Researchers at the Massachusetts Institute of Technology (MIT) have recently discovered that concrete could act as a carbon dioxide absorber, significantly reducing its environmental impact. The key ingredient facilitating this reaction is baking soda!
Concrete is widely favored as a modern building material due to its high strength, low cost, and ease of production. However, its production currently accounts for about eight percent of global carbon dioxide emissions.
This could change in the future. Recent findings by the MIT research team have shown that incorporating new materials into existing concrete production processes can significantly reduce its carbon footprint without altering its fundamental mechanical properties.
Related Articles:
FLEXIBLE CONCRETE – IS IT A REVOLUTION IN THE CONSTRUCTION INDUSTRY?
UNLOCKING THE MYSTERY OF ROMAN CONCRETE DURABILITY
The results were published today in the journal PNAS Nexus by MIT professors of civil and environmental engineering Admir Masic and Franz-Josef Ulm, postdoctoral researcher Damian Stefaniuk, doctoral candidate Marcin Hajduček, and James Weaver from Harvard University’s Wyss Institute.
Concrete is the second most used material in the world after water and forms the foundation of modern infrastructure. However, its production releases large amounts of carbon dioxide, both as a chemical byproduct of cement production and due to the energy required to drive these reactions.
Approximately half of the emissions related to concrete production come from burning fossil fuels like oil and natural gas, used to heat the mixture of limestone and clay that eventually becomes the well-known gray powder called Portland cement.
Although the energy needed for this heating process could be replaced with electricity from renewable sources like solar or wind power, the other half of the emissions are inherent in the material itself. When the mineral mix is heated to temperatures above 1,400 degrees Celsius, it undergoes a chemical transformation from calcium carbonate and clay to a mixture of clinker (primarily composed of calcium silicates) and carbon dioxide, which is then released into the air.
When cement is mixed with water, sand, and gravel to produce concrete, it becomes highly alkaline, creating an almost ideal environment for long-term carbon dioxide storage in the form of carbonate materials (a process known as carbonation).
Despite concrete’s potential to naturally absorb carbon dioxide from the atmosphere, these processes typically weaken the material and reduce its internal alkalinity, accelerating the corrosion of reinforcing bars. These processes eventually destroy the building’s load-bearing capacity and negatively affect its long-term mechanical durability. As such, these slow late carbonation reactions, which can occur over decades, have long been recognized as undesirable processes that accelerate concrete degradation.
In contrast, the new carbon dioxide sequestration processes discovered by the authors rely on the very early formation of carbonates during the mixing and casting of concrete, before the material hardens, potentially eliminating the harmful effects of carbon dioxide absorption after the material has hardened.
The key to this new process is adding a simple, inexpensive ingredient: sodium bicarbonate, better known as baking soda. In laboratory tests with sodium bicarbonate substitution, the team demonstrated that up to 15 percent of the total carbon dioxide associated with cement production can be mineralized during these early stages, potentially significantly impacting the global carbon footprint of this material.
Additionally, the resulting concrete hardens much faster through the formation of a previously unknown composite phase, without affecting its mechanical performance. This process allows the construction industry to be more productive: formwork can be removed earlier, reducing the time required to complete a bridge or building.
Although the idea of early-stage concrete carbonation is not new and several companies are currently exploring this approach to facilitate carbon dioxide absorption after the concrete is poured into the desired shape, the MIT team’s findings highlight that concrete’s capacity to sequester carbon dioxide before hardening is largely underestimated and underutilized.
Photo: Freepik, Unsplash