Optimising performance with low waste design solutions in concrete

Material Efficiency

Material efficiency

2

Definition and Scope‘A significant proportion of the environmental impact of construction arises from the use of resources – principally energy, water and materials. Using materials more efficiently (called ‘materials resource efficiency’) is a highly effective sustainability strategy and involves a balanced approach, ensuring that at each stage in construction (which includes demolition), materials are used in an efficient manner’ [1].

Minimising the production of waste is an important factor in material resource efficiency. The concrete industry is a net user of waste, thereby diverting significant amounts of waste from potential land fill and reducing depletion of natural resources.

About this publicationConcrete is a low waste solution for the construction industry and by optimising its performance characteristics, such as sound, fire and robustness, can be used to improve the overall material efficiency of a building and lower its associated waste production.

This document describes the material resources and waste issues of using concrete at different stages of its manufacture, design and construction. It provides guidance to designers and specifiers on optimising performance and further associated benefits, including projects successfully using fair-faced concrete solutions.

SummaryDesigning ‘low waste’ buildings requires a holistic approach, through

consideration of waste and material resource at each stage. Designing

the fabric of the building itself to be as versatile as possible can reduce

the use of materials by making the structure work harder. For example,

choosing fewer materials for walls and selecting materials that can meet

the designers’ aspirations for both visual appearance and performance

requirements, such as structure, fire and sound insulation.

More Concrete = Less Waste. The concrete industry is a net user •

of waste

Less is more. Exposed soffits and fair-faced concrete reduces the •

need for expensive (and non recyclable) finishes, whilst optimising

the thermal mass and visual benefits of exposed concrete surfaces

Concrete is 100 per cent recyclable•

Concrete is manufactured using efficient low waste processes•

Design strategies can maximise the benefits of pared-down •

construction, making best use of concrete performance

Concrete facilitates waste avoidance and minimisation•

Concrete mixes contain recycled materials diverted from the waste-•

stream of other industries

Long life and robustness facilitate the re-use of existing concrete •

structures, therefore reducing future demolition waste

ContentsWhy reduce manufacturing and construction waste? 3

Concrete industry waste initiatives 4

The components of concrete 5

Low waste production and use of concrete 8

Efficiency through building design and optimising material potential 11

Saving waste on site 15

Optimising at end of life: deconstruction, re-use and recycling 17

References and online resources 19

Benefits of internal fair-faced concrete:

Avoids additional finishing materials and •associated cost, waste and programme time

Visually attractive•

Variety of available finishes, textures and colours •possible

Optimises thermal mass effect•

Cost effective•

Durable•

Minimal long term maintenance requirements•

Non flammable with no spread of flame•

Inert material, so no off-gassing•

Resistant to mould and insects•

Water resistant•

Potential canvas for future finishes if desired•

Optimum material efficiency: •

• Structuralmaterialcanprovidethefinalfinish

• Structuralmaterialoftenexceedsminimum fire resistance requirements and potentially sound insulation.

Material efficiency

3

Why reduce manufacturing and construction waste?The waste associated with the construction industry as a whole has been identified as over a third of all waste generated in the UK. The Government’s current target to reduce waste to landfill includes a reduction of construction, demolition and excavation (CDE) waste volumes by 50 per cent by 2012, and to zero by 2020.

Reduction in waste and improved resource efficiency is an important

part of sustainable construction. For example:

Energy use and CO•2 emissions can be reduced by optimising

resources and reducing the amount of transportation and

processing of waste materials

Decomposition of organic matter in landfill produces methane gas •

which, according to the International Panel on climate change, is

about 21 times more damaging than CO2 as a greenhouse gas.

Apart from the energy and CO2 considerations of sustainable

construction, the UK is running out of space to store and dispose of

waste. This is a challenge not only for Government, but also for the

construction industry, who are likely to find the availability of waste

disposal routes decreasing and costs increasing.

Figure 1: Estimated total annual waste arising by sector.

Agriculture (inc. �shing)

Mining and quarrying

Sewage sludge

Dredged materials

Household

Commercial

Industrial

Constructionand demolition

32%

13%

Total = 335 million tonnesSource: Defra, ODPM, Environment Agency, Water UK

12%

9%

5%

<1%

<1%

29%

Atthetimeofwriting,SiteWasteManagementPlans(SWMP)arerequired

for all projects in excess of £300,000 with increased requirements for

thoseinexcessof£500,000.TheSWMPprovidesamechanismtoplan,

monitor and review the levels of waste generated on a site. They are also

amandatoryelementofBREEAMandtheCodeforSustainableHomesfor

developments with construction costs of £300,000 or more. Credits are

available for incremental improvements in line with best practice. Additional

guidance can be found in the ‘saving waste on site’ section of this document.

WRAP (Waste and Resources Action Programme) is a major Government

programme established to accelerate resource efficiency by tackling

the barriers to waste minimisation and increase recycling. They have

produced a number of useful guides and tools specifically aimed at

reducing waste arising from the construction industry. For further

information visit www.wrap.org.uk.

Figure 2: WRAP guidance on Material Resource Efficiency as part of sustainable construction [1]

Energy Materials Water

MaterialSelection

Waste Management

Using local construction

and demolition waste

Waste avoidance and minimisation

Sustainability GoalsEf

ficie

nt

use

of fi

nit

e n

atu

ral m

ater

ials

Min

imis

ing

en

viro

nm

enta

l dam

age

Returning surplus material

Segregationandrecycling

Using products with high

recycled content

Use renewable materials from

sustainable sources

Specifymaterialswith low

environmental impact

Material efficiency

4

Concrete industry waste initiativesThe vision is that by 2012 the UK concrete industry will be recognised as the leader in sustainable construction, by taking a dynamic role in delivering a sustainable built environment in a manner that is profitable, socially responsible and functions within environmental limits.

