After water, concrete is the most consumed material in the world and a mainstay of construction everywhere, and the environmental impact of concrete production is significant. Researchers have found that by introducing cheap and readily available raw materials into the manufacture of concrete, concrete could become a climate solution rather than a climate villain.
Concrete as a building material has many advantages. Very strong, easy to manufacture, and inexpensive. However, its drawback is that it is not very environmentally friendly. Concrete production is the largest industrial source of carbon pollution, accounting for he 8% of the world’s carbon footprint.
Concrete is made by mixing cement with aggregate (a granular mixture of stones, sand, etc.). Firing limestone, clay, etc. in a kiln produces the familiar gray powder, Ordinary Portland Cement (OPC). Carbon dioxide is released from chemical reactions that occur when the material is calcined and when the mixture is exposed to heat. According to the National Ready Mixed Concrete Association, 0.93 pounds (0.42 kg) of carbon dioxide is released for every pound (0.45 kg) of concrete produced.
Combustion processes can be changed from using fossil fuels to using electricity from renewable sources, but chemical reactions, the second contributor to carbon emissions, pose even more challenges. When the mineral mixture is heated above 2,552 °F (1,400 °C), it transforms from calcium carbonate and clay to a mixture of clinker (mainly calcium silicate) and carbon dioxide. This carbon dioxide escapes into the air.
Over time, carbon dioxide in the atmosphere reacts with calcium oxide in concrete, mineralizing the carbon dioxide to calcium carbonate in a process known as carbonation. Carbonation is the opposite of when making concrete.
Carbonation allows concrete to sequester (capture and store) carbon dioxide, but it also weakens concrete, especially hardened concrete, reduces internal alkalinity, and corrodes steel used as reinforcement. cause Curing is the process of maintaining moisture levels inside cast concrete, resulting in a stronger, more durable and less porous concrete.
A team of MIT researchers devised a way to combat the carbon dioxide problem during the early stages of concrete mixing and pouring before the material hardens by introducing a very cheap ingredient, sodium bicarbonate, also known as baking soda. bottom.
Researchers found that the addition of alternative sodium bicarbonate could initially mineralize up to 15% of the total carbon dioxide associated with cement production. The composite material used by the researchers is a mixture of calcium carbonate and calcium silicon hydrate, an entirely new material.
“Our study is very exciting because it advances the concept of multifunctional concrete by incorporating the additional benefits of carbon dioxide mineralization during production and casting,” said Admir, corresponding author of the study. says Masic.
In addition, “new” concrete sets faster without losing its mechanical properties. Researchers say this will allow the construction industry to complete work more quickly.
While early-stage carbonation of concrete is nothing new, the MIT findings highlight its ability to sequester carbon dioxide in the pre-hardening stage.
“Our new findings, combined further with other recent innovations in the development of low-carbon-emission concrete admixtures, provide greener and even carbon-negative building materials for the built environment, You can turn concrete from a problem into part of the solution,” Masic said.
Research on the long-term performance of concrete is ongoing.
The study was published in a journal PNAS Nexus.
Source: MIT News
