significant reductions in emissions over the last three decades. According to the Portland Cement Association (PCA), since the 1970s the cement industry in the United States has increased its energy efficiency by more than 30 percent, leading to a significant reduction in emissions. In addition, concrete producers routinely use recycled materials, such as fly ash, ground granulated blast-furnace slag, and silica fume or other pozzolans—also known collectively as supplementary cementitious materials, or SCMs—as a component in concrete. This not only may reduce the amount of portland cement in the mix, but can have positive effects on concrete properties.

Precast concrete façade cladding on the new Perot Museum, affords durability, low maintenance costs, and high thermal mass, among other benefits.

Photo courtesy of Holcim (US) Inc.

Although SCMs can be separately added to the concrete mix at the concrete plant, SCMs are often used as an ingredient in a blended cement. In blended cements, the SCM is proportioned and added at the cement plant prior to delivery to the concrete production facility. In some parts of the world, according to Barry Descheneaux, manager of product support and development for Holcim (US), portland cement may be as little as 25 percent of the type of cement used, while the use of cements containing ground limestone, fly ash or other pozzolans, or blast furnace slag, make up the balance.

The concrete mixes for the project included up to 51 percent slag in core walls, and 50 percent fly ash in piers, columns, and slabs.

Photo courtesy of Holcim (US) Inc.

In addition, concrete and precast manufacturing have become more efficient. State-of-the-art cement plants reduce emissions of nitrous oxides, and optimized firing processes further minimize emissions of harmful gases. At the precast shops, new production techniques and lean manufacturing processes have made an already sustainable building method even more attractive.

Sustainability was another key project driver for both the architect and the client—the Perot Museum's leadership. The precast cladding system employs fly ash and recycled materials. Its mass and low air-infiltration rates protect the building from the vagaries of sunlight and seasons. Concrete and aggregates tend to be abundant, local materials, according to the Chicago-based Precast/Prestressed Concrete Institute (PCI). Most important, precast concrete panels have a long average service life due to their durable, low-maintenance surfaces, as PCI explains.

There were more reasons to use precast concrete for the Perot Museum. To break it down, the building concept, design process, and precast system development and jobsite logistics are detailed in this article. The overview will benefit professionals with limited experience in precast concrete building design and construction administration.

Creating Awareness of Science

In designing the Perot Museum of Nature and Science in Dallas, Pritzker Prize-winning architect Thom Mayne, founding principal of the Culver City, California-based firm Morphosis Architects, sought to “create a facility that inspires awareness of science through an immersive and interactive environment that immediately engages visitors,” as he said when the project was unveiled in 2009 by the Museum of Nature and Science, Dallas. “We rejected the traditional notion of museum architecture as a neutral background for exhibits. Instead, the new building and the surrounding outdoor areas will become an active tool for science education.”

As part of realizing that goal, Mayne chose precast concrete as his primary building material, which has uniquely allowed him to achieve the style and long-term sustainability he envisioned for the facility.

The $185-million museum, which is expected to open in January 2013, will relocate collections from a facility in nearby Fair Park, a recreational and educational complex that since 2006 has been home to the collections of the Dallas Museum of Natural History, The Science Place, and the Dallas Children's Museum. “It's important for us to be thoughtful about the environmental aspects of the museum,” Nicole Small, the museum's CEO, recently told The Dallas Morning News. “We are a museum of nature and science. We have to practice what we preach.”

With specific environmental goals in mind, the facility was designed by Morphosis with the local architect Good, Fulton & Farrell to include a landscaped roof featuring native flora, a 50,000-gallon rainwater-collection system, and a solar water-heating system. Its construction would also incorporate recycled and locally sourced building materials. Condensation from the building's air-conditioning system will be collected as well, allowing the museum to keep its water bill closer to that of a residence than the typical costs for a 180,000-square-foot public facility.

The design creates a series of waves for a dynamic effect on the building that changes through the day with the sunlight and shadows.

Photo courtesy of Holcim (US) Inc.

Still, in conceiving what the Perot Museum has described on its website as “a 'living' example of engineering, sustainability, and technology at work,” Mayne, who cofounded Morphosis in 1972, applies the firm's long-held philosophy that the meaning of an architectural work can be understood by absorbing the culture for which it was made. With this in mind, the architect eschewed what many would describe as a conventional approach to green design, at least from an aesthetic perspective.

