Talking of RMC than the designation Mix is certified on the supply challan. Further in case of doubt you can seek copy of the design mix formula followed. As regards slump test it is simply done to check the workability so as to ensure that delay in supply has not stiffened it which can create problems of flow into moulds. Strength is known after 7/8 days of casting which you can randomly do @45 cum of a lot.

Ricardo Kuhn
Construction Foreman