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
6
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
8
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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