Tag Archives: Concrete

Specifying More Resilient Buildings

safer_Comcast Center Inner Core

A high-performance self-consolidating concrete mix containing 40 per cent slag cement helps give the Comcast Center’s massive inner core its needed strength. Photo courtesy Thornton Tomasetti

by Andrew Pinneke, PE, LEED AP
Resisting natural disasters and reducing environmental impacts are major challenges in the United States. During an average year, there are 10 tropical storms (six of which become hurricanes) and more than 1200 tornadoes touching down.

In South Florida, Hurricane Andrew left a wake of destruction in 1992 that totaled more than $25 billion in property damage and resulted in 44 fatalities. Along the Gulf Coast, Hurricane Katrina caused widespread devastation in 2005, resulting in at least 1833 fatalities and $108 billion in property damage. In 2012, Hurricane Sandy affected the entire eastern seaboard and caused $65 billion in damage. In densely populated New York City alone, this superstorm took the lives of 53 residents, destroyed thousands of buildings, and caused $19 billion in damages and lost economic activity.

Almost every state has been affected by extreme windstorms (Figure 1). Each year, tornadoes with gusts as high as 320 km/h (200 mph) in the Midwest and lower Great Plains result in more than 100 fatalities and 1500 injuries. In 2013, a tornado cut a swath 3.2 km (2 mi) wide and 19 km (12 mi) long through Oklahoma City, causing 26 fatalities, 400 injuries, and $2 billion in property damage.

Few regions of the country escape the wrath of Mother Nature. Flooding, which accounts for more than 75 percent of federally declared disaster areas, is the most prevalent disaster event in the United States, and earthquakes pose serious risks not just in California, but also many Midwestern and Eastern areas. About 5000 seismic events occur each year, with approximately 400 capable of causing damage to building interiors and 20 able to cause structural damage. For example, the 1994 Northridge earthquake in California caused 57 deaths, over $20 billion of damage, and destroyed or damaged 90,000 homes, offices, and public buildings.

Figure 1

safer_Wind Zones in US_HROver the past decade, the frequency and overall economic damage inflicted by destructive wildfires also has increased in more than three-fourths of the United States. In 2012, some 38 catastrophic wildfires produced $1.1 billion in economic losses according to estimates in a January 2013 report by Munich Re. The wildfire problems are not limited to California and the Southwest, as there has been a recent trend toward larger and more destructive wildfires in the Southeast and Midwest.

Championing resilience
Standards for construction and code-related enforcement vary widely across the country. Some states have adopted building codes applicable to virtually every type of structure, while others employ lesser degrees of regulation.

The International Code Council (ICC) has developed the most widely adopted set of codes to unify the nation’s building regulatory systems. Based on thoroughly tested scientific and engineering principles, these model codes provide standards used in the design, build, and compliance process to construct safe, sustainable, secure, and resilient structures.

The Federal Emergency Management Agency (FEMA) and National Oceanic and Atmospheric Administration (NOAA) provide additional guidance on how to design buildings to lessen the impact of natural disasters. This guidance to designers includes their support of the ICC standards, which are equivalent to the National Earthquake Hazard Reduction Program (NEHRP) for New Buildings and reflect the current state-of-the-art engineering requirements for wind, such as those found in American Society of Civil Engineers (ASCE) 7, Minimum Design Loads for Buildings and Other Structures.

The Fortified for Safer Business program of the Insurance Institute for Business and Home Safety (IBHS) is another valuable resource. This ‘code-plus’ program offers design criteria and construction techniques that greatly increase a new commercial building’s durability and resilience to natural and manmade hazards.

In recognition of the increasingly important need for enhanced resiliency of buildings, the National Building Museum in Washington, D.C., is hosting a Designing for Disaster exhibition, which runs through August 2. This major exhibition showcases innovative research, cutting-edge materials and technologies, and disaster-resistant designs for creating safer, more durable and disaster-resilient communities. When the exhibition opened in May 2014, a group of 20 prominent industry organizations, led by the National Institute of Building Sciences (NIBS) and the American Institute of Architects (AIA), issued a joint statement pledging to research design and construction best practices, educate their memberships, and advocate for governmental policy changes.

safer_Iowa Tornado Shelter_HR

Constructed in accordance with Federal Emergency Management Agency (FEMA) criteria, the unique design of the concrete tornado shelter at the Iowa State Fairgrounds is a prototype for other shelters across the state. Photo courtesy Tom Hurd, Spatial Designs Architects

Concrete’s role in resilient construction
In areas susceptible to natural disasters, architects must design durable, high-performance buildings with materials that not only offer resistance, but also continue to function after a catastrophic event. High-performance concrete (HPC) structures are especially suited to provide protection against natural hazards and help ensure critical services—like hospitals, evacuation shelters, and emergency operations centers—can remain in operation even under the harshest of environments.

Concrete’s inherent strength and stiffness provide a primary advantage, which can be enhanced through building design, mix formulation, and reinforcement to withstand the forces of extreme winds and flying debris. Concrete not only provides the resilience needed to protect against tornadoes and hurricanes, but its structures are also resistant to flood damage, earthquakes, wind-driven rain, corrosion, decay, insect infestation, and mold and mildew formation. The slow rate of heat transfer and inherent fire resistance enable it to tolerate flames, and slow their spread. Concrete buildings also have excellent aesthetic versatility, providing an almost endless array of colors and textures to help minimize the cost of building repairs following a disaster.

All these attributes are built into a concrete structure, so if disaster strikes, restoration is usually a matter of replacing contents and some finish materials. This is a much less daunting and expensive process than complete rebuild or build out of interiors.

