ICF: The Recipe for Green Concrete

Ulf Wolf and Steven Ferry

April 2008

It’s normally gray and more than a stone’s throw from environmental innocence. Still, in this case, what you add to it, and what you do with it, can make all the difference, and therein lies shades of grey.

The Ugly
Each year, the concrete industry produces approximate 12 billion tons of concrete and uses about 1.6 billion tons of portland cement worldwide. In addition to consuming considerable amounts of natural resources (limestone and sand) and energy, the production of one ton of Portland cement releases one ton of carbon dioxide (CO2) into the atmosphere, accounting for 5 percent or better of the world’s carbon dioxide emissions. Which brings us then to what can be added to concrete.

The Not So Ugly
Fly ash, one of the residues generated in the combustion of coal, is something that finds itself in concrete these days. It is generally captured from the chimneys of power generation facilities, whereas bottom ash is—you guessed it—removed from the bottom of the furnace. In the past, fly ash was released into the atmosphere via the smoke stack, but pollution controls mandated in recent decades now require that it be captured prior to release.

Depending upon the source and makeup of the coal being burned, the components of fly ash vary, but all fly ash includes substantial amounts of silicon dioxide and lime.

Class F Fly Ash. The burning of harder, older coal typically produces Class F fly ash, which contains less than 10 percent lime, and due to its properties requires a cementing agent, such as portland cement, quicklime or hydrated lime, with the presence of water, in order to react and produce cementitious compounds.

Class C Fly Ash. By contrast, fly ash produced from the burning of softer, younger coal has self-cementing properties. In the presence of water, Class C fly ash will harden and gain strength over time. Class C fly ash generally contains more than 20 percent lime (CaO).

Fly Ash and Cement. In the past, fly ash produced from coal combustion was simply entrained in flue gases and dispersed into the atmosphere. This created environmental and health concerns that eventually prompted laws that have since reduced the actual fly ash emissions to less than 1 percent of all fly ash produced.

The remaining, harvested, 99 percent is proving useful as a replacement for a percentage of the portland cement content of concrete. This use was recognized as early as 1914 but did not lead to serious experimentation and confirmation until 1937.

As an aside, before its use was lost to the Dark Ages, Roman structures, such as the aqueducts and the Pantheon in Rome, used volcanic ash (which possesses similar properties to fly ash) as their concrete.

The use of fly ash as a partial replacement for portland cement is generally limited to Class F fly ash, but as such it can replace up to 30 percent of the portland cement, by mass, and can add to the concrete’s final strength as well as increase its chemical resistance and durability.

In fact, recent tests have successfully replaced as much as 50 percent of the portland cement with Class F fly ash.

Replacing portland cement with fly ash also reduces the greenhouse gas signature of concrete. Since the worldwide call for portland cement is expected to reach nearly 2 billion tons by 2010, replacing 30 percent to 50 percent of this amount with fly ash will dramatically reduce global carbon emissions.

The Beautiful
As good as this may be, it is only when you utilize concrete—be it gray or less so—in ICF (Insulated Concrete Forms) that the picture turns truly green.

And this is exactly what Titan Walls of Dayton Beach, Fla., is now doing at the Magnolia Corporate Center project in Oviedo, Fla.

ICF is a sometimes wildly misunderstood technology. Utilizing rigid polystyrene insulation forms, some builders are still unaware that the polystyrene is there to mold, and to fuse with, the concrete poured inside the stacked forms.

"I’ve been asked, more than once, how these Styrofoam walls are supposed to withstand wind, and how they could possibly be load bearing,” says Paul Tomazin of Titan Walls, with a chuckle.

"Some people are quite confused about what we’re doing; they don’t get that ICF is a form for concrete to go into. However, once they see the product, and see that it’s simply another concrete forming system—one that just happens to stay in place and provide insulation, and furring, and that happens to act as a good sound barrier—the light goes on, and they get very interested.

"We’re trying to get engineers and architects to understand that it’s just a matter of concrete. That when all is said and done, it’s just an insulated, solid, steel-reinforced concrete—and load-bearing—wall.”

The Project
The Magnolia Corporate Center is a three-story, 60,000 square foot office condominium project, utilizing ICF technology not only for all outside and inside walls, but also for the second- and third-story floors, and for the roof.

The project owner, Magnolia Enterprise LLC, did not specify ICF in the bid, but did want to go as green as possible, and ICF answered that requirement beautifully.

"ICF hits a lot of LEED points,” Paul Tomazin explains. "You have the recycled materials in the ties and the forms, there’s the fly ash in the concrete, and to top it, the energy efficient insulation of the exterior and interior walls, between the floors, and of the roof as well.

