Field Tests of Cement: Site Checks and IS 4031 Lab Tests

On site, check five things before accepting cement. Look at the manufacturing date on the bag and the colour, which should be a uniform grey with a slight greenish tint. Make sure there are no hard lumps. Feel the cement: it should be smooth and cool. Finally, do a quick float test and pat test.

These checks only screen out bad or old cement; they do not prove the grade. Acceptance is by the lab tests of IS 4031. Under IS 269, OPC must meet these limits:

• Fineness: at least 225 m²/kg
• Initial setting time: at least 30 minutes
• Final setting time: at most 600 minutes
• Le Chatelier expansion: at most 10 mm
• 28-day strength: at least 33, 43 or 53 MPa, depending on the grade

Field tests of cement (site checks)

1. Date of manufacture

Every bag shows the week, month and year it was packed. Cement slowly picks up moisture from the air and loses strength. A commonly quoted thumb rule is a loss of roughly 20% after 3 months and 30% after 6 months of ordinary storage. Actual loss depends heavily on how the cement was stored. If cement is more than about 3 months old, or has been stored badly, get it lab-tested before using it in structural concrete.

2. Colour

The colour should be uniform greenish-grey throughout the bag. Patches of a different shade or a yellowish or brownish tint can mean the cement is adulterated with clay or fly ash, or has been partly hydrated.

3. Lumps

Open a bag and run your hand through it. The cement should be free-flowing. Soft lumps that crumble between your fingers usually come from pressure in the stack and are harmless. Hard lumps that do not break mean the cement has absorbed moisture and started to set. Reject such bags or sieve them out for non-structural use only.

4. Hand feel

Push your hand into the bag: good cement feels cool. Rub a pinch between your fingers: it should feel smooth, like talc. A gritty feel suggests sand or another coarse adulterant.

5. Float test

Throw a small handful of cement into a bucket of still water. Good cement spreads on the surface and floats briefly before sinking. If it sinks at once as a lump, or leaves gritty material at the bottom, suspect adulteration or moisture. This is only an indicative test. Never accept or reject a lot on this alone.

6. Pat (setting) test

Mix about 100 g of cement with water into a stiff paste. Make a pat with thin, sharp edges on a glass plate and keep it under water. After 24 hours it should have set hard, kept its shape and shown no cracks. Cracking, softening or distortion is a warning sign.

Laboratory tests as per IS 4031

Compressive strength requirements for OPC

How the main tests are done

• Standard consistency (Vicat apparatus). Make cement pastes with different amounts of water. The standard consistency P is the water percentage at which the 10 mm plunger stops 5 to 7 mm above the bottom of the mould.
• Setting time. Make a paste with 0.85P water. Initial set is the time at which the 1 mm square needle stops about 5 mm above the bottom of the mould. Final set is the time at which the needle with the annular attachment leaves a mark but the collar does not.
• Soundness (Le Chatelier). Fill the split mould with paste and keep it in water for 24 hours. Measure the gap between the indicator points, boil the mould for 3 hours and measure again. The increase is the expansion.
• Compressive strength. Make 70.6 mm cubes (face area 50 cm²) from 1 part cement and 3 parts standard sand. Cure them and test at 3, 7 and 28 days.

Worked example: reading a test report for 43 grade OPC

1. Standard consistency: the paste with 120 g of water in 400 g of cement met the plunger requirement, so P = 120 ÷ 400 = 30%.
2. Water for the setting-time paste = 0.85 × 30% = 25.5%, which is 0.255 × 400 = 102 g.
3. Setting times recorded: initial 145 min (at least 30, OK) and final 260 min (at most 600, OK).
4. Water for the cube mortar. Each cube uses 200 g of cement and 600 g of standard sand. The water is (P/4 + 3)% of the combined mass = (7.5 + 3)% = 10.5% of 800 g = 84 g.
5. 28-day cube. The failure load is 230 kN and the face area is 70.6 × 70.6 = 4984 mm². Strength = 230,000 ÷ 4984 = 46.1 MPa, which is at least 43, so the result is OK. Report the average of the cubes tested.
6. Soundness. The indicator gap was 12.0 mm before boiling and 17.5 mm after, so the expansion is 5.5 mm. That is within the 10 mm limit, so the result is OK.

This sample meets IS 269 for 43 grade on every test reported.

Site tips

• Stack bags on planks or pallets about 150–200 mm above the floor and away from walls. Cover the stack, and keep it no more than about 10 bags high.
• Use the oldest stock first and keep each grade and brand in a separate stack.
• Do not judge strength by the float test or by colour. Insist on the batch test certificate, and send samples to a lab for important work.
• Good cement still needs the right water content. See water-cement ratio. To choose between cement types, read OPC vs PPC vs PSC.

Cement tests are a favourite topic in PSC AE and JE papers. Try our mock tests.