In Iowa, where the annual State Fair draws thousands of visitors during the heart of tornado season, the State Fair Board called for the construction of a 483-m2 (5200-sf) shelter to help protect campers in the event of a major storm. The Iowa State Fairgrounds tornado shelter features a unique curved design to provide superior wind resistance. The roof and the curved walls of the structure are constructed of 305-mm (12-in.) thick precast concrete panels that use a special framework to retain their shape, and the interior partition walls are constructed of fully reinforced concrete masonry units (CMUs). The building’s exterior concrete canopy is mounted atop concrete piers to provide additional weather protection. The canopy is designed to withstand 400-km/h (250-mph) winds and to prevent them from becoming a debris hazard themselves during a high wind event.

Concrete is also taking center stage in construction projects in the Gulf Coast region, which is still recovering from the devastation caused by Hurricane Katrina in 2005. At the time of the storm, Alabama, Louisiana, and Mississippi did not have statewide building codes for non-state-owned buildings. As a result, Hurricane Katrina’s storm surge, high winds, floodborne debris and long-duration flooding exceeded flood depths and loads used in building design, causing massive and widespread structural failure.

safer_New Orleans Surge Barrier

Construction of the 3,2-km (2-mi) long (IHNC) barrier that protects New Orleans from flooding relied on self-consolidating concrete for monolithic pours above and below the waterline and cast-in-place piles. Photo courtesy David Spielman/GPA

In the wake of Katrina, levees for Greater New Orleans were brought up to modern building code standards, and the U.S. Army Corps of Engineers (USACE) constructed the Inner Harbor Navigation Canal (IHNC) Surge Barrier to improve the resiliency of Gulf Coast communities. The largest of its kind in the world, the barrier incorporates more than 53,520 m3 (70,000 cy) of a self-consolidating concrete mix that achieved strengths greater than 27,580 kPa (4000 psi) within 48 hours. The backbone of the main barrier consists of 1271 concrete vertical piles, each measuring 1676 mm (66 in.) in diameter and 44 m (144 ft) in length and weighing 96 tons.

Another focus of reconstruction efforts is the need for critical and essential facilities to remain functional during a catastrophic event. When completed, the new University Medical Center (UMC) in downtown New Orleans will be the only Level One trauma center in southeast Louisiana, so keeping it functional during future disasters will be essential. The UMC project, scheduled to be competed this year, is using fly ash and slag cement in specialized concrete mix designs for added performance, and to help it meet flood-resistant construction standards.

This 213,700-m2 (2.3 million-sf) project is one of the largest healthcare campuses under construction in the country. It includes 120,775 m2 (1.3 million sf) of concrete decking delivered at a weekly rate of 5575 m2 (60,000 sf). The high-performance concrete building envelope for the seven-story, 52,025-m2 (560,000-sf) Inpatient Tower, just one component of the 15-ha (38-acre) campus, has been designed 
to endure hurricane-force winds up to 240 km/h (150 mph), yielding a facility that will enhance public safety in the event of natural disasters.

HPC for stronger, more durable buildings
The specification of high-performance concrete (HPC) continues to grow as superior structural resiliency and durability performance become increasingly important. HPC mixtures incorporate supplementary cementitious materials (SCMs)—such as slag cement, fly ash, and silica fume—as separate components or combined in blended cement. The greatest physical benefits imparted by SCMs and blended cements (ASTM C595, Standard Specification for Blended Hydraulic Cements, and/or ASTM C1157, Standard Performance Specification for Hydraulic Cement) can be seen in the properties concrete exhibits after hardening.

Strength
Concrete gains strength at a decreasing rate over time, so varying the concrete mixture can significantly alter the rate and/or ultimate strength gain as defined by ASTM C39, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens. Slag cement and fly ash typically lower early strengths (one to 14 days) but can significantly improve long-term strength development (28 days and beyond), depending on the proportions and materials used (Figure 2). For example, Class F fly ashes tend to have a slow strength gain curve contributing mainly to the strength beyond 28 days, whereas silica fume contributes primarily to the three to 28 day strengths. Both compressive and flexural strengths can increase markedly at 28 days and beyond with the addition of most SCMs.

Figure 2

safer_Figure 2 strength development

Test results comparing lower early strengths and higher later strengths of concrete with supplementary cementitious materials (SCMs). Image courtesy Lafarge

Permeability
Slag cement, fly ash, and silica fume all can significantly reduce the permeability of concrete to the ingress of chlorides, sulfates, and other aggressive agents present in rain, groundwater, and seawater. Silica fume has a profound effect on permeability, exhibiting as much as a five-fold reduction in permeability when using only eight percent silica fume.

Alkali-silica reaction
Most SCMs can effectively prevent excessive expansion and cracking of concrete due to alkali-silica reaction (ASR). The amount of slag cement required depends on the nature of the slag cement, the reactivity of the aggregate, and the alkali loading of the concrete. In most cases, 50 percent slag cement is sufficient with highly reactive aggregates. The amount of fly ash required typically is in the range of 15 to 55 percent, depending on the chemical composition of the ash, reactivity of the aggregate, and the alkali loading of the concrete.

Generally, Class F ashes are much more effective in controlling expansion due to ASR than Class C ashes. Silica fume can control ASR, but the amount required generally results in poor constructability. Consequently, blends of slag cement and silica fume, as well as blends of fly ash and silica fume, are often used as an alternative to straight silica fume replacement because they can be used to achieve a synergistic effect in mitigating expansion due to ASR, while producing a workable concrete.

