Sustainability of Concrete

7/30/2019 Sustainability of Concrete

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marketing sustainable concrete through advice, education & information

sustainable concrete


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Concrete is the most commonly used building material

on the planet and most of the infrastructure for modern civi lization

has been built using concrete in some form or other. Concrete has a

low embodied energy and a significant number of inherent characteristics

which contribute to sustainablity of concrete structures.


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sustainable concrete

Cement & Concrete Institute

2011


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ISBN 978-0-9584779-4-9

Copyright, 2011, by Cement & Concrete Institute,

Midrand, South Arica

This publ ication may not be reproduced in whole or

in part without the written permission o

the Cement & Concrete Institute.

Design, layout and production by DesignWright

Printing by the Bureau Digital Media (Pty) Ltdon 100% recycled paper


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Concrete is the most commonly used building material

on the planet and most o the inrastructure or modern

civilization has been built using concrete in some orm

or other. Concrete has a low embodied energy and a

signicant number o inherent characteristics which

contribute to sustainablity o concrete structures.

This document deals with the issue o sustainability, what

it is and why it is important and more importantly the role

which concrete can play in the provision o sustainable

buildings and inrastructure. The owner, developer,

designer and contractor are provided with inormation

indicating that by using concrete wisely, they will be

contributing to sustainability and by incorporating some

o the benets o concrete, save money and resources

during the lie o the structure.

Sustainability is dened and a number o ways in which

it is assessed are mentioned. The document goes on

to indicate the various ways concrete can contribute to

sustainability by reducing embodied energy, consumed

energy and in the use o resources. Finally guidance is

given to indicate where and how all these benets can be

used during the design, construction, use and end-o-lie

phases o a building or structure.

definitions

Sustainability is usually expressed or assessed in

terms o either embodied energy or embodied carbon

expressed in carbon dioxide equivalents (CO2e

) and

consumed energy. For the purpose o this document

the ollowing denitions will be used.

Embodied energy (EE) the energy consumed or the

raw material extraction, transportation, manuacture,assembly, installation, disassembly and deconstruction

or any product system over the duration o a

products lie.

Embodied Carbon (EC) the CO2e released or the

raw material extraction, transportation, manuacture,

assembly, installation, disassembly and deconstruction

or any product system over the duration o a

products lie.

Consumed energy (CE) the energy consumed during

the lie or use o a building or structure.

1

Embodied energy and embodied carbon are linked.

Embodied carbon can be reported as embodied energy

using the various emission actors.

Due to the complex nature and multiple energy sources

contained in the embodied energy o a structure, in this

document the embodied energy will be reported using

embodied carbon measured in tons o CO2e per ton or

cubic metre o concrete (CO2e/ton or CO

2e/m3). In the

context o this report, the terms embodied energy and

embodied carbon are interchangeable.

As the primary energy consumed during the lie o a

building is electricity, and to be able to compare the

embodied carbon with the energy during use, the Eskom

electricity actor o 1 200 tons CO2e/MWh can be used

to convert consumed energy into carbon emissions.

In the case o transport inrastructure, the energy

consumed will be primarily in terms o petrol and diesel

consumption.

what is sustainability?

In order to save the planet and leave a legacy orour children and their children, we all need to ensure

that everything we do is sustainable, be it at work or

home. The Bruntland report commissioned by the

United Nations dened sustainable development as,

Development that meets the needs o the present

without compromising the ability o uture generations to

meet their own needs. Sustainability thereore means

balancing various economic, environmental and social

actors (See Figure 1). This is oten reerred to as the

Triple Bottom Line. Making sure that these three actors

are in balance will result in increased sustainability.

Emphasis on any one actor at the expense o otherstakes the system out o balance, whilst moving towards

the green centre balances the system. However each o

these actors is complex and multi-aceted.

introduction

Concrete has a low embodied energy and a

significant number of inherent characteristics

which contribute to sustainablity of concrete.


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Making structures and buildings sustainable is good

engineering practice and involves using limited resources

to achieve design objectives and balancing competing

and oten contradictory interests over the ull lie-cycle o

the structure. This has always been good engineering,

but now ar more consideration has to be given to

environmental issues (primarily energy consumption and

the depletion o natural resources) and social issues (the

eect the building or structure has on the community)

both during and ater construction. Sustainability in this

context reers to buildings and inrastructure and their

energy consumption during their liespan.

In terms o environmental actors infuencing

sustainability, the primary issue oten considered when

assessing sustainability is energy usage. This includes

the embodied energy in the materials and products

used in the construction o the structure and the energy

consumption during the lie o the building. The energy

usage is aected by a large number o design and other

actors, not necessarily all o which are addressed in this

document. The depletion o natural resources also needs

to be considered.

A number o ways o assessing the sustainability o

structures exist. These include rating systems such as

the Green Star system o the Green Building Council

in South Arica and the LEED system in the USA.

These systems award points or various sustainabilityinitiatives during the design and lie o the building.

Unortunately, these systems oten lead to chasing

points or a particular rating rather than to concentrating

on real sustainability. In South Arica bicycle stands

were provided at a building to gain a point or two: the

surrounding environment is not conducive to cycling,

i.e. no cycle paths, etc. and very ew people cycle.Increased

sustainability

Environmental

Social Economic

localcodes,standardsand

regulationsinplace

Compliance

Vanilla

Beyond Compliance

Green

Future Proo

Deep Green

Energy

Carbon

Materials

Water

Net Zero Primary

Energy

Near Zero CarbonConstruction

Zero UnsustainableMaterials

Zero Waste

Net Zero Water

Figure 2: The Skanska approach to providing sustainable structures

Figure 1:The Triple Bottom Line concept


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Skanska1, a large construction company which operates

in Europe and North America, ound the existing rating

systems such as Green Star and LEED to be very

complex and not entirely appropriate. They thereore

developed their own approach (See Figure 2) which was

to aim or the ollowing during the lie o a structure:

Zeronetprimaryenergyconsumption

Zeronetcarbonconstruction

Zerouseofunsustainablematerials

Zerowasteand

Zeronetwaterconsumption.

The Cement and Concrete Institute (C&CI) believes this is

a very pragmatic approach which ocuses on sustainable

issues by setting targets rather than scoring points as in

most current rating systems. While the zero target may

be dicult to achieve it is a worthwhile target towards

which to strive. C&CI supports the Skanska approach

in this document together with the lie cycle perspective

shown in Figure 3.

