Cement Delivered Three Weeks Early and Stored on Grade
On a two-storey residential project, 150 bags of 40 kg Type 1 Portland cement arrive three weeks before the CHB laying starts because the supplier gave a discount for a single delivery. The designated storeroom is still being painted, so the laborers stack the bags directly on damp ground against the exterior wall of the completed portion. A tarpaulin covers the top of the pile only; the sides are left open. The site is in a coastal town with 30–32 °C daytime temperature, high humidity, and brief afternoon rain. When the mason opens the pile, the bottom 40 bags feel firm and contain hard lumps the size of a thumb; bags higher in the stack are still powdery. The foreman proposes breaking up the lumps and using the hard bags for the 1:4 mortar of the 100 mm CHB wall. The project has no testing laboratory nearby.
1. Decide whether the 40 hardened bags may be used in the 1:4 mortar for the 100 mm CHB wall. Support the decision with the evidence in the scenario and state what should happen to those bags.
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Reject the 40 bags for the wall mortar. Three weeks on damp ground at 30–32 °C and high humidity is enough for partial hydration; hard thumb-sized lumps show the cement has already set in places. Breaking the lumps does not restore the cement's binding capacity, because the hydrated compounds cannot re-form on mixing. The resulting mortar would demand more water, shrink more, and develop lower and more variable strength. On a 100 mm CHB wall, that means weaker bond, higher risk of cracking, and uncertain compressive capacity. The lack of a nearby laboratory removes any way to prove by testing that the affected cement is still acceptable. The correct action is to segregate and reject the 40 bags, use only the powdery bags for the specified 1:4 mortar, and notify the supplier. If a nonstructural use is allowed, a trial mix may be considered, but the material should not be used in the wall.
2. Describe the storage arrangement that should have been used for the 150 bags of 40 kg cement from delivery to consumption.
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Store on a raised, dry platform at least 150 mm above ground and 300 mm clear of walls, with space for air movement. Stack no more than about 10 bags high (for 40 kg bags) to avoid compaction, and do not stack against a damp exterior wall. Cover the top and all sides with a waterproof sheet, but allow ventilation so condensation does not form. Keep bags off the ground with pallets or a timber floor. Apply first-in, first-out: record delivery dates and consume the oldest cement first, within the manufacturer's storage life (commonly about three months). Keep the store clean, dry, and free of oil or chemicals. For 150 bags, arrange several stacks with access aisles rather than one large pile. These controls prevent ground moisture, rain, and humid air from causing the exact lumping seen in the scenario.
3. If the foreman insists on using the hard bags, what trial or controls would reduce the risk, and why is this still not recommended?
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Even if the foreman insists, using the hard bags would be a controlled risk, not a cure. Sieving would remove lumps, but the fine fraction still contains partially hydrated cement; a trial mortar would show only workability, not long-term strength. A practical trial could compare a small batch with fresh cement for setting time and seven-day soundness, but without a laboratory the result is not reliable. The safe control is to keep the suspect cement out of structural mortar, lintels, and reinforced walls, and use it only for nonstructural bedding or blinding if allowed, with a separate batch record. Because the wall is only 100 mm thick, there is little margin for weak mortar. The professional answer is to refuse the material for the wall rather than compensate later with plaster.