Specifying blended cements for sustainable healthcare design

by Catherine Howlett | April 1, 2013 10:58 am

[1]

by Andrew Pinneke, PE, LEED AP

Hospitals, clinics, and other types of medical facilities are striving to create high-performance buildings more conducive to healing, while also reducing energy and water consumption to minimize their environmental footprint.

As the demand for sustainable design and building practices grows, concrete and cementitious-based building materials are making a strong contribution to the construction of new healthcare facilities. Concrete and blended cements can be used to achieve credits under the U.S. Green Building Council (USGBC) Leadership in Energy and Environmental Design (LEED) program in uses ranging from stormwater management to the improvement of indoor air quality (IAQ). They do so while also offering possibilities for versatile design innovations using shape, color, and texture.

With the longest life span of any building material, concrete has all the advantages to respond to the challenges of sustainable healthcare construction. A mixture of natural substances, concrete is locally produced, entirely recyclable, durable, and fire-resistant. It also provides good thermal mass properties and acoustic insulation qualities.

Concrete’s thermal inertia properties enable it to absorb heat during the day, store it, and give it back at night—this makes for substantial heating and air-conditioning savings. As it is a highly resistant and airtight material, concrete can easily be used with other materials to provide optimal insulation, while offering numerous solutions for limiting greenhouse gas (GHG) emissions resulting from the building’s daily use. In high-risk areas, concrete’s resistance properties enable the design of buildings demonstrating superior resiliency performance during natural disasters.

Blended cements (i.e. those under ASTM C595, Standard Specification for Blended Hydraulic Cements, or ASTM C1157, Standard Performance Specification for Hydraulic Cement) contain supplementary cementitious materials (SCMs) as a partial replacement for portland cement. This enhances the material’s strength and versatility. The three most commonly employed SCMs are:

• slag—a reclaimed by-product of the iron- and steel-making process;
• fly ash—a coal-combustion by-product of power plants; and
• silica fume—a by-product of silica metals and ferrosilicon alloys.

[2]

Since they are recycled industrial materials, SCMs enable reuse of by-products that would otherwise be landfilled. Moreover, their use reduces the volume of portland cement required to make concrete, decreasing the amount of energy associated with cement production, lowering GHG emissions, and reducing the virgin material required for making concrete.

How concrete contributes to LEED
Sustainable construction aims to identify building materials and methods that are cleaner and more environmentally responsible while ensuring the highest quality in terms of aesthetics, durability, and strength.

There are several resources to help design professionals tackle sustainability initiatives in the healthcare industry. Though not a rating system, the first guide to enhancing healthcare facilities was the Green Guide for Healthcare (GGHC). Introduced in 2011, the most widely adopted green building rating system in the United States is the LEED for Healthcare (LEED-HC) rating system, which provides sustainable construction standards for inpatient and outpatient facilities and licensed long-term care facilities. The rating system may also be used for medical offices, assisted living facilities, and medical education and research centers.

[3]

In comparison to LEED for New Construction (LEED-NC), LEED for Healthcare modifies existing credits and features new, healthcare-specific ones. In all, six prerequisites and 25 credits were modified, and three prerequisites and 15 credits were added to the rating system. The minimum program requirements for LEED-NC also apply to LEED-HC projects. For structural elements and pavements, concrete containing SCMs contributes to LEED credits in several categories. (Figure 1, lists the specific names.)

Following the official launch of LEED-HC, projects meeting certain criteria (i.e. hospitals, long-term care facilities, and other buildings serving individuals seeking medical treatment) must use the healthcare program rather than LEED-NC. Buildings with other medically related uses, such as medical education and research centers, may use LEED-HC at the project team’s discretion.

Sustainable Sites (SS)
In this category, concrete and blended cements using SCMs contribute to points gained by:

• in-situ soil stabilization with soil cements in brownfield redevelopment;
• reduced footprints and limited site disturbance with above and below ground multi-story concrete structures;
• pervious concrete and permeable grids for stormwater management; and
• lighter-colored, high-albedo concrete pavements in landscape and exterior systems or roof systems with concrete tiles that reduce the urban heat island effect.

Energy and Atmosphere (EA)
Buildings constructed using concrete possess thermal mass, which helps moderate indoor temperature extremes and reduce peak heating and cooling loads. This improves energy performance in structures.