Mayne does not believe that aesthetic uniqueness and building performance have to be mutually exclusive. As he proves with the Perot Museum, a building's design can reflect his vision and that of his client while being environmentally responsible. There are no rules, as Mayne has illuminated through his work, about what a so-called “green building” should look like, and it's not important that a building announce itself as the result of that intention. Mayne, in other words, prefers to show that a building can be visually compelling and environmentally responsible without necessarily having to tell people that's the case.

What Mayne and his colleagues came up with for the Perot Museum is a 14-story cube that appears to be suspended over the thoughtfully landscaped grounds that make up the balance of its 4.7-acre site. The building houses 11 permanent exhibition halls and a traveling exhibition space, educational facilities, a theater, museum store, café, and sprawling podium rooftop. The podium roof is designed with landscaping by Dallas-based Talley Associates that blurs the distinction between where the natural environment ends and the building itself begins.

Evaluating Precast Concrete

Precast concrete panels have a long average service life due to their durable, low-maintenance surfaces, according to the Chicago-based Precast/Prestressed Concrete Institute (PCI). That’s just one reason—and an important one—that precast was selected for a monumental green building like the Perot Museum of Nature and Science in Dallas. The other reasons to consider precast, says PCI, include:

  • Fire and natural-disaster resistance.
    Precast concrete effectively contains fire within its boundaries and is inherently noncombustible. Concrete also resists wind, hurricanes, projectiles, flooding, and water damage.

  • Indoor environmental quality (IEQ).
    Most concrete has negligible levels of volatile organic compounds (VOCs), and it can be used as a finish surface as well as a structure without coatings or sealants.

  • Heat-island mitigation.
    Typically light colored, reflective precast surfaces help minimize solar heat absorption, reducing the urban heat-island effect.

  • Abundant, locally sourced materials.
    Local, naturally occurring sand and stone comprise about 85% of all concrete. Shipping and transportation energy are typically reduced using precast.

  • Noise resistance.
    Concrete provides good noise reduction performance for better indoor acoustics.

  • Energy performance and thermal mass.
    Concrete enclosures are beneficial for reducing heating and cooling loads in a building, which can allow the downsizing of HVAC systems.

  • Durability and resilience.
    Precast concrete building structures and façade cladding tend to have a very long service life. With little maintenance, precast panels are resilient and durable, often outliving the very buildings they enclose.

 

Seemingly Kinetic Exterior

The line between structure and space is audaciously delineated by a 150-foot, glass-enclosed shaft, in which a 54-foot escalator travels at an angle along the building's exterior, opening the museum to its surroundings and inviting those beyond the facility's walls inside. It is a connective feature of which Mayne is particularly proud.

The aesthetically punctuating escalator shaft draws attention to the building's seemingly kinetic concrete exterior. The design intent, according to museum officials, was to “create a series of waves that gives a dynamic effect on the building that changes minute-to-minute through the day with the sunlight and shadows.” The texturing is denser at the bottom of the cube and slowly fades away as the cladding move upwards. According to the museum, “This pattern was done intentionally to create a perception that the building dissolves into the sky.”

The line between structure and space is audaciously delineated by a 150-foot, glass-enclosed shaft, in which a 54-foot escalator travels at an angle along the building’s exterior—a signature feature by the architect Thom Mayne.

Photo courtesy of Holcim (US) Inc.

The museum's exterior is made up of more than 650 precast concrete panels that were fabricated in Hillsboro, Texas, by the Gate Precast Company, a large precast provider with headquarters in Jacksonville, Florida. The panels make up a number of elements, including the vertical portions of the site's large plinth, the 14-story cubelike tower, and the exterior of the building's memorable atrium.

The construction of the building enclosure was no simple feat; it was the result of what Christopher Wolfe, of the project's general contractor, Balfour Beatty Construction, told Engineering News-Record was “the most difficult and challenging precast job I've ever seen.” The design of the concrete panels—which average about 8 feet by 30 feet in size with thicknesses of up to 9-½ inches—resulted in weights of as much as 8 tons each. The panel profiles are intricate and carefully organized to achieve Mayne's design effect; this demanded close coordination among the architect, engineers, the general contractor, the concrete supplier, and Gate Precast's craftsmen, who brought that aspect of the project to fruition.

The resulting building façades, which play with available light and shadows, resemble a massive, completed puzzle whose pieces are as distinct from one another as they are equal parts of a larger composition. To achieve the undulating effect Mayne wanted the building exterior to have, the panels had to be uniform in color and composition but different, to varying degrees, in their non-pigmented, striated outer texture.