The National Ready Mixed Concrete Association in the

USA has indicated the ollowing average savings o

sustainable buildings over conventional buildings:

3

16%

Recycling Phase

Energyuse...................... 30% lower

Carbonemissions...........35% lower

Wateruse ....................... 30 to 50% lower

Wastegeneration............ 50 to 90% lower

current situation

To a large extent, engineers primarily ocus on structural

design, construction materials and the construction

process itsel, and may also consider the use o

secondary industrial products, recycling, resource

conservation and embodied energy. The material supply

industry is concentrating on whether one product is

greener than another or has lower embodied energy.

While these are important, real opportunities are being

missed by ignoring the operational or use phase o

buildings and structures. Research suggests that the

long-term, cumulative benets o considering the whole

lie cycle o structures are staggering.

While it is important to consider and embrace all

sustainability strategies to reap the ull benet, ar more

attention needs to be paid to the use phase and a ull

lie-cycle assessment (LCA) o any structure.

A lie-cycle assessment involves a cumulative analysiso all impacts throughout all stages o the lie cycle.

Recent comprehensive LCA studies have given us clues

as to where we be can be most eective in ensuring

sustainable structures.

While it is important to consider and embrace

all sustainability strategies to reap the fullbenefit, far more attention needs to be

paid to the use phase and a full life-cycle

assessment (LCA) of any structure.

70%

Product Use Phase

20%

Materials Acquisition, Production and Construction Phases

Figure 3a:The lie-cycle approach to sustainable development


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Figure 4: Ecoprole o dierent lie cycle stages o a typical road

End o Lie

Truck Trafc

Car Trafc

Construction &Maintenance

PercentofeachItemUsedorProduced

duringEachStageintheL

ifeoftheRoad

100

90

80

70

60

50

40

30

20

10

0

%

Energy

Water

Res

ources

Waste

Nuclearwaste

Co2

SO

2

PO

4

Ecotoxicity

Humantoxicity

O3

Smog

Odours

Figure 3b:The lie-cycle approach to sustainable development

30%

70%

Materials or

concrete

Concrete

production

Concrete

placingRecycling

Concrete structures in service


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An example rom the roads industry illustrates this point.

Research rom the Centre dEnergetique de lEcole des

Mines de Paris2 determined an ecoprole o dierent lie

stages o a typical road (See Figure 4). It can be seen

that the bulk o the impacts occur during the use or lie

o the road.

Our current conventional tools or improving

sustainability in roads include the use o recycled

concrete and asphalt, the use o extenders, warm mix

asphalt, etc. Even i a 30% improvement is made in the

embodied energy (which is highly unlikely in the short

term) during the initial phase, the improvement is shown

by the yellow line in Figure 6. I however we could

reduce the use phase portion by 5% (which is ar more

possible) this would be represented by the red area inFigure 6.

There is a similar pattern reported in the building industry

where a report rom the Athena Institute3 showed that a

buildings operating energy consumption over its lietime

is between 87 and 97% o the total energy requirement

while the embodied energy only accounts or between

3 and 13 % o the total energy.

These two examples clearly illustrate the need to

consider a ull lie-cycle assessment o all the likely

impacts o the structure and particularly those during the

use phase o the structure which is where the greatest

impacts are going to be made. This is very similar to the

challenge with project cost where it emerged that initial

cost was not a good indicator o total cost.

Figure 5: Overallecoprole

ExtractionProduction

Construction

End o LieUSE PHASE

Figure 6: Overall ecoprole showing impact o improvements

ExtractionProduction

Construction

End o Lie

USE PHASE


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As the operational energy o a structure is reduced, the

relative proportion o embodied energy will increase.

(See Figure 7).

co2

emissions from concrete

The current average worldwide consumption o concrete

is about one ton per year or every living human being.

Because o this extensive use, concrete has a relatively

large environmental ootprint, but worldwide the cement

industry still only accounts or approximately 5% o

man-made CO2

emissions. Approximately 40% o this

is rom burning coal and 60% is rom the calcination o

limestone. While the above inormation on the carbon

dioxide equivalent (CO2e) o cement is readily available,structures are not constructed out o cement but rather

rom concrete, o which cement is but one ingredient.

Figure 7: Increasing eect o embodied energy as operational energy is reduced

Operational Carbon

81%

Embodied Carbon

63%

Operational Carbon

62% Operational Carbon

37%

Embodied Carbon

38%

Embodied Carbon

19%

20%

Energy Reduction

20%

Energy Reduction

Increased Focus

on Construction

Due to an increased demand or inormation on the

carbon ootprint o concrete, the C&CI commissioned

a study to determine the CO2e values or all the

ingredients in concrete and ultimately, the concrete

itsel. The environmental impact o the production

o the most commonly used raw materials (cement,

ground granulated blasturnace slag (GGBS), fy ash

(FA), aggregates, water and admixtures) as well as the

production o ready-mixed and precast concrete was

assessed, resulting in:

AreportassessingthecradletositeCO2e

emissions o raw materials used in concrete,

including transport o those materials, and quantiying

average CO2e emissions or each o the raw materials

used in concrete


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Amodelbasedonthereport,allowingthedesigner

to experiment with dierent material combinations

or concrete mixes to accurately quantiy the CO2e

impact or one cubic metre o concrete cast in

situ or precast, and assess the eect o dierent

raw material properties on the R/m3 cost and the

environmental impact o the concrete.

The report and model are reely available at:

www.cnci.org.za

The direct, indirect and other indirect emissions as

dened by the Green House Gas Protocol were

determined and incorporated into the model, using

the data gathered rom 128 production activities o the

concrete industry based on 2007 data. The total CO2e

emissions rom each contributing activity were then

compiled into a single model to determine the overallemissions per cubic metre o concrete specic to the

South Arican industry.


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Cement Type Average Emission Values

(kg CO2e/ton)

CEM I 985CEM II A-L 840

CEM II A-S 815

CEM II A-V 790

CEM II B-L 720

CEM II B-S 730

CEM II B-V 690

CEM III A 560

CEM IV A 640

CEM IV B 570

CEM V A 590

CEM V B 415

Table 1: Average CO2e per ton o cement

cement

An accepted international gure or CO2e isapproximately 1 000 kg per ton o cement. This value

is being reduced by new technology and the use o

alternative uels in cement kilns. The primary method

o signicantly reducing the emissions is to reduce the

clinker actor in cement by extending the cement using

materials such as GGBS, FA, limestone and other

materials.

