- 2078 Kartik · 4+4 marks
Aggregate properties and their influence on concrete
Short answer
Key aggregate properties: grading, shape, texture, strength, absorption, soundness, deleterious matter. Grading controls voids and water demand; shape affects workability and bond; strength limits concrete strength; high absorption raises water demand; deleterious matter weakens bond and promotes corrosion; soundness prevents disintegration.
Write down the properties of aggregates for concrete. How do the aggregate properties influence the concrete properties?
Properties of aggregates for concrete
Physical: particle size and grading, shape, surface texture, specific gravity, bulk density, porosity, water absorption, moisture content (bulking), voids. Mechanical: crushing, impact, abrasion value, hardness and strength. Chemical/other: soundness, alkali-aggregate reactivity, deleterious matter (clay, silt, coal, salts), thermal properties, fineness modulus.
Influence on concrete properties
| Aggregate property | Influence |
|---|---|
| Grading | Fewer voids, less cement/water, better workability, less segregation, higher strength and density |
| Maximum size | Larger size reduces water demand (surface area); too large reduces strength at high grades |
| Shape | Rounded: better workability. Angular: better bond and strength. Flaky/elongated: poor workability, low strength and durability |
| Surface texture | Rough texture gives better bond (higher flexural strength), smooth gives better workability |
| Strength (crushing/impact) | Weak aggregate limits concrete strength, especially at high grades; affects modulus of elasticity |
| Abrasion / hardness | Wear resistance of floors and pavements |
| Specific gravity / bulk density | Determines weight of concrete (light or heavy concrete) and mix proportioning |
| Porosity and absorption | High absorption increases water demand, lowers frost resistance and durability; affects w/c control |
| Moisture content | Surface moisture changes w/c; bulking changes volume batching |
| Soundness | Unsound aggregate causes disintegration and pop-outs |
| Deleterious material (clay, silt, organic, chloride) | Reduces bond, strength, causes corrosion, retards set |
| Alkali reactivity | Expansion, map cracking, loss of durability |
| Thermal properties and elasticity | Affect shrinkage, creep, thermal cracking |
✓ Answer checked by Claude Opus 5.5 (high effort)
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