Gate Precast was able to achieve all the specifications and design intent. After the project was complete, the company was lauded for its work by PCI, earning the institute's design award in the “Best Government and Public Buildings” category as well as a Sidney Freedman Craftsmanship Award, which recognizes “excellence in manufacturing” of precast building components.

Mayne's use of precast concrete also allows the Perot Museum to present a building that is as much a part of the natural landscape as a complementary element of it. The building's design has a sense of movement, lending the museum a part of its desired living quality—if not evoking a sense of time passing. That is, the Perot Museum is less an interruption of the natural, surrounding landscape and more a continuance and development of it, with its planted surfaces and water collection.

Likewise, the museum's mission to educate and inform younger generations about the natural world and their place within it is actually served by the structure itself. Mayne's design presents a number of valuable lessons from the building's aesthetic design to its efficiency-focused construction—a lesson in savings that begins with its precast concrete visage.

From Design to Construction

To benefit the project's coordination and schedule, the concrete subcontractor Gate Precast was called in early to assist with design development and advise on construction approaches. Building information modeling (BIM) would be beneficial to ensuring a faster and more accurate fabrication phase, by using the BIM model for mold shaping and speeding the coordination of panel design and installation.

In Engineering News-Record, Gate Precast's president Dean Gwin said, “We couldn't have done this job without BIM,” with all the related trades “sharing in the 3D modeling.” For its part, the consulting engineer Buro Happold used BIM to simulate engineering elements, integrate design elements, analyze costs, and detect clashes. For the façade work, Gate Precast modeled more than 100,000 square feet of precast cladding in total, which was integrated into the structure's final 3D model.

After the schematics were complete, Morphosis used parametric digital modeling in design development to articulate each individual panel separately using a family of design modules. Developed with the construction team, the Morphosis façade cladding design required about 670 panels in total, each with a unique profile and shape, with each module circumscribed by a 1/8-inch round outline. The modules required a variety of panels, including:

  • The plinth. The 27,000-square-foot plinth comprises about 220 panels, including curving, radiused and tilted geometries, which wrap the massive structure. The smallest are about 2 feet by 6 feet, and the largest up to 8 feet wide and 28 feet long.

  • The tower. The cube-shaped, 70,000-square-foot tower set atop the plinth landscape is clad with 350 panels—most 8 feet by 28 feet—with alternating ends sloped at 20 degrees. To make the tower appear more like solid stone, at the corners the panels wrap 90 degrees around and extend at least 4 feet on each side.

  • The atrium. The light-filled lobby atrium, where visitors enter the escalator, has about 100 exterior panels, 10 feet by 10 feet, of which about 90 have a radius—a challenging and unique geometrical puzzle. Adding to the difficulty, a rank of transition panels at the third level appear to be twisted because the top half and bottom half of each panel have opposing curves.

Just as important as the panel forming and profiles to Mayne's aesthetic vision was consistent panel coloration with interesting, nuanced variations. The gray color seems to reflect the natural color of geological features in the Dallas area, suggesting that the building is cut from a rough topological condition. To achieve the desired effect, the architect required a very consistent concrete source, so that the castings would be vary little from panel to panel.

The concrete manufacturers for the job would have to use materials that would produce consistent and uniform characteristics of the final product, according to Descheneaux, Holcim (US) manager, product support. For this key project component, Gates Precast identified a cement plant in Midlothian, Texas, about 30 miles south of Dallas. The source was deemed sufficient to produce this high-quality specification. For the other structural components, the nearby company Lattimore Materials would provide the concrete. The concrete mixes for the project included up to 51 percent of the cement replaced with slag in core walls, and select columns, and 50 percent fly ash in everything else, such as piers, columns and slabs. As an added benefit, the cement plant and concrete suppliers were nearby, which would reduce costs and environmental impact from transportationt.

“It was really driven by LEED. The architect wanted to use fly ash or slag,” says Chris Wolfe, project manager for Balfour Beatty, “in lieu of new material or cement.”

Precast Design Challenges

Part of the Gate Precast Company's challenge in fabricating the individual concrete panels was the sheer scale and weight of each individual panel. (Each tower panel, for example, weighs about 8 tons.) Because of their size, the solid concrete panels needed to be as lightweight as possible—for obvious reasons of logistics, staging and erection. Yet any changes made to affect weight had to allow the cast panels to retain their structural and compositional integrity.