TheUKConcreteIndustryStrategyforSustainableConstruction,

published in June 2008, is an industry initiative aligned with the UK

GovernmentSustainableConstructionStrategy,toreport,monitorand

set targets for environmental performance indicators related to the

production of concrete.

The first Concrete Industry Sustainability Performance Report [4], published

in March 2009, brought together data from all parts of the industry and

set out current activity and future actions against key sustainability

indicators. Key targets for performance by 2012 in each sector have

subsequently been set, including those for waste minimisation and

material efficiency.

The concrete industry uses and recycles more waste than it produces

and is therefore a net user of waste. It is committed to increasing the

use of by-products and secondary materials from other industries in the

production of cement and concrete and to reducing the waste produced

in the manufacturing process. For further details refer to The Concrete Industry Sustainability Performance Report: 2nd Report: 2008 performance data and release of 2012 targets [5].

The UK cement sector actively seeks waste derived materials as

replacement for natural raw materials and fossil fuels. In this way the

industry is a major contributor to helping UK government meet its

recycling targets. In 2008 the percentage of fuel comprising waste

material used in the cement industry was 26.5 per cent, representing a five

fold increase from 1998 and exceeding targets set with government [2].

An example of alternative fuel: pelletised sewage sludge. Courtesy of Lafarge

There is research that indicates that there is actually very little hard

demolition and construction waste sent to landfill [5].

The concrete industry uses over 18 times more waste, by-products and secondary materials from other industries than the waste it sends to landfill.

The concrete industry uses 5.01 million tonnes of by-products and secondary materials diverted from the waste-stream and produces 0.28 million tonnes of waste [5].

Material efficiency

5

The components of concreteConcrete uses materials from sustainable sources

Concrete is an inert material created from natural minerals found locally

in the UK. The relative proportions of cement, sand, larger aggregates,

water and other materials vary, depending on individual product

and specification requirements. Aggregates typically are the largest

proportion, often comprising 80 per cent of concrete by weight.

Further information on the sustainability credentials of concrete’s

constituent materials is available in Concrete Credentials: Sustainability

[8], published by The Concrete Centre.

Recycled and secondary aggregates in concreteIn addition to an abundance of local naturally occurring aggregates,

recycled and secondary aggregates can be used in the production of

concrete. The viability and practicality of their use will depend upon

geographicallocation,butalsotheperformancerequirements.BS8500

sets out allowable percentages of recycled aggregate for different

concrete mixes and their use is summarised in The Concrete Centre

publication Concrete Structures 7 [7]. In general, it is permissible to use

high levels of RA and RCA in lower strength concrete. This tends to be

mass concrete (i.e. not reinforced) used for trench fill, footings etc.

Other alternative aggregates are available for use as part of the concrete

specification, include stent and lightweight aggregates made from fly

ash. These are classed as secondary aggregates, or by-products of other

processes. Concrete itself can also be re-used as recycled aggregate in

concrete.Highrecycledcontentcanaffecttheconcretepropertiesand

material behaviour and should be appropriate for its specification.

Definitions of recycled aggregates:

Recycled Aggregates (RA)aggregate resulting from the reprocessing of inorganic •

material previously used in construction e.g. brick,

mortar, roof tiles

Recycled Concrete Aggregates (RCA)recycled aggregate principally comprising crushed concrete•

Secondary Aggregatesaggregates made from by-products from other processes•

Stentisaby-productofthechinaclayindustryprincipallylocatedinCornwall in the UK. It is the waste granite rock material that has been separated from kaolin (china clay) by high-pressure water jets and is usually tipped to form surface spoil heaps.

It has had a long history of use in concrete in Cornwall and Devon and more recently has been used as recycled content in concrete for various high profile projects including the London Olympic Park, One Coleman StreetofficedevelopmentandOneBrightonresidentialdevelopment.

“Aggregates are plentiful in the UK. Friends of the Earth estimated that minerals such as aggregates would last hundreds of thousands of years at current rates of extraction in the UK”. [3]

One Coleman Street, London

Recycled concrete content credentials:

100 per cent secondary aggregate (stent) resulting in •

a reduction of 6,000 tonnes of tipped china clay waste

and 6,000 fewer tonnes of virgin aggregates.

100 per cent recycled reinforcement•

up to 40 per cent fly ash used as additional •

cementitious material

OneColemanStreetusedprecastconcretecladdingandstentasasecondary aggregate.

Material efficiency

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ExposedconcretewasusedintheawardwinningIdeasStore,utilisingthebenefitsof thermal mass. Architects: Adjaye Associates, Engineers: Arup

The current BRE Green Guide and other environmental profile

methodologies reward the increased proportion of recycled aggregates

in construction projects.

It is worth noting that when available close to site, recycled aggregates

canimprovethesustainabilityofconcrete.However,theincreasedCO2

generated by transporting recycled aggregates over longer distances

by road, can result in a less sustainable solution than the use of locally

available primary aggregates. The use of recycled aggregates is only a

lower carbon option when used within 10 miles (15km) of their source.

Detailed figures are provided in The Concrete Centre publication Concrete and the Green Guide [6].

Approximately 25 per cent of all aggregates used in Great Britain are

either recycled or secondary aggregates. This is the highest for all

countries in Europe [14].

In 2008 the amount of recycled and secondary aggregate used in the

UK concrete industry was over 2 million tonnes, with the majority being

used by the precast concrete sector [5]. The question of whether the

diversion of larger volumes of recycled and secondary aggregates would

produce a more sustainable result nationwide, taking into account

transport, production and mix design is difficult to answer in simple

terms. The feasibility and impact of their use needs to be assessed for

individual contracts and will depend largely on scale and location.

Nearly 100 per cent of hard demolition waste is already used in the UK

and until demolition rates increase, this means that specification of

recycled aggregates may not reduce virgin aggregate extraction, but

simply change the location in which recycled aggregates are used.

