How to save carbon dioxide by recycling concrete


Concrete is found in a large number of structures, be they buildings, bridges or roads. A lot of carbon dioxide is generated in the manufacture of the building material. Concrete takes but also over time CO2 from the atmosphere again. At the FH Campus Vienna a process has now been developed with which this Strengthen storage capacity can. The recycling of demolished concrete is a key factor in this.

“Step towards the circular economy”

For four and a half years the project has been Life cycle engineering in structural concrete construction on the one hand investigates how old concrete buildings can be preserved longer, and on the other hand how best to recycle demolition material. “Our goal is to take a step towards the circular economy in concrete construction”, say Markus Vill, head of the competence center for building and design as well Course leader for technical building equipment, construction and renovation technology for the real estate industry at the FH Campus Wien and his research assistant Marc-Patrick Pfleger, in conversation with futurezone.

Concrete is a valuable materialThe researchers believe that a lot of energy is used to generate this and that large amounts of CO2 are emitted. Demolition concrete is also a valuable resource that can also increase the storage capacity of CO2 in new structures.

In the test chamber, concrete blocks are treated with concentrated CO2

In the test chamber, concrete blocks are treated with concentrated CO2

Generation and absorption of CO2

In concrete production, CO2 is mainly used in the manufacture of the component cement generated. In order to increase its adhesiveness, its raw materials are used at over 1400 Degrees Celsius burned. A lot of CO2 is burned out of the raw material limestone. The whole process is also great energy consumingwhich leads to additional CO2 emissions when using fossil fuels.

Once it is finished, however, concrete also absorbs CO2 again. By natural Carbonatisierung the greenhouse gas slowly penetrates the surface of the concrete. On the one hand, this increases the strength of the concrete, and on the other hand, the CO2 attacks the steel, which forms the so-called reinforcement in reinforced concrete. “That’s why the reinforcement is now being placed deeper in the concrete,” says Vill. However, the CO2 does not get that far. In 50 years the gas penetrates about up to 2 centimeters below the surface.

Deeper inside

As the scientists from the FH Campus Wien have found out, you can also use old ones to produce concrete Demolition concrete use. In this CO2 is already stored. Even if the demolition material is deep inside the concrete, the gas there no longer has any effect on the corrosion of the reinforcement. “The carbon dioxide is bound in the grains of the demolition concrete and stays there,” says Vill. This is how you get carbon dioxide deeper into the concrete cross-section into it.

With a newly developed process, the storage capacity of the demolition concrete can be increased even further. The demolition concrete is put in a chamber and is flowed through at 40 degrees with concentrated CO2. “It takes every millimeter CO2 uptake naturally years. Our procedure takes one or two hours“, explains Pfleger. The concentrated CO2 comes from industrial processes, where it occurs as a by-product. In tests, 21 grams of CO2 per kilogram of concrete was absorbed within 24 hours.

Cross-section through a concrete block with purple-colored CO2 deposits

Cross-section through a concrete block with purple-colored CO2 deposits

Time of cancellation

The concrete enriched with CO2 and recycled in this way can, according to the researchers, be used for a large number of structures. That is above all interesting for the public sector. “Now the time begins when many bridges of the 50s and 60s have reached the end of their life. It is advantageous to consider in advance how the demolition material that is generated can be reused as effectively as possible,” said Vill. In the coming decades, in the course of the Traffic turnaround many construction projects in the infrastructure sector to be expected. The project was financially supported by the Vienna Municipal Department 23.

However, there is still no concrete use of the new process further research necessary. “We still have a lot to do,” says Pfleger. Follow-up projects are already being planned.

This article was created as part of a cooperation between futurezone and FH Campus Wien.

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