Part 1 fixes how a representative sample of fresh concrete is taken — multiple increments from the discharge (not the first or last alone), combined and remixed, sampled within a time limit. Every downstream result — slump, density, air, and the IS 516 acceptance cubes — is only as valid as this sample, so it is the foundation clause of all concrete testing.
Key Requirements
•Composite sample from several increments across the discharge (not just the first/last portion)
•Combine and remix the increments before testing; sample/test within the specified time limit
•Sample at the point of placement for acceptance-relevant tests (transport/pumping change the concrete)
•Sample size adequate for all intended tests (slump + density/air + cubes)
•A non-representative sample invalidates every fresh and hardened test built on it
Practical Notes
✓Acceptance cubes and slump are only meaningful if the sample was representative and remixed — a convenience scoop off the chute certifies nothing.
✓Test at the point of placement: pumping/vibration/transport change slump and air from the as-batched values.
Common Mistakes
⚠Sampling only the first or last of the discharge.
⚠Not remixing the composite before sub-sampling.
⚠Sampling as-batched when the acceptance-relevant condition is as-placed.