Truly sustainable construction solutions include the appropriate

concrete design mix, balancing cost, environment, social and life cycle

requirements.

The use of recycled aggregates is only a lower carbon option when used within 10 miles (15km) of their source.

Material efficiency

7

Cementitious Materials Waste products used as cementitious content

GroundGranulatedBlastFurnaceSlag(GGBS)isproducedfromwaste

material from iron production and Fly Ash (FA) is waste material from

electricity generation, sourced from coal fired power stations. Both

have been used with Portland cement in concrete, for many years. The

percentage of allowable replacements in particular concrete mixes

isdefinedbyBS8500-1:2006butcanbesummarisedasbetween

therangesof6-55percentforflyashand6-80percentforGGBS,

depending on the intended application. The reported percentage of

additional cementitious material used in the UK is over 30 per cent [5].

In addition to diverting materials from the waste-stream and from

landfill,thebenefitsofusingflyashandGGBSincludereducingthe

embodied CO2 of a concrete mix, improved durability and a change in

the inherent pigmentation of the final concrete colour.

Portland cement remains an essential component of concrete, and high

replacement rates can alter its properties, such as early strength gain

and therefore striking times for formwork.

Further technical guidance of their use can be found in How to design

concrete structures using Eurocode 2, by The Concrete Centre.

Waste materials in cement production

Waste derived materials are actively sought by the UK cement industry

as replacements for natural raw materials and fossil fuels. The industry

now productively uses over 1.4 million tonnes of waste in this way.

Every cement plant in the UK is replacing a proportion of fossil fuels by

safely burning alternatives such as solvents, tyres, meat and bone meal,

sewage sludge, paper and plastics. The industry now replaces 26.5 per cent

of virgin fossil fuels by waste derived materials and has a target of 50 per

cent replacement by the year 2020. As a result, CO2 emissions from cement

production have been reduced by nearly 40 per cent in the past 20 years [2].

17.3 per cent of the energy used by the concrete industry comes from the use of materials diverted from the waste-stream as a fuel source [5]

HearthHouse.Flyashwasusedtocreateasmokeygreycolourtothecentralstaircasefeatureandrecycledparquetflooringwasusedasformwork.

Material efficiency

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Precast concrete: O ff-site solutions

The use of precast concrete off-site solutions has the potential to

significantly reduce on-site waste and the manufacturing process

produces on average, less than 1 per cent waste to landfill [9]. Most

building elements can be manufactured in concrete off site in factory

conditions. These range from whole building structural systems such as

crosswall construction, through to individual precast building elements

such as columns, floor units or wall cladding. The waste associated with

each precast product varies according to its size, nature of delivery and

place of manufacture but in general off-site solutions offer a very low

waste construction option. Many factories operate a close-loop system,

generating very little, if any, waste at the point of manufacture.

Additional benefits of precast concrete off-site solutions with respect to

waste include:

’Just in time’ delivery with installation direct from the delivery •

vehicle. This minimises wastage due to the lack of temporary works

and pallets/protection etc. for site storage required

Avoids waste resulting from damage during site storage and •

double handling

Products are made to order, omitting wastage through ‘adaptation •

to fit’

Panels can be simply removed as part of demolition or for •

alterations

Highqualityfinishesarepossibleavoidingtheneedforadditional•

finishing materials

Multiple re-use of factory based formwork systems•

Precast concrete sector low waste initiatives include:

Use of recycled materials in concrete mix•

Extended use of returnable cradles and pallets•

Waste take back schemes•

Increase level of repair and reclamation of precast elements•

E-tagging or radio frequency identification devices (RFID) to •

encourage and facilitate the re-use of precast components.

OundleSchool-Architects:FeildenCleggBradleyStudios,Engineers:JaneWernickAssociates. (c)TimSoarPhotography.

Blockwork

The waste associated with the manufacture of concrete blocks is

typically very low and they share many of the benefits listed for off-site

concrete solutions.

Blocks are essentially pre-manufactured concrete of standard sizes

with varying densities and, as for other precast units, some factories

are reporting almost zero waste due to the closed loop nature of the

manufacturingprocess.Highlyrepetitive,durablemouldsresultinvery

little waste.

The recycling of waste materials within the manufacturing process

makes good economic sense and is simply achieved due to the nature of

the material.

As well as recycling concrete as part of the manufacturing process, many

concrete blocks contain high levels of other recycled materials, up to

90 per cent in some cases, including furnace bottom ash aggregates,

industrial slags and returned concrete products.

One third of blockwork in the UK is in the form of aircrete, a major use of

fly ash from power station waste-streams.

Concrete blocks remain by far the preferred method of construction for

the structure of homes in the UK. The familiarity with the material on site,

its abundance and high value and also a simple, safe recycling process,

has traditionally lowered the perceived priority of improving the waste

management of blockwork construction.

With the increased focus on waste reduction in general, improvements

have been made in the industry to limit waste arising from blockwork

on site and the standard practice wastage rate can be significantly

improved through very simple procedures.

Take back schemes exist for unused or damaged blocks and these can

be utilised to meet on site waste targets and reduce landfill charges.

Simpleandcosteffective,theyencouragetherecyclingofblockwaste

andofferafullaudittrailforSiteWasteManagementPlans.

As an inert waste product, rejected or damaged blockwork has many

uses on site, such as in hard core or landscaping, so its journey to landfill

can be eliminated. In 2008 less than 0.5 per cent of concrete used in the

precast concrete industry was disposed to landfill [9].

Low waste production and use of concrete

Material efficiency

9

Suggestions for improving wastage rates using

blockwork:

Design to modular sizes to avoid cutting and wastage •

on site

Careful storage and handling to avoid damage in •

delivery / construction

Arrange just-in-time delivery on site•

Consider thin joint techniques *•

Utilise take back schemes•

* Thin joint technology is classed as a Modern Method of

Construction and is an alternative method of blockwork

construction that uses less mortar, and by association, less

mortar wastage.