Sulfate attack
Concrete containing SCMs generally offer superior resistance to sulfate attack as they lower the permeability, restricting the ingress of sulfate-bearing ions. In numerous cases, they additionally reduce the compounds that can react with sulfates to form deleterious compounds. Typically, slag cement, silica fume, and Class F fly ashes are effective in improving sulfate resistance. The effectiveness of Class C fly ashes depends on the ash chemistry and the replacement level.

Thermal stress
If the temperature differential between the concrete’s surface and interior is too high, the result can be cracking and loss of structural integrity. Employing high replacement levels of slag cement and/or fly ash in properly proportioned mixes can reduce the peak temperatures, as well as the rate of heat generation. Reducing the heat of hydration of the mix can moderate the development of thermal stresses within the concrete and prevent cracking.

safer_Perez Art Museum Miami

Due to its unique combination of strength, durability, aesthetics and ductility, this proprietary ultra-high-performance concrete (UHPC) product was used to construct 100 long-span, hurricane-resistant mullions for the eloquent and resilient Pérez Art Museum in Miami. Photo courtesy Herzog & de Meuron

Soaring to new heights in resiliency
A major advantage of concrete construction for high-rise buildings is the material’s inherent properties 
of heaviness and mass, which create lateral stiffness, or resistance to horizontal movement. Occupants of concrete towers are less able to perceive building motion than occupants of comparable tall buildings with non-concrete structural systems. High-strength concrete also provides the most economical way to carry a vertical load to the building foundation.

By employing high-strength concrete, the column size is reduced. At the same time, the amount of vertical reinforcement can be reduced. The net result is the least expensive column is achieved with the smallest size column, the lowest amount of reinforcement and the highest readily available concrete strength. As a result, concrete has become the material of choice for many tall, slim towers.

Two recently-constructed, high-profile skyscrapers feature concrete designed to offer the utmost safety and resilience. Philadelphia’s Comcast Center, the tallest building in the city at 297 m (975 ft), required 38,230 m3 (50,000 cy) of concrete containing slag cement for the high-performance project, of which 27,525 m3 (36,000 cy) was specified at 68,950 kPa (10,000 psi) for the central inner core. The building’s thick exterior core walls—1370 mm (54 in.) up to the 20th floor—further minimize deflection due to wind forces, and all its elevators, sprinklers, communications systems, and stairwells are encased within the concrete core.

However, it is Manhattan’s One World Trade Center that is setting a new standard for stronger, safer urban landscapes. Rising a symbolic 1776 ft (i.e. 541 m), this landmark skyscraper is the tallest in the Western Hemisphere. It has a massive cast-in place, reinforced concrete inner core that runs the full height of the tower—an extra-strong backbone that provides support for gravitational loads as well as resistance to wind and seismic forces. The concrete core walls are 1 m (3 ft) thick or more above ground and up to twice that below grade. Higher up, the concrete core walls slim down to 0.6 m (2 ft) thick.

The 152,910 m3 (200,000 cy) of concrete used in the tower’s superstructure—with a strength that has never been used on such a scale in building construction—was custom-designed to ensure high levels of durability, as well as control the heat of hydration during the mass concrete pours to minimize cracking. Supporting columns on the first 40 floors were made from 82,740 to 96,525 kPa (12,000 to 14,000-psi) self-consolidating concrete and the upper floors with 59,295 to 68,950-kPa (8600 to 10,000-psi) mix designs.

To meet the compressive strength requirements, the design and engineering team relied on a highly specialized concrete mix that included fly ash, silica fume, and slag cement. High-strength concrete was the ideal material for meeting the high-priority safety requirements for One World Trade Center because elevators, stair enclosures, and other supporting members relied on to resist wind, seismic, and other impact forces are designed with an extra measure of durability and resilience.

Innovative new UHPC materials
The concrete industry continues to explore new ways of making buildings stronger, safer, and, as demonstrated by one of its newest products, more aesthetically pleasing. Ultra-high-performance concrete (UHPC) is blended with high carbon metallic or polyvinyl alcohol (PVA) fibers, and has a unique combination of properties including strength, ductility, durability, and aesthetic design flexibility.

The Perez Art Museum in Miami is situated on Biscayne Bay, where frequent tropical storms and exposure to the salt and sea air can cause serious problems for buildings. UHPC was used for the building’s approximately 100 long-span, precast vertical mullions to blend with its cast-in-place concrete elements and support the large curtain wall glazing that surrounds the building. Due to its exceptional strength, the UHPC made it possible to create thin, sinuous mullions up to 5 m (16 ft) tall, allowing unobstructed views over the museum’s veranda while meeting the area’s hurricane resistance standards and offering increased resistance to corrosion from the sea air.

Conclusion
Although the frequency of natural disasters has not increased in the last 40 years, their safety risks and economic costs are rising dramatically due to increased urbanization and population concentration along the coasts and flood-prone areas. More than 50 percent of the U.S. population and $10.64 trillion 
of insured property is located in areas vulnerable to hurricane destruction, and nearly 134 million people will be living in hurricane-prone states by 2020.

It is clear stronger, safer concrete buildings will play an important role in protecting these growing communities from the humanitarian and economic costs of major natural disasters. In addition to satisfying minimum life safety provisions, enhancing the resilience of buildings through mandatory requirements should be a priority for every jurisdiction, especially communities in disaster-prone communities.

Relevant ASTM Standards
• 
ASTM C989, Standard Specification for Ground Granulated Blast-Furnace Slag for Use in Concrete and Mortars;
• 
ASTM C618, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete;
• 
ASTM C1240, Standard Specification for Silica Fume Used 
in Cementitious Mixtures;
• 
ASTM C150, Standard Specification for Portland Cement;
• 
ASTM C595, Standard Specification for Blended Hydraulic Cements; and
• 
ASTM C1157, Standard Performance Specification for Hydraulic Cement.