The sourcing o synthetic gypsum rom other industries

such as industrial by-products rom the ertilizer and

sulphuric acid industries or use in cement urther

contributes to sustainability.

The cement industry is active in reducing energy

consumption and in particular in reducing the amount

o non-renewable ossil uels through the introduction o

modern technology and equipment. This includes the

use o alternative uels and resources. The introduction

o waste tyres in current kilns will also address the

sustainable management o used tyres.

Table 1 below shows average CO2e emission values

or dierent cements and the eect o extenders on the

overall CO2e per ton.

Note that these are average fgures and the actual

fgures will vary rom supplier to supplier. Your

supplier should be contacted or the CO2e or the

particular cement that you intend to use.

8

cement extenders

Cement extenders have a dramatic eect on reducingthe CO2e per ton o cement as well as adding benets

ranging rom better workability o resh concrete through

to more durable, impermeable concrete. These materials

are generally secondary products which end up in

landlls i not used by the concrete industry. The average

values or South Arican extenders are shown below.

Table 2:Average CO2e per ton o extender

Extender Type Average Emission Values

(kg CO2e/ton)

FA 2

GGBS 130

aggregates

The average value or aggregates is 5 kg CO2e per ton.

Aggregates are high-volume, low-cost materials. It is

energy ecient and sustainable to extract them close to

communities and industries where they are to be used.

In terms o choosing aggregates or sustainable

concrete, it is important to not only take immediate cost

implications into account. Less may be more: choosing

the less expensive option may aect both short- and

long-term savings. The C&CIs CO2e emissions model

allows assessment o the eect o dierent aggregates

on concrete properties, and in particular highlights the

cost implications o choosing poor quality sands.

The use o recycled concrete as an aggregate will

urther reduce the CO2e o the concrete and at the same

time reduce the depletion o natural resources and the

dumping o old concrete at landll sites.


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admixtures

The average value or admixtures is 220 kg CO2e

per ton.

Although the proportion o admixture in a concrete

mix is tiny compared to other raw materials, recentdevelopments in admixture technology now allow

admixtures to be used to control properties o concrete

such as workability or pumpability, durability, aesthetics

and cost eectiveness very precisely. Although

the negative impact on the environment is minimal,

admixtures have a major positive eect on sustainability.

water

The average value or water is 1kg CO2e per ton.

Concrete ready-mix plants are recycling wash and waste

water, saving costs and reducing consumption o this

precious resource.


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Durability, economy, energy efciency,

fre resistance, low maintenance costs,

recycling and thermal mass, all add

to the sustainability o concrete in

our built environment

11


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Mix No Binder Water Reducer Water Demand o Aggregate

1 CEM l Y Low

2 CEM l N Low

3 70/30 CEM l/FA Y Low

4 70/30 CEM l/FA N Low

5 50/50 CEM l/GGBS Y Low

6 50/50 CEM l/GGBS N Low7 CEM l Y High

8 CEM l N High

Table 3: Mix details

concrete

With the intention o determining the CO2e emissionsresulting rom the production o a cubic metre o

concrete in South Arica, the C&CI developed a model

or the determination o CO2e emissions related to

the production o concrete. The production energy

inormation gathered was used to determine the carbon

dioxide equivalent (CO2e) emissions o each sector.

The total emissions rom all sectors were then compiled

into a single model to determine the overall emissions

per cubic metre o concrete specic to the South Arican

industry.

The C&CI model allows the user to input specic

concrete mixes to determine the CO2e emissionsresulting rom a cubic metre o the specic concrete

going into products such as roo tiles, bricks, precast

concrete slabs or in-situ concrete.

In order to determine the eects on CO2e emissions o

varying a concrete mix design, the C&CI commissioned

the design o specic mixes.

All the mix designs used raw materials in varying

amounts in order to quantiy the CO2e emissions and

to evaluate the eects o:

BlendingextenderssuchasGGBSandFAwitha

CEM I 42.5

Admixture(waterreducer)usageand

Aggregatecharacteristics.

A total o eight 30-MPa concrete mixes were designed.

Dolomite aggregates (with low water demand) were used

or six o the mixes. Mixes were carried out with andwithout a water-reducing admixture as indicated in

Table 3.

In addition two mixes were made with CEM l and

decomposed granite sand rather than dolomite, to

illustrate the eect o using sand with a high water

demand as opposed to one with a low water demand.

The model was used to determine the eect o these

dierent combinations on the CO2e emissions and

the results are shown in Figure 8. It was ound that an

average cubic metre o in-situ concrete containing

CEM I 42.5 with an extender (GGBS) and a water

reducing admixture with a specied strength o 30 MPa,

resulted in a range o between 215 and 240 kg

CO2e/m3 or 90 to 100 kg CO

2e/ton. An equivalent

strength mix using CEM I without extender or admixture

resulted in 376 kg CO2e/m3 or 157 kg CO

2e/ton.

These gures should be compared with the average

CO2e or a CEM l o 985 kg CO

2e/ton. As stated

previously, structures are constructed with concrete

(not cement) and the above example indicates that the

carbon ootprint o concrete is signicantly less than

previously thought.


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Figure 8: CO2

emissions resulting rom various mix designs

Admix

No admix

600

500

400

300

200

100

0

kgCO2/m3

CEM I 70/30 FA 50/50 GGBS CEM I

Dolomite Sand DecomposedGranite Sand

Using concrete makes environmental sense. Properties

such as economy, thermal mass, fire resistance and

water-tightness add to the sustainability of concrete in

our built environment. And at the end of the usage phase,

concrete can easily be recycled.

Concrete carbonates during its lie and absorbs

CO2

rom the environment. This process is generally

very slow and is deleterious to the concrete in that

it can promote the corrosion o steel reinorcement.

Steps are thereore taken to reduce as much

carbonation o the concrete as possible during the

lie o the structure. However, the concrete will still

carbonate. The carbonation or absorption o CO2rom the atmosphere increases signifcantly when

the concrete is demolished and crushed.