TheNewForestHouse.Formworkwaslinedwithlocaltimber.Theformworkwasre-used throughout the project and at the end of construction was used to line the garage walls. Courtesy of Perring Architects and Design.

Ready Mixed Concrete

Waste associated with the manufacture and use of ready mixed concrete

is very low. It is a unique material for use on site in that its raw materials

can be simply stored at nearby batching plants until required, mixed for

specific orders and then delivered directly to site for use. This made to

order and just-in-time delivery process is inherently material efficient.

Contractors are accustomed to the economic benefits of accurate

ordering. In the event of over ordering, ready mixed concrete suppliers

offer take back schemes to reduce and manage waste on site, though in

reality an alternative use on site is often found.

The wastage rates for cast in situ concrete depend upon the nature

of its use and scale of installation but they are generally very low

by comparison with other structural materials. The WRAP net waste

tool assumes a range of 2-2.5 per cent under good site practice for

installation of most types of in-situ foundations, frames and slabs.

The relatively small amounts of unused concrete returned to batching

plants is rarely wasted. If an alternative use for the returned concrete

cannot be found elsewhere it is recovered into other batches and

separated aggregates stored for future use. Alternatively wet concrete

is allowed to dry and periodically crushed to create recycled concrete

aggregate.

‘Waste from production of ready mixed concrete is extremely low with

most recent data (2008) being only 2.28kg/tonne or 5.40kg/m3 (0.22 per

cent) of waste to landfill as a proportion of production output. BRMCA

have a target to reduce waste to 50 per cent of 2008 level by 2012 [1].

Formwork and falsework

Formwork and falsework is an essential part of all concrete construction

as it provides the mould in which concrete is cast either off site or in situ.

It is standard practice to re-use form and falsework due its relatively high

cost compared to the rest of the manufacturing process. The extent of its

re-use will depend upon the type specified and this may of course depend

upon the type of final finish required to the concrete. Metal forms made

from recycled steel, for example, are a common means of achieving good

quality fair-faced concrete and may be re-used hundreds of times.

Many falsework systems are highly efficient and are designed to

incorporate health and safety barriers and fixing systems, designed for

repeated installation and dismantling for use by the specialist installer.

They are designed to be used hundreds, if not thousands of times over.

All formwork can be recycled. Whilst facing plywood on forms has a

finite number of re-uses the formwork panels themselves are returned

to suppliers to be repaired and resurfaced for re-use over and over

again. The plywood can be recycled. On occasion it may be possible to

re-use formwork for an alternative use, such as site hoarding, or plywood

formwork cleaned and used as bespoke furniture. At the Millennium

Village in Greenwich, London, for example, after many uses the formwork

was broken down to use as mulch for the planting areas.

Other options include the use of circular column formwork made from

recycled cardboard.

Material efficiency

10

Insulated and permanent concrete formwork systems

There are a number of systems available which utilise formwork that is

designed to remain on site following placement of the concrete, as part

of the final building design.

Insulated Concrete Formwork (ICF) is a generic term for systems that

create concrete formwork using blocks or panels of expanded or

extruded polystyrene. The formwork therefore remains in place as the

insulation of the building. Waste rates are low, especially if the redundant

or damaged polystyrene is returned to the factory where it can be 100

per cent recycled.

Other permanent formwork systems include twinwall construction

where thin precast units form the permanent shuttering, provide a

high level of finish and dimensional accuracy. This system combines

the benefits of off-site solutions and cast in situ concrete. The precast

concrete casing typically has good dimensional accuracy and finish,

providing the option for minimising additional finishing materials.

More information on both systems is available from The Concrete Centre.

Visit www.concretecentre.com/publications

Foundations

Mass concrete foundations and footings typically have a higher

percentage of allowable recycled concrete than other applications.

Hardcorecommonlycompriseson-sitedemolitionwasteandisan

energy efficient use for inert demolition waste since it requires no

transportation and saves importing virgin material.

Considerations for further waste minimisation in

foundations includes:

Single,largediameterpilestosupportcolumnloads•

instead of spread foundations, as this minimises spoil

Precast sub-structure systems to minimise waste on site•

Geotextile formwork for in-situ foundations to provide •

a low waste alternative to shuttering

Displacement piles to avoid excavation waste•

Boardmarkedconcrete,theCityandCountyMuseum,Lincoln.ImagecourtesyofTheConcreteSociety.

Material efficiency

11

Ways in which improvements can be made in the use

of concrete by designers and contractors:

Efficient structural design to avoid over-specification •

of materials

Re-use of existing concrete structure on site as part of •

new design proposals

Specificationoflowwasteconcreteproducts•

Specificationofconcretewithrecycledcontent•

Design of structure and choice of construction to •

optimise material use and reduce wastage of concrete

Use concrete structure to minimise use of finishing •

materials and therefore reduce waste in general

Design structure for longevity and re-use•

Efficient design of new concrete structures

Efficient structural design can avoid over specification and therefore

material wastage. Guidance is available for structural engineers from

The Concrete Centre through various publications and training courses

for optimising the use of structural concrete.

Regular plan forms can often result in more efficient use of materials,

particularly in association with good dimensional coordination to avoid

off-cuts. These aspects can make significant savings to waste on large

projects with repeated elements.

Concrete is a unique building material in that it has the potential to act

as support and enclosure for walls, floor and roofs; providing fire and

acoustic separation and decorative, robust surface finishes. Efficient

design will optimise the performance benefits of concrete. Examples

include perimeter structural walls acting also as the internal facade or

structural internal walls providing party wall separation.

TheWasteHierarchy[11]:wastereduction;materialre-use;recyclingand

composting; energy recovery; landfill. A waste hierarchy is commonly

used to illustrate the potential impact designers can have on material

efficiency and is an expansion of the reduce, reuse, recycle sequence.

