Recycled “green” concrete uses construction waste and captured CO2.

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2021-10-24 20:00:20

Concrete is the most widely used construction material in the world but it is one of the materials that have a huge impact on the environment. Engineers in Japan have developed a technique for making “green” concrete by recycling waste concrete and combining it with captured CO2.

It is estimated that up to 8% of global CO2 emissions result from the production of concrete, and most of that comes from heating limestone to very high temperatures to produce calcium, a key ingredient. of the chemical reaction that forms concrete.

Previous research has investigated ways to reduce or replace the binder, use CO2 captured in the mix, or even enhance the finished product’s ability to absorb atmospheric CO2.

For the new study, researchers from the University of Tokyo and others have developed a process that reduces concrete’s environmental impact in several ways. First, the new material is made from old concrete piles, which are often wasted and thrown away as they are no longer usable.

Not only does that extend the life of older materials, but the process can be done at about 70°C, much lower than the temperature needed to heat limestone at more than 1,000°C. Another benefit is that the mixed CO2 can be taken from industrial emissions or sucked straight out into the environment.

In the tests, the team created sample blocks from one of two common construction wastes, hardened cement paste (HCP) or silica sand. The process begins with a solution of calcium bicarbonate and is made up of limestone powder, deionized water and CO2. The solution is then injected into a mold containing one of the aggregates of HCP powder or silica sand, which is then heated to 70°C. The end result is a new block of material that the team calls calcium carbonate concrete.

Recycled

Although it is better for the environment, calcium carbonate concrete is not as sturdy as expected. The average compressive strength of the blocks is 8.6 MPa, much lower than the 20 to 40 MPa of concrete made from Portland cement. However, the team believes that it can still be used in small-scale buildings and can be further improved in the near future.

Takafumi Noguchi, an author of the study said: “It’s been exciting to make progress in this area but there are still many challenges to overcome. As well as increasing the strength and size limits of calcium carbonate concrete, it would be even better if we could. However, in the coming decades, calcium carbonate concrete will become the mainstream concrete and will be one of the solutions to combat climate change. Queen”.

The study was recently published in the journal Advanced Concrete Technology.

Refer to Newatlas

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