Concrete has an excellent ecological prole compared to

other construction materials, with a number o inherent

characteristics that contribute towards achieving balance

in accordance with the Triple Bottom Line concept.

The social contribution o concrete to our civilization

cannot be overestimated. Concrete is the second most

used resource in the world ater water and contributes

signicantly to our standard o living, rom the houses we

live in, the schools and universities that we attend, the

oces we work in, the inrastructure o water reticulation

and sewers, the dams that hold our water, to the roads

that make transport or us and all our needs possible.

Using concrete makes environmental sense. Properties

such as economy, thermal mass, re resistance and

water-tightness add to the sustainability o concrete

in our built environment. And at the end o the usage

phase, concrete can easily be recycled.

From an economic viewpoint, although cement is

relatively costly to produce in both nancial terms and interms o embodied energy, concrete is a cost-eective

material with low embodied energy. In the long-term,

concretes durability, low maintenance and re-usability

have very positive economic eects, and concrete

structures have optimal energy perormance with

associated positive eects on whole-lie energy

usage.

Up to 40% o all materials used in human activity are

directed into the built environment. This has a direct and

visible impact on the worlds nite resources.

The concept o sustainable development includes the

ability to build the acilities and structures needed today

without compromising resource supply or the uture.


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Figure 9: Labour-intensive construction

Figure 10: Bus stop showing design fexibility o concrete

In practice, many o the actors aecting the

contribution o concrete to sustainable development

are inter-related: the use o cement extenders has a

positive environmental impact (less production o

cement = less CO2

emissions, use o other industry

secondary products, resulting in waste minimisation

and hence saving in landll space), social impact (less

use o nite resources, better durability, less secondary

products dumped in landlls), and economic impact

(better value or money in the long-term).

To achieve substantial sustainability benet during a

building or structures lie cycle, the designer, specier

and owner need to take into account a myriad o actors

during the design, construction, usage and end-o-lie

phases, not only in terms o saving energy and reducing

the use o nite resources, but also in terms o exploring

other inherent advantages o concrete.

Some o these advantages and attributes o concrete

are dealt with below.

local material

All the primary materials used in concrete, with the

possible exception o some sophisticated admixtures,

are produced locally. The extenders and slag aggregates


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used are secondary products and would otherwise

be dumped i not used by the cement and concrete

industry. While the cement actories are generally

located close to their raw material sources, sources o

aggregates and ready-mix plants can be placed close

to the areas o demand thereore reducing the energy

required or transport.

The materials used in concrete make ecient use o

natural resources, and again the potential or recycling

at lie-end saves quarrying o nite resources. Concrete

mixes or ready-mix plants and precast yards are

designed specically to use aggregates sourced rom

local quarries, and more recently, recycled concrete,

thus saving uel in transporting these materials.

Importing cement would increase its embodied energy

due to the energy involved in transport.

labour intensive construction

Concrete and concrete products lend themselves in

most cases to labour-intensive construction whether this

is the small-scale manuacture o concrete products or

the use o concrete in various orms o construction. In

the provision o human settlements, concrete roo tiles,

concrete bricks or blocks, concrete kerbs, concrete

reticulation poles, concrete block paving and concrete

pipes may be used, all o which may be installed using

labour-intensive construction methods. Most concrete

Figure 11: Concrete nish

construction uses a signicant labour component

thereby creating jobs when concrete is used.

design flexibility

As concrete products and elements can be constructed

into any shape and can be cast in various ways

including in situ, precast, etc., this oers the designer

a large amount o fexibility. For the architect this allows

expression in dierent orms while or the engineer,

the fexibility allows or complex sections and shapes.

The act that concrete can be constructed in situ or

by precasting, or using a hybrid o the two methods

provides the designer a large degree o fexibility when

programming a project, particularly i the project needsto be ast-tracked.

variety of finishes

There are unlimited possibilities or nishes when

concrete is used. Concrete nishes can be designed in

a range o attractive colours and a multitude o textures

and nishes. In eect, the nish is put into the concrete

during the construction stage, rather than applied later

as a separate operation. The use o concrete as a nal

nish means no other nishing activities such as painting,

tiling or coating are required. This saves energy and

materials at construction stage and also reduces uture

maintenance costs.

In addition, concrete nishes do not emit any toxic or

volatile products into the environment and have no

detrimental eects on the environment during their

entire liecycle.


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Figure 12: A durable strong structure

16


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cost-effectiveness

The initial costs o well-engineered designs orappropriate products constructed with concrete as the

major material should be equally or more cost eective

than designs using other materials. Lie-cycle cost

analyses show that, because o concretes durability, the

whole lie cost o many projects is lower when concrete

is used as the major construction material.

structural integrity

The structural design and construction o concrete

elements in buildings (including in-situ reinorced

concrete, precast concrete, tilt-up, hybrid construction

and post-tensioned concrete elements) is well

understood by architects, structural engineers and

contractors. South Arican design and construction

codes regulate the structural requirements o concrete

buildings. This leads to sae structures, able to withstand

any permanent, imposed, wind and earthquake actions.

For common spans, the relatively high mass o concrete

foors leads to natural damping and low vibration. For

more-stringent criteria, such as or laboratories or

hospital operating theatres, the additional cost to meet

stricter vibration criteria is negligible.

fire resistance

Concrete does not burn and does not emit any toxic

umes when subjected to re. It will not produce smoke

or drip molten particles. For these reasons, in the

majority o applications, concrete can be described

as re resistant. The concrete in structures, unlike a

number o other construction materials, generally does

not require re-proong or protection i appropriately

designed, because o concretes inherent re resistance.

This obviates the time, cost, additional materials and

labour required to provide separate re protection

measures. During a re, the concrete cover will protect

the reinorcement rom buckling or yielding.

Concretes inherent re resistance can restrict smoke

rom spreading, and will largely maintain the buildings

strength during a re. Ater a re, the continuingstructural integrity and reduction in smoke damage also

reduces the magnitude o insurance claims. Ater a re,

concrete structures generally remain intact, allowing or

relatively quick repair and re-occupation, saving time and

money, as well as nite resources.

Fire-damaged concrete buildings generally do not require

demolishing and rebuilding.

Concrete structures both protect lie and preserve

property, thereby contributing to enhanced social and

economic perormance o the built environment.

durability

Concrete is one o the most durable materials on

earth. Well-designed, well-constructed concrete oers

exceptional durability and long lie in any structure.

