Achieving Sustainability with Precast concrete Upload_372.pdf

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42 PCIJOURNAL

Achevg Ssaal whPrecas Ccree

Sustainability is oten defned as development thatmeets the needs o the present without compromis-ing the ability o uture generations to meet theirown needs.1 While other building materials mayhave to alter their confgurations, properties, orboth to be applicable to sustainable structures, pre-cast concretes inherent properties make it a naturalchoice or achieving sustainability with todays newbuildings. In this paper, sustainability concepts are

outlined and dierent rating systems or evaluatingsustainable design are introduced. Finally, ways areprovided in which precast concrete meets or ex-ceeds one rating systems requirements to achievesustainability.

Marha VaGeem, P.E.,LEED A.P.Principal EngineerCTLGroupSkokie, Ill.

Worldwide, people are cur-

rently using 20% more

resources than can be re-generated. In particular, the U.S. popu-

lation consumes more resources on a

per capita basis than any other nation.

The environmental impact o buildings

in the United States is signicant. Con-

sider that buildings consume 65% o

the electricity generated in the United

States and more than 36% o the pri-

mary energy (such as natural gas);

produce 30% o the national output o

greenhouse gas emissions; use 12% o

the potable water in the United States;and employ 40% o raw materials (3

billion tons annually) or construction

and operation worldwide.2

Building materials can have a signi-cant eect on the environmental impact

o the construction and operation o a

building. Some materials may have to

be used in special congurations, or em-

ploy dierent combinations, to achieve

sustainability; the inherent properties o

precast concrete, however, make it a nat-

ural choice or achieving sustainability

in buildings. Precast concrete contrib-

utes to sustainable practices by incorpo-

rating integrated design, using materials

eciently, and reducing constructionwaste, site disturbance, and noise.

Although most consumers are con-

cerned with the present and uture

health o the natural environment, ewpeople are willing to pay more or a

building, product, process, or inno-

vation that minimizes environmental

burdens. The concept o sustainability,

however, balances sustainable design

with cost-eectiveness.

Using integrated design (also called

the holistic or whole-building ap-

proach), a buildings materials, sys-

tems, and design are examined rom the

perspective o all project team mem-

bers and tenants. Energy eciency,cost, durability (or service lie), space

sustainability


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JanuaryFebruary2006 43

fexibility, environmental impact, and quality o lie are all

considered when decisions are made regarding the selection

o a buildings design.

SuStAinAbiLity ConCEPtS

trple bm Le

The triple bottom lineenvironment, society, and econ-

omyemphasizes that economic consequences are relatedto environmental and social consequences. Consequences

to society include impacts on employees, communities, and

developing countries, as well as ethics, population growth,

and security. Reducing materials, energy, and emissions used

by buildings has impacts ar beyond those o the buildings

themselves, such as:

Fewer new quarries are needed;

Fewer new power plants need to be constructed, less

pollution is emitted into the air, and dependence on or-

eign sources is reduced;

The number o respiratory conditions, such as asthma,

is reduced; and

Demands on the inrastructure to nd new sources o

water decrease.

All o these examples indicate how building energy and

utility use aect the local community.

The community can also be considered globally. Carbon

dioxide (CO2) emissions in the United States were reduced

in 2002 or the rst time; this reduction, however, was due

to a decrease in manuacturing and a stagnant economy. That

same year, Chinas production o CO2 increased by more than

the reduction realized in the United States, but this increase

was primarily due to production o materials consumed by

U.S. citizens.Energy, materials, waste, and emissions to air,

land, and water need to be considered rom a global perspec-tive in a global market.

Cs bldg Gree

A sustainable design can result in reduced project costs

and a building that is energy and resource ecient. Buildings

that are ecient with energy and water have lower operating

costs (in the range o $0.60 to $1.50 per square oot versus

$1.80 per square oot) and a higher acility value than con-

ventional buildings.2

Lower energy use translates into smaller capacity require-

ments or mechanical equipment (heating and cooling) andlower rst costs or such equipment. Eective use o day-

light and passive solar techniques can urther reduce heat-

ing and cooling costs. Reusing materials, such as demolished

concrete or base or ll material, can reduce costs associated

with hauling and disposing o materials.

I sustainability is an objective at the outset o the design pro-

cess, the cost o a sustainable building is competitive. Oten,

green buildings cost no more than conventional buildings because

o the resource-ecient strategies used, such as downsizing o

more costly mechanical, electrical, and structural systems.

Reported increases in rst costs or green buildings range

rom 0% to 2%, with costs expected to decrease as project

teams become more experienced with green building strate-

gies and design.3 Generally, a 2% increase in construction

costs will result in a savings o 10 times the initial investment

in operating costs or utilities (energy, water, and waste) in

the rst 20 years o the buildings lie.

Buildings with good daylight and indoor air qualityboth

common eatures o sustainable buildingshave increased

labor productivity, worker retention, and days worked. These

benets contribute directly to a companys prots because

salarieswhich are about 10 times higher than rent, utilities,

and maintenance combinedare the largest expense or most

companies occupying oce space. In schools with good day-

light and indoor air quality, students have higher test scoresand lower absenteeism.

tale 1. Strategies used during sustainable design to incorporate multiple building team disciplines.

Integration Strategy Sustainability Attribute

Use precast panel as interior surace. Saves material; no need or additional raming and drywall.

Use hollow-core panels as ducts. Saves material and energy; eliminates ductwork and charges

thermal mass o panel.

Use thermal mass in combination with appropriate insulation

levels in walls.

Thermal mass with insulation provides energy benets that exceed

the benets o mass or insulation alone in most climates.

Design wall panels to be disassembled or building unction

changes.

Saves material; extends service lie o panels.

Use durable materials. Materials with a long lie cycle and low maintenance will require

less replacement and maintenance during the lie o the building.

Use natural resources such as daylight, trees or shading, and

ventilation.

Reduces lighting and cooling energy use. Increases indoor air

quality and employee productivity.

Reduce and recycle construction waste. Reduces transportation and disposal costs o wastes. Less

virgin materials are used i construction waste is recycled

or another project.

Use building commissioning to ensure that building standards

are met.

Energy savings and indoor air quality are most likely attained dur-

ing the building lie i inspections are made to ensure construction

was as designed.


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44 PCIJOURNAL44 PCIJOURNAL

Hlsc/iegraed Desg

A key tenet o sustainable design is the holistic or inte-

grated design approach. This approach requires coordinating

the architectural, structural, and mechanical designs early in

the schematic design phases to discern possible system inter-

actions and then deciding which benecial interactions are

essential or project success. For example, a well-insulated

building with ew windows that ace east and west will re-

quire less heating and air-conditioning.This added eature could aect the mechanical design by

requiring ewer ducts and registers and perhaps would allow

or the elimination o registers along the building perimeter.

Precast concrete walls act as thermal storage to delay and

reduce peak thermal loads, while also aecting the structural

design o the building. Table 1 provides other integrated de-

sign strategies.

A holistic approach will also take into account the sur-

rounding site environment. Will shelters be needed or people

who take public transportation to work? Will bike paths be

incorporated or those who bike to work? Can native land-

scaping be used to reduce the need or irrigation?

The eight elements o integrated design are:

1. Emphasize the integrated process;

2. Consider the building as a wholeoten interactive,

oten multi-unctional;

3. Focus on the lie cycle;

4. Have disciplines work together as a team rom the

start;

5. Conduct relevant assessments to determine require-

ments and set goals;

6. Develop tailored solutions that yield multiple benets

while meeting requirements and goals;

7. Evaluate solutions; and

8. Ensure that requirements and goals are met.Contracts and requests or proposals should clearly describe

sustainability requirements and project documentation.

Redce, Rese, Reccle

Reduce the amount of material used and the toxicity

of waste materials. Precast concrete can be designed to op-

timize (or lessen) the amount o concrete used. Industrial

wastes such as fy ash, slag cement, and silica ume can be

used, thereby partially reducing the amount o cement used

in concrete. Precast concrete generates a low amount o waste

with a low toxicity. It is generally assumed that 2% o theconcrete at the plant is waste, but because it is generated at

the plant, 95% o the waste is used benecially elsewhere.

Reuseproducts and containers; repair what can be re-

used. Precast concrete panels can be reused when buildings

are expanded. Concrete pieces rom demolished structures

can be reused to protect shorelines. Because the precasting

process is sel-contained, ormwork and nishing materials

are reused. Wood or berglass orms can generally be used 40

to 50 times without major maintenance, while concrete and

steel have practically unlimited service lives.

