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High-Performance Concrete Comes in Many Varieties,
Including These Six Popular Systems
by Jennifer G. Prokopy
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| Winner of the NCMA’s Award of Excellence in
residential design, the Brems family house in Salt Lake City demonstrates
the sustainability of concrete. Photo courtesy of NCMA. |
When it comes to using concrete wallsystems in sustainable building construction,
the options are limitless. There are many types of walls, and within each
category, many variations.
Tilt-Up
Tilt-up concrete walls have been used for a century; today, more than
15 percent of industrial buildings in the U.S. are made with tilt-up concrete
panels, according to the Tilt-Up Concrete
Association (TCA). When building with tilt-up, the site is prepared,
walls are cast on-site on the floor slab, and then—just like the
name says—tilted up and secured in place. The panels can be finished
in myriad ways.
Tilt-up systems offer many environmental benefits, says TCA executive
director Ed Sauter. Because they are cast on-site, transportation costs
are minimized. Typically, the thermal mass of tilt-up eliminates the need
for insulation. Of the approximately 25 percent of panels that are insulated,
most use non-conductive ties to take best advantage of thermal mass properties—creating
solid, insulated walls that offer high energy efficiency. The large panels
(the record is just over 90 feet tall) require minimal energy and labor
when it comes to erection and finishing. And tilt-up buildings can be
designed to accommodate change, with panels easy to remove and reuse,
or even recycle if necessary.
Insulating Concrete Forms
Long the province of residential builders, insulating concrete forms (ICFs)
are rapidly gaining popularity in commercial construction. The stay-in-place
forms are placed in the shape of a structure and connected with plastic
ties, and reinforcing steel is installed to provide additional support.
Concrete is pumped into the forms and allowed to set, creating a wall
with foam insulation on each side, sandwiching the reinforced concrete
core.
According to the Insulating Concrete Form
Association (ICFA), the high R-value of the insulation, the thermal
mass of the concrete, and the ability to moderate temperature swings,
make the system ideal for climates with large temperature variations—but
ICFs may increase energy efficiency in any region. The forms can be installed
quickly and easily, and the wide variety of manufacturers, shapes and
sizes makes it easy to custom-design homes and smaller commercial structures.
Precast
Precast concrete panels are used for both structural and architectural
applications, primarily in commercial structures. Components are precast
at a manufacturing facility and transported to the site. Precast walls
offer high durability and strength plus thermal mass, which contributes
to increased energy efficiency. They also use locally derived materials,
and can incorporate recycled materials like fly ash and slag cement.
According to the Precast/Prestressed Concrete
Institute (PCI), one of the biggest benefits of precast walls is in
their design: tight controls mean more efficient mix designs, resulting
in smaller structural members and longer spans. Construction waste is
reduced, because the exact amount of necessary components is delivered
to the site. Any spare components can easily be recycled. Creative precast
wall design can also reduce material redundancy.
Masonry
Concrete masonry units are available in a rainbow of colors, textures,
shapes and sizes. They can be used to create structural walls in residential
and commercial applications or to build other structures like retaining
walls or hardscaping.
According to the National Concrete Masonry
Association (NCMA), concrete masonry units offer sustainable benefits,
including eliminating the need for VOC-emitting paints. Concrete masonry
units create walls with high thermal mass. Masonry offers durability and
sound attenuation. For hardscaping applications, concrete landscaping
units help to reduce stormwater runoff and support plant growth.
Removable Forms
Concrete walls built with removable forms (also called vertical-pour walls)
are used both above- and below-grade, primarily in residential applications,
according to the Concrete Foundations
Association (CFA).
There are a variety of systems—some that place concrete on two sides
sandwiching foam in the middle, and some that place insulation on one
side and concrete on the other—but the basic process is the same.
Aluminum forms are placed, filled with concrete, and removed once the
material sets, leaving solid structural walls. The aluminum forms can
be used up to 3,000 times and are recyclable at the end of their service
life.
Although vertical-pour walls historically have been used for external
walls, Ed Sauter, executive director of CFA, says that some companies
are now introducing systems for interior walls and decks, which, when
used together, produce a total concrete shell poured in a single operation.
Innovators are also refining the product to create walls that use less
concrete but offer the same performance characteristics.
Autoclaved Aerated Concrete
Walls built with autoclaved aerated concrete (AAC) typically are constructed
in a fashion similar to masonry, with blocks held together by mortar,
but these blocks are made with only fine aggregates, cement, lime and
a natural expansion agent that causes the concrete to “rise,”
filling it with tiny air pockets. The resulting material is lightweight
and easy to work with.
AAC comes in wall, floor and roof panels, cladding pieces, and specialty
shapes, according to the Autoclaved Aerated
Concrete Products Association (AACPA). Ronald Barnett, vice president
and general manager of manufacturer AERCON Florida, LLC, says one significant
benefit of AAC is cost, especially for fire walls, which can be constructed
4 inches thick to achieve a four-hour UL fire rating.
The material’s lighter weight means shipping costs, fuel and pollution
are reduced. The durable material will last indefinitely, and thin mortar
joints help provide a tight building—and excellent indoor air quality.
In some areas, AAC even incorporates fly ash, mine tailings, slag cement
and other byproducts that would otherwise be landfilled.
About the Author: As principal of Orange
Grove Media, an independent communications firm, Jennifer
G. Prokopy provides expert writing, editing and media relations services
to the construction industry. As president of the Construction Writers
Association (CWA), Jenni works with the nation’s top construction
journalists and publicists to improve the quality of construction communications.
She is a winner of the CWA Marketing Communications Award, recognizing
her writing on sustainable construction with concrete, and a graduate
of Northwestern University’s Medill School of Journalism.
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