Andrew Pinneke, PE, LEED AP, is a construction specialist at Lafarge, consulting on a wide range of sustainable construction and building performance issues while coordinating sustainable construction and concrete technology transfer efforts. He worked as a structural engineer for almost a decade before joining Lafarge. He sits on the National Ready Mixed Concrete Association (NRMCA) Sustainability Committee, and several American Concrete Institute (ACI) committees, along with the ACI Foundation’s Strategic Development Council (SDC). Pinneke can be contacted via e-mail at andrew.pinneke@lafarge.com.

 

 

A Well-cast Stone (in Concrete)

slaton patterson FAILURES
Deborah Slaton, and David S. Patterson, AIA

Cast stone is a highly refined architectural precast concrete manufactured to resemble natural building stone. Its popularity was related to the rapid development of the portland cement and concrete industries in the late 19th century, with numerous patents taken out for a range of related products.

Employed as a cost-effective alternative to building stone for architectural ornaments or wall claddings, the material is fabricated with various mixes to resemble different natural stone types. Similar to precast, it is subject to failures including surface erosion (i.e. weathering of paste and aggregate), crazing (i.e. fine hairline cracking), cracking, and delamination.

Deterioration may result from corrosion of embedded metals, as well as cyclic freezing and thawing. Issues during fabrication may include improperly graded aggregate (resulting in an overly porous material vulnerable to deterioration) or poor compaction, consolidation, or curing, which can lead to delamination and other distress.

The cast stone cornice on this 1920s building is severely deteriorated due to water infiltration through open joints and cracks, and corrosion of steel reinforcement. The dark gray area is a failed cementitious patch. Photos courtesy Kenneth M. Itle

The cast stone cornice on this 1920s building is severely deteriorated due to water infiltration through open joints and cracks, and corrosion of steel reinforcement. The dark gray area is a failed cementitious patch. Photos courtesy Kenneth M. Itle

Corrosion of embedded, unprotected steel can lead to cracking and delamination. Ferrous staining may indicate presence of corroding metal within or behind the cast stone units. Where steel reinforcement and anchorage components are located too close to the cast stone surface, spalling of the adjacent cast stone can occur. Less common problems include:

  • deterioration of specific components of the cast stone (e.g. aggregate, cement);
  • reaction between components (e.g. alkali-silica reaction);
  • fading or deterioration of pigmented facing layers; and
  • failures due to improper mix proportions or use of inappropriate admixtures.

Repair procedures for cast stone should follow methods and techniques for precast concrete. Corroding embedded metals should be exposed, cleaned, and coated, or removed and replaced. New reinforcement or anchorage should be stainless steel, if possible. Patching materials must be compatible with the original mix—compositional analysis of samples of the existing cast stone and preparation of trial repairs are required to achieve an aesthetic match.

This cast stone coping on a 1990s building exhibits significant cracking attributed to water infiltration, corrosion of embedded steel, and cyclic freezing and thawing.

This cast stone coping on a 1990s building exhibits significant cracking attributed to water infiltration, corrosion of embedded steel, and cyclic freezing and thawing.

A delaminated facing layer can sometimes be repaired by through-face pinning with fine diameter stainless steel anchors. Cleaning procedures for cast stone should use the gentlest approach possible. After repair or cleaning, clear penetrating sealers may be appropriate to reduce moisture infiltration in cast stone.

Severely deteriorated units cannot be repaired. In these cases, research and analysis of the original cast stone can help develop an appropriate mix to match color and texture for the replacement unit. As with concrete, the durability of new cast stone can be enhanced by using air entrainment; quality control during fabrication is essential.

The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of the CSI or The Construction Specifier.

Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates, Inc. (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com.
David S. Patterson, AIA, is an architect and senior principal with WJE’s Princeton, New Jersey, office, specializing in investigation and repair of the building envelope. He can be e-mailed at dpatterson@wje.com.

Specifiers cautioned in use of adhesive anchors

by Gary Higbee, CSI, AIA

Contractors in Arizona participate in an American Concrete Institute-Concrete Reinforcing Steel Institute (ACI-CRSI) adhesive anchor installer certification program. Photo courtesy ACI Arizona Chapter

Contractors in Arizona participate in an American Concrete Institute-Concrete Reinforcing Steel Institute (ACI-CRSI) adhesive anchor installer certification program. Photo courtesy ACI Arizona Chapter

Designing proper construction details is an important part of architecture and engineering practice that involves more than just a grasp of building technology. If designers are not also alert to market conditions, then their details—no matter how elegant—can be ineffective and hinder the pace of a project. Overlooking the complications surrounding the specification of adhesive anchors is a prime example, as recent code changes regarding their use threaten to stall building projects in some of the United States’ largest jurisdictions.

The complications stem from the International Building Code (IBC) referencing a provision in American Concrete Institute (ACI) 318-2011, Building Code Requirements for Structural Concrete, requiring workers installing adhesive anchors in certain orientations to have ACI certification. In big construction markets poised to enact the provision, such as New York City, contractors are finding a lack of opportunities for their installers to become certified places them in an impossible position. They cannot use adhesive anchors on jobs unless their installers are certified, and if they install without certification, they risk a violation or stop work order.

How did this problem arise? It seems the only path to certification is by completing ACI/Concrete Reinforcing Steel Institute (CRSI) Adhesive Anchor Installation Certification Program—a two-day course costing from $500 to $900 per person and requiring success in both written and skills tests.

