The best aggregate for a concrete mix depends on the specific application, but generally, sharp sand and 20mm gravel are the most suitable choices for many common concrete applications.
Understanding Concrete Aggregates
Aggregates are crucial components of concrete, making up a large portion of its volume. The type of aggregate significantly influences the concrete's strength, workability, and durability. When selecting aggregates, consider the following:
- Sand: Acts as a fine filler, occupying the spaces between larger gravel particles.
- Sharp sand is preferred for general concrete mixes due to its coarser texture and angular grains, which provide better interlocking and strength.
- Gravel: Provides bulk and strength to the concrete.
- 20mm gravel is a common choice for many applications because it offers a good balance between strength and workability.
- 10mm gravel is suitable for finer concrete mixes, providing a smoother finish for projects that do not need high strength, but prefer a less coarse look and feel.
Choosing the Right Aggregate
General Purpose Concrete
For standard concrete mixes, you can use a combination of:
- Sharp sand: Provides strength and structural integrity.
- 20mm gravel: Adds bulk and contributes to the overall strength of the concrete.
Finer Concrete Mixes
When a finer texture is desired, such as for rendering or surface repair work:
- Use sharp sand as the fine aggregate.
- Use 10mm gravel as the coarse aggregate, resulting in a smoother mix.
Considerations
- Application: The specific purpose of your concrete dictates the appropriate aggregate size. For example, very small and detailed molds, may require an even finer mix.
- Workability: The size and type of aggregate impact the ease of mixing and placing the concrete. Larger aggregates typically result in concrete that is more difficult to place.
- Strength: The aggregate contributes to the overall strength of the hardened concrete.
- Finish: Smaller aggregates generally result in a smoother finish.
Summary
| Aggregate Type | Description | Ideal Use |
|---|---|---|
| Sharp sand | Coarse and angular sand | General concrete mixes, all-purpose mix |
| 20mm gravel | Medium-sized gravel | Standard structural concrete, most common concrete projects. |
| 10mm gravel | Smaller gravel | Finer concrete mixes, surface repairs, when a smoother texture is preferred. |
By understanding the properties and purpose of different aggregates, you can achieve the desired qualities in your concrete mix.
