CSLB General Building (B)Site Work, Foundations and ConcreteEasy
A concrete supplier delivers aggregate for a footing pour that includes a mix of particle sizes ranging from fine sand to 3/4-inch stone, rather than aggregate that is all one size. What is the primary benefit of using this well-graded aggregate in the mix design?
- AIt fills voids between larger particles, reducing paste demand and improving workability and strength
- BIt increases the total volume of cement paste needed
- CIt allows the concrete to be placed without vibration
- DIt eliminates the need for a water-cement ratio calculation
Show answer & explanationAnswer & explanation
Correct answer: A. It fills voids between larger particles, reducing paste demand and improving workability and strength
Well-graded aggregate contains a range of particle sizes that interlock and fill voids, minimizing the amount of cement paste needed to fill gaps, which improves workability, reduces shrinkage, and increases strength.
Why the other options are wrong
- B. Well-graded aggregate reduces, not increases, paste demand.
- C. Vibration is still required to consolidate concrete regardless of aggregate gradation.
- D. Water-cement ratio is still critical regardless of gradation.
Aggregate Gradation
A well-graded mix of aggregate particle sizes fills voids efficiently, reducing the cement paste required and improving concrete workability and strength.
- Gradation refers to the distribution of particle sizes
- Poorly graded aggregate requires more paste to fill voids
- Good gradation improves density, workability, and reduces shrinkage
Memory trick: Mixed sizes fit like puzzle pieces — fewer gaps, less glue needed.