How do you control concrete slumps?

Concrete slumps can be managed by mixing at very high slump, this will leave the residual slump very standard.... It can also be control using concrete retarders/water reducer... 

Keeping the temperature low is another good way of controlling slump loss.....

Only a true slump is of any use in the test. A collapse slump will generally mean that the mix is too wet or that it is a high workability mix, for which the slump test is not appropriate.[1][3] Very dry mixes having slump 0 – 25 mm are typically used in road making, low workability mixes having slump 10 – 40 mm are typically used for foundations with light reinforcement, medium workability mixes with slump 50 – 90 mm, are typically used for normal reinforced concrete placed with vibration, high workability concrete with slump > 100 mm is typically used where reinforcing has tight spacing, and/or the concrete has to flow a great distance.[5]:68