Parts 7 and 8 cover fresh-concrete density (unit weight), air content and the yield check. Unit weight on a calibrated measure (IS 10079) gives the yield = total batch mass / unit weight — a check that the mix delivers the cubic metres assumed in design/costing/cover. Air content (pressure meter, IS 9799) links to strength loss (~5% per 1% air) and freeze-thaw durability.
Key Requirements
•Fresh unit weight (density) on a calibrated measure (IS 10079), compacted by the standard method
•Yield = total batch mass / fresh unit weight — verify against the design volume (short yield = cover/cost problem)
•Air content by the pressure method (IS 9799) with the aggregate correction; control to the target band
•Test on a representative sample (Part 1) at the relevant point
•Excess air silently cuts strength (~5% per 1%) and short-yields the batch
Formulas
Yield = total batch mass / fresh unit weight
Volume of concrete produced by the batch — checked against design volume
total batch mass = sum of all batched material massesfresh unit weight = measured fresh density (IS 10079 measure)
Practical Notes
✓The yield check is the cheapest way to catch an over-/under-yielding mix — a short yield silently means thin cover and fewer cubic metres than paid for.
✓Air content is dangerous in either direction: too little fails freeze-thaw (hill/cold), too much steals strength and yield.
Common Mistakes
⚠Never running the yield check (hidden over-/under-yield).
⚠Air content trusted from the admixture chart, not measured as-placed (IS 9799).
⚠Uncalibrated density measure (IS 10079) → wrong unit weight, wrong yield.