Recycle as much as possible, which includes buying

products with recycled content. Concrete in most urbanareas is recycled as ll or road base. Wood and steel orms

are recycled when they become worn or obsolete. Virtually

all reinorcing steel is made rom recycled steel. Many ce-

ment plants burn waste-derived uels such as spent solvents,

used oils, and tires.

GREEn buiLDinG RAtinG SyStEMS

Lie Cycle Inventory (LCI) and Lie Cycle Assessment

(LCA) are valid methods o assessing sustainability, but they

are a complex accounting o all materials, energy, emissions,waste, and their respective impacts (see Lie Cycle Cost,

LCI and LCA on pp. 5657). Conversely, green building

rating systems have gained popularity because they are com-

paratively easy to use and straightorward. Focus groups have

shown that consumers are interested in urthering sustainabil-

ity but are unable to dene it. Labeling a green building with

Leadership in Energy and Environmental Design (LEED),

Green Globes, or Energy Star certication sends the mes-

sage the building is green without having to perorm a com-

plex LCI or LCA.

Eerg Sar Cerfca

Energy Star4 is a government/industry partnership de-signed to help businesses and consumers protect the environ-

ment and save money through energy eciency. Energy Star

labeling is available or oce equipment, such as computers

and monitors; appliances, such as rerigerators; and residen-

tial and commercial buildings. Buildings that meet certain

criteria and achieve a rating o 75 or better are eligible to

apply or the Energy Star.

The rating consists o a score on a scale o 1 to 100. The

score represents a benchmark energy perormance; or ex-

ample, buildings that score 75 or greater are considered to be

among the United States top 25%. In addition, the building

must maintain a healthy and productive indoor environment.At the present time, ve commercial building types are

eligible or Energy Star certication: oces, K12 schools,

supermarkets/grocery stores, hotels/motels, and acute care/

childrens hospitals. These building types are broken down

urther into a number o specic occupancies. For example,

oce buildings include general oce, bank branch, court-

house, and nancial center.

Demonstrating conormance is accomplished through a

web-based sotware tool called Portolio Manager.5 The pro-

gram hinges on the unbiased opinions o a proessional engi-

neer who must visit the building and veriy that data entered

about the building are correct.Through the Portolio Manager, the engineer inputs the

building location and energy consumption and describes its

physical and operating characteristics. Operating characteris-

tics include average weekly occupancy hours, number o oc-

cupants, and amount o equipment and types such as personal

computers, rerigeration cases, cooking acilities, and laundry

acilities. Energy consumption is based on all sources o en-

ergy used per month. In addition to energy perormance, the

engineer is responsible or demonstrating compliance with

industry standards on thermal comort, indoor air quality, and

illumination.

The proessional engineer is expected to give an opinionabout the capability o the building to provide acceptable


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thermal environmental conditions per the American Society

o Heating, Rerigerating, and Air-Conditioning Engineers

(ASHRAE) Standard 556 and its capability to supply accept-

able outdoor air per ASHRAE Standard 62.7 The engineer is

also expected to give an opinion about the capability o the

building to provide minimum illumination levels per the Lu-

minance Selection Procedure in the Illuminating Engineer-

ing Society o North America Lighting Handbook.8 In addi-

tion, Portolio Manager has the capability to manage energy

data, analyze trends in energy perormance (to make budgetand management decisions regarding investments in energy-

related projects), veriy building perormance, and track the

progress o building improvements.

LEED Rag Ssem

The LEED green building rating system is a voluntary,

consensus-based national standard or developing high-per-

ormance, sustainable buildings. The LEED system is both a

standard or certicationand adesign guide or sustainable

construction and operation. As a standard, it is predominantly

perormance-based, and as a design guide, it takes a whole-

building approach that encourages a collaborative, integrated

design and construction process.

The system is administered by the U.S. Green Building

Council (USGBC). The LEED-NC9 is a document that ap-

plies to new construction and major renovation projects and

is intended or use with commercial, institutional, and high-

rise residential new construction and major renovation.

Essentially, LEED is a point-based system that providesa ramework or assessing building perormance and meet-

ing sustainability goals. Points are awarded when a specic

intent is met, and a building is LEED certied i it obtains at

least 26 points. The points are grouped into ve categories:

sustainable sites, water eciency, energy and atmosphere,

materials and resources, and indoor environmental quality.

The more points that are earned, the greener the building is

considered. Silver, gold, and platinum ratings are awarded or

a minimum o 33, 39, and 52 points, respectively.

tale 2. LEED* project checklist: precast concrete points.LEED Category Credit or Prerequisite

Points

Available

Sustainable Sites Credit 5.1: Site Development, Protect or Restore Habitat 1

Sustainable Sites Credit 5.2: Site Development, Maximize Open Space 1

Sustainable Sites Credit 7.1: Heat Island Eect, Non-Roo 1

Energy and Atmosphere Prerequisite 2: Minimum Energy Perormance

Energy and Atmosphere Credit 1: Optimize Energy Perormance 110

Materials and Resources Credit 1.1: Building Reuse, Maintain 75% o Existing Shell 1

Materials and Resources Credit 1.2: Building Reuse, Maintain 95% o Existing Shell 1

Materials and Resources Credit 2.1: Construction Waste Management, divert 50% by weight or volume 1

Materials and Resources Credit 2.2: Construction Waste Management, divert 75% by weight or volume 1

Materials and Resources Credit 4.1: Recycled Content, the post-consumer recycled content plus one-hal o the pre-

consumer content constitutes at least 10% (based on cost) o the total value o the materials

in the project

1

Materials and Resources Credit 4.2: Recycled Content, the post-consumer recycled content plus one-hal o the pre-

consumer content constitutes at least 20% (based on cost) o the total value o the materials

in the project

1

Materials and Resources Credit 5.1: Local/Regional Materials, Use a minimum o 10% (based on cost) o the total

materials value1

Materials and Resources Credit 5.2: Local/Regional Materials, Use a minimum o 20% (based on cost) o the total

materials value1

Indoor Environmental

QualityCredit 3.1: Construction Indoor Air Quality Management Plan, During Construction 1

Innovation and DesignProcess

Credit 1.1: Apply or other credits demonstrating exceptional perormance 1

Innovation and Design

ProcessCredits 1.2: Apply or other credits demonstrating exceptional perormance 1






ProcessCredit 2.1: LEED Accredited Proessional 1

Project Totals 23

*LEED: Leadership in Energy and Environmental Design.

Up to 4 additional points can be earned, must be submitted and approved (not included in total).Note: Scoring System: Certied, 2632 points; Silver, 3338 points; Gold, 3951 points; and Platinum, 5269 points.


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Appropriate use o precast concrete can help a building earn

up to 27 points; 26 points are required or LEED certication.

Using concrete can help meet minimum energy requirements,

optimize energy perormance, and increase the lie o a build-

ing. The constituents o concrete can be recycled materials,

and concrete itsel can also be recycled. These materials are

usually locally available.

These attributes o concrete, recognized in the LEED rat-

ing system, can help lessen a buildings negative impact on

the natural environment. Points applicable to precast concreteare summarized in Table 2 and are explained throughout this

paper. Points must be documented according to LEED pro-

cedures to be earned. The USGBC website contains a down-

loadable letter template that greatly simplies the docu-

mentation requirements or LEED.

Gree Gles

Green Globes is an online, point-based green building rat-

ing system administered by the Green Building Initiative.10

Many o the points are similar to those in LEED, though the

point structure diers; Green Globes has 1000 total points

compared with the 69 or LEED-NC. Certication or GreenGlobes is available at 35% achievement compared with LEED

at 38% (26 points). It is easier to obtain certication in Green

Globes, however, because points that are not applicable to the

building are subtracted rom the total number o points so a

higher percentage is obtained or those criteria that are met.

DuRAbiLity

A key actor in building reuse is the durability o the origi-

nal structure. Precast concrete panels provide a long servicelie due to their durable and low-maintenance concrete surac-

es (Fig. 1). A precast concrete shell can be let in place when

the building interior is renovated. Annual maintenance should

include inspection and, i necessary, repair o joint material.

Modular and sandwich panel construction with concrete

exterior and interior walls provides long-term durability, in-

side and out. Precast concrete construction provides the op-

portunity to reurbish the building i the building use or unc-

tion changes, rather than tearing it down and starting anew.

These characteristics o precast concrete make it sustainable

in two ways: It avoids contributing solid waste to landlls

and it reduces the depletion o natural resources and produc-

tion o air and water pollution caused by new construction.

Fg. 1. The buildings in the corporate campus or CH2M Hill in Englewood, Colo., are ramed with a total precast concrete system,

including precast shear walls, double tees, inverted tee beams, and load-bearing exterior walls. The buildings are some o the frstLeadership in Energy and Environmental Design (LEED)certifed total precast ofce buildings.

