You cannot directly make new concrete using existing hardened concrete. However, you can use concrete in two main ways in the process of creating new concrete: as an aggregate or by using the existing concrete to make a cementitious paste.
Using Concrete as an Aggregate
Old concrete, after being crushed, can be used as an aggregate in making new concrete. This process is quite common in the construction industry for recycling and cost reduction.
How to use concrete as Aggregate:
- Demolition: First, old concrete structures need to be demolished safely.
- Crushing: The demolished concrete is then crushed into smaller pieces using specific crushing machines.
- Screening: The crushed concrete is screened to separate the particles based on size, ensuring the right size distribution for an aggregate.
- Mixing: The crushed concrete, now in the form of an aggregate, is mixed with portland cement, water, and other fine aggregates (sand) to make new concrete.
According to the provided reference, to make concrete: a mixture of portland cement (10-15%) and water (15-20%) make a paste. This paste is then mixed with aggregates (65-75%) such as sand and gravel, or crushed stone. As the cement and water mix, they harden and bind the aggregates into an impenetrable rock-like mass.
Using Concrete in making Cementitious Paste
New technology is also exploring the option of using hardened concrete to create a kind of "recycled cementitious paste" using a chemical activation process. This paste, is then used to bind new aggregate for a more eco-friendly concrete alternative.
How to use Concrete in making cementitious Paste:
- Grinding: The hardened concrete is ground into a fine powder.
- Chemical Activation: The powder goes through a chemical activation process to break down the original cement structure.
- Paste Formulation: The resulting substance is mixed with water and activators to create a new cementitious paste.
- Mixing: The cementitious paste is then combined with new aggregates to create new concrete.
The Bottom Line
In conclusion, while you can't directly mix old concrete to create new concrete, you can recycle and re-use it by utilizing the old concrete as an aggregate or by chemically processing old concrete to make a cementitious paste.
| Component | Function | Percentage |
|---|---|---|
| Portland Cement | Acts as the binding agent | 10-15% |
| Water | Hydrates cement, enables paste to form | 15-20% |
| Aggregates | Provide bulk and strength | 65-75% |