The hurdle is ACI restricts the training and testing to entities it designates. Typically, these are ACI chapters, which, in the larger construction markets are ill-equipped to handle the volume of requests. In New York City, the group tapped to provide this training (one of only three sponsoring groups throughout the state) is only able to certify 15 to 20 installers each month.

With many building trades installing adhesive anchors, this will only produce a small percentage of certified installers needed in the city for projects getting underway in 2015. Solutions such as sending installers to programs out of the city for certification are unlikely to make a dent in the need and only add to the training’s cost. Since ACI developed the certification requirement in response to the anchor failures that caused the collapse of several ceiling panels in the Boston Tunnel of Big Dig infamy, it is surprising this deficiency has not received more attention.

Impact on the industry
The bottleneck resulting from this shortage of training opportunities has the potential to interrupt construction schedules citywide. In correspondence with Louis J. Coletti, president/CEO of the Building Trades Employers Association (BTEA), the author was warned “at least 40,000 tradespersons must be certified by the effective date of the new code if we are to avoid stalling major public and private projects in the city.”

For specifiers, steering clear of adhesive anchors in favor of other types is a way to elude this glitch. However, in some applications, these products may be the preferred, or only acceptable, anchorage method because of the superior holding power in cracked or damaged concrete. Thus, it is important to clarify not all adhesive anchor installations require the installer to be certified. Only when anchors are installed in a horizontal or overhead orientation and under a sustained tension load is the ACI requirement applicable.

Due to the history of failures in these orientations, ACI requires special inspection. This adds to both the project team’s responsibilities and expenses. The architect and engineer must identify on plans filed with a building department those adhesive anchors for which special inspection is required. Subsequently, the owner must engage an independent testing laboratory to perform the inspections, which ACI 318-11 requires to be continuous—meaning no drilling and installing of adhesive anchors should occur unless an inspector is observing the installers’ procedures.

The special inspector must furnish a report to the engineer of record and to the building official affirming whether the installation procedures and materials covered by the report conform to the approved contract documents and the manufacturer’s printed installation instructions. However, before any installation is performed—and this is critical—the inspector must verify the installer’s certification. This circles back to the original problem: limited opportunities for installers to get certified.

While the designers and owners incur added costs and responsibilities, only the contractors are accountable for maintaining certified personnel to perform the installations. If construction activity is to move forward without expensive delays, these contractors must be able to find certified installers.

Until alternatives—such as moratoriums on enforcement, and permitting other qualified entities to conduct the certification training—are in place to address this looming problem, designers should be alert to the potential for added costs and delay when specifying adhesive anchors for installations requiring special inspection.

GaryHigbeeAIAGary Higbee, CSI, AIA, is the director of industry development for the Steel Institute of New York (SINY) and the Ornamental Metal Institute of New York (OMINY). Formerly the assistant director for technical services with New York State’s Building Codes Division and in architectural practice for three decades, he served in various capacities throughout this period on NYS, HUD, and ICC code drafting and development committees. Higbee is a member of the American Institute of Architects (AIA), American Institute of Steel Construction (AISC), American Society of Civil Engineers (ASCE), along with other national associations. He can be reached at higbee@siny.org.

Innovation with Insulating Concrete Forms

Photo courtesy Nudura Insulated Concrete Forms Ltd.

Photo courtesy Nudura Insulated Concrete Forms Ltd.

by Andy Lennox

In the construction industry, ‘innovation’ can be viewed as speed or efficiency of construction, increased durability, sustainable, new materials, systems, or processes. While innovation can also translate into safety and other aspects, it is generally spurred by economic benefit—for example, the speed of construction is a major driver, as its achievement offers cost advantages from labor, financing, and occupancy perspectives. Such is the case with insulating concrete forms (ICFs).

The ICF technology has been in the North American market for almost a half-century. It has recently made great strides over the past 25 years in the residential realm as market forces—such as lumber’s fluctuating price—have put the industry in the position of looking for other material solutions. However, over the last decade, there has been a move to use ICFs in commercial and high-rise residential applications. ASTM E2634, Standard Specification for Flat Wall Insulating Concrete Systems, describes the requirements for the manufacture of units for walls with uniform cross-sections. The respective concrete standard is American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete.

ICFs are a permanent formwork system for reinforced concrete construction. The interlocking modular units are dry-stacked into position and filled with concrete. They can be used for almost any concrete wall—interior or exterior, below-grade or above-grade, short or tall. The concept can be seen as the marriage of two proven technologies: concrete mass sandwiched between two layers of expanded polystyrene (EPS) foam insulation.

A traditional exterior concrete wall contains six building components:

● concrete;
● reinforcement bar;
● insulation;
● air barrier;
● vapour barrier; and
● studs/strapping.

ICFs combine these six components into a single building system installed by one crew at the same time. The thermal mass effect of the concrete enhances the insulation’s energy efficiency and the forming system’s airtightness, creating an opportunity for owner/developers to realize savings through the operation of the building.

ICFs can also minimize drywalling and electrical work onsite, but care must be taken with the placing of concrete in any form. Vibration is the key to proper consolidation, specifically around windows and doors. Specially designed door and window bucks are used for ICF systems—some are proprietary and some are site-manufactured.

With innovation, there sometimes are unexpected discoveries with the use of new technology in an application. For example, innovative contractors who used the ICF system in a non-residential application found there were significant constructability advantages with the speed of construction in addition to the high-performance attributes of the ICF wall. In Canada, one Ontario builder saw a significant uptake for the construction of high-rise residential student residences. The speed of construction recognized by the owner/developers provided them with completion dates that not only saved them money, but also achieved the early occupancy they required.

