Concrete is one of the most common materials on the planet due to its high strength and low cost, but it is also one of the largest single sources of carbon footprint. Engineers at Washington State University (WSU) have developed a new way to make concrete that absorbs more carbon than it emits.
The cement manufacturing process requires very high temperatures and typically requires burning fuel, which of course emits CO2. This can be partially offset by switching to renewable energy sources, but this is difficult to avoid as the chemical reactions in the mixture release large amounts of CO2. Overall, cement production is estimated to account for 8% of mankind’s total carbon footprint.
Scientists are using limestone instead of volcanic rock to reduce the carbon footprint of concrete, as well as materials such as titanium dioxide, construction waste, baking soda, and clay commonly discarded during mining. I added it and fine-tuned the composition. Other teams have even tried using microalgae to grow the necessary limestone.
For the new study, WSU researchers investigated new methods involving biochar, which is charcoal made from organic waste. Biochar has been added to cement before, but this time it was treated first using concrete washing wastewater. This increases strength and allows for higher proportions of additives. But most importantly, biochar was able to absorb up to 23% of its own weight in carbon dioxide from the surrounding air.
In experiments, the team created cement containing 30% treated biochar and found that the resulting concrete was carbon negative. In fact, it absorbed more carbon dioxide than was released during the production of the material. Researchers have calculated that 1 kg (2.2 lbs) of 30% biochar concrete removes about 13 g (-0.5 oz) of CO2 from its production emissions. That may not sound like much, but it’s a big difference considering that regular concrete typically releases about 0.9 kg (2 pounds) of CO2 per kg of material.
Washington State University
According to the team, overall profit could be even better if downstream differences were taken into account in the analysis. For example, using biochar for eco-friendly purposes like this concrete can divert the biomass that makes it up from other destinies that could release more CO2. Additionally, new concrete is expected to continue to absorb CO2 for decades of service life.
Importantly, biochar concrete also retains its strength. When measured after 28 days, the concrete had a compressive strength of 27.6 MPa (4,003 psi), which is comparable to that of regular concrete.
The researchers plan to continue optimizing and scaling up the method and testing how the resulting concrete is resistant to weathering and other types of damage.
A study was published in a journal material letter.
Source: Washington State University