The project team had estimated that about 4 million pounds of grey-cement-based material were required to form the distinctive panels. By using only an expanded shale coarse aggregate, the project's precasters were able to reduce by 20 percent the weight of each panel. While the resulting panels were still relatively large and heavy, those same specifications allowed for a relatively quick installation process that cut down on project costs and construction waste.

Fabricating concrete panels that were not only uniform in color but unique in their textures presented another challenge for the project's precasters, who used a series of specially designed molds of varied sizes to create the more than 650 concrete panels that make up the exterior of the building. Precast concrete is versatile enough that it can be molded into virtually any shape and given whatever appearance and texture design specifications call for. But Mayne's design was intricate and had few repetitive conditions.

About a dozen modular molds were developed that could be arranged as needed to produce the appearance designed by the architects. The standardized molds improved the efficiency of the fabrication process, cutting both time and cost by allowing repetitive concrete pours. By inserting rubber molds into the panels as needed, and caulking between the molds, the team could cast the proper profiles. Some panels required a many as 130 mold modules to produce the correct design.

Careful Cement Specs

Portland cements are classified by type, and there are six main types in the standard ASTM C150 / C150M - 12. Type I (and Type IA) designate general purpose cements suitable for all uses where special properties are not required, according to the Portland Cement Association (PCA). Type II cements contain 8% or less tricalcium aluminate. This type of cement can help produce concrete with moderate sulfate resistance. For more information on all cement types, see www.cement.org

For the precast panels on the Perot Museum in Dallas, the cement specified met the Type II requirement for sulfate resistance while also meeting all Type I traits for compressive strength. In total, about 2,400 tons of the Type I-II cement was delivered for use on the Dallas building project.

While many architectural precast panels are pigmented on the exterior portion and sandwiched against the grey concrete, which typically comprises the interior, the Perot Museum panels are designed so they are composed entirely of grey concrete.

To develop the concrete mix, Gate Precast’s team met with Holcim’s senior market manager, Tim Mummey, and the local senior technical service representative, Tony Sorcic to discuss the project requirements:

  • Weight Reduction
    An important attribute of the mix for the panels was that its weight be minimized without compromising durability and sustainability. For this reason, the precast elements contained only gray cement and a lightweight coarse aggregate of expanded shale. The expanded shale aggregate would reduce the calculated unit weight by about 20% as compared to ordinary concrete.

  • Local Production
    Lattimore Materials Corp., a wholly owned subsidiary of Aggregate Industries (US), worked closely with general contractor Balfour Beatty to deliver about 23,000 cubic yards of concrete for piers, foundations, and slabs. The Lattimore ready-mix concrete facilities were located in downtown Dallas—ideal for reducing project transportation and energy savings, says Bill Hickle, sales manager for Lattimore.

Concrete placement began in the summer of quarter of 2010 with the laying of the museum’s piers and foundation. Later came the building’s signature precast panel façades.

 

One major challenge was inspecting the molds and casts to ensure that in spite of the numerous different profiles and conditions, the exposed surfaces would be consistent and within allowed tolerances.

The team that fabricated the precast concrete forms and panels had a lot to do with the successful installation, says Todd Petty, Gate Precast Company's vice president for operations. “Architectural precasters are skilled craftsmen for many reasons, but they have to be cerebral for complex projects like this,” Petty says. “The in-house panel tickets used on projects similar to the Perot Museum are difficult to digest. And the precasters have to be able to work within tight, industry-mandated tolerances.”

Erection and Installation

Petty talked about what made the Perot Museum project particularly challenging for his company's precasters. “On the production side it was the number of non-flat panels,” he said, “while on the erection side the most difficult part was hanging all of the under-structure panels and those panels that leaned away from the building.”

To hang the panels, the precasters recommended locations for gravity-load embeds that would be likely to work in many of the building's perimeter conditions. Working alongside the structural steel detailer, the project team found a zone for the embeds that would work on every floor. Then the precasters labeled the panels with their module and with the panel number on each corner.

At the project site, the panels were held in a staging area set by general contractor Balfour Beatty that could hold up to five trailers near a tower crane. Three crews worked on separate parts of the building to set the panels, using nonstandard methods developed specifically for the project.

In spite of the BIM modeling and detailed planning, installation moved slowly. Surveying was required to ensure that each panel was set properly, which allowed the installation of only about four to six panels per day—and sometimes fewer. The installation of the building skin was substantially complete by the end of 2011.