"It’s a high-end three-story office condominium that not only utilizes ICF technology throughout the project, but also incorporates an expanded polystyrene floor/roof system.

"This particular product is … a panelized Styrofoam system that is set in place, reinforced with rebar, and covered with a concrete topping. As a result, this building will have a complete concrete wall, floor and roof system. The exterior coatings will consist of a textured acrylic finish, which has been specifically engineered and designed for ICF.

"Titan Walls is working this project with Baylor Plastering & Drywall, Inc., and together we provide a complete package for the owner and GC, which I see as an important part of landing large ICF projects.

"It will be a green building with many benefits for the owner, general contractor and occupants.”

AWCI’s Construction Dimensions will revisit this project with follow-up articles as the job progresses.

It’s Not EIFS
When it comes to exterior insulation and finish systems versus ICF, Tomazin goes on to explain, "In people’s minds, there is still a connection between EIFS and ICF, but while the two technologies both utilize Expanded Polystyrene (EPS) as technologies, they are nevertheless far apart.

"In an EIF system, you adhere Styrofoam to a concrete or masonry wall, and then apply a finish on top of that.

"With ICF, you still use a base coat, a mesh and a finish, but you’re not applying the Styrofoam to anything: it is integral to the wall once the concrete has cured. So, we try to stay away from comparisons to EIFS, as people tend to confuse them.

"Also, ICF has none of the leakage issues that, in the past, plagued poorly installed EIFS, as the ICF forms are pre-molded and then bonded to the concrete, as it cures against the inside panels of the forms.

"And this is one of the main advantages with ICF: There are no open areas, there are no gaps or hollow areas for mold to grow.

"ICF is bonded solid. It forms a strong adhesion to the concrete and as the concrete cures, it fuses to it.

"Once the concrete is cured, you apply the same finishes on top of the ICF: a synthetic, a based coat, a mesh and a synthetic finish. But it is important to understand that ICF is not EIFS. It uses some of the same components, but it’s not an EIFS.”

ICF and Building Codes
Tomazin then goes on to say, "One myth about ICF, if you will, is that it is not up to code. Nothing could be quite as far from the truth. ICF is accepted by building codes across the country. However, our GC and the owner did not know this, and before we began construction, they wanted us all to meet with the building department to make sure there were no issues with this ‘new’ product.

"We had the meeting and, of course, there were no issues. ICF has long since been approved for construction. The GC and owner were relieved, as they thought that they were going to have problems getting this ‘new’ product past the building department.”

Every major code body in North America, including the International Code Council and the Canadian Construction Materials Centre, has approved ICFs. Also, ICFs are listed as a prescriptive method of building in the International Residential Code and can be built to commercial design specification using the International Building Code. ICFs are also listed as a building system in the newest edition of the Canadian National Building Code.

As Tomazin puts it, "It’s just a matter of people not being up-to-date.”

The Green
Green construction today is typically evaluated against, and certified by, the U.S. Green Building Council’s LEED (Leadership in Energy and Environmental Design) criteria, and ICF is emerging as a very viable option for building owners and designers who want to maximize LEED points.

A quick review of the 69 possible points available in the LEED-NC (New Construction) category identifies energy savings as the most heavily weighted criteria, with up to 10 points (more than a third of the points needed for basic LEED-NC Certification) achievable for buildings designed to improve energy efficiency over the requirements set in code standards. The focus on energy savings is very appropriate considering that the majority of a building’s environmental footprint is caused by the energy consumed in heating and cooling a structure over the course of its lifetime. The high performance thermal envelope of ICFs offers a significant contribution toward achieving all 10 Optimize Energy Performance Credits in the Energy & Atmosphere category.

The LEED Sustainable Sites Credit calls for reducing the development footprint and limiting site disturbance in order to conserve existing natural areas. ICF construction can help reduce impact to a construction site, as the ICF bracing is typically erected on the inside of the ICF wall, with limited construction activity around the perimeter.

ICF contributes to the Materials & Resource Credits in three areas. The first two concern the Construction Waste Management subcategory. When you compare the typical ICF waste factor of 2 percent to 5 percent with the current norm for alternative construction methods, the architect can easily identify and document the quantities diverted for possible points.

Additionally, there are possible credits to be earned in the Recycled Contents subcategory, as some ICF manufacturers now incorporate recycled content in the plastic ties, and in the expanded polystyrene (EPS) used for the forms. Also, the concrete mix used for ICFs normally incorporates high percentages of fly-ash, which is 100 percent post-consumer recycled (the reinforcing steel is generally 80 percent plus post consumer recycled).

For LEED calculations, this recycled content is determined by weight. The recycled fraction of the assembly is then multiplied by the cost of assembly to determine the recycled content value. The values of all materials used in a project building are then added for a combined percentage.

