BS 8500 — Concrete Specification

What BS 8500 covers

BS 8500-1:2023 covers how to specify concrete and guides the specifier (Annex A links exposure class, intended working life and cover to a concrete quality); BS 8500-2:2023 covers the constituent materials and the concrete itself. Both were published on 30 November 2023 and are current.

The standard sets out several ways to specify concrete rather than a single recipe: 'designated' concrete (ordered by a standard reference like GEN, RC, FND or PAV, with the producer responsible for meeting it), 'designed' concrete (you specify the performance, the producer designs the mix), and 'prescribed' / 'standardised prescribed' concrete (specified by its constituents). For most domestic work a designated concrete ordered from a ready-mix supplier is the simplest compliant route.

Designated concretes use job-based reference names rather than just a strength number — for example GEN-series for general unreinforced use, RC-series for reinforced concrete, FND-series for foundations (including in sulfate-bearing ground) and PAV-series for paving and external slabs subject to freeze-thaw and de-icing salts. This is the language a merchant quotes, alongside the strength class.

Durability is driven by exposure class, not just strength: BS 8500 (via BS EN 206) classifies the environment the concrete sits in — carbonation (XC), chlorides from de-icing salt or seawater (XD/XS), freeze-thaw attack (XF) and chemical/aggressive ground (XA) — and the exposure class drives the required concrete quality and cover. A driveway exposed to frost and salt has a different durability requirement to a sheltered internal slab of the same strength.

The 2023 edition is focused on lower-carbon concrete: it brings in BS EN 197-5 cements (up to 65% of Portland cement replaced by lower-carbon additions) as general-purpose cements, supporting net-zero targets as GGBS availability tightens — so multi-component cements are increasingly the default rather than a substitution.

A notable durability change in 2023 is that minimum cement content and water/cement ratio were removed as limiting values for carbonation-related durability — so older rules of thumb quoting fixed minimum cement contents no longer reflect the standard.

This page covers how concrete is specified and why; the volume and bag/ready-mix maths stays on the tool — use the concrete calculator to work out quantities once you've chosen the concrete for your job.