OPC or PCC cement: which to use for which job

What is in the bag

OPC, ordinary Portland cement or CEM I, is almost entirely ground clinker with a little gypsum. PCC, Portland composite cement or CEM II, replaces part of the clinker with materials such as slag, fly ash and limestone. The bag states the type, for example CEM II/B-M, and a strength class such as 42.5 N.

How they behave differently

• Early strength: OPC gains strength faster in the first days. PCC catches up over the following weeks.
• Heat: PCC releases less heat as it sets, which reduces cracking risk in thick pours such as rafts and pile caps.
• Durability: the added materials in PCC generally make concrete denser and more resistant to sulphates and salts, which helps in foundations and coastal areas.
• Workability: PCC mixes are often easier to place and finish.

Choosing between them

OPC is the usual choice where early strength matters: precast work, fast formwork turnover, repairs and cold-weather pours. PCC suits foundations, mass concrete, plaster and brickwork, and most general building work, and it is the larger share of what is sold in Bangladesh.

The structural engineer's specification decides. If the drawing names a cement type and strength class, supply that. If it does not, ask before ordering rather than after pouring.

Storing cement on site

• Keep bags in a dry, closed room, on pallets or planks, off the floor and clear of the walls.
• Stack no more than about ten bags high so the lower bags do not compact.
• Use the oldest stock first. Cement steadily loses strength in storage, so try to use it within about three months of manufacture.
• Reject bags that have hard lumps which do not crumble in the hand.

Buying in the right quantity

A bag weighs 50 kg. Because cement ages, it is better delivered in step with the pours than bought once for the whole project. Agree a delivery schedule with your supplier and fix the price basis up front.