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.”