Specifying Sustainable Concrete:

BS 8500
This guide is intended to be read in conjunction with other documents in the Specifying Sustainable Concrete series.

Introduction
This guide gives a brief overview of the methods of concrete specification
using BS EN 206[1] and BS 8500[2], and how the method selected may impact
the embodied carbon of the concrete. It is not a fully comprehensive
method of specification and so reference should be made to BS 8500-
1:2023 Specification of Concrete to BS 8500.

In the UK, concrete is specified in accordance with the European Standard

for Concrete, EN 206, and the UK complementary Standard, BS 8500. BS
8500 is published in two parts: BS 8500-1, Method of specifying and guidance
for the specifier, and BS 8500-2 Specification for constituent materials and
concrete.

For some applications, reference to alternate standards or specialist

literature may also be an option. For agricultural buildings, BS 5502‑21 and
BS 5502‑22 could be appropriate for guidance and, for maritime works, BS
6349‑1‑4 should be used. BS EN 13369 covers common rules for precast
concrete products and there is further information in some individual
concrete product standards, however, BS 8500 is the preferred method of
specification and is appropriate for most building and civil engineering
structures in the UK. It also provides a practical method to specify concrete
structures designed to Eurocode 2 (BS EN 1992-1-1)[3].

BS 8500 sets out five standard methods for the designer to specify concrete.
These are:
• designed concretes,
• designated concretes,
• prescribed concretes,
• standardized prescribed concretes, and
• proprietary concretes.
1 New Park Square, Edinburgh used a 40% GGBS mix for the main structure.
The term ‘concrete mix’ is sometimes used to refer to a prescribed concrete Image: Timothy Soar
or the proportions of the constituent materials but otherwise it is always
a ‘concrete’ that is specified. All concrete specified using the different reinforcement required to achieve the structural performance and service
methods contains the same raw materials, but it is how the requirements of life. The designer’s technical specification is passed to the contractor
the concrete, both fresh and hardened, are communicated (specified) that where the final concrete specification is completed with the addition of
differs which, in turn, will determine the concrete mix design and therefore requirements for fresh concrete properties, such as consistence. Once the
affect the embodied carbon. fresh concrete properties are known, the concrete producer can determine
the required cement content that meets all the limiting values.
Note: the “designer” is the person or body responsible for the specific technical
requirements of the concrete, but not the fresh concrete properties. Note There has been a large increase in the number of cements and
combinations available for specification and supply in the latest revision to BS
Methods of Specification 8500. As not all of these cements and combinations may be available in the
local market, and availability may vary depending on supplier, it may be of
Designed concretes are for the informed specifier, where the designer benefit for the designer to only specify the required CPC and allow the concrete
considers all the requirements for the hardened concrete such as strength producer to supply the lowest embodied option available that meets this
and durability to derive the necessary strength class and other properties requirement.
such as minimum cement content, maximum water/cement ratio, and
combined performance category (CPC). These together are known as the Due to its inherent durability, most reinforced concrete for building
limiting values. structures is designed for a minimum intended working life of at
least 50 years, but often a performance of 100 years, usually reserved
Normally it is the designer that will assess the exposure conditions for infrastructure, can be achieved with little or no increase in cover
and consider the recommendations set out in BS 8500-1:2023, Annex or concrete quality. The longevity of concrete in use is an important
A to determine the concrete properties and the minimum cover to