Concrete structures built over 100 years ago (some

as long ago as Roman times) are still in active service

today. Such extended lie span results not only in

less expenditure o energy in building new homes,

inrastructure, etc. but also in less maintenance and

impact on the use o nite resources.

The rst line o deence against deterioration is good

quality, impermeable concrete. In the case o reinorced

concrete, the quality o the cover concrete is extremely

important in protecting the reinorcing steel against

aggressive agents and re. This zone o concrete is

intended to act as the barrier between the reinorcing

steel and external aggressive environment and its quality

is o primary importance in durability considerations.

Good material choice, mix proportioning and good

construction practice are essential to ensure

durable concrete.

Ensuring the concretes integrity and durability is

essential in order to utilize the equity already in the

existing structure and not to re-invest in materials and

energy sooner than is necessary.


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energy efficiency

The use o local materials in the production o

concrete minimises uel requirements or handling and

transportation. Once in place, concrete oers signicant

energy savings over the lietime o the structure.

The embodied energy in the construction o a structureis generally minimal relative to the energy likely to be

consumed during the lie or use phase o a structure.

This has been illustrated earlier. Any reduction in energy

during the use phase is likely to have a signicant eect

when the lie cycle assessment is analysed. See also the

eect o thermal mass on the energy consumption

o structures below.

In the case o roads and transport inrastructure, any

aspect reducing uel consumption will have a major

impact on the energy usage over the lietime o a busy

motorway. A large Canadian study quantied a 2.35%uel saving by using concrete roads, with a subsequent

reduction in the emission o polluting gases. See also

the section on reduced lighting energy later in

this document.

Internal temperature Internal temperature External temperature

with high thermal mass with low thermal mass

30C

15C

Day Night Day

Peak temperaturedelayed by up tosix hours

Up to 6-8C d ierencebetween peak externaland internal temperature

Figure 13: Stabilising eect o thermal mass on internal temperature

thermal mass

Thermal mass (also called thermal capacitance or

heat capacity) is the ability o a body to store heat.

Together with eective ventilation, solar shading and

building orientation, the use o thermal mass is a

critical component o passive solar design o buildings.

Buildings with a medium to high level o thermal massare characterised by their inherent ability to store thermal

energy, and then release it several hours later. Thermal

mass can make a signicant contribution to reducing

energy consumption and green house gas emissions,

while maintaining occupancy comort during the lie o

the building (See Figure 13).

For a material to provide a useul level o thermal mass,

a combination o three basic properties is required:

Highspecicheatcapacitytomaximisetheheat

that can be stored per kg o material

Highdensitytomaximisetheoverallweightofthematerial used

Moderatethermalconductivitysothatheat

conduction is roughly in synchronisation with the

diurnal heat fow in and out o the building.

Building Density Thermal Specifc Heat Eective Thermal

Material (kg/m3) Conductivity (W/m.K) Capacity (J/kg.K) Mass

Timber 500 0.13 1 600 Low

Steel 7 800 50 450 LowConcrete 2 400 1.75 1 000 High

Brick 1 750 0.77 1 000 High

Table 4: Thermal properties o common construction materials


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Figure 14: Thermal mass in summer

Figure 15:Thermal mass in winter

Winter day

DuringthecoldseasoninSouthAfrica,thelow

angle o the sun shines through north-acing

windows, and heat is absorbed by thermal mass

in the foor and the walls.

Intheeveningwhenthesungoesdownandthe

temperature drops, heat fow is reversed and

passes back into the room.

Winter night

Atnight,curtainsaredrawnandwindowskept

shut to minimise heat loss.

Heatcontinuestobereleasedbythethermal

mass, and supplementary heating is adjusted so

only the minimal amount is used.

Bymorningthethermalmasswillhavegiven

up most o its heat and the occupants rely on

supplementary heating until later in the day.

Summer day

Duringveryhotweather,windowsarekeptshut

to keep warm air out.

Overhangsonthenorthelevationcankeepoutthe high angle o the sun during the hottest part

o the day.

Coolingisprovidedbythermalmassintheoor

and walls.

Summer night

Thewindowsareopenedatnighttoventilatethe

building and cool the thermal masses.

Ifanotherhotdayisexpected,thewindowsare

closed again in the morning and the cycle is

repeated.

North

North


24/3720

building, the concrete absorbs heat during the day and

releases it slowly over the evening. Temperatures inside

are lower than outside during the day, and higher than

outside during the night, with ventilation allowing the heat

to escape. Both summer and winter evenings are likely

to be within comortable range, with consequent minimal

supplementary daytime heating or cooling required (See

Figures 14 and 15).

light and heat reflectance(albedo effect)

The light colour o concrete has a number o benets.

The two primary benets are reduced lighting energy

consumption and a reduction in the heat island eect

in urban areas. An additional benet is a signicant

contribution to combatting global warming.

This is summarised or dierent materials in Table 4.

Harnessing the eect o concretes high thermal mass

has positive implications in terms o energy usage

during the buildings entire lie cycle. Using heat or

cold absorbed by exposed thermal masses gives an

increased time-lag between peak heating/cooling loads

and outside temperatures, allowing the use o o-peak

energy as a top-up instead o the primary source. This

also allows the use o smaller, more ecient heating/

cooling equipment, with less energy usage to maintain

the same interior temperatures.

The process can be assisted by natural ventilation or by

water-cooling (up to 80 W/m2), and exposed sots and

underfoor heating can exploit the thermal mass in

250-mm or thicker concrete slabs.

Reverse mass designs are particularly suited to cool and

temperate regions, but also create cool daytime reuges

in tropical climates. I the building is well-insulated and

the concrete thermal masses are exposed inside the

Figure 16: Increased visibility with concrete paved areas

Figure 17: Illustration o heat island eect

Rural Commercial Urban Suburban

Residential ResidentialSuburban Downtown Park Rural

Residential Farmland

C

33

32

31

30

F

92

85

Lateafternoontemperature


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Figure 18: Illustration o the temperature dierencebetween dierent pavement suraces in Rio Verde, Arizona

21

reduced lighting energy

The light colour o concrete provides a saer environmentand also enables lighting requirements to be reduced,

both internally and externally.