A Green Façade System

In addition to giving the museum a striking aesthetic, precast concrete was chosen for its sustainability. The museum is pursuing Green Globes, LEED, and Sustainable Sites Initiative certifications. Despite his commitment to sustainability, Mayne was quoted by the San Francisco Chronicle in 2007 as saying, with regard to his design for that city's Federal Building, “I have no interest in being a 'green architect'…I find the term ridiculous.”

Of that building's design, Mayne told the Chronicle, “I'm interested in skin as a sculptural idea”—an idea he and his colleagues at Morphosis would explore further through the design of a Parisian tower, of which he said, “We're writing the script for the performance of the façade…The aesthetics and the performance are inseparable.”

Mayne achieves this goal anew with his Perot Museum design by way of the use of precast concrete, which not only reflects the building's natural surroundings but also acts as an insulating and temperature-regulating material due to its thermal mass. That is, the museum's precast concrete exterior will absorb and release heat as outside temperatures rise and fall. By naturally regulating to a large degree the building's interior temperature, the museum's concrete exterior will take some of the burden off the facility's HVAC system, thereby contributing to the facility's energy efficiency.

“The thermal mass of the precast concrete reduces the daily temperature swings on the building by absorbing and releasing heat slowly, shifting air conditioning and heating loads to allow smaller, more efficient heating, ventilating, and air-conditioning systems,” says Perot Museum spokesperson Becky Mayad. “A smaller HVAC system also requires significantly less power to operate and reduces the demand on the overall power consumption for the building.”

The Perot Museum also notes that the use of precast helps achieve significant reductions in heating and cooling costs and contributes to an overall energy performance that exceeds Texas Building Energy Code by 14 percent, based on a building energy analysis by the project team. According to its State Energy Conservation Office (SECO), the Texas energy code seeks to achieve 90 percent compliance with the recently adopted 2009 International Energy Conservation Code (IECC) by 2017. “In addition to exceeding the Texas Energy Code by 14 percent, precast concrete contributes to green building practices which have both a direct and indirect effect on energy use and cost savings,” says Mayad.

Mayad explained, for example, that, “The sand, aggregate, water, and cement used in the panels were sourced locally and the panels were poured within 500 miles of the building site,” adding, “Because precast concrete is factory-made, there is little waste created in the plant and it reduces construction waste and debris on site.” With these and other green advantages to the building technique, says Mayad, “The use of precast concrete had a direct contribution to the reduction of construction waste on site due to the inherent qualities of the materials used, casting process, and erection process.”

In the case of the Perot Museum, “The panels did not receive any post finishing such as acid etching or sandblasting,” nor did they “need to be sealed or painted,” says Mayad. Once it's been fabricated, precast concrete can be installed fairly quickly, which cuts down on construction costs. Its durability means it requires little in the way of maintenance, she adds.

Built-in Science Lessons

Not only is the building an object lesson in environmental awareness, it is also a teaching tool. In fact, the didactic quality of the Perot Museum may upstage the exhibits and displays inside.

So why did Mayne choose the form a cube seemingly floating over a landscaped plinth? In essence, the plinth is meant to symbolize an ecosystem, and is composed of rock and drought-resistant grasses native to Texas that will grow and develop over time. The building and outdoor areas merge ideas of natural resources and processes alongside human interventions such as engineering, technology and conservation. The lessons learned cut across our human role in the natural world, and the consequences of our thoughtful interaction with the earth.

The Perot Museum has been described as a living example of engineering, sustainability, and technology at work. The concrete panels themselves are used to evoke the geological striations seen in natural rock formations. The building sources local and recycled building materials, many of which are exposed and can be pointed out to visitors. Also highly evident to visitors is the sustainable podium roof and systems for solar-powered water heating. In fact, all the building's nonpotable water needs are to be met by the rainwater collection system, which captures run-off from both the parking lot and the roof and channels it into two, 25,000-gallon cisterns.

“From start to finish it's all concrete,” says Lattimore's Hickle. “It's a great sight for the Dallas skyline.”

Aesthetic Intrigue—and Efficient Performance

Mayne and his colleagues at Morphosis have been recognized for designs that are as aesthetically intriguing as they are efficient in their performance. Settling on precast concrete as the primary building material for the Perot Museum allowed the architects to combine style and long-term sustainability in a building project that called for both.

The building's end-users, ultimately, are its visitors—in particular, the young people who'll visit the museum as part of their educational and cultural development. While the structure is new, its façade offers a nod to geological history, which of course is categorized and celebrated throughout the museum's collections.