This article highlights growing use of ICFs in four sectors in North America—hotels, mid-rise, schools, and tall walls—to show how the building technology significantly enhanced the speed of construction.

This insulating concrete form (ICF) tall wall bracing mechanically fastens to the concrete core in the wall and provides 2.1-m (7-ft) work and wind bays every 10.7 m (35 ft). Photo courtesy Logix Insulated Concrete Ltd.

This insulating concrete form (ICF) tall wall bracing mechanically fastens to the concrete core in the wall and provides 2.1-m (7-ft) work and wind bays every 10.7 m (35 ft). Photo courtesy Logix Insulated Concrete Ltd.

Building hotels with ICFs can allow construction to advance at a rate of one fl oor per week. Photo courtesy Nudura

Building hotels with ICFs can allow construction to advance at a rate of one floor per week. Photo courtesy Nudura

 

 

 

 

 

 

 

 

Hotels on the horizon
Hotel builders are seeing the benefits ICF construction can offer in various areas. The faster a hotel can open, the sooner its owners start generating revenue. With insulating concrete formwork, construction typically progresses much faster than traditional concrete masonry unit (CMU) block construction—this factors in ICFs being insulation, forming, and attachment surfaces all in one, whereas the block is but one component. In other words, ICFs combine formwork, structure, interior and exterior strapping, and air and vapor barriers, resulting in more efficient construction with less sub-trade congestion onsite. On average, installers are able to complete a floor a week, depending on the project size. The various manufacturers provide specialized training for the application of their proprietary system.

Another contributing factor to getting the hotels open sooner is the ability to build in differing climates. Weather can play a key role in any construction project; winter can often halt a job entirely. The versatility with ICFs offers builders the advantage of building year-round. This is because the curing process offered by the forms means concrete can be poured on the coldest days. The EPS foam containing the concrete actually serves to store the natural heat produced inside the concrete core during the hydration or curing process. Studies have proven concrete installed in this condition can be placed and maintained at temperatures as low as −20 C (−10 F), even sustained for as long as three days.1 In such conditions, the process of hydration has been proven to increase to levels as high as 27 C (80 F) within the formwork, based on a concrete core of 160 mm [6 ¼ in.] thick.

National model energy codes, such as the International Energy Conservation Code (IECC), are advancing the way in which commercial and residential exterior wall construction is approached by emphasizing the use of continuous insulation (ci) systems. As the name suggests, these assemblies provide a continuous insulation layer over an entire wall, rather than just in the wall cavities. With other traditional building systems on the market, this ci layer has to be applied, but it is an integral part of ICFs.

In addition to energy performance benefits, ICFs are non-combustible and can offer fire protection ratings of up to four hours. As an added advantage for hotels, the assemblies also provide greater sound attenuation, offering sound transmission class (STC) ratings of up to 55—the material provides a further break than traditional concrete, thanks to the addition of the insulation changing the material density. EPS, the key component of ICF products, is also resistant to mold growth, lowering long-term maintenance costs for owners compared to wood-frame hotel construction.

For this ICF-intensive condominium project, the normal percentage of insulating concrete forms was doubled by incorporating the assemblies for not only walls, but also suspended fl oors and roofs. Photos courtesy Quad-Lock Insulated Concrete Forms Ltd.

For this ICF-intensive condominium project, the normal percentage of insulating concrete forms was doubled by incorporating the assemblies for not only  walls, but also suspended floors and roofs. Photos courtesy Quad-Lock Insulated Concrete Forms Ltd.

Complex reinforcing requirements presented installation challenges overcome by an ICF design offering separate panels and ties that fi t around the rebar.

Complex reinforcing requirements presented installation challenges overcome by an ICF design offering separate panels and ties that fit around the rebar.

 

 

 

 

 

 

 

 

 

 

 

Mid-rise revolution
One great success story in mid-rise ICF construction is the La Concha Pearl condominium project in La Paz, Mexico. ICF installation on this seven-story, 33-unit luxury beachfront development took place over an eight-month period, putting the building into service far ahead of the expected norm in the region. The sales team reported the reduction in the ‘pre-construction’ sales phase, where potential customers had no real building to see, was a huge benefit in persuading would-be residents to buy. If this holds true for other projects, there may be more developers and owners actively requesting ICFs.

In this particular case, the developers, having already made a commitment to minimize the impact on the local community, undertook some re-design of the building to optimize it for ICF, minimizing wasted materials and time onsite. The design phase was also shortened because the ‘flat-wall’ ICF design meant the project engineer could confidently rely on known, published design parameters for poured-in-place concrete structures via American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete. Though a departure from the more common masonry block building found in the region, the project engineer and local building officials were well within their comfort zone, meeting no unfamiliar challenges posed by ICFs.

The general contractor, despite starting with only a few experienced ICF hands, was able to offer great training and oversight. His efforts resulted in a doubling of average production over the course of the 240-day installation, cutting the average time-per-floor in half. Crews quickly and eagerly accepted the new technology, taking great pride in learning a new craft.

The La Concha Pearl project is ICF-intensive—the assemblies were employed for both walls and floors, more than doubling the usual amount of concrete forms found on the typical project. Only 43 per cent of the total ICF area was a wall system; the majority was used for the floors.

The general contractor reported that, once shoring was in place, his crew would lay an entire 557-m2 (6000-sf) floor in about three hours, using the ICF T-beam floor forms. Since ICF floor forms replace about half of conventional suspended floor forms, post-pour removal of only primary shoring frames and beams was easily and quickly completed. Resumption of construction on the succeeding upper floors was never delayed, as each floor was fitted with a minimal amount of re-shoring (temporary posts) to carry construction loads through to the ground-floor level.

