5. Aggregates – Properties, Grading, Testing
Aggregates play a crucial role in construction, affecting the strength, durability, and workability of concrete. Their classification, properties, grading, and testing methods are essential for civil engineers to ensure quality and performance in concrete structures. An understanding of both natural and recycled aggregates, along with their physical, mechanical, and chemical characteristics, contributes to more sustainable construction practices.
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What we have learnt
- Aggregates constitute 70%-80% of concrete volume, influencing its properties significantly.
- Different classifications of aggregates, such as by size, origin, and shape, have distinct implications on their use in construction.
- Testing and grading of aggregates are vital to guarantee structural integrity and performance in concrete.
Key Concepts
- -- Fine Aggregates
- Particles that pass through a 4.75 mm sieve and are retained on a 75-micron sieve, commonly sand.
- -- Coarse Aggregates
- Particles that are retained on a 4.75 mm sieve, typically gravel or crushed stone.
- -- Specific Gravity
- The ratio of the weight of a volume of aggregate to the weight of an equal volume of water, crucial for calculating mix designs.
- -- Grading
- The distribution of different sizes of particles in an aggregate sample, important for optimizing concrete mix.
- -- Water Absorption
- The ability of aggregates to take in water, influencing the water-cement ratio in concrete mixes.
- -- AlkaliSilica Reactivity (ASR)
- A chemical reaction between alkalies in cement and reactive silica in aggregates that can cause expansion and cracking.
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