PhotocourtesyofBarberArchitecture.


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Crrs Ressace

The most common reason or surace spalling o concrete

in buildings is corrosion o reinorcing steel due to inadequate

concrete cover. Precast concrete oers increased resistance to

this type o spalling because reinorcement and concrete are

placed in a plant, with more quality control than cast-in-place

construction. This reduces variations in concrete cover over re-inorcing steel and reduces the likelihood o inadequate cover.

iedle

Vermin and insects cannot destroy concrete because it is

inedible. Some soter materials are inedible but still provide

pathways or insects. Due to its hardness, vermin and insects

will not bore through concrete. Gaps in exterior insulation to

expose the concrete can provide access or termite inspectors.

RESiStAnt to nAtuRAL DiSAStERS

Concrete is resistant to wind, hurricanes, foods, and re.

Properly designed, reinorced precast concrete is resistant to

earthquakes and provides blast protection or occupants.

Fre Ressace

Precast concrete oers noncombustible construction

that helps contain a re within boundaries. As a separation

wall, precast concrete helps to prevent a re rom spreading

throughout a building or jumping rom building to building.

During wild res, precast concrete walls help provide pro-

tection to human lie and the occupants possessions. As an

exterior wall, concrete that endures a re can oten be reusedwhen the building is rebuilt.

The re endurance o concrete can be determined by its

thickness and type o aggregate. The American Society or

Testing and Materials (ASTM) E119 lists procedures or de-

termining re endurance o building materials. Another good

resource is PCIs Manual on Design or Fire Resistance o

Precast, Prestressed Concrete (MNL 124-89).

Concrete generally ails by heat transmission long beore

structural ailure, whereas other construction materials ail

by heat transmission when collapse is imminent. A 2-h re

endurance or a precast concrete wall will most likely mean

the wall gets hot (experiences an average temperature rise o

250 F [140 C] or all points or 325 F [180 C] at any one

point). Concrete helps contain a re even i no water supply is

available, whereas sprinklers rely on a water source.

trad, Hrrcae, ad Wd Ressace

Precast concrete is resistant to tornadoes, hurricanes, and

wind. In 1967, a series o deadly tornadoes hit northern Il-

linois, killing 57 people and destroying 484 homes. Dam-

ages at the time were estimated at $50 million. Two precast,

prestressed concrete structures, a grocery store and a high

school, were in the direct path o two tornadoes that struckalmost simultaneously. Repairs to the structural system o

the grocery store (limited to a single crack in the fanges and

stem o a beam subjected to uplit) were less than $200. In

the high school, structural damage was limited to the fange

o one double-tee member (24 t [7 m] o which was broken

o by fying debris) and blown out concrete diaphragm end

closures rom between the webs near the damaged tee.

Fg. 2. The Joe Serna Jr. Caliornia EPA Headquartersa27-story LEED Platinumcertifed ofce building in downtownSacramentohas precast concrete panels with punched

openings. The panels were pre-mounted, glazed, and caulkedat the precast plant ater casting.

PhotocourtesyofA.

C.

MartinPartners.

LEED Maerals Cred 1 bldg Rese

The purpose o this credit is to encourage builders to leave

the main portion o the building structure and shell in place

when renovating, thereby conserving resources and reducing

wastes and the environmental eects o new construction. The

building shell includes the exterior skin and raming but ex-

cludes window assemblies, interior partition walls, oor cov-

erings, and ceiling systems. This credit should be obtainable

when renovating buildings with a concrete skin, since concretegenerally has a long lie. This is worth 1 point i 75% o the

existing building structure/shell is let in place and 2 points i

95% is let in place.


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Fld Ressace

Concrete is not damaged by water; concrete that does not

dry out continues to gain strength in the presence o moisture.

Concrete submerged in water absorbs very small amounts o

water over long periods o time, so the concrete is not dam-

aged. In food-damaged areas, concrete buildings are oten

salvageable.Concrete will only contribute to moisture problems in build-

ings i it is enclosed in a system that does not let it breathe

or dry out, trapping moisture between the concrete and other

building materials. For instance, a vinyl wall coverings in hot

and humid climates will act as a vapor retarder and moisture

can get trapped between the concrete and the wall covering.

For this reason, impermeable wall coverings (such as vinyl

wallpaper) should not be used.

Earhqake Ressace

Precast concrete is resistant to earthquakes. Earthquakes in

Guam, the United States (Richter scale 8.1); Manila, the Phil-ippines (Richter scale 7.2); and Kobe, Japan (Richter scale

6.9) have subjected precast concrete buildings to some o

natures deadliest orces. Precast concrete raming systems

have a proven capacity to withstand these major earthquakes.

Precast panels are a material o choice in seismic areas be-

cause they can span long distances between attachments to

the main structure (Fig. 2).

Another pertinent example is the 1994 Northridge, Cali.,

earthquake (Richter scale 6.8). It was one o the costliest nat-

ural disasters in U.S. history, with total damages estimated at

$20 billion. Most engineered structures within the aected

region perormed well, including structures with precast con-

crete components.

In particular, no damage was observed in precast concrete

cladding due to either inadequacies o those components, or

inadequacies o their connections to the buildings structural

systems, and no damage was observed in the precast compo-

nents used or the rst foor or rst-foor support o residen-

tial housing. It should be noted that parking structures with

large plan areasregardless o structural systemdid notperorm as well as other types o buildings.

Fg. 3. A U.S. Green Building Council (USGBC) LEED-registered, mixed-use development, the Bookends in Greenville, S.C.,eatures street-level retail and residential condominiums. The precast concrete walls have a combination o sandblasted and cast-inthin brick fnishes. The acade o this building has our distinct architectural styles to appear as our separate and unique buildings.

PhotocourtesyofJohnstonDesignGroup,

LLC.


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WEAtHER RESiStAnCE

Hgh Hmd ad Wd-Drve Ra

Precast concrete is resistant to wind-driven rain and moist

outdoor air in hot and humid climates. Concrete is imperme-

able to air inltration and wind-driven rain. Moisture that en-

ters a precast building must come through joints between pre-

cast concrete elements. Annual inspection and repair o joints

will minimize this potential. More importantly, i moisture

does enter through joints, it will not damage the concrete.

Good practice or all types o wall construction is to have

permeable materials that breathe (are allowed to dry) on at

least one surace and not encapsulate concrete between two

impermeable suraces. Concrete breathes and will dry out.

Thereore, as long as a precast concrete wall is allowed to

breathe on at least one side and is not covered by an imper-

meable material, the potential or moisture problems within

the wall system is minimal.

ulravle Ressace

The ultraviolet portion o solar radiation does not harm

concrete. Using colored pigments in concrete retains thecolor in concrete long ater paints have aded due to the suns

eects. Precast concrete is ideal or using pigments because

the controlled production allows or replication o color or

all panels or a project (Fig. 3).

MitiGAtinG tHE uRbAn HEAtiSLAnD EFFECt

Precast concrete provides refective suraces that minimize

the urban heat island eect. Cities and urban areas are 3 F to

8 F (2 C to 4 C) warmer than surrounding areas due to the

urban heat island eect. This dierence is attributed to build-

ings and pavements that have taken the place o vegetation.

Trees provide shade that reduces temperatures at the surace.

Trees and plants provide transpiration and evaporation thatcool the suraces and air surrounding them. Research has

shown that the average temperature o Los Angeles has risen

steadily over the past hal century and is now 6 F to 7F

(3 C to 4 C) warmer than it was 50 years ago.11

Warmer Srace temperares

Urban heat islands are primarily attributed to horizontal

suraces, such as roos and pavements, that absorb solar radi-

ation. In this context, pavements include roads, streets, park-

ing lots, driveways, and walkways. Vertical suraces, such as

the sides o buildings, also contribute to this eect. Using

materials with higher albedos, such as concrete, will reducethe heat island eect, save energy by reducing the demand or

air-conditioning, and improve air quality (Fig. 4).

Studies indicate people will avoid using air conditioners at

night i temperatures are less than 75 F (24 C). Mitigating the

Fg. 4. In cities such as Cape Coral, Fla., mitigating the heat island eect is especially important. Note the white color o thearchitectural precast concretebuilt or the city o Cape Coral City Hall.


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urban heat island eect to keep summer temperatures in cit-

ies less than that temperature at night has the potential to save

large amounts o energy by avoiding air conditioner use.

Smg Eecs

Smog levels have also been correlated to temperature rise.