www.concretecentre.com 1
 SPECIFYING SUSTAINABLE CONCRETE: BS 8500

sustainability consideration. Designed concretes offer flexibility which Concretes specified by either the designed or designated routes will have a
can enable specifiers and suppliers to achieve sustainability goals. With similar embodied carbon for a particular application as they are effectively
designed concretes, lower carbon cements or combinations can be the same. Having sight of the limiting values associated with each can be
used together with recycled or secondary aggregate, when considered useful to have an understanding of the approximate embodied carbon
beneficial, to provide the lowest embodied carbon concrete for a specific of the specified concrete. As the limiting values of designated concretes
application and location. are not shown within BS 8500-1, it can be difficult to assess the effect of
selecting one designation over another. Reference should be made to BS
Designated concretes are types of predetermined designed concretes
8500-2:2023, Table 7 which provides requirements for designated concretes
(see above) that have been developed for a limited number of common
for general applications. Without understanding the limiting values there is
applications with each being given a specific “designation” depending
a risk that specifiers select a designated concrete that has an unnecessarily
on their intended use. Designated concrete is the preferred method of
high embodied carbon.
specifying when working to the NHBC Standards[4].
For example:
Using the designated concrete specification route allows the specifier
to ensure the requirements of the specification are achieved based on Unreinforced floors with permanent finish (screed or floating floor)
the designation they require, e.g. FND2 is a concrete suitable for use in require a GEN1 concrete but unreinforced floors without permanent finish
ground assessed as ‘DC-2’, Design Chemical Class 2. Similarly, RC28/35 is a (carpeted) require a GEN 2 concrete.
designated concrete of C28/35 strength class suitable for use in an internal
GEN1 = C8/10 with a minimum cement content of 180 kg/m3.
suspended floor. Designated concretes are quality-assured designed
concretes that conform to a specification detailed in BS 8500-2. These GEN2 = C12/15 with a minimum cement content of 200 kg/m3.
concretes have been selected to be fit for their intended use, and they can
If, for ease, it is decided that the concrete for an unreinforced garage floor,
only be supplied by ready-mixed concrete producers who have third-party
GEN3, is to be used throughout the ground floor slab of a house, this would
product conformity certification. A QSRMC or BSI Kitemark logo on the
have a strength class of C16/20 and a minimum cement content of 220 kg/
delivery ticket provides this confirmation. Purchasers can be confident
m3, 40 kg/m3 more than the GEN1 concrete.
that the concrete will be delivered as specified and ordered, and as the
concrete is optimised by the producer it is likely to have the lowest possible Guidance entitled Concretes for Housing - Designated concrete[5] is available
embodied carbon within the limits of the standard and embodied carbon from the British Ready-Mixed Concrete Association (BRMCA). Designated
requirements of the specification. concretes are not appropriate where concrete needs to resist the risk of
corrosion by the ingress of chloride. In such cases a designed concrete
should be specified.

Table 1: BS 8500-1: Guidance on the selection of designated concrete in housing and other applications

Typical application Designated concrete Recommended slump class

Foundation (fully buried)

Unreinforced foundations in DC-1 soils GEN1 S3

Reinforced foundations in DC-1 soils RC25/30 S3

Reinforced or unreinforced foundations in Design Chemical Classes DC-2 to

DC-4
DC-2 FND2
DC-2z FND2Z
DC-3 FND3 S3A)
DC-3z FND3Z
DC-4 FND4
DC-4z FND4Z
DC-4m FND4M

FloorsB)

Unreinforced floors with permanent finish (screed or floating floor) GEN1 S2

Unreinforced floors without permanent finish (carpeted) GEN2 S2

Unreinforced garage floor GEN3 S2

Reinforced house floor RC20/25 S2

Reinforced garage floor with greater than 40 mm nominal cover to the

RC28/35 S2
reinforcement

Other applications

As recommended by the
Infill to Insulated concrete formwork (ICF) above ground C20/25C)
manufacturer

Oversite below suspended slabs GEN1 S3

2 www.concretecentre.com
 SPECIFYING SUSTAINABLE CONCRETE: BS 8500

Kerb bedding and backing GEN0 S1

Drainage works in DC-1 soils GEN1 S1

Domestic driveways, parking, and external paving (no de-icing salts) PAV1 S2

Heavy-duty external paving (no de-icing salts) PAV2 S3

A) For trenchfill, use S4

B) Floors with any embedded metal should be treated as reinforced

C) Specify an 10 mm aggregate size

Designated concrete example:

For a building with reinforced vertical elements exposed to rain (exposure class XC3/4 to BS 8500) with an intended working life of at least 50 years, a range
of concretes are appropriate depending on the minimum cover to the reinforcement. These are shown in Table 2.
Table 2: Designated concretes for exposure class XC3/4 and minimum 50 years working life

Minimum cover (mm) Strength class Min cement content (kg/m3) Max w/c ratio Designated concrete

30 C40/50 340 0.45 RC40/50

35 C35/45 320 0.50 RC35/45

45 C32/40 300 0.55 RC32/40

50 C30/37 300 0.55 RC30/37

An allowance for deviations in reinforcement fixing (generally taken as 10mm for in-situ concrete) is added to the minimum cover to give the nominal cover
to reinforcement. The minimum cement contents and maximum water/cement ratios shown in the table are for a Dmax of 20 mm. The limiting values for
other Dmax are given in BS 8500-2.

In practice, for reasonable quality aggregate, RC30/37, RC28/35 and Standardized prescribed concretes are intended for situations where
RC25/30 should be achievable at the minimum cement content with the volume of concrete required is insufficient for delivery. The concrete is
the use of water reducing or high range water reducing admixtures. This either mixed by hand or in a small (less than 150 litre) concrete mixer, and
applies to all cements incorporating not more than 20% limestone, 35% are designated “ST”. There is no requirement to demonstrate the strength of
fly ash or 65% ggbs. At higher levels of additions, a cementitious content ST concrete but BS 8500-1:2023 Annex A provides some indicative values
above the minimum should be expected. for the strength class that may be assumed for structural design, e.g. the
highest grade of standardized prescribed concrete is ST5, where this may
Since the water/cement ratio has a large impact on the strength of the
be assumed to be at strength class not greater than C20/25.
concrete, with higher water/cement ratios producing lower strength
concretes for the same cement content, the use of water reducing and To ensure the ST designation recommendation is safe for the indeterminate
high range water reducing admixtures can reduce the cement content range of materials and site supervision the required cement content is
and hence the eCO2, while providing the same strength and improved higher than for other concrete with equal performance, and so the use
durability characteristics. of ST concretes should be avoided where a ready-mixed concrete in the
form of a designated or designed concrete can be used. The high cement
Prescribed concretes allow the informed designer to specify concrete by
content within standardized prescribed concretes results in a much higher
prescribing the composition. This method is rarely used but is useful where
embodied carbon than the equivalent designated concrete. If it is assumed
a particular ratio of constituents is required such as for exposed aggregate
that the designated concretes can be supplied with a CEM III/A cement
concrete finishes.
type, and the standardized prescribed concretes with a bagged CEM II/A-L,
It is not possible for the concrete producer to optimise the concrete mix then the equivalent ST concretes will have more than twice the embodied
design (and so the embodied carbon) of a prescribed concrete and so carbon of the designated concrete. See Table 3.
early engagement with a supplier may be beneficial to ensure the lowest
The GEN series of designated concretes are the more sustainable option
carbon constituent materials are used that meet all the requirements of the
because the cement content is optimised to that required for strength.
designer. This is a common route for specification of architectural precast
concrete.
Table 3: Standardized prescribed and equivalent designated concretes

Standardized prescribed concrete Designated concrete equivalent Additional cement required for ST concrete (kg/m3)

ST1 GEN0 110 (192%)

ST2 GEN1 85 (147%)

ST3 GEN2 95 (147%)

