Concrete can be recycled - it is done already in the industry. Old concrete can be reused as aggregates for new concrete production and save natural resources. Sika offers solutions to improve concrete recycling, thereby helping to reduce the CO₂ footprint of concrete production.
All the Facts about Concrete Recycling and How It Works:
Can Concrete Be Recycled?
Yes, concrete can be recycled and can be completely reused for new concrete production.
It is important to distinguish between reusing and down cycling the material, versus reusing for the same purpose as before. When reusing the crushed concrete material as a base for roads or foundations, for example, this is down cycling. As in a linear economy model, the material has a new purpose and can no longer be brought back to its original use in new concrete production.
However, within a recycling economy, old concrete may be recycled and reused within new concrete production. This is already being done in the concrete industry. Ultimately, we strive for a circular economy, where there is no waste at all in the concrete production and recycling process.
Understand the Difference Between Linear, Recycling and Circular Economy
Can Concrete Be Crushed and Reused?
Yes, concrete can be crushed down, separated and reused. Since the demolished concrete contains aggregates and cement stone, reuse has some limitations.
With the reCO2ver process, the Sika patented process of concrete recycling, the fragments are broken down into their component parts - namely fine powder, sand and aggregates. This technology paves the way for a circular economy in concrete.
Learn how concrete recycling works, step-by-step:
The pre-crushed concrete demolition waste is filled into the hopper.
Then it's transported to the top container, where the heart of the plant is located.
The material makes contact with CO2 in the rotating chamber. Due to the rotation, the carbonated cement stone is removed from the surface and separated from the aggregates.
At the end of the chamber, the cleaned aggregates fall out.
Sika's additives for optimization of the process and output materials are added automatically. Also, the CO2 is added automatically to the process air.
The fine particles of the removed, carbonated cement stone are transported via the process air and are separated with a filter system. The air can be heated or dehumidified depending on the required conditions.
At the end of the process, the separated materials are collected. The carbonated powder and the cleaned aggregates are collected separately.
The cleaned aggregates are separated into fractions in a sieving unit and in this case, into 0-4 mm, 4-8 mm, 8-16 mm and 16-32 mm sizes.
The powder is collected in a big bag.
What Can Recycled Concrete Be Used For?
When concrete recycling is done by crushing the concrete and reusing it as aggregates again, the concrete can only used for certain applications as described in standards. For example, in some countries it cannot be used for any applications that require freeze-thaw resistance. The high porosity of the crushed concrete leads to a lower value of frost resistance.
With Sika's new reCO2ver process, the aggregates can be cleaned from the cement paste. With this step, the potential applications can most probably be extended.
What Are the Benefits of Using Recycled Concrete?
With this process, there is less concrete demolition waste going into landfills, leading to increased nature preservation.
High-quality sands and aggregates are becoming a scarce resource where the materials may need to be shipped over far distances. Concrete recycling reduces this effect and saves natural resources.
The amount of transport needed is reduced, thanks to local availability of resources (e.g. urban mining).
Recycled Concrete Aggregates vs. Natural Aggregates
There is some difference when using either recycled concrete aggregates, also called crushed concrete, or natural aggregates in new concrete. The main difference is in the water absorption and water demand in the prepared concrete using these different aggregates.
The crushed concrete demolition waste contains aggregates and cement stone. The cement stone increases the porosity of the material and leads to a higher water demand and therefore, higher cement demand in the concrete mix. For manufactured (crushed concrete) aggregates, the surface is larger than naturally-sourced gravel or natural aggregates. This also leads to a higher water demand in the concrete.
By cleaning the recycled aggregates from cement-stone, the material can be used comparable to naturally-sourced gravel and aggregates. This reduces the cement demand in the recycled concrete and also the CO2 footprint.
Comparison of components as used in new concrete
| Manufactured aggregates | Crushed concrete from recycling | Gravel |
|
|---|---|---|---|
| Nature of the material | Crushed aggregates from larger blocks with larger surface area than gravel | Crushed concrete demolition waste containing aggregate and high-porosity cement stone | Type of aggregates naturally-sourced from rivers with small surface area |
| Water demand in new concrete | (---) High | (--) Mid | (-) Low |
| How good for concrete production | (++) Good | (++) Good, when prepared and cleaned | (+++) Ideal |
Does Sika Offer Products for Concrete Recycling?
Sika offers the ground-breaking reCO2ver process as well as the whole range of concrete admixture solutions for recycling concrete.
Sika also developed a concept for analyzing problematic sands and aggregates to offer the best possible solutions for our customers in what we call the Sika CODE concept.
With our experience in more than 100 countries worldwide, we can offer customized solutions and professional support.
Author
Carsten Rieger
Market Development Manager
Target Market Concrete
Sika Services AG