Thus, as the temperature o urban areas increases, so does the

probability o smog and pollution. In Los Angeles, the prob-

ability o smog increases by 3% with every degree Fahrenheit

o temperature rise.Studies or Los Angeles and 13 cities in Texas have ound

that there are almost never any smog episodes when the tem-

perature is below 70 F (21 C). The probability o episodes

begins at about 73 F (23 C) and, or Los Angeles, exceeds

50% by 90 F (32 C). Reducing the daily high in Los Ange-

les by 7 F (4 C) is estimated to eliminate two-thirds o the

smog episodes.11

Smog and air pollution are the main reasons the Environ-

mental Protection Agency (EPA) mandates expensive, clean

uels or vehicles and reduced particulate emissions rom in-

dustrial acilities such as cement plants and asphalt produc-

tion plants. The EPA now recognizes that air temperature isas much a contributor to smog as nitrogen oxide and volatile

organic compounds (VOCs) are. The eort to reduce particu-

lates in the industrial sector alone costs billions o dollars

per year, whereas reduction in smog may be directly related

to the refectance and colors o the inrastructure that sur-

round us. Installing low albedo roos, walls, and pavements

is a cost-eective way to reduce smog.

Aled

Albedo, which in this case is synonymous with solar refec-

tance, is the ratio o the amount o solar radiation refected

rom a material surace to the amount shining on the surace.Solar radiation includes the inrared and ultraviolet as well

as the visible spectrum. Albedo is measured on a scale o not

refective (0.0) to 100% refective (1.0). Generally, materials

that appear to be light-colored in the visible spectrum have

high albedo and those that appear dark-colored have low al-

bedo. Because refectivity in the solar radiation spectrum de-

termines albedo, color in the visible spectrum is not always a

true indicator o albedo.

Suraces with lower albedos absorb more solar radiation.

The ability to refect inrared light is o great importance

because inrared light is most responsible or heating. On a

sunny day when the air temperature is 55 F (13 C), sur-aces with dark acrylic paint will heat up to 90 F (50 C)

more than air temperatures, to 145 F (63 C). Light suraces,

such as white acrylic, will heat up 20 F (11 C) more to a

temperature o 75 F (24 C). The color and composition o

the materials greatly aect the surace temperature and the

amount o absorbed solar radiation. The eect o albedo and

solar radiation on surace temperatures is reerred to as the

sol-air temperature and can be calculated.

Traditional portland cement concrete generally has an al-

bedo or solar refectance o approximately 0.4, though values

can vary; measured values are reported in the range o 0.4 to

0.5. The solar refectance o new concrete is greater when the

surace refectance o the sand and cementitious materials in

the concrete are greater.

Surace nishing techniques also have an eect, with

smoother suraces generally having a higher albedo. For

white portland cement, values are reported in the range o

0.7 to 0.8. Albedo is most commonly measured using a solar-

spectrum refectometer (ASTM C 1549)12 or a pyranometer

(ASTM E 1918).13

Emace

In addition to albedo, the materials surace emittance a-ects a surace temperature. While albedo is a measure o the

solar radiation refected away rom the surace, surace emit-

tance is the ability o the material to emit, or let go o, heat.

A white surace exposed to the sun is relatively cool because

it has a high refectivity and a high emittance. A shiny metal

surace is relatively warm because it has a low emittance,

even though it has a high albedo.

The emittance o most non-refecting (non-metal) building

suraces such as concrete is in the range o 0.85 to 0.95. The

emittance o aluminum oil, aluminum sheet, and galvanized

steel, all dry and bright, are 0.05, 0.12, and 0.25, respectively.

Msre

Moisture in concrete helps cool the surace by evapora-

tion. Concrete, when placed, has a moisture content o 100%

relative humidity. The concrete surace gradually dries over a

period o one to two years to reach equilibrium with its sur-

roundings. Concrete suraces exposed to rain and snow will

continue to be wetted and dry.

This moisture in the concrete surace will help cool the

concrete by evaporation whenever the vapor pressure o the

moisture in the surace is greater than that o the air. In sim-

pler terms, when the temperature and relative humidity o the

air are less than that just beneath the concrete surace, theconcrete will dry and cool somewhat by evaporation.

The albedo o concrete decreases when the surace is wet.

Consequently, albedo is lower when concrete is relatively

new and the surace has not yet dried or when the concrete

becomes wet. The albedo o new concrete generally stabi-

lizes within two to three months.

Mgag he Hea islad Eec

One method to reduce the urban heat island eect is to

change the albedo o the urban area. This is accomplished by

replacing low albedo suraces with materials o higher albedo.

This change is most cost-eective when done in the initial de-

sign or during renovation or replacement due to other needs.

Planting trees or shade near buildings also helps mitigate

LEED Ssaale Ses Cred 7.1 Hea isladEec, n-R

The intent o this credit is to reduce heat islands. The re-

quirements are met by placing a minimum o 50% o parkingplaces underground or in a covered by parking structure. Pre-

cast concrete parking structures can be used to help obtain

this point. Any roo used to shade or cover parking must meet

specifed criteria. This credit is worth 1 point.


10/20


the urban heat island eect. Shade also directly reduces the

air-conditioning load on buildings. Using deciduous trees

shades the buildings in the summer and allows the sun to

reach the buildings in the winter.

thermal Mass ad ncral Eecs

The thermal mass o concrete delays the time it takes or a

surace to heat up but also delays the time to cool o. For ex-

ample, a white roo will get warm aster than concrete during

the day but will also cool o aster at night. Concrete suracesare oten warmer than air temperatures in the evening hours.

Concretes albedo and thermal mass will help mitigate heat

island eects during the day but contribute to the nocturnal

heat island eect. The moisture absorbed by concrete helps

reduce the daytime and nocturnal heat island eect when

it evaporates. The challenge is to use concrete to mitigate

heat islands while keeping evening temperatures as cool as

possible.

EnViRonMEntAL PRotECtion

Rada ad txc

The goal o sustainability is to reduce radiation and toxic

materials; concrete provides an eective barrier against ra-

diation and can be used to isolate toxic chemicals and waste

materials. Concrete protects against the harmul eects o x-

rays, gamma rays, and neutron radiation.

Concrete is resistant to most natural environments, but it is

sometimes exposed to substances that can attack and cause

deterioration. Concrete in chemical manuacturing and stor-

age acilities is especially prone to chemical attack. The re-

sistance o concrete to chlorides is good, and using less per-

meable concrete can increase it even more. This is achievedby using a low water-cementitious materials ratio (approxi-

mately 0.40), adequate curing, and supplementary cementi-

tious materials, such as slag cement and silica ume. The best

deense against sulate attack is the measures suggested pre-

viously, in addition to using cement specially ormulated or

sulate environments.

Ressace nse

Precast concrete walls provide a buer between outdoor

noise and the indoor environment. Because land is becoming

scarcer, buildings are being constructed closer together and

near noise sources such as highways, railways, and airports.The greater mass o concrete walls can reduce sound pen-

etrating through a wall by over 80% compared with wood or

steel rame construction. Although some sound will penetrate

the windows, a concrete building is oten two-thirds quieter

than a wood or steel rame building. Precast concrete panels

also provide eective sound barriers separating buildings rom

highways or industrial areas rom residential areas (Fig. 5).

PRECASt ConCREtE PRoDuCtion

The production o precast concrete has many environmen-

tal benets. Fewer materials are required because precise

mixture proportions and tighter tolerances are achievable.

Optimal insulation levels can be incorporated into precast

concrete sandwich panel walls. Less concrete waste is created

because o tight control o quantities o constituent materials.

Waste materials are more likely to be recycled because con-

crete production is in one location. For example, gray water

is oten recycled into uture mixtures; hardened concrete isrecycled (about 5% to 20% o aggregate in precast concrete

can be recycled concrete); sand and acids or nishing surac-

es are reused; and steel orms and other materials are reused.

Less dust and waste is created at the construction site because

only precast concrete elements that are needed are delivered;

there is no debris rom ormwork and associated asteners.

Fewer trucks and less time are required or construction be-

cause concrete is made o site, which is particularly bene-

cial in urban areas where minimal trac disruption is criti-

cal. Precast concrete units are normally large components,

so greater portions o the building are completed with each

activity. And nally, there is less noise at the constructionsite because the concrete is made o site.

Less concrete is generally used in precast buildings than in

other concrete buildings because o the optimization o mate-

rials. A properly designed precast concrete system will result

in smaller structural members, longer spans, and less mate-

rial used on site; this translates directly into economic sav-

ings, which can also result in environmental savings. Using

ewer materials means using ewer natural resources and less

manuacturing and transportation energynot to mention the

avoided emissions rom mining, processing, and transporting

raw and nished material.

Concrete products can provide both the building structure,and the interior and exterior nishes. Structurally ecient

Fg. 5. Precast concrete panels provide eective sound barriersseparating buildings rom highways or industrial areas romresidential areas.