ST4 GEN3 110 (150%)

www.concretecentre.com 3
 SPECIFYING SUSTAINABLE CONCRETE: BS 8500

Proprietary concretes are developed by the concrete producer and are Specification for embodied carbon
marketed on their enhanced fresh or hardened properties. The producer
will normally guarantee the performance of these products and provide The impacts of specification on embodied carbon are not transparent
test certificates They may be covered by third-party product conformity when using BS 8500 and so designers should include their embodied
certification. For commercial reasons, the producer may not disclose the carbon requirements as part of their specification requirements. The
exact composition and is not required to do so by the concrete Standards, traditional top-down method of specification, where the designer decides
EN 206 and BS 8500. the structural and durability requirements of the concrete and the
contractor completes the specification with their requirements for placing
Many producers have lower-carbon proprietary concretes in their product and construction limits the opportunities for reducing the embodied
range that simplify the specification of these for the required application. carbon of concrete.
This option can be of benefit to the designer due to the large increase in
cement types and combinations available for specification in BS 8500- Early engagement between all parties about the structural and durability
2:2023, Table 1. requirements, those for construction, and the materials available in the local
market will allow the designer to specify a realistic upper carbon limit using
For more information on specifying to BS 8500, refer to How to design a static system such as the Universal Classification[9]
concrete structures using Eurocode 2: BS 8500 for building and civil structures[6],
published by The Concrete Centre. References
Additional aids to specification of concrete include the National Structural 1. BS EN 206:2013+A2:2021, Concrete. Specification, performance, production
Concrete Specification (NSCS) Edition 4[7] and the National Building and conformity, BSI, 2021.
Specification (NBS)[8]. 2.a) BS 8500-1:2023, Concrete - Complementary British Standard to BS EN 206,
Part 1: Method of specifying and guidance for the specifier, BSI, 2023.
Note At the time of publication of this guide, NSCS Edition 4 is current, however
2b) BS 8500-2:2023, Concrete - Complementary British Standard to BS EN 206,
Edition 5 is due to be published in 2025 and so reference should be made to
Part 2: Specification for constituent materials and concrete, BSI, 2023.
that document when available. Edition 5 will have provision for including
3. BS EN 1992-1-1:2004+A1:2014, Eurocode 2. Design of concrete structures.
sustainability specification criteria.
General rules and rules for buildings, bridges and civil engineering

Optimising strength class structures, BSI, 2014

4. NHBC Standards, National House-Building Council (NHBC), 2025
There can be situations when specifying concrete using the designed 5. Concretes for Housing, British Ready-Mixed Cement Association (BRMCA),
concrete route leads to a mismatch between the derived limiting values. 2009
For example, a structural element may only require a modest characteristic
6. How to design concrete structures using Eurocode 2: BS 8500 for building and
strength but due to aggressive environmental conditions, needs a low
civil structures, The Concrete Centre, 2024
water/cement ratio. In an instance such as this, the actual concrete strength
7. National Structural Concrete Specification for Building Construction – edition 4,
may be significantly greater than is required by the design, so it could be of
The Concrete Centre, 2010
benefit to reassess the element to optimise for that additional strength.
8. NBS, RIBA: www.thenbs.com
It follows that specifying a lower embodied carbon concrete may not 9. Classification methodology for embodied carbon of concrete, The Climate
result in a lower carbon structure. There is a balance between the specified Group, 2024
concrete and the design where a concrete with a slightly greater embodied
carbon may result in significant carbon savings through efficient design.

Where there is excess strength due to low water/cement ratios, this could
also be mitigated by using a greater proportion of limestone fines as part of
the cement. This would lower the concrete strength whilst maintaining the
water/cement ratio.

The guidance given in Annex A of BS 8500:2023 is based on standard

28-day compressive strength. Consideration can be given to extending
strength conformity to 56-days, or longer, to allow the use of lower cement
contents or greater proportions of SCMs to lower embodied carbon.

Note: The requirements for the XC exposure class are calibrated at 28-day
strength and so the designer should consider what cover is required for strength
conformity at later ages.

To view and download other Specifying Sustainable Concrete documents, visit www.concretecentre.com/publications

All advice or information from MPA The Concrete Centre is intended for 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 MPA The Concrete Centre or its subcontractors, suppliers or advisors. Readers should note that publications
from MPA The Concrete Centre are subject to revision from time to time and they should therefore ensure that they are in possession of the latest version.
© MPA The Concrete Centre, 2025 TCC Ref: TCC/05/41 ISBN: 978-1-908257-41-3

4 www.concretecentre.com