By reducing the quantity of materials used in the first instance, material

purchasing costs and waste are lowered as are subsequent handling and

disposal costs.

Efficient flat slab design

The omission of downstand beams can result in a considerable saving

in materials and waste. Bends in services are eliminated, and the

installation of walls and partitions require less time, cost and off-cuts to

install. The formwork is also simpler, and particularly suited for multiple

re-use, and can be designed to bring waste to a bare minimum.

A flat slab is likely to be thicker than the slab in a beam and slab solution,

unless it is post-tensioned. The relative waste and resource implication of

each solution will vary according to specific details of project and needs

to be evaluated as such.

GreenfieldsCommunityHousingheadoffice.Thesoffitsofthein-situconcreteframe are exposed and feature a circular recess that is accentuated by the pendant lights. Image courtesy of Richards Partington Architects.

Efficiency through building design and optimising material potentialConcrete is in general an inherently low waste construction solution, but there are still effective ways of further reducing the waste burden of projects through the design process.

Material efficiency

12

Post-tensioned slabs

Post-tensioned slabs can provide thinner, flat soffit slabs than

traditionally reinforced slabs and are viable for spans from 7-13 metres.

For longer spans, or heavier structural loads, post-tensioned concrete

band beams can be used. Band beams are wide, shallow concrete

downstand beams that can span up to 18 metres, thus providing a viable

alternativetolongspansteelbeams.Sincetheytendtobesimpleand

repetitive, the formwork is suitable for multiple re-use.

Voided slabs

Voided slabs incorporate air voids into the thickness of the slab, reducing

the weight of the slab, hence are able to provide longer spans for similar

amounts of concrete material. For example, precast hollowcore floor

slabs can provide a simple efficient flooring system for spans up to 14

metres.

Alternatively, permanent void formers are an innovative solution where

cast in situ concrete is placed over a matrix of recycled plastic balls. This

could increase the overall thickness of the slab, but using significantly

lessconcrete.Hybridsystemsincorporateadeckofprecastconcrete

permanent shuttering to the soffit side, further reducing the need for

additional formwork.

The use of voided floor slabs can reduce the design loads of a buildings

and can therefore also save materials, costs and waste associated with

foundations.

Factors to take into account when using voided or

post-tensioned slabs for waste minimisation:

Any reduction in slab thickness will reduce the acoustic •

properties of the floor, which may then require a

suspended ceiling to compensate, particularly in

residential properties

There may be a cost premium but this is offset by •

savings elsewhere i.e. programme, materials, labour

Consider exposing soffits to reduce the need for •

finishing materials and optimise thermal mass benefits

The use of slabs will almost certainly speed up the •

construction programme but sequencing needs to be

taken into account. Post-tensioned slabs can save time

on site due to the reduction in reinforcement required

Specifictrainingandguidanceisoftenavailablefrom•

the manufacturers of voided precast systems

Bonded post-tensioned slabs are easier to demolish •

at the end of the building’s life due to the reduction in

embedded reinforcement. Unbonded PT slabs require

specific sequencing for demolition

Using concrete to reduce use of additional finishes and wastage

Concrete can be used to provide design solutions to optimise the

materials function and reduce the need for other materials on site and

therefore reduce waste in general.

The use of concrete for floors, walls and or frame can meet the •

many performance requirements of a room or building enclosure

without the need for many other materials to be used. These

include acoustic and fire separation, structural support, air

tightness and thermal mass as well as a durable, attractive finish.

Fewer materials and construction phases reduce the amount of •

waste produced and facilitate recycling by simplifying the process

of segregating waste.

Significantcostsavingsarepossiblethroughreductionin•

installation costs and construction programme by optimising the

structure as a finish.

The thermal mass benefits associated with heavyweight concrete •

walls and floors are maximised by omitting subsequent wall

finishes.

Exposed concrete is very durable. Potentially less maintenance is •

required than for other ‘wearing’ finishes.

A wide variety of colours, textures and forms are possible either as •

standard products or bespoke requirements.

Concrete is a robust material and is unique in that it is appropriate •

for long term use internally, externally, below ground, on roofs and

in water.

Floor finishes, in particular carpets, are a major contributor to landfill

waste due to their manufacture, but principally through the frequency

of their replacement over the life of the building. They can also have a

very high embodied CO2 content. The specification of exposed concrete

floors can therefore make a significant impact on waste reduction of a

project. Exposed concrete floors provide an attractive hard wearing floor

finishes that is particularly cost effective over large areas.

Exposed concrete soffits are an excellent means of distributing comfort

benefits of thermal mass across spaces, particularly deep plan areas.

They are therefore frequently an essential part of a low energy strategy,

which has resultant waste advantages through the reduction of the

mechanical and electrical installations.

Material efficiency

13

PerformanceSolidconcretewalls,eithercastinsitu,blockworkorother•

precast units, can provide structural support, fire and

sound separation with out the need for additional finishes,

significantly reducing waste levels on site.

Exposing the surface of concrete will optimise the thermal •

mass benefits, which can be used to control daytime peak

temperatures and therefore reduce or minimise the need

for external ventilation and air-conditioning. It also has the

potential to reduce space heating requirements by acting as

a fabric energy store.

FinishExposed concrete is often more durable than potential •

finishing materials and requires little long term maintenance

saving future waste production. Paint or thin render are

alternative low waste finishing options for concrete if

a different aesthetic is required. There is some ongoing

maintenance as a result of adding these finishes.

A range of colours and self finishes are possible and should •

be considered at the early stages of design to ensure

correct specification and programming on site. These can be

proprietary or bespoke. Finishing textures include polished,

honed, grit blast, acid etched and inlaid.

More uniform floor finishes can be provided by using dry-•

shake pigments during the curing process, combining pigment

into the upper few millimetres of the concrete or screed.

Decorative finishes can be installed at a later date if •

requirements change.