PhotocourtesyofPortlandCementAssociation.


11/20


columns, beams, and slabs can be let exposed with naturalnishes. Interior and exterior concrete walls oer a wide

range o prole, texture, and color options that require little

or no additional treatment to achieve aesthetically pleasing

results.

Exposed ceiling slabs and architectural precast panels are

some examples o this environmentally ecient approach.

This structure/nish combination reduces the need or the

production, installation, maintenance, repair, and replace-

ment o additional nish materials. It also eliminates prod-

ucts that could otherwise degrade indoor air quality.

ConStituEnt MAtERiALS

Prlad Ceme

Portland cement (hereater called cement) is made by heat-

ing common minerals, primarily crushed limestone, clay,

iron ore, and sand, to a white-hot mixture to orm clinker.

This intermediate product is ground with a small amount o

gypsum to orm a ne gray powder called cement. To trigger

the necessary chemical reactions in the kiln, these raw mate-

rials must reach a temperature o about 2700 F (1500 C),

the temperature o molten iron. Although the portland cement

industry is energy intensive, the U.S. cement industry has re-

duced energy usage per ton o cement by 35% since 1972.14

Carbon dioxide emissions rom a cement plant are divid-

ed into two source categories: combustion and calcination.

Combustion accounts or approximately 35% and calcination

65% o the total CO2 emissions rom a cement manuacturing

acility. The combustion-generated CO2 emissions are related

to uel use. The calcination CO2 emissions are ormed when

the raw material is heated and CO2 is liberated rom the cal-cium carbonate.

When concrete is exposed to the air and carbonates, it re-

absorbs some o the CO2 released during calcination. Calci-

nation is a necessary key to cement production; the ocus o

reductions in CO2 emissions during cement manuacturing is

on reducing uel and energy use.

White portland cement is a true portland cement that di-

ers rom gray cement chiefy in color. The manuacturing

process is controlled so that the nished product will be

white. White portland cement is made o selected raw mate-

rials containing negligible amounts o iron and magnesium

oxidesthe substances that give cement its gray color. Whitecement is used primarily or architectural purposes in struc-

tural walls, precast and glass berreinorced concrete acing

panels, terrazzo suraces, stucco, cement paint, tile grout, and

decorative concrete. White cement is also used to manuac-

ture white masonry cement meeting ASTM C 91 (the stan-

dard specication or masonry cement).

Ada Maerals

Concrete is used in almost every country o the world as a

basic building material. Aggregates, which comprises about

85% o concrete, are generally low-energy, local, naturally

occurring sand and stone. The limestone and clay needed tomanuacture cement are prevalent in most countries. Con-

crete contributes to a sustainable environment because it does

not use scarce resources.

Limestone and aggregate quarries are easily reused. While

quarrying is intense, it is closely contained and temporary.

When closed, aggregate quarries are generally converted to

their natural state or into recreational areas or used or agri-

culture. In contrast, other material mining operations can be

extensive and involve deep pits that are rarely restored, and

deorestation can have negative environmental eects.

Fl Ash, Slag Ceme, ad Slca Fme

Fly ash, slag cement, and silica ume are industrial by-

products; their use as a replacement or portland cement does

not contribute to the energy and CO2 eects o cement in

concrete. I not used in concrete, these pozzolans would use

valuable landll space. Fly ash (Fig. 6) is a by-product o

the combustion o pulverized coal in electric power generating

plants. Slag cement (Fig. 7) is made rom iron blast-urnace

slag. Silica ume (Fig. 8) is a by-product rom the electric arc

urnace used in the production o silicon or errosilicon alloy.

These types o industrial by-products are considered post-

industrial or pre-consumer recycled materials. Fly ash is

commonly used at cement replacement levels up to 25%; slagcement up to 60%; and silica ume up to 5% to 7%. WhenFg. 6. Fly ash, a by-product o the electric industry, can beused as a partial replacement or portland cement.

PhotocourtesyofPortandCementAssociation.

LEED Ssaale Ses Cred 5.1 SeDevelpme, Prec r Resre Haa

The intent o this credit is to encourage the conservation o

natural areas on the site and the restoration o damaged ones.

The requirements are met by limiting site disturbance to pre-

scribed distances. Tuck-under parking, such as precast con-

crete parking structures, can be used to help obtain this point.

This credit is worth 1 point.

LEED Ssaale Ses Cred 5.2 SeDevelpme, Maxmze ope Space

The intent o this credit is to provide a high ratio o open

space to development ootprint. The requirements are met by

limiting the size o the development ootprint, specifcally by

exceeding the local zonings open space requirement or the

site by 25%. Tuck-under parking, such as precast concrete

parking structures, can be used to help obtain this point. This

credit is worth 1 point.


12/20


slag cement replaces 50% o the portland cement in 7500 psi

(50 MPa) concrete, greenhouse gas emissions per cubic yard

o concrete are reduced by 45%. Because the cementitious con-

tent o concrete is about 15%, these pozzolans typically account

or only 2% to 5% o the overall concrete material in buildings.

Testing determines the optimum amounts o supplemen-

tary cementing materials used with portland or blended ce-

ment, the relative cost and availability o the materials, and

the specied properties o the concrete. When supplementary

cementitious materials are used, the proportioned mixture(using the project materials) should be tested to demonstrate

that it meets the required concrete properties or the project.

Some pozzolans increase curing times, but this is not as great

a concern or precast concrete manuacturing as it is in cast-

in-place applications where the construction schedule has a

greater impact.

The durability o products with recycled content materials

should be careully researched during the design process to

ensure comparable lie cycle perormance. There would ob-

viously be a net negative impact i a product oering a 20%

to 30% recycled content had only hal the expected service

lie o a product with a lower or no recycled content.

Reccled Aggregaes

The environmental attributes o concrete can be improved by

using aggregates derived rom industrial waste or using recy-

cled concrete as aggregates. Blast urnace slag is a lightweight

aggregate with a long history o use in the concrete industry.

Recycled concrete can be used as aggregate in new con-

crete, particularly the coarse portion. When using the recy-

cled concrete as aggregate, the ollowing should be taken intoconsideration:

Recycled concrete as aggregate will typically have a

higher absorption rate and lower specic gravity than

natural aggregate and will produce concrete with

slightly higher drying shrinkage and creep. These di-

erences become greater when recycled ne aggregate

amounts are increased;

Too many recycled nes can produce a harsh and un-

workable mixture. Many transportation departments

have ound that using 100% coarse recycled aggregate,

but only about 10% to 20% recycled nes, works well.15

The remaining percentage o nes is natural sand;

When crushing the concrete (Fig. 9), it is dicult to

control particle size distribution, meaning that the

aggregate may ail to meet grading requirements o

ASTM C 3316; and

The chloride content o recycled aggregates is o con-

cern i the material will be used in reinorced concrete.

Fg. 7. Slag cement is a cementitious material and also a by-product o the iron industry.

Fg. 8. Silica ume, an industrial by-product, is commonly usedto replace cement in quantities rom 5% to 7%.



LEED Maerals Cred 4 Reccled Ce

The requirements o this credit state: Use materials with

recycled content such that the sum o post-consumer recycled

content plus one-hal o the pre-consumer content constitutesat least 10% (based on cost) o the total value o the materials

in the project. The percentage is determined by multiplying

the price o an item by the percent o recycled materialson a

mass basisthat make up that item.

To earn this credit, the project must meet the threshold per-

centages based on the total o all permanently installed build-

ing materials used on the project. Supplementary cementitious

materials, such as y ash, silica ume, and slag cement, are

considered pre-consumer. Because the cementitious content o

concrete is about 15%, these pozzolans typically account or

only 2% to 5% o the overall concrete material in buildings.

For this reason, LEED-NC v2.2 allows the recycled content o

concrete to be based on the recycled content o the cementi-

tious materials.

Using recycled concrete or slag as aggregate instead o

extracted aggregates qualifes as post-consumer. Although

most reinorcing bars are manuactured rom recycled steel, in

LEED, reinorcement is not considered part o concrete. Rein-

orcing materials should be considered as a separate item. This

credit is worth 1 point or the quantities quoted previously and

2 points or double the amount.


13/20


This is particularly an issue i the recycled concrete is

rom pavements in northern climates where road salt is

reely spread in the winter. The alkali content and typeo aggregate in the system is probably unknown, and

thereore, i mixed with unsuitable materials, a risk o

alkali-silica reaction is possible.

