Cement That Has Sat Through the Monsoon
A government school extension site received 180 bags of OPC 43 grade cement in the first week of July. By the end of August about 120 bags are still unused. The store is a lean-to shed with CGI sheeting; one sheet is displaced and monsoon rain blows in. The bags stand directly on the concrete floor, twelve bags high, with the stack touching the outside wall. When the mason opens a bag for 1:6 brickwork mortar, the cement comes out partly as hard lumps, and a few bags are caked solid like a brick. The contractor says the lumps will break up in the mixer and wants the whole stock used for brickwork and 12 mm internal plaster. The junior engineer must decide what may be used, what must be rejected, and how the decision is recorded, before the next pour of the lintel and slab is taken up.
1. Diagnose what has happened to the cement and set out the field checks you would use to separate usable bags from bags that must be rejected.
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What has happened. OPC starts to hydrate the moment it absorbs moisture. These bags have stood on a damp floor through eight weeks of monsoon humidity, with rain entry near the wall, so part of the cement has already reacted.
Two kinds of lumps must be distinguished:
- Pressure lumps - formed where the weight of twelve bags compacts cement at the bottom of the stack. They are soft, crumble between the fingers, and the powder around them is still cement.
- Set lumps - hard, caked, resist thumb pressure, and sound like stone when tapped. These are hydrated cement. The powder around them has also lost strength, and no amount of re-mixing restores it.
Field checks, in the order I would apply them:
- Read the date of manufacture on the bag. Cement older than three months, and any cement stored through a monsoon, needs testing even if it looks sound.
- Slice a bag open and judge the flow. Cement should be powdery and free-flowing.
- Crush a lump between palm and thumb and listen for grit.
- Drop a handful into a glass of water. Good cement settles; excessive floating matter suggests adulteration.
- Thrust a hand into the bag - fresh cement feels cool.
The decisive test. None of these checks quantifies strength. Send a 5 kg composite sample of the sieved, non-caked cement to a laboratory for mortar cube tests at 7 and 28 days against the grade requirement, and quarantine the stock until the report arrives.
2. Decide what portion may be used, where it may be used, and how you would record and dispose of the rest.
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Segregate first, decide second. Open and screen the whole 120 bags into three lots before any mixing: sound powder, friable lumps, and hard caked material.
Caked bags - reject. Cement that has set into a brick-shaped mass has no recoverable value. Count them, photograph the lot with the bag markings visible, make a joint record with the contractor's representative, and enter a rejection memo in the stores register. Give notice to the supplier or insurer within the period allowed by the purchase order; do not simply write the loss off.
Friable-lump cement - conditional use only. Sieve through a 2.36 mm sieve to remove hard pieces. Even then it goes only into non-structural work, and only after laboratory approval: bedding mortar for internal non-load-bearing partition masonry, or mortar for filling and levelling. It must not go into RCC, into load-bearing masonry, into external plaster, or into any waterproofing course. A degraded cement in 1:6 mortar reduces masonry strength and, in plaster, produces shrinkage cracks and a dusty surface.
Records. Stores indenture, rejection memo, laboratory report, and a measurement book entry naming the work, the quantity and the approving authority. Never quietly blend rejected cement with fresh stock - that destroys traceability and transfers the risk into the structure.
3. Recommend storage changes so that this does not recur on the site.
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The loss was caused by siting and order quantity as much as by the weather, so the fix must address both.
Physical storage:
- A raised platform at least 150 mm above floor level - timber pallets on a concrete plinth, not loose bricks.
- A clear gap of 300 to 450 mm between the stack and any wall, so moisture does not wick across.
- A maximum stack height of 8 bags (10 at most for short-duration storage); twelve bags crushes the bottom layer and creates false lumps.
- Full tarpaulin cover over the top and down the weather side, and repair of the displaced CGI sheet before the next delivery.
- Separate bays by consignment with a date board on each, so first-in-first-out actually happens.
Procedural controls:
- Order size matched to consumption. A site using about 60 bags a month should not hold 180 bags; the excess is simply ageing.
- Monthly physical stock verification against the register, with ageing flagged at 60 days.
- Issue only against an approved indent, and record the bag count on issue.
- Brief the storekeeper that a bag is accepted only if the manufacture date, the batch and the condition are checked and entered.
A cheap platform and a smaller order would have prevented the entire loss.