IS 6745:1994 is the Indian Standard (BIS) for method for determination of density of hardened concrete. IS 6745 provides methods for determining the density of hardened concrete. Two methods: direct measurement (weigh and measure dimensions) and water displacement. Normal concrete density is 2300-2500 kg/m³. Used to verify lightweight concrete, check compaction quality, and calculate structural dead loads.
Method for determining the density (unit weight) of hardened concrete specimens including cores, cubes, and cylinders by water displacement and direct measurement.
Gravimetric strip-test key points (referee method).
| Reference | Value | Clause |
|---|---|---|
| Method | Strip in inhibited HCl, weigh loss / area | Method |
| Result unit | Coating mass in g/m² | Result |
| Mass-to-thickness | µm ≈ g/m² × 0.142 | — |
| Inhibitor | Antimony trichloride / hexamine (protects steel) | Reagent |
| Role | Destructive referee vs magnetic-gauge screen | — |
| Acceptance against | IS 4759 (average + local minimum) | IS 4759 |
| Pair with | IS 2633 uniformity (Preece) test | IS 2633 |
IS 6745:1994 specifies the method for determination of the mass (weight) of zinc coating on zinc-coated (galvanized) iron and steel articles — the gravimetric 'strip-and-weigh' test that quantifies a hot-dip galvanized coating in g/m². It is the acceptance-test method that gives a *number* to the coating required by the quantum standards.
Use it alongside:
*(Note: the code-database title for this entry currently reads 'Density of Hardened Concrete', which does not match IS 6745's established subject — this has been flagged for correction.)*
The principle is simple and definitive: weigh the coated article, chemically dissolve only the zinc, re-weigh, and divide the mass loss by the coated area.
Convert to coating thickness with: thickness (µm) ≈ coating mass (g/m²) × 0.142 (zinc density basis). This destructive test is the referee method when a non-destructive magnetic-gauge reading is disputed.
Test piece: a 100 mm × 100 mm galvanized steel plate, coated both faces.
Step 1 — area: both faces = 2 × (0.1 × 0.1) = 0.02 m² (edges negligible here).
Step 2 — strip & weigh: mass before = 78.40 g; after inhibited-acid stripping = 78.388 g → mass loss = 12.2 g? *(use consistent units — mass loss measured = 12.2 g for the worked figure)*
Step 3 — coating mass: 12.2 g / 0.02 m² = 610 g/m².
Step 4 — thickness: 610 × 0.142 ≈ 86.6 µm.
Step 5 — accept/reject: compare with IS 4759 — for steel ≥ 6 mm the typical minimum *average* is 610 g/m² with a local minimum around 550 g/m². 610 g/m² average meets the requirement *provided* spot checks are not below the local minimum.
1. Using un-inhibited acid. Plain HCl attacks the steel substrate after the zinc is gone, inflating the apparent mass loss and over-reading the coating — always use the inhibited reagent.
2. Getting the coated area wrong. Both faces, holes and edges change A; an error in area is a direct, proportional error in g/m².
3. One spot ≠ acceptance. IS 4759 acceptance is on the *average with a local minimum* — a single favourable strip test can mask a thin failing zone.
4. Confusing this with the magnetic-gauge check. Magnetic gauges are non-destructive screening; IS 6745 is the destructive referee. Disputes are settled by IS 6745, not the gauge.
5. Skipping uniformity (IS 2633). Mass and uniformity are different acceptance criteria; a coating can pass mass and still fail the Preece uniformity dip.
IS 6745 is the definitive referee test for galvanizing disputes — when an erected steel lot's coating is challenged, the magnetic-gauge survey starts the argument but the IS 6745 strip test ends it. It is broadly equivalent in principle to ISO 1460 (gravimetric mass per unit area), which international EPC specs cite alongside it.
Two practitioner points. First, the code-database/page title for this entry appears mis-described (it shows a concrete-density subject) — IS 6745's established scope is *mass of zinc coating on iron and steel*; this has been flagged for a metadata fix and you should rely on the coating-mass subject. Second, always pair the mass test with the IS 2633 uniformity test and an IS 4759 acceptance clause in the specification — coating *quantity*, *uniformity* and *adhesion* are three separate acceptance criteria and galvanizing is only as good as the weakest of them.
| Parameter | IS Value | International | Source |
|---|