For concrete roads or parking areas, research in the USA

has shown that surace refectance readings on concrete

pavements and other suraces are our to ve times

higher than other road suracing materials which means

increased visibility o the road, pedestrians and other

vehicles or drivers and increased security in urban areas

(See Figure 16).

Similar research has shown that the increased

refectance o concrete pavements results in a reduction

in lighting masts and thereore energy requirements by

up to 24%. This principle applies also to urban areas and

car parks.

heat island effect

In urbanised parts o the world, the towns and cities are

generally hotter than the rural areas surrounding them.

As these centres increase in size, ambient temperatures

increase accordingly. On hot summer days, ambient

conditions in urban areas can be 2 to 6C warmer thanin the adjacent countryside. This phenomenon is known

as the urban heat island eect; and is quite separate

rom global warming caused by greenhouse gasses.

In addition to the discomort so caused, and the

additional demand or articial cooling, urban heat

islands can infuence rainall patterns, with increased

rainall downwind o cities compared to the upwind

areas. The common measure o the urban heat island

eect is albedo. This is the ratio o refected to incident

electromagnetic radiation energy, and is indicative o the

refectivity o a surace (See Figure 17).

Albedo or solar refectance is the ratio o refected solar

radiation to the amount that alls on the surace, rated

rom 0 (no incoming radiation refected) to 1 (all incoming

radiation refected). The lighter the surace colour, the

more solar radiation it will refect, and the less heat it will

absorb. The solar refectance o concrete varies between

0.2 and 0.4, and that o asphalt rom 0.05 to 0.2.

Albedo depends on the nature and colour o the surace,

the requency o the incident radiation and the direction

and directional distribution o the incident radiation.

Exposed building materials with high albedo refect more

heat, and lead to cooler cities. The albedo o normal

concrete is approximately 0.35, with values as high as

0.7 to 0.8 or white concrete made with white cement.

In contrast, dark materials such as new asphalt can have

an albedo as low as 0.05.

The incorporation o high-albedo concrete products in

exposed suraces such as pavements can signicantly

reduce the heat island eect and lead to cooler urban

areas (See Figure 18). Due to the increased albedo

value o concrete, the temperature dierence between

adjacent concrete and asphalt roads in summer in

Arizona was measured as 11C.

Using concrete can lower average summer aternoon

temperatures in surrounding buildings by as much a 3C,

cutting air-conditioning usage by 18%.


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Figure 20: The lime cycle

CO2

CaCO3

(Limestone)

Ca(OH)3

(Concrete)

CaO

(Cement)

Water

Hydration

CO2

Carb

onatio

n Calcinatio

n

Figure 19:Albedo eect o dierent road suracing materials

70

65

60

55

50

45

40

MaximumSurfaceTemperature(C

)

Albedo

0 0.1 0.2 0.3 0.4 0.5

12

3

5

7

8

11

6

4

9 10

12

1 Thin Asphalt Rubber2 Thick Asphalt Rubber3 Thin Asphalt Rubber with White Paint4 Thin Hot Mix Asphalt5 Chip Seal6 Thick Hot Mix Asphalt

7 Thin Hot Mix Asphalt with White Paint8 Thick Hot Mix Asphalt with White Paint9 Crumb-Rubber Concrete

10 Ultra Thin White Topping11 Thick Asphalt Rubber with White Paint12 Concrete

LEGEND


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combating global warming

A study by Menon

5

indicated that the 100 largestmetropolitan areas cover 0.26% o the earths land area

and that approximately 60% o US urban suraces are

pavements and roos. She indicated that i the albedo or

pavements could be increased by 0.15 or the biggest

100 metropolitan areas in the world, this would result

in an emitted CO2

oset o a total o approximately 20

Gigatons which would oset the eect o the growth o

CO2e or some 5 years. Concrete pavements can oer

such an increase in albedo values.

low maintenance

Because o its inherent durability, stiness and strength,

maintenance requirements are reduced which reduces

costs, user inconvenience and the use o nite resources.

acoustic performance

Excessive noise has an adverse eect on personal

health and wellbeing, ability to perorm quiet tasks and

productivity in general. Hearing loss due to prolonged

exposure to noise is well documented. The issue o

sound insulation and acoustic perormance o homesand oces has grown in importance, due in part to

the growing demand or increased density o urban

development. In general, increasing the mass o a wall

or foor improves the sound insulation o a room; hence

concrete oers a good barrier to airborne sound. Impact

sound can be controlled with appropriate foor and

ceiling nishes.

The inherent mass o concrete can minimise the

need or additional nishes required to meet acoustic

requirements, with concrete walls providing an

eective buer between outdoor noise and the indoor

environment and road noise in residential areas.

The same inherent mass gives concrete structures good

damping abilities in terms o acoustic perormance. This

is especially important in congested housing complexes.

co2

absorption

As has been shown earlier, the production o cement

results in CO2

emissions into the environment. However,

concrete carbonates during its lie and absorbs CO2

rom the environment. This process is generally veryslow and is deleterious to reinorced concrete as it

promotes the corrosion o steel reinorcement. Steps are

thereore taken during design and construction to reduce

carbonation o the concrete as much as possible during

the lie o the structure. However, the concrete will still

carbonate and the carbonation or absorption o

CO2 rom the atmosphere increases signicantly when

the concrete is demolished and crushed. Research

rom the Nordic Innovation Centre4 has indicated that as

much as 57% o the CO2

emitted due to the calcination

process in the manuacture o the cement (60% o the

total) will be reabsorbed by the concrete over 100 years

(See Figure 20).

pollution reduction

Air pollution is an increasing problem in densely

populated areas with pollutants due to trac includingvolatile organic compounds (VOCs) and nitrous oxides.

The use o titanium dioxide (TiO2) in the surace o

concrete elements can improve the air quality near

the structures. The titanium oxide acts as a catalyst

and when exposed to ultra-violet light and also visible

light, results in the conversion o harmul compounds

such as nitrogen monoxide and nitrogen dioxide into

relatively harmless nitrates (NO3). This process has been

demonstrated on concrete block paving in Belgium and

a concrete overlay in Paris, France with demonstrated

reductions in NOX

o around 20%.