Light-colored concrete materials can be produced using SCMs to reduce lighting energy costs. Reflective surfaces help reduce the amount of fixtures and lighting required. Additional benefits with concrete envelope systems include:

• thermal mass and acoustical properties;
• pest resistance; and
• increased resistance to natural disasters, including earthquakes, hurricanes, floods, and fire.

Materials and Resources (MR)
SCMs can extend a structure’s useful service life because they improve concrete durability. Well-constructed concrete walls, floors, and roofing elements containing these supplementary materials can be left in place when the building is refurbished, its interior renovated, or its function changed. The purpose of the reuse credit is to extend the life of the existing building stock, conserving resources and reducing waste and the environmental impact of new construction.

Concrete-producers recycle returned concrete, aggregate, and wash water during the construction process, which can contribute to construction waste management credits. Additionally, crushing and recycling of concrete waste materials into clean fill or road base applications diverts usable resources from landfills.

Recycled content credits are easily obtained with blended cements and SCM use in concrete. Concretes containing multiple SCMs can contribute to more LEED credits because the percentage of virgin material replaced by recycled content determines points. Moreover, SCMs extend concrete service life through improved durability, further reducing impact on landfills and lessening the economic burden of construction.

Cement manufacturers often replace fossil fuels with recycled materials; many also include post-industrial recycled content materials to replace conventional materials for manufacturing portland cement. This may contribute to achievement of this credit by reducing the demand for virgin materials, materials sent to landfills, and energy required in cement manufacture.

Indigenous resources used to manufacture cement and concrete, including SCMs, are usually obtained or regionally extracted within 800 km (500 mi) of the project site, reducing the environmental impact of transportation. Projects with large amounts of concrete can typically achieve both regional materials credits.

[4]

Indoor Environmental Quality (EQ)
Concrete building materials contain low to negligible levels of volatile organic compounds (VOCs) that degrade IAQ when they off-gas from new products, such as interior finishes, carpeting, and furniture. Additionally, VOCs combine with other chemicals in the air to form ground-level ozone. As concrete building materials serve as a structural and finish material in wall and floor applications, they reduce the need for applied finishes or flooring materials and contribute to a healthier indoor environment.

Concrete-based building envelopes offer significant long-term economic advantages and provide quieter, more comfortable, safer, and environmentally considerate structures. Unbroken exterior envelopes offer air and moisture barriers, preventing mold growth and providing fewer cold spots and drafts offering thermal comfort to occupants. Thermal mass affects temperature perceived by the occupants through radiance rather than air temperature.

Finally, concrete can help a structure admit more daylight deeper into a building that can be used to facilitate daylighting strategies. Higher strength concretes can minimize beam depths and maximize daylight and views through windows. An interior concrete core can be designed to accommodate higher structural loads and shear forces, allowing fewer obstructions along the building perimeter. Post-tensioning can be used to obtain longer spans, minimizing the number of columns obstructing views.

Innovation and Design (ID)
Concrete building materials containing SCMs provide incentives going beyond LEED requirements and create innovative strategies not specifically addressed in the rating system. Several potential credits have been identified that relate to exemplary performance of concrete building materials containing SCMs. Three examples are:

• decreased lifecycle environmental impact, due to concrete’s low embodied energy and long life, durability, and low maintenance needs;
• IAQ improvements thanks to eliminating the need to paint or adhere finishes by choosing either architectural or prefaced concrete building systems;
• high percentage of SCM use in comparison to the usual modest percentages of fly ash, slag cement, or silica fume.

[5]

Fly ash and LEED milestones
The $53-million Boulder Community Foothills Hospital (Colorado) was the first hospital in the U.S. to receive LEED-NC. With a LEED Silver rating, the 18,580-m² (200,000-sf) facility contains many sustainable features, including a concrete mix incorporating 25 percent fly ash to improve durability, enhance performance, and obtain LEED points for recycled content. The cast-in-place concrete structural system used for the hospital building frame and floor systems was selected based on functionality and environmental impact considerations.

Concrete strengths included:

• 20,684-kPa (3000-psi) foundations;
• 27,579-kPa (4000-psi) columns;
• 34,474-kPa (5000-psi) floor slabs; and
• 41,369-kPa (6000-psi) concrete core and shear walls.