The intent of the Regional Materials LEED category is to increase demand for building materials and products that are extracted and manufactured within the region, thereby supporting the regional economy and reducing the environmental impacts resulting from transportation.

Depending on the manufacturer, the ICFs may fall within the 500-mile radius for manufacturing, and certainly, most of the time, the concrete aggregate is locally extracted.

Canada has introduced a Materials & Resources Credit, Durable Building, with the intent of minimizing construction waste due to premature failure of the building and its constituent components and assemblies. This credit was designed to address moisture and structural deterioration causing collapse of building envelopes.

The Canadian Standards Association’s Guidelines on Durability in Buildings identifies concrete as a durable material, with resistance to mold and mildew. Indeed, the architecture of ancient Rome is time-tested evidence of the endurance of concrete.

Moreover, using ICFs, the concrete is protected by the layers of EPS foam, which is itself inorganic and not subject to deterioration.

It would be true to say that durability is at the core of sustainable architecture, and in that regard, ICF plays a big role.

ICF structures can also achieve points in the Indoor Environmental Quality category. The insulation, combined with the reduced air infiltration of an ICF assembly, results in an interior air space that is "neutral.” There are no convective currents caused by temperature fluctuation of the wall material; nor are any drafts caused by air leaks. Therefore, the ambient temperatures throughout the space show little variance.

The Indoor Environmental Quality credits also concern the reduction of pollutants. The EPS foam used in most ICF forms emits no volatile organic compounds or formaldehyde. Neither do they produce chlorofluorocarbons or hydrochlorofluorocarbons during production, nor will they contribute to off-gassing, as the material is inorganic and inert. The adhesives and low expanding foams used in the ICF assembly are equally non-toxic, as is the concrete mass.

In addition to the points delimited by the USGBC LEED system, ICFs contribute to sustainable construction in many other ways. One example is the sound dampening properties of the concrete and foam, which provides ideal protection from urban noise. Also, the solid monolithic concrete wall can withstand the worst of rainstorms, fires and high winds. It is also impenetrable to insects, including termites.

ICF Benefits
The ICF industry is basically driven by consumer demand for energy efficient, environmentally safe, and element resistant housing and commercial structures.

Consequently, the slow-to-start Styrofoam ICF industry of the 1970s has now morphed into a strong and viable industry sustaining 37 manufacturers, some large, some small.

The bottom line is this: The ICF industry is here to stay and is gaining a considerable market share over other construction materials and methods.

In 2006, the ICF industry produced 78 million square feet of wall. According to the latest research, 110-million square feet were produced by the ICF industry in 2007.

Looking over the various benefits of ICF, it is easy to see why this is probably the fastest growing segment of the construction industry:

Energy Efficiency. ICF has a performance rating of R-50 making it equivalent to R-50 batt insulation and can provide 50 to 80 percent savings on annual heating and cooling costs, while allowing for a 40 percent reduction in HVAC equipment tonnage.

Quality and Comfort. ICF provides sound resistant walls with a Sound Transmission Class Rating of 53+. It is resistant to mold and mildew development as well as termites and other insects. ICF walls act as a barrier to airborne dust, pollen and other allergens, providing superior air quality.

Safety and Security. The steel reinforced concrete walls have a 200 mph +/– sustained wind rating, providing the ultimate in hurricane and tornado protection. Further, the ICF walls have a UL approved two- to four-hour fire rating. These wind and fire ratings also help ICF projects to qualify for insurance premium reductions.

Design Flexibility. The ICF adapts easily to any floor plan. It is able to form any angle, arch or radius, with no height limitations. Building plans can easily be converted to ICF at any stage of the project.

LEED Credits for Architects. Using ICF contributes greatly to LEED green building certification. It can earn up to 22 of the 26 points needed to qualify a building for LEED.

Construction Advantages. ICF walls go up faster than any other type of wall construction—in as little as 25 percent of the construction time of conventional walls. As a result, lending costs are reduced and occupancy earnings start sooner.

The 5-in-1 wall system provides wall structure, insulation, sound barrier, vapor barrier and furring in a one-step process.

ICF is dimensionally equivalent to CMU (concrete masonry unit) providing an easy transition to projects with completed plans. And because ICF produces less waste, it also makes for a cleaner job site.

Here, then, is the recipe for green concrete:

Take a ton or two of portland cement. Add a ton or so of Class F Fly Ash. Stir well. Build and shore up a nice ICF wall form. Pour the cement/fly ash mixture into the ICF form. Let cure until rock solid. Add topping (finish) to taste.

Los Angeles–based Ulf Wolf, and Clearwater, Fla.–based Steven Ferry, write for the construction industry as Words & Images.