How we supply it: PSC is arranged through a partner dealer who quotes, supplies and bills it, and pays us a referral commission. Because PSC is not always on Tamil Nadu shelves, we ask the dealer to confirm stock before you fix the footing date, then send the bags with the 40 mm and M-Sand for that pour.
In one line: PSC is a blended cement made by intergrinding OPC clinker and gypsum with 25–70% granulated blast-furnace slag, as specified in IS 455.
What the slag in PSC does
PSC is a blended cement made by intergrinding OPC clinker and gypsum with 25–70% granulated blast-furnace slag, as specified in IS 455. The slag is a glassy by-product of iron making that hardens once the clinker's lime activates it.
Slag concrete is less permeable and binds chlorides, which slows rusting of the steel inside. IS 455 sets the same 28-day minimum as PPC, 33 MPa, and the concrete is often paler than OPC concrete.
Exposure class decides the cement and the mix
IS 456 sorts every concrete member by how harsh its surroundings are, and tightens the mix as the class gets worse. Sites within reach of sea air or brackish groundwater usually fall in the severe class or above.
| IS 456 exposure | Example on a Chennai-belt site | Minimum RCC grade | Max. water-cement ratio |
|---|---|---|---|
| Mild | Interior members protected from rain | M20 | 0.55 |
| Moderate | Exposed to rain or buried in ordinary soil | M25 | 0.50 |
| Severe | Coastal environment, alternate wetting and drying | M30 | 0.45 |
| Very severe | Sea-water spray or aggressive subsoil and groundwater | M35 | 0.45 |
| Extreme | Tidal zone or direct contact with aggressive chemicals | M40 | 0.40 |
PSC vs PPC vs OPC 53
| Factor | PSC | PPC | OPC 53 |
|---|---|---|---|
| Blended material | 25–70% slag | 15–35% fly ash | None |
| Early strength | Lowest | Low | Highest |
| Chloride and sulphate resistance | Best | Good | Lowest |
| Heat while setting | Low | Low | High |
| Availability at Tamil Nadu dealers | Limited | Wide | Wide |
| Minimum moist curing (IS 456) | 10 days | 10 days | 7 days |
Bags for footings in harsh exposure
Typical estimate: . IS 456 Table 5 sets minimum cement contents; your design mix sets the real figure.
- Severe exposure RCC: at least 320 kg/m³, about 6.4 bags
- Very severe exposure RCC: at least 340 kg/m³, about 6.8 bags
- One isolated footing 1.2 × 1.2 × 0.3 m is 0.43 m³, about 3 bags at 7 bags per m³
Delivery checks for slag cement
- The bag must read Portland Slag Cement and IS 455, with the ISI mark and licence number.
- Check the packing date; slag cement's slow start leaves little margin for part-hydrated old stock.
- Open one bag per lot: the powder should run free and look slightly paler than OPC.
- Take the whole pour's quantity from one lot so setting behaviour stays even.
- File the dealer's bill showing type and quantity with your structural drawings.
Handling PSC around wet excavations
- Store it like any cement: raised, covered, clear of walls, in low stacks.
- Schedule delivery close to the footing pour; lumped slag cement has lost the property you paid for.
- Below-ground pours often wait on dewatering, so keep a tarpaulin ready for delays.
- Never leave opened bags overnight beside a wet pit.
Mistakes with PSC below ground
- Choosing PSC for durability and then pouring a wet, high water-cement mix.
- Stripping sump walls early in the monsoon while slag concrete is still weak.
- Undercutting cover: IS 456 asks for at least 50 mm in footings.
- Assuming PSC will be on the shelf on pour day instead of booking it.
- Pouring into a flooded trench and trapping mud in the concrete.