The use of locally produced concrete eliminated the environmental impacts of transporting it from other regions and helped the design team achieve its performance, cost, and sustainability goals. The project obtained a total of 33 LEED points, including five points for a 35 percent improvement in energy performance over American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings.

The first hospital to receive LEED Platinum, Dell Children’s Medical Center of Central Texas, also relied on fly ash to achieve its performance and sustainability goals. As part of its LEED effort, the project team made the most of the $200-million facility’s location on a brownfield site originally part of a former airport in Austin, Texas. Approximately 47,000 tons of runway materials were reused onsite, and the building’s concrete mix incorporated 40 percent fly ash in the 31,347 m³ (41,000 cy) used for the foundation and walls. During construction, 92 percent (more than 32,000 tons) of waste was recycled. Additionally, local building materials were used on the structure’s exterior.

On the same brownfield site is the adjacent Ronald McDonald House of Austin, which provides nurturing programs and a supportive home-like environment for families while children receive treatment in local medical centers. Sustainable design elements that qualified the 2648-m² (28,500-sf) facility for LEED Platinum included:

• building products selected for their contribution to a healthy indoor environment;
• construction materials procured within an 800-km (500-mi) radius of the site; and
• use of concrete containing fly ash for structural components.

Ternary blends: the right prescription for Gundersen Lutheran and Mayo ClinicOne of the largest healthcare construction projects in Wisconsin, Gundersen Lutheran Health System’s campus renewal initiative in La Crosse includes a new six-floor hospital designed to meet LEED-HC standards. Many of the project’s construction materials are being produced locally, including the concrete supplied by La Crosse-based River City Ready Mix.

Work on the 37,161-m² (400,000-sf) hospital began in January 2011 and is scheduled to be completed late this year. The 15,290 m³ (20,000 cy) of concrete placed for the slab, walls, and other structural applications relied on a ternary mix design of 20 percent slag cement, 15 percent fly ash, and 65 percent portland Type I/II. This enabled the material to achieve specified strengths of 31,026 kPa (4500 psi) at 28 days.

About 120 km (75 mi) from La Crosse, the Mayo Clinic is building a 10,220-m² (110,000-sf), $188-million proton beam therapy center in Rochester, Minnesota. The specialized cancer treatment center’s design includes 14,847 m³ (19,419 cy) of concrete containing a ternary mix of 33 percent Type I/II portland cement, 33 percent fly ash, and 33 percent slag cement to achieve a low heat of hydration and 28- and 56-day strengths exceeding 62,053 kPa (9000 psi) for the multiple mass concrete placements.

In March 2012, crews from Rochester-based Ready Mix Concrete placed 1246 m³ (1630 cy) of concrete for more than eight hours to complete a base slab 20 m wide by 57 m long by 1.1 m deep (66 by 187 by 3 ½ ft). Two months later, this was followed by the ‘big pour’—the largest in the history of Rochester—that involved more than 500 truckloads of concrete. Over the course of 28 hours, three pumps were used to place 4205 m³ (5500 cy) of concrete for the mass concrete foundation walls, the thickest of which measured 6.6 m wide by 4.3 m high (21 ft, 9 in. by 14 ft). The first treatment rooms are expected to be open in the summer of 2015.

[6]

Green medical facilities going beyond hospital walls
While healthcare organizations are demanding sustainable design and construction as a matter of course, green building is no longer limited strictly to hospital projects. Sustainable building materials and design options with low carbon footprints are being prioritized to minimize environmental impacts and safety concerns, as well as achieve operational and wellness goals, throughout the medical campus, including parking facilities, ramps and sidewalks, healing gardens, and other specialized applications.

On Gundersen Lutherans’ campus, a new three-level underground parking ramp was designed with many green qualities, including concrete containing a silica fume-portland cement blend to achieve a life expectancy of 100 years. Park Nicollet Methodist Hospital in Minneapolis also relied on a silica fume-portland cement blend for the concrete in the post-tensioned decks of  its 55,742-m² (600,000-sf) parking garage, as well as for loading docks and sidewalks to ensure a durable surface that can withstand snowplows and harsh de-icing chemicals.

Slag cement is also increasingly being specified in sustainable parking structures, such as the transit center serving Tuality Hospital and Pacific University’s Health Services campus in Hillsboro, Oregon. More than 4205 m³ (5500 cy) of concrete containing slag cement were used in the columns around the perimeter, the post-tensioned cast-in-place concrete beams, and post-tensioned concrete elevated decks in the parking facility.

