Fresh concrete is concrete in its unset, plastic state — the workable mixture of cement, sand (fine aggregate), gravel (coarse aggregate), and water that has been mixed but has not yet begun to harden. During this phase, the concrete can be transported, poured into formwork, spread, compacted, and finished. Once the cement reacts with the water and the mixture cures, it transforms into the hard, durable material we simply call concrete.
The period during which concrete remains fresh is limited. Depending on the mix design, temperature, and any added retarders or accelerators, fresh concrete typically stays workable for 60 to 120 minutes after mixing. After that, it begins to stiffen and can no longer be properly placed or compacted.
Application
Understanding fresh concrete matters because the quality of the finished hardened concrete depends heavily on how the material is handled while it is still fresh. Poor practices during this stage — such as adding too much water, inadequate compacting, or delays in placing — lead to weaker, less durable concrete.
Key properties of fresh concrete that builders need to monitor include:
Workability (slump): How easily the concrete flows and fills the formwork. A higher slump means a more fluid mix. The required slump depends on the application — a floor slab might use a slump of 100 mm, while a pumped mix may need 160 mm or more.
Cohesion: The mix should hold together without the water and cement paste separating from the aggregates (a defect called segregation).
Air content: Some mixes intentionally include tiny air bubbles for frost resistance. Too much unintentional air reduces strength.
For DIY builders, the most important rule is: never add extra water to fresh concrete to make it easier to work with. While tempting, this weakens the final product significantly. If you need a more fluid mix, ask your supplier to adjust the slump at the plant, or use a plasticiser additive that improves flow without extra water.
Always have your formwork, reinforcement, and tools ready before the concrete arrives or is mixed, so you can place and finish it while it is still properly workable.
Related terms
- Concrete
- Cement
- Ready-mix concrete
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