Admxres

Adding chemical admixtures, usually in liquid orm, to the

concrete during batching may change the resh and hardened

properties o concrete. Chemical admixtures are commonly

used to adjust setting time or hardening, reduce water de-

mand, increase workability, intentionally entrain air, and ad-

just other resh or hardened concrete properties. Admixturesprovide enhancing qualities in concrete but are used in such

small quantities that they do not adversely aect the environ-

ment. Their dosages are usually in the range o 0.005% to

0.2% o the concrete mass.

Clr Pgmes

Color pigments are used to provide the decorative colors in

precast concrete. They are generally insoluble and non-toxic,

though they may contain a heavy metal component like many

other materials (Fig. 10).

Lcal Maerals

Using local materials reduces the transportation required to

ship heavy building materials and the associated energy and

emissions. Most precast concrete plants are within 200 miles

(300 km) o a building site. The cement, aggregates, and rein-

orcing steel used to make the concrete and the raw materials

used to manuacture cement are usually obtained or extracted

rom sources within 200 miles o the precast concrete plant.

The primary raw materials used to make cement and concrete

are abundant in all areas o the world.

Precast concrete elements are usually shipped eciently

because o their large, oten repetitive sizes and the ability toplan their shipment during the normal course o the project.

Fg. 9. Crushed concrete rom other sources can serve as recycled aggregate.

PhotocourtesyofCTLGroup.

Fg. 10. The color pigments that provide the decorative colorsin precast concrete are generally insoluble and non-toxic.



14/20


EnERGy uSE in buiLDinGS

Energy conservation is a key tenet o sustainability. About

90% o the energy used during a buildings lie is attributed

to heating, cooling, and other utilities. The remaining 10% is

attributed to manuacturing materials, construction, mainte-

nance, replacement o components, and demolition.

Approximately 5% o the worlds population resides in the

United States, yet 25% o the worlds energy is consumed in

the United States. The United States dependence on oreignenergy sources is greater than ever, which has an eect on

U.S political and deense policies. Meanwhile, many devel-

oping nations, like China and India, have increased energy

demands due to increased manuacturing and urbanization.

Eerg Cdes

Energy codes provide cost-eective, minimum building

requirements that save energy. The energy saved is a cost

savings through lower monthly utility bills, and smaller, and

thus less expensive, mechanical equipment. More than two-

thirds o the electricity and one-third o the total energy in the

United States are used to heat, cool, and operate buildings.

17

This means that implementing and enorcing energy codes

will result in ewer power plants and natural resources being

used to provide electricity and natural gas. It also means ewer

emissions will be released into the atmosphere. In the United

1960

1962

1964

1968

1966

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

Total Electricity Use, per capita, 1960 2001

(estimated for California in 2000 and 2001)

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

12,000

8,000

7,000

California

U.S.

kWh

Fg. 11. Energy savings due to implementation o energy codes in 1976 in Caliornia.

LEED Maerals Cred 5 Regal Maerals

The requirements o this credit state: Use building ma-

terials or products that have been extracted, harvested or

recovered, as well as manuactured, within 500 miles (800

km) o the project site or a minimum o 10% (based on cost)

o the total materials value. This means that a precast plant

within 500 miles o the building would qualiy i the mate-

rials to make the concrete were extracted within 500 miles.

Calculations can also include concrete either manuacturedor extracted locally.

Precast concrete will usually qualiy because precast plants

are generally within 200 miles to 500 miles (300 km to 800 km)

o a project. Precast plants generally use aggregates that are

extracted within 50 miles (80 km) o the plant and within 200 to

500 miles o the project. Cement and supplementary cementi-

tious materials used or buildings are also primarily manuac-

tured within 500 miles o a project. Reinorcing steel is also

usually manuactured within 500 miles o a project and is typi-

cally made rom recycled materials rom the same region.

Using materials that are extracted or manuactured locally

supports the regional economy. In addition, reducing ship-

ping distances or material and products to the project mini-mizes uel requirements or transportation and handling. This

credit is worth 1 point or the quantities quoted above and 2

points or double the amount, or 20% o the materials.


15/20

56 PCIJOURNAL

Alie cycle cost analysis is a powerul tool used to make

economic decisions or selection o building materi-

als. This analysis is the practice o accounting or all

expenditures incurred over the lietime o a particular struc-

ture. Costs at any given time are discounted back to a xed

date, based on assumed rates o infation and the time-value

o money. A lie cycle cost is in dollars and is equal to theconstruction cost plus the present value o uture utility, main-

tenance, and replacement costs over the lie o the building.

Using this widely accepted method, it is possible to com-

pare the economics o dierent building alternatives that may

have dierent cash fow actors but that provide a similar

standard o service.

Quite oten, building designs with the lowest rst costs or

new construction will require higher costs during the build-

ings lie. So, even with their low rst cost, these buildings

will have a higher lie cycle cost. Conversely, durable ma-

terials such as precast concrete oten have a lower lie cycle

cost. In the world o selecting the lowest bid, owners needto be made aware o the benets o a lower lie cycle cost so

that specications require durable building materials such as

precast concrete.

The building lie cycle cost sotware1 rom the National In-

stitute o Standards and Technology provides economic anal-

ysis o capital investments, energy, and operating costs o

buildings, systems, and components. The sotware includes

the means to evaluate costs and benets o energy conserva-

tion and complies with the American Society o Testing and

Material (ASTM) standards related to building economics

and Federal Energy Management Program requirements.

Accepted methods o perorming lie cycle cost analyses obuildings assume a 20-year lie with the buildings maintain-

ing 80% o its residual value at the end o this time period.

Buildings can actually last hundreds o years i they are not

torn down due to obsolescence. Sustainability practitioners

advocate that the oundation and shell o new buildings be

designed or a service lie o 200 years to 300 years. Allow-

ing extra capacity in the columns or extra foors and foor

loads and extra capacity in roos or roo-top gardens adds to

the buildings long-term fexibility.

EnViRonMEntAL LCi AnD LCA

A lie cycle assessment (LCA) is an environmental assess-

ment o the lie cycle o a product. An LCA looks at all aspects

o a products lie cyclerom the rst stages o harvesting

and extracting raw materials rom nature to transorming and

processing these raw materials into a product to, using the

product, and ultimately recycling it or disposing o it back

into nature. Figure 1 shows the our phases o an LCA.

The LCA o a building is necessary to evaluate the envi-

ronmental impact o a building over its lie. Green buildings

rating systems, models such as Building or Environmental

and Economic Sustainability (BEES)1, and programs that

ocus only on recycled content or renewable resources pro-

vide only a partial snapshot o the environmental impact abuilding can have. An LCA o a building includes environ-

mental eects due to:

Extraction o materials and uel used or energy;

Manuacture o building components;

Transportation o materials and components;

Assembly and construction;

Operation, including energy consumption, mainte-

nance, repair, and renovations; and

Demolition, disposal, recycling, and reuse o the

building at the end o its unctional or useul lie.

A ull set o eects includes land use, resource use, climate

change, health eects, acidication, and toxicity.An LCA involves a time-consuming manipulation o large

quantities o data. A model such as SimaPro2 provides data

or common building materials and options or selecting

LCA impacts. The Portland Cement Association3 publishes

reports with lie cycle inventory (LCI) data on cement and

concrete. All models require a separate analysis o annual

heating, cooling, and other occupant loads using a program

such as DOE2.1e.4

An LCI is the rst stage o an LCA. An LCI accounts or

all the individual environmental fows to and rom a product

throughout its lie cycle. It consists o the materials and en-

ergy needed to make and use a product and the emissions toair, land, and water associated with making and using that

product.

Several organizations have proposed how an LCA should

be conducted. Organizations such as the International Orga-

nization or Standardization5,the Society o Environmental

Toxicology and Chemistry (SETAC)6, and the U.S. Environ-

mental Protection Agency 7 have documented standard proce-

dures or conducting an LCA. These procedures are generally

consistent with each other; they are all scientic, transparent,

and repeatable.

LCi bounDARyThe useulness o an LCA or LCI depends on where the

boundaries o a product are drawn. A common approach is

to consider all the environmental fows rom cradle to gate.

For example, the system boundary in Fig. 2 shows the most

signicant processes or precast concrete operations. It in-

Le Ccle Cs, LCi, ad LCA

56 PCIJOURNAL

Conduct the life

cycle inventory

Assign the

inventory data to

impact categories

Rank the

significance of the

impact categories

Define the

goal and scope

Fg. 1. The our phases in the process o developing an LCA.


16/20

cludes most o the inputs and outputs associated with pro-ducing concreterom extracting raw materials to producing

concrete ready or placement in orms. The system bound-

ary also includes the upstream prole o manuacturing ce-

ment, as well as quarrying and processing aggregates, and

transporting cement, fy ash, and aggregates to the concrete

plant. Energy and emissions associated with transporting the

primary materials rom their source to the concrete plant are

also included in the boundary. It does not include, however,

upstream proles o uel, electricity, water, or supplemen-

tary cementitious materials. This LCI also does not include

orm preparation, placing the concrete in the ormwork, cur-

ing, and stripping. A complete precast concrete LCI wouldinclude all these steps.