[7]

Almost half of the concrete placed contained at least 40 percent slag cement, qualifying it for an ID point under LEED-NC. The average slag content was 19 percent of all cementitious materials used in the concrete, but cement with as much as 93 percent slag cement content was used for some mixes. Another sustainable benefit of using slag cement in this project is the resulting lighter-colored, high-performance concrete mix absorbs less heat from solar radiation and helps to lower the heat island effect. The pervious concrete used also stores less heat due to its relatively open pore structure.

Recognizing the unparalleled growth driven by construction of its Heart and Vascular Institute, the Cleveland Clinic built the largest and most sophisticated healthcare material-handling and order fulfillment system in the United States. With a concrete superstructure of more than 139,355 m² (1.5 million sf), the East 89^th Street Garage and Service Center stands as one of the largest concrete structures in Cleveland. Its construction used almost 76,455 m³ (100,000 cy) of concrete with a mix containing 20 percent fly ash.

To create the slab for the structure’s 96 by 168-m (315 by 550-ft) footprint, the first stage involved 415 truckloads of concrete and four pump trucks, with crews from Donley’s placing more than 3058 m³ (4000 cy) of concrete, covering 3066 m² (33,000 sf). This was followed by three more large placements—totaling 8180 m³ (10,700 cy) of concrete—to complete the slab over the entire building area. Most of the building products used in the $192-million LEED Silver facility came from sources within 80 km (50 mi) of the site.

The concrete used for deep foundation and structural support elements, as well as the heavy concrete used for radiation bunkers and X-ray rooms, also typically include high levels of SCMs. A 34,474-kPa (5000-psi) self-consolidating concrete (SCC) containing slag cement and fly ash was used in the auger cast piles for the parking garage at the new Science + Technology Park at Johns Hopkins in Baltimore. At Holy Cross Hospital, one of the largest hospitals in Maryland, a proprietary flow mix containing about 75 percent fly ash is being used in sheeting and shoring applications to support a major campus expansion program.

Conclusion
The healthcare industry is making great strides in implementing sustainable design and construction practices for creating healing environments as healthy as possible, and green building certification has proven to be the best method possible to achieve this goal. Concrete and cementitious-based building materials offer extensive sustainable construction benefits and can help achieve LEED for Healthcare certification in many ways.

While the proper use of blended cements and supplementary cementitious materials can be more complex, the results achieved can provide higher-performance and more environmentally-friendly concrete mixtures. Various organizations, including the American Concrete Institute (ACI) and the Slag Cement Association (SCA), offer recommendations design professionals can consult on how to specify such substitutions. Additionally, manufacturers can provide technical assistance to help develop or modify specifications; most can provide detailed test results, and additional support.

Case Study: Slag Cement for Moses H. Cone

[8]

Slag cement is playing a key role in the construction of the new $200-million, six-story North Tower at the Moses H. Cone Memorial Hospital (Greensboro, North Carolina). The largest construction project in the hospital’s 58-year history, the tower takes advantage of natural light and passive energy, features noise-reducing design, relies on locally sourced building materials, and uses less energy and natural resources in its construction and operation.

The approximately 6700-m² (263,713-sf) expansion specified 40 percent cementitious replacement to target credits under the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design for Healthcare (LEED-HC) program. The project, targeting LEED Silver, uses a portland-slag cement blend to achieve greater strength potential and long-term durability. By successfully combining these cements, the hospital is aiming to reduce its building’s carbon footprint. Completion is expected for June.

Andrew Pinneke, PE, LEED AP, is a construction and building system specialist at Lafarge. He serves as a consultant on a wide range of sustainable construction issues and coordinates the company’s sustainable construction efforts throughout the United States. Pinneke previously worked as a structural engineer for almost a decade. He sits on the National Ready Mixed Concrete Association (NRMCA) Sustainability Committee, the American Concrete Institute (ACI) Building Information Modeling Committee 131, and the ACI Foundation’s Strategic Development Council (SDC), as well as participates in the American Society of Civil Engineers (ASCE) and the U.S. Green Building Council (USGBC) local and national chapters. Pinneke can be contacted via e-mail at andrew.pinneke@lafarge-na.com.

Source URL: https://www.constructionspecifier.com/specifying-blended-cements-for-sustainable-healthcare-design/

---