IS 7325 : 1974Specification for apparatus for determining constituents of fresh concrete

IS 7325:1974 is the specification for the apparatus for determining the constituents of fresh concrete — the washing/separation kit used to *analyse a fresh concrete sample* and back-calculate its actual proportions (cement, water, fine and coarse aggregate). It is the tool that answers the on-site question 'is the concrete in front of me actually the mix that was specified?' *before* it hardens.

It sits with fresh-concrete verification:

• IS 1199 Part 2 — sampling & fresh-concrete tests (the analysed sample comes from here) · IS 456 — concrete (the specified mix being verified)
• IS 10262 — mix design (the target proportions being checked) · IS 4926 — ready-mixed concrete (delivered-mix verification)

Hardened-concrete forensics are slow and destructive; IS 7325's apparatus lets you check the mix *while it's still plastic*. The kit supports washout/separation to estimate:

• Coarse aggregate content — wet-sieving the sample on the relevant sieve and weighing the retained, surface-dry aggregate (the most reliable single check; the most sensitive to wrong batching/segregation)
• Fine aggregate — by washing out the paste and separating
• Cement / water content — by inference from the separated fractions and sample mass

The engineering point: this turns a dispute that would otherwise wait 28 days into a same-shift answer. If the delivered concrete's coarse-aggregate fraction or apparent cement content is off, you find out at the truck, not after the cubes fail — which is the difference between rejecting a load and demolishing a slab.

Scenario: a ready-mixed M30 delivery looks lean/over-sanded; the slump is high.

Step 1 — sample: take a representative fresh sample per IS 1199 Part 2, weigh it.

Step 2 — wash & separate (IS 7325 kit): wash out the paste; wet-sieve to recover the coarse aggregate, bring to saturated-surface-dry, weigh; separate and weigh the fine fraction.

Step 3 — back-calculate: compare the measured coarse-aggregate (and inferred cement/water) content against the IS 10262 design proportions for M30.

Step 4 — decide at the truck: materially short on aggregate or cement, or watered down → reject the load and raise it with the supplier now; within tolerance → accept. Either way the decision is made before the concrete is in the structure, not after a 28-day cube failure forces a demolition argument.

This pre-hardening check is exactly why the apparatus exists.

1. Waiting for cubes instead of analysing fresh. A wrong mix found at 28 days means demolition; found fresh, it means rejecting a load.

2. Non-representative sample. Garbage in — sample per IS 1199 Part 2, not a convenient scoop, or the analysis is meaningless.

3. Sloppy wet-sieving / wrong moisture state. Not bringing aggregate to SSD before weighing biases the coarse-aggregate result.

4. Over-claiming precision. The method estimates proportions with real scatter — use it to catch *gross* batching/RMC errors, not to argue ±2% on cement.

5. Not doing it on RMC at all. Delivered concrete is exactly where surreptitious water/lean batching happens and where this fast check pays for itself.

• IS 1199 Part 2 — sampling & testing fresh concrete (source of the analysed sample)
• IS 456 — concrete (the specified mix being verified)
• IS 10262 — mix design (target proportions for the back-calculation)
• IS 4926 — ready-mixed concrete (delivered-mix verification & tolerances)
• IS 2386 Part 1 — sieve analysis (the wet-sieving basis)

IS 7325 is old (1974) and under-used, but it answers the most practically valuable question on a concrete site at the only time the answer is cheap: is this the mix I specified, before it sets? With ready-mixed concrete the norm, water added in transit and lean batching are real risks, and the alternative to a fresh-concrete check is discovering the problem from failed 28-day cubes — by which time the dispute is about demolition, not a rejected load. The method is approximate, so use it to catch gross errors (over-sanded, watered-down, short on cement), not to litigate small tolerances. A site that washes out a suspect load the same shift is in a completely different negotiating position than one waiting on cubes.