An upstream prole can be thought o as a separate LCI

that is itsel an ingredient to a product. For example, the

upstream prole o cement is essentially an LCI o cement,

which can be imported into an LCI o concrete. The LCI o

concrete itsel can then be imported into an LCI o a product,

such as an oce building.

To get the most useul inormation out o an LCI, precast

concrete should be considered in the context o its end use.

For example, in a building, the environmental impact o the

building materials is usually dwared by the environmental

eects associated with building operations such as heating,ventilating, cooling, and lighting.

The LCI o materials generally do not consider embodiedenergy and emissions associated with construction o manu-

acturing plant equipment and buildings, nor the heating and

cooling o such buildings. This is generally acceptable i their

materials, embodied energy, and associated emissions account

or less than 1% o those in the process being studied. For ex-

ample, SETAC guidelines indicate that inputs to a process do

not need to be included in an LCI i they are less than 1% o

the total mass o the processed materials or product; they do

not contribute signicantly to a toxic emission; and they do

not have a signicant associated energy consumption.6

REFEREnCES

1. National Institute o Standards and Technology, Building or

Environmental and Economic Sustainability, Gaithersburg,

MD.

2. PR Consultants, SimaPro 6, Amersoot, the Netherlands.

3. Portland Cement Association, Skokie, IL, www.cement.org.

4. Architectural Energy Corporation, Visual DOE 4.0, Boulder,

CO, www.archenergy.com.

5. International Organization or Standardization, Geneva,

Switzerland, www.iso.org.

6. The Society o Environmental Toxicology and Chemistry,

Pensacola, FL, www.setac.org.

7. The United States Environmental Protection Agency,Washington, DC, www.EPA.gov.


Water

Preparation

of forms

Cement

manufacture

Cement storage

Placement

of concrete

Aggregate

production

Stockpiling

Mixing

The system boundary

defines the limits of the LCI

Curing

Supplementary

cementitious

materials

Energy

Form stripping

Form stripping

Transportation

energy

Transportation

energy

Fg. 2. Precast concretesystem boundary


17/20


States, most buildings are constructed to meet minimum en-

ergy code requirements; energy codes contribute to sustain-

ability by saving energy and protecting the environment.

Energy codes are eective in reducing per capita energyusage (energy use per person). Caliornias per capita energy

use has remained steady due to the states active use and en-

orcement o energy codes or buildings, while in the rest o

the United States, that energy use has increased (Fig. 11).

The U.S. National Energy Policy Act requires that each

state certiy it has a commercial building code that meets

or exceeds ANSI/ASHRAE/IESNA Standard 90.1-1999.18

In this sense, commercial means all buildings that are not

low-rise residential (three stories or less above grade). This

includes oce, industrial, warehouse, school, religious, dor-

mitories, and high-rise residential buildings. The ASHRAE

standard and most codes recognize the benets o thermalmass and require less insulation or mass walls.

Thermal mass in exterior walls delays and reduces peak

loads, reduces total loads in many climates and locations,

works best in commercial applications, works well in resi-

dential applications, works best when mass is exposed on the

inside surace, and works well regardless o the placemento mass.

Mass works well in commercial applications by delaying

the peak summer load, which generally occurs around 3:00

pm. As a case in point, the blackout in the Northeast United

States in August 2003 occurred at 3:05 pm.19 A shit in peak

load would have helped alleviate the demand and, possibly,

this peak power problem.

Also, many commercial and industrial customers incur

signicant time-o-use utility rate charges or the highest

use o electricity or any one hour in a month in the sum-

mer. Thermal mass may help shit the peak hour o electric

demand or air-conditioning to a later hour and help reducethese time-o-use charges. Nighttime ventilation can be used

to cool thermal mass that has been warmed during the day.

Local outdoor humidity levels infuence the eectiveness o

nighttime ventilation strategies.

As occupant and equipment heat is generated, it is absorbed

not only by the indoor ventilated air but also by the massive

elements o the building. Interior mass rom interior walls,

foors, and ceilings will help moderate room temperatures

and reduce peak energy use.

Thermal mass is most eective in locations and seasons

where the daily outdoor temperature rises above and alls

below the balance point temperature o the building. Thebalance point temperature is the outdoor temperature below

which heating will be required. It is less than room tempera-

ture, generally between 50 F and 60 F (10 C and 15C),

at the point where internal heat gains are about equal to the

heat losses through the building envelope. In many climates,

buildings with thermal mass have lower energy consumption

than non-massive buildings with walls o similar thermal re-

sistance. In addition, heating and cooling needs can be met

with smaller equipment sizes.

Lghg

Light-colored precast concrete and other suraces will re-

duce energy costs associated with indoor and outdoor light-

tale 3. Measured air leakage or selected building materials.21

Material Average Leakage at 0.3 in. Water Surface (cfm/ft2)

6 mil (0.15 mm) polyethylene No measurable leakage

1 in. (25 mm) expanded polystyrene 1.0

12 mm (0.47 in.) berboard sheathing 0.3

Breather type building membranes 0.0020.7

Closed cell oam insulation 0.0002

Uncoated brick wall 0.3

Uncoated concrete block 0.4

Precast concrete wall No measurable leakage

Note: 1 in. = 25.4 mm; 1 cm/t2= 0.3048 m3 per min/m2

LEED Eerg ad Amsphere Prereqse 2 Mmm Eerg Perrmace

All buildings must comply with certain sections on building

energy efciency and perormance as required by the ANSI/

ASHRAE/IESNA 90.1-2004, Energy Standard or Buildings

Except Low-Rise Residential Buildings. In certain cases, local

energy codes can be used or compliance i they have been

shown to be equivalent or exceed the ASHRAE standard. This

prerequisite is a requirement and is not worth any points. The

requirements o the ASHRAE standard are cost-eective and

not particularly stringent or concrete. Insulating to meet or

exceed the requirements o the standard is generally a wise

business choice. Determining compliance or the envelope

components is relatively straightorward using the tables in

Chapter 5 o the ASHRAE standard. Minimum requirements

are provided or mass and non-mass components, such as

walls and oors.


18/20


ing. Refective suraces will reduce the amount o xtures

and lighting required.

Ar iflra

Precast concrete panels have negligible air inltration.

Minimizing air inltration between panels and at foors and

ceilings will provide a building with low-air inltration. These

eects will lower energy costs and help prevent moisture

problems rom inltration o humid air. In hot and humid cli-

mates in the southeastern United States, inltration o moist

air is a source o unsightly and unhealthy moisture problems

in buildings. Some building codes20 now limit air leakage

o building materials to 0.004 cm/t2

(0.0012 [m3

/min]/m2

)under a pressure dierential o 0.3 in. (7.6 mm) water (1.6

ps [0.75 kPa]); precast concrete meets this requirement.

Table 3 lists the measured air leakage values or select build-

ing materials.

Advaced Eerg Gdeles

Sustainability or green building programs (such as LEED

or Energy Star) encourage energy savings beyond minimum

code requirements. The energy saved is a cost savings to the

building owner through lower monthly utility bills and small-

er, less expensive mechanical equipment. Some government

programs oer tax incentives or energy-saving eatures.Other programs oer reduced mortgage rates. The Energy

Star program oers simple computer programs to determine

the utility savings and lease upgrades associated with energy-

saving upgrades.

Many energy-saving measures are cost-eective even

though they exceed minimum codes. Insulation and other

energy-saving measures in building codes generally have a

return investment cycle o about 5 years, even though the

building lie may be anywhere rom 30 years to 100 years.

The New Buildings Institute has developed theE-Benchmark

guidelines to save energy beyond codes.21 The ASHRAEAd-

vanced Energy Design Guide For Small Ofce Buildings22

has a similar purpose. Many utilities are interested in these

advanced guidelines to delay the need or new power plants.

The panelized construction o precast concrete lends it-sel to good practice and optimization o insulation levels.

To maximize the eectiveness o the insulation, thermal

bridges should be minimized or avoided. Metal thermal

bridges may occur as asteners that penetrate insulation

to connect concrete layers. Concrete thermal bridges may

occur at the tops and bottoms o concrete panels. Using -

berglass composite asteners or thermal breaks may mini-mize thermal bridges.

tale 4. LEED* NC v2.2 points awarded or energy costs saved beyond minimum code.

