IS 5512 : 1983Specification for flow table for use in tests of hydraulic cement and pozzolanic materials

IS 5512:1983 is the specification for the flow table used in tests of hydraulic cement and pozzolanic materials — the standardised drop-table that measures mortar flow (workability) and is central to the lime/pozzolana reactivity (compressive strength) test where mortar is brought to a fixed flow before moulding. It standardises the workability reference so strength comparisons are made at equal consistency.

It sits with the pozzolana/cement test stack:

• IS 1727 — methods of test for pozzolanic materials (uses flow to fix mortar consistency) · IS 4031 — cement physical tests
• IS 3812 — fly ash (pozzolana, reactivity assessed via flow-controlled mortar) · IS 269 — OPC

Mortar strength depends on water content, so comparing a pozzolana's reactivity is only fair if every mortar is mixed to the same flow, not the same water. IS 5512 fixes the instrument that defines 'same flow':

• A rigid flow table ≈ 300 mm diameter that is mechanically dropped through ~12.5 mm, 25 times in ~15 s — a fixed, repeatable jolting energy
• A standard flow mould (frustum) to form the mortar cone on the table
• Flow = the increase in mean base diameter after the 25 drops, expressed as a % of the original

The engineering point: in the IS 1727 pozzolana strength/reactivity test, the mortar's water is adjusted until it reaches a *target flow* on this table, then cubes are cast — so the table's drop height, count and timing directly set the water content and therefore the strength. A non-standard or worn table biases every reactivity result built on it.

Scenario: assessing a fly ash's pozzolanic contribution (lime/cement-replacement mortar).

Step 1 — control mortar: make the reference mortar; bring it to the target flow on the IS 5512 table (25 drops / ~15 s) by adjusting water.

Step 2 — test mortar: make the pozzolana-containing mortar and bring it to the same flow — equal workability, not equal water.

Step 3 — mould & cure: cast cubes from both at equal flow; cure per IS 1727.

Step 4 — compare strength: the strength ratio (test/control) is the reactivity measure — *valid only because both were at the same standardised flow*.

If the table's drop height or count is off, 'same flow' is a different water content than intended, and the reactivity verdict on the fly ash (and any IS 456 cement-replacement decision built on it) is biased.

1. Worn/non-standard drop mechanism. Wrong drop height or count changes the jolting energy → wrong flow → biased strength.

2. Comparing mortars at equal water, not equal flow. Defeats the purpose; reactivity must be judged at equal consistency.

3. Sloppy timing/technique. The 25 drops in ~15 s and clean mould lift are part of the standard; rushing them scatters flow.

4. Dirty or non-planar table top. Build-up changes the spread; the surface is part of the calibration.

5. Treating flow as a strength substitute. Flow standardises consistency for the strength test — it is not itself the strength.

• IS 1727 — methods of physical tests for pozzolanic materials (flow-controlled mortar)
• IS 3812 / IS 1344 — fly ash / calcined clay pozzolana (reactivity via this test)
• IS 4031 Part 1 — cement physical tests · IS 269 — OPC
• IS 456 / IS 10262 — concrete & mix design (pozzolana replacement decisions)

IS 5512 is a niche apparatus standard, but it underpins something engineers increasingly rely on: the decision to replace cement with fly ash / pozzolana for cost, durability and embodied-carbon. That decision rests on reactivity numbers, and those numbers are only fair if the comparison mortars were at the same standardised flow — which is exactly what this drop table defines. The recurring error is comparing at equal water rather than equal flow, or trusting a worn table. Keep the table's drop height and count verified, run the 25-drop procedure cleanly, always compare at equal flow, and the pozzolana reactivity feeding your IS 10262 mix decisions is defensible.