As an additional note, the La Concha project is situated in an extreme seismic zone. This led the project engineer to an extreme reinforcing bar specification. On lower floors, a double mat of steel, pre-tied into place, was specified. The knock-down design of the ICF wall system allowed the crews to fit ICF components through the pre-tied rebar mats, row by row, without disturbing pre-positioned reinforcing.

Crews often quickly adapt to ICF technology, increasing their production rates as the project progresses.

Crews often quickly adapt to ICF technology, increasing their production rates as the project progresses.

The speed of construction offered with ICFs can mean early completion dates for owners and fi nancial benefi ts. Photos courtesy Logix Insulated Concrete Forms Ltd.

The speed of construction offered with ICFs can mean
early completion dates for owners and financial benefits.
Photos courtesy Logix Insulated Concrete Forms Ltd.

 

 

 

 

 

 

 

 

School sounds
In Pincher Creek, Alberta, a 930-m2 (10,000-sf) private school was built utilizing ICFs. The school board and designers decided on this route for a faster build as well as improved energy, long-term resiliency, and sound efficiency. The contractor was pleased, noted the recorded time spent building with ICF was about half the time of that of a typical wood build, while providing the best in insulation and sound barrier—this latter criterion was especially important given the often-powerful, noisy southern Alberta winds.

The ICF walls included the standard 1.2-m (4-ft) frost wall and 2.7-m (9-ft) walls, with 3.7-m (12-ft) walls for the gymnasium. No other form of insulation or vapour barrier was required by using the forms. The gymnasium walls provided an especially strong barrier for sporting activities with no need for plywood, which would have otherwise been required behind the gypsum in wood builds. The solidness and strength of rebar-reinforced ICF blocks was a definite factor in the choice to employ this construction methodology.

During construction and concrete pouring, use of ICF bracing made it easy to straighten walls while providing solid, safe scaffolding for construction workers. The design of the block makes it a quick and efficient to attach the upright channels for bracing utilizing simple screws. Workers have a safe platform to work from, with a built-in hand rail and no need for tie-offs that would normally be used with other construction scaffolds.

The school board was satisfied with the decision to choose ICFs in the construction of the school. In the few years since completion, there have been no complaints or issues. The fewer labor-hours in the building of the school continues to be a deciding factor for the contractor and architect as they have since used ICFs in other construction business and plans design.

Whether for retail or hospitality applications, completed ICF projects should yield sustainable, resilient, comfortable, and effi cient buildings.

Whether for retail or hospitality applications, completed ICF projects should yield sustainable, resilient, comfortable, and efficient buildings.

Photo courtesy Nudura Insulated Concrete Forms Ltd.

Photo courtesy Nudura Insulated Concrete Forms Ltd.

 

 

 

 

 

 

 

 

Greener education
Richardsville Elementary (Warren County, Kentucky) is the first net-zero ICF school in the United States. Designed by Sherman-Carter-Barnhart Architects and engineered by CMTA, this building was constructed to be a two-story, energy-efficient structure that incorporates renewable materials and insulated concrete forms for its superior building envelope.

Generating its own energy, the 6715-m2 (72,285-sf) Richardsville is the next generation of educational building standards, and a valuable tool to educate students on energy and water conservation as well as the value of recycling. The project is designed to use only 18 kBtu/sf annually—75 percent less than the nation average standard set out by American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings.

Richardville was a learned lesson from previous schools built with ICFs elsewhere in the Bluegrass State. During construction onsite, the Warren County School District experienced reduced time in construction schedules. With CMU-constructed schools, running electrical can add to the construction schedule. Tyically, conduit has to be placed and fished through the walls. ICF construction offered this project’s electrical contractors the ability for quick installation times and having the wiring easily accessible on the face of the wall.

Tall walls
Retail chain Cabela’s is one the world’s foremost outfitters of hunting, fishing, and outdoor gear. Looking for energy efficiency and lower long-term operating costs, its architectural firm specified insulating concrete forms for the exterior walls of a new facility in Saskatoon, Saskatchewan. As the project progressed, it became evident ICFs not only delivered high-performance tall walls, but also a faster build.

This Cabela’s store measures about 64 x 64 m (210 x 210 ft) with the exterior tall walls ranging from 8.8 to 9.5 m (29 to 31 ft) in height. The wall’s assembly included six construction steps:

● concrete core;
● steel reinforcement;
● exterior and interior insulation;
● air barrier;
● vapor barrier; and
● stud work/furring strips.

According to 2014 RS Means data, if these walls were built with CMUs and finished to the same degree, the expected labor rate to build a comparable wall assembly would be 0.217 man-hours per square foot. On this particular job, however, the ICF installation crew recorded a labor rate of 0.109 labor hours per square foot. This suggests the walls were completed using half the labor that would have been traditionally required.

Several factors contributed to this speed. For example, the exterior tall walls were designed for maximum efficiency. The 203-mm (8-in.) concrete core provided sufficient room for rebar placement and concrete consolidation. The horizontal rebar was specified at 406 mm (16 in.) on center (oc) to be consistent with the course height of the ICF system.

By specifying the vertical rebar at 20m at 406 mm oc (versus, say, 10m at 203 mm oc), less bar had to be handled and placed, resulting in lower labor costs and easier and quicker concrete consolidation. Further, the designers were mindful of the ICF block dimensions in order to minimize the time spent cutting the blocks to make them fit.