New Buildings,

Energy Saved

Existing Buildings,

Energy SavedPoints

10.5% 3.5% 1

14% 7% 2

17.5% 10.5% 3

21% 14% 4

24.5% 17.5% 5

28% 21% 6

31.5% 24.5% 7

35% 28% 8

38.5% 31.5% 9

42% 35% 10

* LEED: Leadership in Energy and Environmental Design.

LEED Eerg Cred 1 opmzg EergPerrmace

This credit is allowed i energy cost savings can be shown

compared to a base building that meets the requirements o

ANSI/ASHRAE/IESNA 90.1-2004, Energy Standard or Build-

ings Except Low-Rise Residential Buildings. The method o

determining energy cost savings must meet the requirements oAppendix G, Perormance Rating Method, o the standard.

Many engineering consulting frms have the capability

to model a building to determine energy savings as required

using a computer-based program, such as DOE2.23 When con-

crete is considered, it is important to use a program, such as

DOE2, that calculates annual energy use on an hourly basis.

Such programs are needed to capture the benefcial thermal

mass eects o concrete. Insulated concrete systems used in

conjunction with other energy-saving measures will most likely

be eligible or points. The number o points awarded will de-

pend on the building, climate, uel costs, and minimum require-

ments o the standard. From 1 to 10 points are awarded or en-

ergy cost savings o 10.5% to 42% or new buildings and 3.5%to 35% or existing buildings (Table 4). A small ofce build-

ing less than 20,000 sq t (1900 m2) complying with ASHRAE

Advanced Energy Design Guide For Small Oce Buildings

2004 can achieve 4 points, and a building complying with

E-Benchmark v1.1 can achieve 1 point.


19/20


inDooR EnViRonMEntAL QuALity

Concrete contains low to negligible VOCs. These com-

pounds degrade indoor air quality when they o gas rom

new products, such as interior nishings, carpet, and urni-

ture. Manuactured wood products such as laminate, particle-

board, hardboard siding, and treated wood can also lead to ogassing. In addition, VOCs combine with other chemicals in

the air to orm ground-level ozone.

Table 5 presents the VOC concentration and emission rates

or common materials. Complaints due to poor indoor air

quality routinely include dryness o the mucous membranes

and skin, nose bleeds, skin rash, mental atigue, headache,

cough, hoarseness, wheezing, nausea, dizziness, increased

incidence o asthma, and eye, nose, and throat irritation.

Polished concrete foors do not require carpeting. Exposed

concrete walls do not require nishing materials. The VOCs

in concrete construction can be urther reduced by using low-

VOC materials or orm release agents, curing compounds,

dampproong materials, wall and foor coatings and primers,

membranes, sealers, and water repellants.

DEMoLition

Precast concrete panels can be reused when buildings are

expanded, and precast concrete can be recycled as road base

or ll at the end o its useul lie. Concrete pieces rom de-

molished structures can be reused to protect shorelines. Most

concrete rom demolition in urban areas is recycled and not

placed in landlls.

ConCLuSion

Sustainable practices contribute to saving materials andenergy and reducing the negative eects o pollutants. The

LEED indoor Envronmental Qualty Credt 3.1 on

Constructon iAQ Management Plan, Durng Constructon

This credit prevents indoor air quality problems resulting

rom the construction process. The intent is to reduce and con-

tain dust and particulates during construction and to reduce

moisture absorbed by materials that are damaged by moisture.

During construction, the project must meet or exceed the rec-

ommendedControl Measures o the Sheet Metal and Air Con-

ditioning National Contractors Association IAQ Guidelines or

Occupied Buildings under Construction, 1995, Chapter 3 on

Control Measures.

Using precast concrete can help meet the requirements be-

cause it is delivered to the site in pieces that do not require

abrication, processing, or cutting, thereby reducing dust and

airborne contaminants on the construction site. Concrete is not

damaged by moisture and does not provide nutrients or mold

growth. This credit is worth 1 point.

tale 5. Concentrations and emission rates o VOCs* or common materials.

Building Material VOC Concentration, mg/m3 VOC Emission Rate, mg/m2h

Concrete with water-based

orm-release agent

0.018 0.003

Acryl latex paint 2.00 0.43

Epoxy, clear foor varnish 5.45 1.3

Felt carpet 1.95 0.080

Gypsum board N/A 0.026

Linoleum 5.19 0.22

Particle board N/A 2.0

Plastic silicone sealer 77.9 26.0

Plywood paneling N/A 1.0

Putty strips 1.38 0.34

PVA glue cement 57.8 10.2

Sheet vinyl fooring 54.8 2.3

Silicone caulk N/A < 2.0

Water-based EVA wall and foor glue 1410.0 271.0

*VOCs: volatile organic compounds.

PVA: polyvinyl acetate.

EVA = ethylene vinyl acetate.

Note: 1 mg/m3= 0.000009 oz/yd3; 1 mg/m2h = 0.00001 oz/yd2h.


20/20

use o precast concrete contributes to these practices by in-

corporating integrated design, using materials eciently,

and reducing construction waste, site disturbance, and noise.

Concrete is durable, resistant to corrosion and impact, and

inedible.

Precast concrete structures are resistant to res, wind, hur-

ricanes, foods, earthquakes, wind-driven rain, and moisture

damage. Light- or natural-colored concrete reduces heat is-

lands, thereby reducing outdoor temperatures, saving energy,

and reducing smog. Recycled materials such as fy ash, slag

cement, silica ume, and recycled aggregates can be incorpo-rated into concrete, thereby reducing the amount o materi-

als that are taken to landlls and reducing the use o virgin

materials.

Concrete structures in urban areas are recycled into ll and

road base material at the end o their useul lives. Cement and

concrete are generally made o abundant local materials. The

thermal mass o concrete helps save heating and cooling en-

ergy in buildings. Concrete acts as an air barrier, reducing air

inltration and saving more energy. Concrete has low VOC

emittance and does not degrade indoor air quality.

Sustainability attributes can be evaluated by perorming a

lie cycle assessment Because these procedures are time con-i b ildi ti t h LEED h

become popular. Precast concrete can help a project earn up

to 23 points toward LEED certication or new buildings (a

total o 26 points are required).

REFEREnCES

1. World Commission on Environment and Development, Report

on Our Common Future, Oxord University Press, New York,

NY, 1987.2. U.S. Green Building Council, An Introduction to the U.S.

Green Building Council and the LEED Green Building Rating

System, PowerPoint presentation on the USGBC website,

October 2005, www.usgbc.org.

3. GreenValue, Green Buildings Growing Assets, www.rics.org/

greenvalue.

4. www.energystar.gov.

5. Portolio Manager, www.energystar.gov.

6. American Society o Heating, Rerigerating, and Air-

Conditioning Engineers, ASHRAE Standard 55Thermal

Environmental Conditions or Human Occupancy, Atlanta, GA,

www.ASHRAE.org.

7. American Society o Heating, Rerigerating, and Air-

Conditioning Engineers, ASHRAE Standard 62.1-2004

Ventilation or Acceptable Indoor Air Quality, Atlanta, GA.

8. Illuminating Engineering Society o North America,Illuminating

Engineering Society o North America Lighting Handbook, 9th

edition, December 2000, New York, NY, www.IESNA.org

9. LEED or New Construction, Version 2.2, United States

Green Building Council, October 2005, www.USGBC.org.

10. Green Globes, www.thegbi.org.

11. Heat Island Group Home Page, eetd.lbl.gov/HeatIsland/.

12. American Society or Testing and Materials, ASTM C

1549, Standard Test Method or Determination o Solar

Refectance Near Ambient Temperature Using a Portable Solar

Refectometer, Conshohocken, PA, www.ASTM.org.13. American Society or Testing and Materials, ASTM E 1918,

Standard Test Method or Measuring Solar Refectance o

Horizontal and Low-Sloped Suraces in the Field, West

Conshohocken, PA.

14. Portland Cement Association, 1998 U.S. and Canadian Labor-

Energy Input Survey, Skokie, IL, www.cement.org.

15. Portland Cement Association, Design and Control o Concrete

Mixes, Chapter 5, EB001, 2002, Skokie, IL.

16. American Society or Testing and Materials, ASTM C 33,

Standard Specication or Concrete Aggregates, West

Conshohocken, PA, www.ASTM.org.

17. An Introduction to the U.S. Green Building Council and

the LEED Green Building Rating System, a PowerPoint

presentation on the USGBC website, October 2005, www.

usgbc.org.18. 1992 National Energy Policy Act, U.S. Department o Energy,

www.DOE.gov.

19. U.S. Department o Energy, Final Report on the August 14,

2003 Blackout in the United States and Canada: Causes and

Recommendations, 2004, Washington, DC.

20. Massachu

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