- Asked 2/26
- 2075 Asoj · 1 mark
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Define admixtures in brief
Short answer
Admixtures are materials (other than cement, water, aggregate) added before or during mixing to modify concrete properties. Examples: accelerators for early strength, retarders to delay setting, plasticizers for workability, air-entrainers for freeze-thaw resistance, mineral admixtures for durability.
Define admixtures. Explain their engineering application.
Admixtures are materials, other than cement, water and aggregate, added to concrete or mortar just before or during mixing to modify its properties in the fresh or hardened state. They are used in small doses (usually less than 5% of the cement weight).
Engineering applications
| Type | Purpose / application |
|---|---|
| Accelerators (calcium chloride, for plain concrete) | Faster setting and early strength; cold-weather concreting, urgent repairs |
| Retarders (sugar, gypsum) | Delay setting in hot weather, long hauls and large pours |
| Plasticizers / superplasticizers | Increase workability or cut water by 10-30% for high strength, pumping, congested reinforcement |
| Air-entraining agents (resins, fats) | Entrain tiny air bubbles for freeze-thaw resistance and workability |
| Water-proofing agents | Reduce permeability of basements, water tanks, roofs |
| Mineral admixtures (fly ash, silica fume, slag) | Higher durability, lower heat of hydration, economy |
| Pigments | Coloured concrete and plaster |
| Bonding agents | Join new concrete to old |
✓ Answer checked by Claude Opus 5.5 (high effort)
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