Designed - ready-mixed concrete
British Standard BS 8500-1: has been used by the ready-mixed concrete industry since December 2003 (replacing BS 5328).
For flexibility in specifying and purchasing concrete, designed mixes are appropriate as they cover the application and constituent materials. It is a mix for which the purchaser is responsible for specifying the required performance and the producer is responsible for selecting the mix proportions to produce the specified performance. Effectively, the producer has responsibility for the mix design to meet the purchasers needs e.g. exposure environment, design life, strength, workability etc.
The mix is ordered by its required performance in terms of its strength class subject to any restrictions on materials, minimum or maximum cement content, maximum w/c ratio and any other properties required. The purchaser must supply all the relevant information on use to enable the producer to design the concrete accordingly.