Design coordinationThe strategy for distribution of services and subsequent •

setting out requires consideration at early stages of design in

order to minimise or avoid the amount of surface mounted

conduit.

The robust self finish enables services to be installed before •

the building is completely water-tight, with consequential

programming benefits.

Under floor heating works very effectively without carpet or •

timber floor finishes. While it is possible to integrate heating

pipes into a structural slab it is commonly installed, to good

effect, within a screed finish; which can of course be self

finishing.

Settingoutofprecastcomponentsandformworkshould•

be considered by designers at pre-tender stage and then

reviewed and agreed with specialist contractors before

construction or manufacture.

Concrete walls provide strong support for any future fixings •

or wall mounted furniture. Consideration should be given

to providing pin boards or permanent battens in order to

accommodatefixtures.Holesinfair-facedconcretecanbemore

difficult to conceal.

Soundreverberationwillincreaseinroomswithhard•

finishes and can be controlled to suit the specific internal

environment using soft furnishings, and hanging or wall

mounted acoustic panels.

Separatingfloorsbetweendwellingswithrequirearesilient•

layer below the screed to reduce impact sound if exposed

floors are proposed.

Quality controlCorrect specification, quality control and appropriate •

protection on site are essential to minimise variations in

concrete appearance.

Repairs or adaptations to large monolithic areas are •

sometimes difficult to conceal. Design the layout of

expansion joints to avoid cracks from shrinkage and to

facilitate pouring schedule on site.

Design considerations for exposed concrete walls, structure, soffits and floors

Material efficiency

14

Significantwasteandexpenditureisincurredthroughstripping

out existing finishes in new office fit-outs, in order to meet the

specific requirements of new tenants, which can be avoided by the

use of fair-faced finishes.

Over and above the previously noted advantages of exposed

concrete, it is common to provide a ‘developers finish’ in the

construction of new offices. This includes all finishes, suspended

ceilings, raised floors, carpets and the extension of mechanical and

electrical services into the office area. The level of provision varies

slightly from developer to developer.

With the provision of a more stripped back or lean finish, or shell

and core development, the first fit-out of the development can be

tailored to meet the new occupants’ requirements.

The use of concrete structure has the advantage of meeting all

necessary fire and sound requirements of the building regulations

without the additional costs, time and waste associated with

finishing trades and therefore ideal as a shell core.

Flat concrete soffits provide robust surfaces for fixtures and

facilitate simple services installation with the potential to be

exposed with all associated long term maintenance benefits.

The benefits of using thermal mass as part of the energy efficient

strategy for the heating and cooling of buildings, are well

documented e.g. reduction in the installation costs of mechanical

and electrical (M&E) installations and running costs together with

associated reduction of CO2 emissions over the lifetime of the

building. The use of fair-faced or visual concrete can therefore be

incorporated into the whole building low energy strategy saving

additional waste from reduction in service installations.

In summary, potential waste benefits of using a concrete structure

for speculative office space include:

Savingwasteandresourcefrominitialfit-out(materialsand•

trades)

Savingwasteandresourcefromsecondphaseoffit-out•

materials and trades

Savingwastefromstrippedoutunwantedfit-outmaterials•

and trades on future occupation

Savingwasteandresourceassociatedwithfuture•

maintenance

SavingwasteandresourceassociatedwithreducedM&E•

installation through use of thermal mass for energy efficient

strategy.

Speculative office fit-outs: Exposed concrete finishes to minimise waste

Van der Meij College precast cladding. Courtesy of Decomo UK Ltd.

Material efficiency

15

Saving waste on siteLow waste construction systems can save cost and time on site.

A principal benefit of low or zero waste projects is the reduction in time

and cost associated with wasted materials, transport away from site,

landfill costs etc. Re-using materials on site can save money, but also

saves time and money in sourcing alternative products. It is therefore

highly beneficial to both client and contractor to keep wastage rates

low, to re-use materials on site where possible, and to adopt design

strategies that minimise waste when the building comes to be

refurbished or replaced. Concrete, in its various forms can fulfil these

criteria, simplifying the achievement of waste targets and the resulting

cost and programme benefits.

Site Waste Management Plans

TheSiteWasteManagementPlans(SWMP)regulationssetouttwolevels

ofSWMPtobeproducedbeforeworkcommencesonsite.

Basic - for projects with estimated project costs of between £300,000 and

£500,000. Detailed - for projects with estimated project costs greater

than £500,000.

TheSWMPprovideamechanismtoplan,monitorandreviewthelevels

of waste generated on a site. Both levels require a waste champion to be

identified and estimation of the predicted volume of each waste type.

The detailed plan also requires records of the types and quantities of

waste generated.

ThroughtheSWMP,designersandcontractorsareabletodemonstrate

ways in which waste has been avoided or minimised through design or

procurement decisions and site practice. Improvements over standard

practice are designated as either good or best practice. The framework

supports the dialogue between designers and contractors to ensure

targets of waste minimisation are achievable.

Predetermined estimates of associated waste generation and recovery

ratesarelistedbyWRAP’sNetWasteTool[10]andtheBRE’sSMARTWaste

plan [12] . The recovery rate of waste concrete, as stated by WRAP, for

good practice on-site processes is 95 per cent and for best practice on-

site processes is 100 per cent [11]. Both are relatively simple to achieve

as this document illustrates.

ForfurtherinformationonSWMPseetheNetRegsguidance,Site Waste

– Its Criminal www.netregs-swmp.co.uk, or for practical guidance on

howtocompleteaSiteWasteManagementPlan,WRAP’sdesigningout

waste guide: www.wrap.org.uk/construction/tools_and_guidance/designing_out_waste.html.

