Trial Mixes and Initial Testing
A calculated mix design is a starting point, not a finished product. EN 206 (Annex A) sets out initial testing — trial batching with the actual project materials — as the way a mix design is confirmed before it is used, and conformity control as the way ongoing production is checked once concreting starts.
Initial testing
Initial testing means producing trial batches of the proposed mix, using the actual cement, aggregates, admixtures and water intended for the project (not generic assumed properties), and testing them for the properties that matter — compressive strength, consistence, and any durability-related properties relevant to the exposure class. Because real materials vary from the assumed specific gravities and water demands used in a preliminary calculation, initial testing is what confirms the calculated proportions actually deliver the required performance, and allows adjustment before full-scale production.
Conformity control
Once concreting is underway, EN 206 requires ongoing conformity control — checking that production continues to meet the specification, generally assessed on strength test results grouped over a production period, rather than judging each single test result in isolation. This is what distinguishes a one-off calculated design from a concrete supply that can be relied on for a whole project.
UK producer certification
In the UK, ready-mixed concrete is normally supplied by a producer holding third-party product certification (for example under a BS 8500-2-referenced scheme), which covers the producer’s factory production control, testing regime and conformity assessment. Specifying concrete from a certified producer is part of how BS 8500 conformity is normally achieved in practice, alongside the initial testing and conformity control requirements of EN 206 itself.
Frequently asked questions
Can a mix design be used without trial batching?
For anything beyond the most preliminary estimate, no — the calculated proportions rely on assumed material properties (specific gravities, water demand) that should be confirmed against the real materials before committing to full-scale placement.
How many trial batches are normally needed?
This is set by the producer’s own quality system and, where applicable, the requirements of their BS 8500-2 third-party product certification scheme — it is not a single fixed number for every project.
What is checked besides strength?
Consistence (workability), and any exposure-class-related durability property relevant to the project, such as air content for freeze-thaw exposure — see air entrainment.