Hardened concrete contains no substances harmul to

human or animal lie.

water conservation

The use o pervious concrete or permeable block paving

in pavements and parking areas allows rain, gardening

and other water to percolate through to replenish natural

aquiers. Run-o rom impervious suraces washes

grease and chemical products into surrounding rivers,

streams and dams, but pervious paving naturally lters

out pollutants.

Pervious concrete or permeable block paving can also

be used or stormwater attenuation to replace retention

ponds. This can also reduce the number and size o

drainage inrastructure elements, saving both materials

and energy, as well reducing uture maintenance.


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Figure 21: Precast concrete construction

construction flexibility

Concrete is an incredibly versatile material that can bedesigned and proportioned to meet a very wide range o

requirements. These may include various properties o

resh concrete such as consistence, fow, setting times,

etc. and hardened properties such as varying strengths

at early or late ages, dierent types o strength, densities,

abrasion resistance, shrinkage, etc.

Concrete structures oer a huge amount o fexibility

in the ways and methods in which they can be

constructed. Concrete can be constructed in situ using a

number o transport and placing mechanisms. Concrete

can be transported rom the batch plant to the structure

in any number o ways, including wheelbarrows,

dumpers, trucks, conveyors, cranes, pumps, etc.

Concrete can be placed by cranes, pumps, tremies (or

underwater construction), trunks, spraying and in many

other ways. Sel-compacting concrete oers urther

fexibility in placing concrete and the achievement o

excellent o-shutter nishes.

Concrete has an advantage over other materials in that

the concrete elements (walls, columns, beams, trusses

and slabs) can be constructed in situ on site, or precast

on site on the ground and lited into their nal position on

site (tilt up and stack casting) or precast in a precast yardand transported to site and erected into position as a

hybrid o precast and in-situ concrete.

Concrete has an additional benet in that all o the above

options can be combined on one project. This may mean

some elements are constructed in situ, while others may

be precast on site and still others precast o site (See

Figures 22 to 28).

Precast concrete is a construction product produced by

casting concrete in a reusable mould or orm, which is

then cured in a controlled environment, transported to

the construction site and lited into place. (As opposed

to standard concrete which is poured into site-specic

orms and cured on site.)

By producing precast concrete in a controlled

environment (typically reerred to as a precast yard), it

is possible to monitor all stages o production including

adequate curing, ensuring that products ully comply

with strength requirements.

The precast yard may be an established actory or it

may be on site. Precast concrete is generally cast at

ground level which helps with saety and productivitythroughout a project. There is greater control o the

quality o materials and workmanship in a precast plant

than when concrete is cast in situ. This oten results in

better durability and the products or structure lastinglonger with consequent saving in maintenance costs,

inconvenience, materials and energy. The orms used

in a precast plant may be reused hundreds to thousands

o times beore they have to be replaced which ensures

the cost o ormwork per unit is lower than or in

situ construction.

Oten, i the structure has been appropriately designed,

precast products can be removed and reused ater

the structure has reached the end o its lie and is to

be replaced.

There are many dierent types o precast concrete

products. Precast architectural panels are used to clad

all or part o a building acade. Stormwater drainage,

water and sewage reticulations make use o precast

concrete units such as pipes, culverts, manholes, sumps

and tunnels. Precast concrete building components

are used architecturally as cladding, trim products,

accessories and curtain walls. Structural applications

o precast concrete include bricks, blocks, oundations,

beams, foors, walls and other structural components.

Precast concrete products are used in the construction,

saety and site protection o various transportation

systems. Products include culverts, bridge beams and

segments, railway sleepers, sound walls or barriers,

saety barriers and kerbs.


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Figure 25: Liting cast panels

Figure 26: Orlando stadium stacked cast elements

Figure 27: Precast beams and trusses

Figure 22: Liting stack cast panels

Figure 23: Positioning stack cast panels

Figure 24: Liting pre-cast elements


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A signicant amount o precast concrete was used in the

construction o the 2010 stadia and the Gautrain.

Although precast manuacturing does not in itsel save

resources, better control over the production phase

ensures less non-compliant product and commensurate

saving o raw materials, as well as speeding up

construction on site. Well-sited, highly sophisticated

precast yards manuacture precast products to very

high tolerances, with subsequent time savings on site.

Good examples o this were the precast plants that

manuactured the precast concrete tunnel and bridge

segments or the Gautrain inrastructure.

recycling and reuseWhile the sustainability o buildings can be signicantly

increased by extending their useable lie by retrotting

and reuse, there comes a time when they must be

demolished and replaced.

recycling

The demolition o in-situ, precast and tilt-up reinorced

concrete can be achieved relatively easily by modern

cutting, breaking and liting equipment (See Figure 29).

The demolition o post-tensioned concrete however

requires more careul consideration. Once demolition has

been completed, the concrete and reinorcing steel can

be separated or recycling.Figure 28: Liting precast elements


31/3727

A demolished concrete structure provides a potentially

rich source o recycled aggregate or a range o

applications. Recycled concrete can be used as an

aggregate or building products such as bricks and

blocks, in road construction or layerworks, or or land

reclamation, thereby reducing the amount o material

sent to landlls. This recycling also reduces the need or

new virgin materials thereby saving resources and the

energy required to process them.

An additional benet o crushing the concrete is the

additional absorption o CO2

which was discussed

earlier.

In a number o ready-mixed concrete plants, wash water

is collected and reused in resh concrete, and aggregaterom returned concrete is screened out and reused.

This reduces the amount o waste generated at such

plants. This waste reduction is less likely to occur where

concrete is batched on site.

retrofitting and reuse

Oten, precast components rom structures may

be reused in new buildings rather than demolishing

and recycling the concrete. Structures using precast

elements can be designed or such reuse.

In ormer industrial areas and inner city precincts, there

are many old actories, old warehouses and the like that

can be converted into very desirable dwellings. Concrete

buildings can oten be adapted airly easily or new uses,

e.g. unused oce space in buildings can be retrotted

or use as residential accommodation. Eective building

retrotting usually requires the building structure to be let

largely intact.

Reuse and retrotting:

Savesnaturalresources,includingtherawmaterials,

energy and water otherwise required or newstructures

Reducesthequantityofsolidwastesenttolandll

Reducestheenergyconsumptionandpollutionthat

would result rom the extraction, manuacturing and

transportation o virgin materials.

The durability o concrete in structures is a key actor in

their suitability or reuse.