Waste of construction materials on site occurs largely

due to:

Over ordering•

Poor design brief resulting in off-cuts from varying •

sizes of materials and products

Changes in the construction programme, e.g. materials •

delivered too early

• Changesindesignspecificationleadingtorework

Storageandmovementofmaterials•

Siteclearance•

Packaging•

Inefficient working practices e.g. using incorrect •

materials (because it is easier to do so) or wasteful

cutting of materials

Use of demolition waste on site

Samuel Rhodes School, Islington.

Concrete from the demolished existing school was crushed on

site for use as hard core and construction of the piling mat.

Once redundant, the piling mat was broken up and used as

an aggregate finish to the roof. Brown roofs encourage local

ecological biodiversity. Architects and Engineers: BDP

Imagecourtesyof:©SannaFisher-Payne,BDP

Material efficiency

16

SWMP and Code for Sustainable Homes (CSH)

It is mandatory for projects with estimated construction value above

£300,000tohaveaSWMPunderWasteCategory5ofCSH.Uptotwo

credits are awarded, each point awarded for improvements broadly

inlinewiththerequirementsofaBasicandDetailedSWMP.Formore

informationrefertothelatestCSHtechnicalguide[13].

SWMP and BREEAM

A key requirement in BREEAM is best practice performance in the

planningandcommitmenttoaSWMP.Inordertoscorepointsunder

BREEAMtheamountofnon-hazardouswastepredictedintheSWMP

has to be demonstrated within the amounts specified below.

Table 1: Amount of waste generated per 100m2 (gross internal floor area)

BREEAM credits m3 tonnes

One credit 13.0 - 16.6 6.6 - 8.5

Two credits 9.2 – 12.9 4.7 - 6.5

Three credits <9.2 <4.7

An additional credit is available where at least 75 per cent by weight or

65 per cent by volume of waste has been re-used or recycled. This is also

an area where innovation credits can be achieved where 90 per cent by

weight or 80 per cent by volume of waste has been demonstrated as

re-used or recycled [17].

The use of recycled or secondary aggregates over 25 per cent of the

total will gain a credit under BREEAM: the recycled aggregates need to

be available on site or within 30km radius. This provides the option to

gain credits for waste used on site or exchanged between sites in the

same area.

There are also BREEAM points for re-use of existing buildings under

section MAT 4. One point is awarded for facade retention if it exceeds 50

per cent of the total facade by area and 80 per cent by mass. One point is

also awarded for re-using 80 per cent of the primary structure provided

it is at least 50 per cent of the volume of the final primary structure.

Concrete waste is simply segregated and recycled

On new build projects it is easy to segregate •

concrete waste for return or recycling on site as few

other materials will be on site at this stage in the

programme.

With demolition waste, brick and block waste can be •

stored together. This combination is useful for hard

core and use as general fill, highway sub-base or

landscaping.

Separatedconcretewasteisahighergradeproduct•

which can be crushed for use as recycled concrete

aggregate in the production of new concrete.

Concrete is defined as inert waste which means it does

not harm or cause adverse affects to the environment if

disposed of and does not decompose when buried.

SWMP and CEEQUAL

TheSWMPisacriticalelementindemonstratingtheperformance

requirements to gain points under the waste management section of

CEEQUAL. The implementation, monitoring and achievement of targets

withinaSWMPallgainpointsunderthisscheme.Thedemonstrationof

waste minimisation requires evidence form the client briefing, design

and construction stages of the project, which supports an approach to

the management of waste.

SimilartoBREEAM,pointsareawardeddependingonthereductionof

waste to landfill that has been achieved and the re-use of demolition

waste. In addition CEEQUAL also includes points for the re-use of unused

materials delivered to the site.

In the materials efficiency section of CEEQUAL; the re-use and recycling

of the key raw materials is considered, as well as the design attention to

deconstruction.

Ordering and storage on site

Concrete is typically a robust material and therefore less prone to

damage from the elements on site than other materials. Careful handling

and storage on site can however assist in reducing waste through

damage, primarily caused by impact.

As with all building materials, this can be further reduced by an

organised site layout and just in time deliveries.

Cost and programme benefits can be achieved through careful calculations

and estimations of materials required. The benefits of local concrete

production and storage are that additional materials can often be obtained

quickly, promoting more efficient ordering practice and therefore less waste.

Material efficiency

17

Optimisation at end of life: deconstruction, re-use and recyclingThere is research that indicates that very little hard demolition and

construction waste is sent to landfill [15]. Most concrete waste is

generated from the demolition of exiting buildings. This is almost

always due to the structure itself becoming redundant and not that the

concrete has come to the end of its life.

Re-use

Re-using an existing structure is often the optimum sustainable solution

for a redundant building or structure since relatively little energy is

required in the process, either for transportation or adaptation of form,

and little waste produced.

Concrete structures are durable and robust and frequently able to be

adapted for re-use. This extention of the life of a building is a highly

effective measure to reduce waste and resource depletion with many

other added potential benefits including, cost effectiveness, site

pollution and respect for historical context. This potential extension to

the life of a building highlights the benefits of designing in concrete

when new build is the only option, reinforcing the long term benefits

and halving the carbon footprint after each re-use.

The concept of fully remountable and reusable concrete structures is also

being developed, facilitated by effective tracking and documentation of

the life cycles of a precast concrete unit through, for example, E-tagging or

similartechnologies.Someconcreteelements,suchaspanels,pipesand

units can also be re-used in their original form on other sites.

90% of concrete products are estimated to be reused or recycled. [16]

55 Baker Street, London

The55BakerStreetprojectwastheextensivere-invention

of a 1950s concrete framed building, re-inventing the large

site into a new office, retail and residential centre. Instead of

demolishing the existing structure, it was stripped back to its

original concrete frame and a simple yet innovative interior

design solution ensured massive reductions in demolition

waste, tonnes of construction material savings and reducing

the time required to complete the overall construction

programme. Engineers: Expedition Engineering, Architects:

Make.

Courtesy of photographer Zander Olsen, Make.

