Frequency of Slump testing is carried based on project specifications, however I would recommend following depending on where you are !
In your case one test should be good or one test for every transit mixer you receive. Transit mixer comes in 8m3 capacity.
At site receiving end of concrete :
- One test for every 50m3 concrete placed or very time you cast cubes.
- If you find variation in workability perform a test.
At batching plant :
Slump test is carried at every 1000m3 concrete produced per grade.