Standards for concrete
In 2004, BS 8110 was replaced by EN 1992 (Eurocode 2). The Concrete Centre provided a range of resources for designers to help with the use of Eurocode 2.
The key UK standard for concrete, BS 8500, is published in two parts:
- BS 8500-1:2023 Concrete – Complementary British Standard to BS EN 206 – Part 1: Method of specifying and guidance for the specifier, and
- BS 8500-2:2023 Concrete – Complementary British Standard to BS EN 206 – Part 2: Specification for constituent materials and concrete.
This standard complements BS EN 206, Concrete – Specification, performance, production and conformity, and provides United Kingdom national provisions where required or permitted by BS EN 206. It also covers materials, methods of testing and procedures that are outside the scope of BS EN 206, but within national experience.
On 30 November 2023, BS 8500-1:2023 and BS 8500-2:2023 were updated. This change to the standard increases the range of lower carbon concretes that can be specified.
The specifier is offered five approaches to the specification of concrete, with the standard describing the correct way of compiling specifications for designated, designed, prescribed, standardized prescribed, and proprietary concretes.
This part of BS 8500 gives detailed guidance for the specifier, including advice on exposure classes for durability, aggregate classes, intended working life and consistence etc., presented as a series of tables with accompanying explanatory text.
BS 8500-2:2023 is intended for use by producers of concrete.
This part of BS 8500 specifies a number of basic requirements for concrete and its constituent materials, and gives specific requirements relating to the types of concrete listed in BS 8500-1. It also specifies requirements relating to delivery, conformity testing, production control and transport.
This standard gives UK national provisions where required or permitted by BS EN 206, and also covers materials, methods of testing and procedures that are outside the scope of BS EN 206, but within UK national experience. The requirements in this part of BS 8500 are given for defined materials with an established or accepted adequate performance in UK conditions.
The 2023 update
BS 8500:2023 incorporates the use of multi-component cements (codified in BS EN 197-5:2021, Cement – Portland-composite cement CEM II/C-M and Composite cement CEM VI). This allows for a reduction in the proportion of Portland cement used for a given volume, hence reducing the embodied carbon in the concrete produced. The cements defined in BS EN 197-5 offer up to 65% Portland cement replacement by two, or more, low-carbon supplementary cementitious materials (SCMs) which are called additions in the standard.
Cement production emits carbon dioxide through the fuel to heat the raw materials, and process emissions from calcining the calcium carbonate. The largest proportion of embodied carbon in concrete is attributable to the cement. This new update to BS 8500 provides options to reduce the mass of Portland cement and reduce the embodied carbon of concrete.
Since the 1980s, the UK experience of using SCMs has been combining Portland cement (CEM I) with either fly ash or ground granulated blast furnace slag. This can be done at the cement factory or at the batching plant**.
BS EN 197-1:2011 introduced the concept of multi-component cements, CEM II/A-M and CEM II/B-M which allow more than one addition to be combined with CEM I. The barrier to widespread adoption of these cements had been that replacement rates were limited to 20% and 35% respectively. The publication of EN 197-5:2021 introduced two new cements; CEM II/C-M and CEM VI. This allows up to 65% of the CEM I to be substituted with two or more additions so providing multi-component equivalents to the binary combinations that have become well established in the UK.
Studies commissioned by the Mineral Products Association found that the inclusion of limestone fines in a CEM I and GGBS ternary system improved material efficiency, demonstrating that the limestone fines could be used as a replacement for both the CEM I and GGBS portions of the blend. This results in concrete with both a lower embodied carbon and a reduced use of GGBS, whilst producing an equivalent performance.
Table 1, from Concrete Futures, spring 2023, published in March 2023.
BS 8500:2023 has also considered the durability performance of ternary combinations consisting of a range of proportions of CEM I, GGBS and limestone fines, and CEM I, fly ash and limestone fines. These cements, and their equivalent combinations, have been categorized according to their relative resistance to chloride diffusion coefficient (1-4) and sulfate resistance (A-G). This grouping, the Combined Performance Category, simplifies the specification of the wider range of cements. This categorisation is based on the cement groupings from Concrete Society Technical Report 61: TR61 Enhancing reinforced concrete durability and BRE Special Digest 1, Concrete in Aggressive Ground.
BS 8500:2015+A2:2019 uses the limiting value concept to ensure the durability of concrete. These limiting values do however reduce the opportunities to decrease overall cement contents. BS 8500:2023 has moved towards removing unnecessary limits.
BS 8500:2023 has removed the minimum recommended characteristic strength for the exposure classes where there may be corrosion of reinforcement due to chlorides (XD and XS).
The recommendations when regarding the corrosion of reinforcement due to carbonation have gone further in BS 8500:2023, with the removal of the minimum cement content and maximum water/cement ratio limiting values, leaving just a minimum recommended characteristic strength.
To find out more:
• Webinar: Lower Carbon Concretes – Revision of BS 8500
• Coming soon – How to guidance for BS 8500:2023
** Note - Cements produced at a cement factory are denoted “CEM” whereas the combinations of Portland cement and additions produced at the concrete plants have a slightly different nomenclature being denoted “C”.