No matter what construction material is used, the

architect or designer needs to apply many dierent

strategies to ensure that the structure is sustainable in

terms o its environmental and social impact, to minimise

the use o energy, whether embodied or consumed

during the use phase, to minimise the use o water and

the generation o waste during the entire lie cycle o the

building. All o this can only be assessed by carrying out

a ull lie-cycle assessment o the structure.

In order to save the planet and leave a legacy

for our children and their children, we all need

to ensure that everything we do is sustainable,

be it at work or home.


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The potential increase in cost during the design and

construction phases in providing a green structure

will generally be more than oset by the savings rom

reduced energy usage during the use phase o concrete

structures.

The designer or architect needs to assess the inter-

relationship o all actors while the owner or user needs

to understand the sustainability eatures incorporated

in the structure. For example, a deep concrete heat

trap slab designed to capture the heat o winter sun will

be totally negated i the owner installs heavy curtaining

or blinds to keep the sun out in the aternoons! On

the other hand, drawing heavy curtains during the

early evening will keep the heat rom the warm foor

percolating into the room.

Design considerations which are not material-dependent

or structures whether commercial, industrial or

residential, to ensure minimal energy usage during the

ull lie o the structure include:

Ensuringthatthebuildingisorientedtotake

advantage o natural elements to provide natural

lighting, heating during winter, cooling during summerand natural ventilation.

Ensuringcorrectwindowanddoortypeand

placement to take advantage o sunlight during

winter, as well as the fow o air rom prevailing winds.

Eave depths may be designed to shade the inside o

the building during summer, but allow winter sun to

warm rooms.

Usingatriums,wind/stackventilatorsorventilation

panels to assist natural ventilation, and under-foor

vents or permeable ceilings to unlock the thermalmass in the upper part o slabs.

Choosingroongandexternalwallmaterial,and

colours or these that will either refect heat away

rom the building (lighter colours) or absorb solar

energy (darker colours, dark foor tiling), reducing

energy demand or heating and/or cooling.

striving for sustainable structures

Choosingthecorrectinsulationtypeandlocation.

A well-insulated roo and foor slab may keep the

interior temperature cooler in summer, resulting in

less air-conditioning costs, but may prevent the

winter solar heat rom being absorbed into the house.

Air-andweather-proongtoensurethatdraughts,

etc. do not negatively aect energy usage or heating

and cooling.

Designingbuildingsandotherstructurestousesolar

energy, and tap into the benets o thermal mass to

save energy.

Designingstructurestoreducetherequirementsfor

maintenance or to make maintenance simple and

cost eective.

Designingstructurestopromotesavingofnite

resources by, e.g., designing systems to promote

rainwater harvesting, reuse o grey water and other

water-use eciencies.

concretes role

Most o the ways in which concrete can contribute to

sustainability, which have been covered extensively in

this document. All o these issues need to be considered

during the design and construction o a building or

structure even though they may only have a signicant

eect during the use or end-o-lie phase. Table 5

indicates where the various attributes o concrete need

to or will play a role during the lie o the structure and

give guidance as to when they should be considered,

be they design, construction, use or end-o-lie

considerations.


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conclusion

29

Concrete continues to play a pivotal role in overall

economic growth both locally and globally. In order to

improve the sustainability o all concrete structures, there

is a need to understand the interactive eect o the many

issues rom cradle to grave in the design phase, during

construction and end-o-lie and, most importantly, the

energy savings achievable during the use phase.

This document has summarised what sustainability is,

what it means and why it is important in the provision

o sustainable buildings and inrastructure. Most

importantly, the document describes the role which

concrete can play in contributing to the sustainability o

our inrastructure.

This document provides the owner, developer, designer

and contractor with inormation which demonstrates

that by using concrete wisely, they will be contributing to

sustainability and by incorporating some o the benets

o concrete, save both money and resources during the

lie o the structure. Finally guidance is given to indicate

where and how all these benets can be used during

the design, construction, use and end-o-lie phases o a

building or structure. The only true method o assessing

a building or structures impact is via a lie-cycle

assessment.

Four urther documents are envisaged to complement

this document, ocussing specically on concretes role

in the provision o sustainable structures, sustainable

architecture, sustainable roads and sustainable human

settlements.

Property Design Construction Use End o Lie

Local material x x

Labour intensive x x

Design fexibility x x x

Variety o nishes x x x

Cost eectiveness x x x x

Structural integrity x x

Fire resistance x x

Durability x x

Energy eciency x x

Thermal mass x x

Light and heat x x

Low maintenance x x

Acoustic perormance x x

CO2

absorption x x

Pollution reduction x x

Water conservation x x

Construction fexibility x x

Recycling and reuse x x x

Table 5: Guide to area in which various concrete properties aect sustainability


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acknowledgements

The Cement and Concrete Institute grateully acknowledges the use o material rom the ollowing organisations:American Concrete Pavement Association

National Ready Mixed Concrete Association, USA

Skanska

Nordic Innovation Centre

The Concrete Centre, UK

European Concrete Paving Association

Arizona State University

Cement Concrete and Aggregates Australia

Cement Association o Canada

references

1. Morrin, N. Green building inormation modelling,

The cement sustainability initiative orum,

Warsaw, September 13 -15, 2010.

2. Rens, L. Concrete Roads: A smart and sustainable

choice. European Concrete Paving Association:

Brussels, 2009.

3. Cement Association o Canada, Concrete thinking

or a sustainable uture. Ontario: CAC, 2003.

(Publication Number SD-ICI-001-B).

4. Kjellsen, K.O., Guimaraes, M. and Nilsson, A.

The CO2

balance o concrete in a lie cycle

perspective, Oslo: Nordic Innovation Centre, 2005.

(Nordic Innovation Centre Report).

5. Menon, S. Short-term osets to CO2: Role o

refective particles and suraces, The International

Conerence on Sustainable Concrete Pavements:

Practices, Challenges and Directions, Sacramento,

September 15 - 17, 2010.


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Concrete continues to play a p ivotal role

in overall economic growth both locally and globally.

In order to improve the sustainability of all concrete structures,

there is a need to understand the interactive effect of

the many issues from cradle to grave in the design phase,

during construction and end-of-life and, most importantly,

the energy savings achievable during the use phase.


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marketing sustainable concrete through advice, education & information


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Sustainability of Concrete

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