From Ashburton Court to Elizabeth II Court

AshburtonCourt,oneofHampshireCountyCouncil’soffice

buildings, is a project where the re-use of concrete has

significantly assisted in meeting the designers challenge

to address the sustainability of the structure, whilst

maintaining its required functionality. The existing concrete

frame was retained, significantly reducing the demolition

waste of the project, whilst the concrete cladding that was

removed was re-used as aggregate in other materials. The

concrete frame’s thermal mass capability has also been

utilised, improving the energy efficiency of the entire

structure. Architects: Bennetts Associates, Engineers: Gifford

Material efficiency

18

Demolition and recycling

Concrete as a material is 100 per cent recyclable. The rubble from a

demolished structure can be relatively simply segregated and crushed

for re-use. The feasibility of whether this takes place on or off site will

depend on various factors including scale of operation and intended re-

use of the material. A common, cost effective use of concrete demolition

waste is as rubble for hard core, fill or in landscaping, on site, especially

if still mixed with other inert materials such as brick. This process of

recycling is sometimes referred to as downcycling, since the resultant

materials are deemed less valuable than when in their original form. This

rather negative term does not reflect the broader sustainability benefits

of avoiding energy and CO2 emissions associated with transporting the

potential waste, or the material efficiency of using a recycled material in

place of virgin materials.

As discussed earlier in this document, the crushed material can also be

used as recycled aggregates for general use, or use in new concrete.

Durability combined with its inert in-use state, makes concrete a highly

resource efficient material and a highly versatile, low waste material

either in its original form.

Recycling post-tensioned slabs

Contrary to popular understanding, post tensioned (PT) concrete slabs

can be no more difficult to alter or demolish than other structural forms.

For example, alteration permits the re-use of redundant office space

for residential use. Alternatively if demolished, the concrete and

reinforcement can easily be separated out for recycling.

Bonded post-tensioned slabs are easier to demolish at the end of

the building’s life due to the reduction in embedded reinforcement.

Unbonded PT slabs require specific sequencing for demolition. Further

guidance on post-tensioned concrete can be found in Post-tensioned

Concrete Construction, published by The Concrete Centre.

Sustainablespeculativeofficedevelopment.Featuresincludeuseofhollowconcretecolumnsasairductsandexposedconcretesoffitstoreducecoolingloadofbuilding.Perimeterpanelsproviderobustinternalfinishandstructuralsupport.Architects:AHMM,Engineers:Arup.

“ The Lean O ffice” Tooley Street, London

Summary: Considerations for designing out waste with concreteEnsure efficient design and modelling to optimise structure•

Specifyconcretetopermituseofrecycledaggregatesandcementadditions(e.g.GGBSandFA)bysuppliers•

Consider low waste concrete solutions•

Design and co-ordinate to modular sizes•

Expose structural surfaces where possible •

Ensure accurate estimation of materials when ordering•

Re-use or recycle waste materials on site where possible e.g. brown roofs/ landscaping•

Establish clear communication for specification and manufacturing to minimise mistakes•

Ensure careful handling and storage on site•

References[1] Designing out waste: A design team guide for buildings, WRAP

[2] Performance 2008, A sector plan report from the UK cement Industry, MPA Cement, 2009

[3] McLaren,Bullock&Yousef,TomorrowsWorld:Britain’sShareinaSustainableFuture,EarthScan,1999

[4] The1stConcreteIndustrySustainabilityPerformanceReport,2009,TCC/05/16,MPA-TheConcreteCentre,2009

[5] TheConcreteIndustrySustainabilityPerformanceReport:2ndReport:2008performancedataandreleaseof2012targets,

MPA-The Concrete Centre, 2010

[6] Concrete and the Green Guide, TCC/05/17, MPA - The Concrete Centre, 2009

[7] ConcreteStructures7,TheConcreteCentre,2006

[8] ConcreteCredentials:Sustainability,TCC/05/20,MPA-TheConcreteCentre,2010

[9] SustainabilityMatters.FourthAnnualreportontheprecastindustriesprogressonsustainability,BritishPrecast,2009

[10] WRAP NW net waste tool data - available on-line Jan 2010

[11] SiteWasteManagement–Guideandtemplatesforeffectivesitewastemanagementplans,WRAP/NHBC,2008

[12] BuildingResearchEstablishment(BRE)–SMARTWaste–www.bre.co.uk/page.jsp?id=5

[13] CodeforSustainableHomes-Technicalguide,CLG,availablefromwww.comunities.gov.uk

[14] TheCementSustainabilityInitiative–RecyclingConcrete,WorldBusinessCouncilforSustainableDevelopment(WBCSD),2009

[15] SurveyofArisingsandUseofAlternativestoPrimaryAggregatesinEngland2005,ConstructionandWaste,DCLG,2007

[16] AgreedwastemanagementroutesfortheGreenGuidetoSpecification,quotefrom:BeAware-Improvingresourceefficiencyinconstruction

productmanufacture,Sectorreport–Precastconcrete,BRE

[17] BREEnvironmentalandSustainabilityStandard-BREEAMOffices2008AssessorManual,BREGlobal,2008

Online resourcesDefraWasteDataHub-www.defra.gov.uk/environment/statistics/wastedatahub/index.htm

WRAP – www.wrap.org.uk/construction/

NationalIndustrialSymbiosisProgramme–www.nisp.org.uk/

Envirowise–www.envirowise.gov.uk/uk/Sectors/Construction.html

Guidance from The Concrete Centre can be downloaded at www.concretecentre.com/publications

Material efficiency

19

www.concretecentre.com

All advice or information from MPA -The Concrete Centre is intended only for use in the UK by those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted by Mineral Products Association or its subcontractors, suppliers or advisors. Readers should note that the publications from MPA - The Concrete Centre are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.

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ISBN978-1-904818-93-9

First published 2010

© MPA - The Concrete Centre 2010

The Concrete Centre is part of the Mineral

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and silica sand industries.

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