The Perot Museum itself offers plenty of educational lessons—from its environmentally responsible design elements to the science and efficiency of its construction and sustainability—all while presenting itself as part of both the landscape and the city. While on its face, precast concrete might not evoke thoughts of high-tech green design, its use yields efficiencies during the construction process and long thereafter.

In fact, concrete is a common and relatively low-tech materials choice. That's part of its appeal: Sand, water and aggregate are perpetual resources that cover the earth's crust, and they make up at least 80 percent of the typical concrete mix, according to Lionel Lemay, senior vice president of Technical Resources at the National Ready Mixed Concrete Association (NRMCA), Silver Spring, Md. “Concrete is the most widely used building material in the world, and is used in nearly every type of construction,” says Lemay.

Yet concrete is also sophisticated and highly engineered, especially when it comes to precast. Its profile as a sustainable design choice confirms this happy combination of low-tech savings and high-tech formulations. Some of the green benefits, according to Lemay, include basic green building traits that contribute to good life-cycle performance, as shown by life-cycle assessments (LCAs) reviewed by the project team:

Resource efficiency. Most concrete materials are acquired and manufactured locally. This minimizes energy use needed for transportation. The component materials generally do not require much processing, and may include ingredients otherwise destined for the landfill, such as fly ash, slag, silica fume and burned slate.

Energy efficiency. Concrete building systems combine good R-value with high thermal mass and low air infiltration, contributing to a more energy-efficient enclosure and building.

Durability. Concrete has a long service life, and it is resilient and durable. The need for renovation or repair is minimal and infrequent as compared to many other façade cladding choices. This also minimizes the future resource and energy requirements for repair, maintenance and renovation.

Local heat island and CO2 mitigation. As a pavement, cladding and roofing material, concrete minimizes the urban heat-island effect. New light-colored concrete has a solar reflective index (SRI) exceeding 29. This solar reflectance level considered the threshold where reflectance contributes to heat island mitigation. Some concrete also may absorb CO2 through natural carbonation, helping shrink total emissions.

Mayne and his colleagues chose concrete for its sustainability, certainly, but also for its design versatility, permanence and inherent beauty. In the end, through close coordination and collaboration with the general contractor, supplier, and fabricator, Morphosis delivered a building that is as much a part of the museum's mission as it is a home to the collections it houses. The building's concrete façade is at once modern and timeless.

While it's understandable that in 2009 The Dallas Morning News described the Perot Museum of Nature and Science as “possibly the boldest piece of modern architecture ever proposed for Dallas,” the reaction from peer architects may be even more revealing. One, a juror for Architectural Record's 2012 Advertising Excellence Awards, reportedly commented upon seeing an image of the museum's precast concrete exterior, “I didn't know you could do this with concrete.”

Quantifying Precast Cost Savings

Was the choice of the Perot Museum’s façade cladding a way to save money up front, or long-term? Both, argue the museum’s operators, pointing to the following ways to quantify the cost savings realized through the use of precast concrete:

  • The sand, aggregate, water, and cement used in the panels were sourced locally and the panels were poured within 500 miles of the building site.

  • Precast concrete is extremely durable which will maintain its appearance overtime without utilizing precious resources such as water and power to clean and maintain it.

  • Because precast concrete is factory-made, there is little waste created in the plant and it reduces construction waste and debris on site.

  • The light color of the precast concrete helps reduce the heat island effect on the surrounding microclimate as well as human and wildlife habitat.

  • The panels did not receive any post finishing such as acid etching or sand blasting.

  • Precast concrete does not off-gas nor does it need to be sealed or painted.

  • The efficient erection process reduces the use of energy and materials that are typically required for other façade types.

  • As with all concrete, precast components can be recycled or down-cycled. Down-cycled building materials are easily broken down, because it comes apart with a minimum amount of energy and retains its original qualities. An example of down-cycling would be the use of crushed precast concrete as aggregate in new concrete or as base materials for roads, sidewalks, or concrete slabs.

Sources: Morphosis Architects and Good, Fulton & Farrell, on behalf of the Perot Museum of Nature & Science.

 

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Customers have relied on Holcim for approximately a century to help them design and build better communities. Today, Holcim is one of the world’s leading suppliers of sustainably manufactured cementitious materials. The Holcim Awards for Sustainable Construction promote and support the timely solutions of architects for a better future and built environment. www.holcimawards.org

 

Originally published in the November 2012 issue of Architectural Record