Unassembled (i.e. knockdown) ICF blocks were assembled around the pre-built rebar cages used in the pilasters every 6 m (20 ft) of tall wall. This was much faster than the alternative method of building the rebar cages around the in-situ ICFs. Rugged rebar chairs built into the webs enabled the 6-m lengths of horizontal rebar to be quickly ‘snapped into place’ by a single crew member. Additionally, slide-in end caps quickly terminated wall sections and created vertical seams for expansion control.

Contact lap splices were used in the corners to allow concrete to easily flow through the corner forms. Use of running bonding (as opposed to stack bonding) was also maximized to reduce the installation and removal of temporary form support on both sides of the tall walls. Protecting the interlock during the concrete pours also eliminated any potential delays during subsequent course placement.

Further, the tall-wall scaffolding bracing system (which can be used to brace ICF walls up to 38 m [125 ft] without additional engineering) had many additional time-saving features. For example, it quickly connected directly to the concrete core providing an improved safety factor (required by Occupational Safety and Health Administration [OSHA] standards) and the ability to quickly precision-plum the walls.

As the guardrail was attached, no tie-offs for the crew members were required. The scaffolding’s wind-bays, which also function as 2.1-m (7-ft) work-bays, were located every 10.1 m (35 ft)—this means material was easily available at high heights. With extra scaffolding onsite, sections could be erected while others were being taken down.

Conclusion
Insulating concrete form applications are only limited by the designers. Some applications may require small redesigns to handle the structural loads, but many of these formwork systems have specially designed blocks or sections to deal with any unusual details. Technological advances are also allowing the creation of larger units, which will speed up construction even more.

The recent formation of the Council of ICF Industries (CICFI) is also expected to yield additional resources for building owners and project team members interested in exploring the suitability of this material. The group represents itself as the voice of the North American ICF manufacturing industry, and will serve as the information source for all information about the forms.

Notes
1 For more, see the report, “Cold Weather Construction of ICF Walls” by John Gadja (Portland Cement Association [PCA], 2002). (back to top)

Andy Lennox is a vice president of Logix Insulated Concrete Forms Ltd. He has worked in the ICF industry for 17 years in various sales, marketing, and management capacities. Lennox is the inaugural chair of the Council of ICF Industries (CICFI). He can be contacted by e-mail at andy@logixicf.com.

Association Cooperation

In the October issue of The Construction Specifier, authors Ward R. Malisch, PhD, PE, and Bruce A. Suprenant, PhD, PE (both of the American Society of Concrete Contractors [ASCC]) wrote our cover story, “Bridging the Specification Gap between Divisions 03 and 09: Concrete and Floorcovering Associations Unite.” The piece looked at how their association teamed up with six other flooring groups to find a solution to a ‘specification gap’ between Divisions 03 and 09 in terms of floor surface flatness requirements.

For space reasons, we had to hold off including a little more background on how these associations collaborated. That ‘missing’ information follows, in the words of Malisch and Suprenant:

The impetus for developing the American Society of Concrete Contractors (ASCC) Position Statements came from a group of contractor members who became aware of a paper published by a national wood flooring organization—not, it should be noted, the National Wood Flooring Association (NWFA)—that stated the organization did not believe in F-numbers and felt they should not be used to measure slabs for gym floors. Rather than trying to decide how they could build a floor that meets unreasonable requirements, ASCC contractors realized they needed to spend their time and resources to educate the industry on the limitations of concrete floors. Thus was born this series, including ASCC Position Statement 6, Division 3 versus Division 9 Floor Flatness Tolerances.

Then, rather than continuing to fight their fellow contractors in the floorcovering industry, ASCC made an effort to get them on board, realizing the greater strength of a united front. ASCC first approached NWFA. With only minor rewriting, that association was eager to endorse the Position Statement.

“For the first time, instead of disagreeing, the two sides have come together to find a common solution to a problem that has cost both groups hundreds of thousands of dollars in rework,” said NWFA president/CEO Michael Martin.

Shortly thereafter, ASCC invited the National Tile Contractors Association (NTCA) to participate in a panel discussion on this topic featuring contractors and technical personnel from both disciplines. Both sides acknowledged the wisdom of a bid allowance to compensate for the incompatibility of the measuring methods, and NTCA became the second flooring association to sign on.

Bart Bettiga, NTCA executive director, commented on the reasons for the document’s usefulness.

“It is our belief this position statement is one of the most important documents we have supported in the past several years,” he said. “This statement accomplishes its goals on many levels. It educates the construction professional about important considerations that must be taken when specifying floorcovering products over concrete substrates.”

“The most important point emphasized in this position statement centers on the disparity related to meeting industry standards in the respective divisions,” Bettiga continued. “Equally important is the call for communication between the related parties and for a proactive approach to be determined prior to the commencement of the work. We strongly support the use of this statement to our members in their communication to the general contractor and architect/specifier on their projects.”

These two organizations were followed by the Flooring Contractors Association. Then, last year, Scott Conwell, director of industry development and technical services for the International Masonry Institute (IMI) contacted the ASCC, asking to add the group’s name, along with those of the Tile Contractors Association of America (TCAA) and the International Union Of Bricklayers and Allied Craftsmen (BAC) to the list of supporters.

“This ASCC Position Statement succinctly brings to light the disparity in requirements for floor flatness between the concrete and the ceramic tile trades,” says Conwell. “The paper effectively brings expectations in line, leading to increased cooperation on the job site to make any corrections to the floor that may be necessary prior to installation of the tile finish.”

Two trades with distinctively different practices and obstacles to overcome but with one goal: to deliver a high-quality product to a satisfied owner.