2023-03-29 10:45:12
Despite the many advantages of concrete as a modern building material, such as its high strength, low cost and ease of manufacture, its production today accounts for approximately 8% of global carbon dioxide emissions.
Scientists have discovered that the introduction of certain additives into current concrete manufacturing processes could significantly reduce this carbon footprint, without altering the mechanical properties of the concrete.
The finding was made by a team that includes Admir Masic, Franz-Josef Ulm, Damian Stefaniuk and Marcin Hajduczek, from the Massachusetts Institute of Technology (MIT) in the United States, as well as James Weaver from the Wyss Institute, dependent on Harvard University. in United States.
About half of the emissions associated with concrete production come from burning fossil fuels like oil and natural gas, which are used to heat a mixture of limestone and clay that eventually turns into the familiar gray dust known as cement. Portland. Although the energy required for this heating process could be replaced in the future by electricity generated from renewable sources (basically solar or wind energy), the other half of the emissions is inherent to the material itself: when the mineral mixture is heated to higher temperatures at 1,400 degrees Celsius, it undergoes a chemical transformation that leads to the release of carbon dioxide, which enters the atmosphere.
When ordinary Portland cement is mixed with water, sand and gravel or the like during concrete production, it becomes highly alkaline, creating a seemingly ideal environment for the capture and long-term storage of carbon dioxide in the form of carbonate materials ( a process known as carbonation). Despite this good potential for concrete to naturally absorb carbon dioxide from the atmosphere, when these reactions occur spontaneously, primarily within cured concrete, they can both weaken the material and decrease internal alkalinity, thereby accelerating Corrosion of internal steel rods in reinforced concrete structures. Ultimately, these processes destroy the load-bearing capacity of the building and negatively affect its long-term mechanical performance. Therefore, these slow delayed carbonation reactions, which can occur over decades, have long been recognized as an undesirable phenomenon that accelerates the deterioration of concrete.
Instead, the new carbon dioxide capture pathways discovered by Masic and his colleagues rely on the very early formation of carbonates during the mixing and pouring of the concrete, before the material sets, which could largely eliminate carbonates. detrimental effects of carbon dioxide absorption after the material has set.
The introduction of an additive in the concrete manufacturing process could significantly reduce the carbon footprint of the material without altering its mechanical properties, as determined in the investigation. (Image: research team. CC BY-NC-ND 3.0)
The key to the new process is the addition of a simple and cheap ingredient: sodium bicarbonate. In laboratory tests carried out with sodium bicarbonate, the team showed that up to 15% of the total amount of carbon dioxide associated with cement production could be mineralized during these early phases, enough to significantly reduce the global carbon footprint. of the material.
Masic and his colleagues report the technical details of their finding in the academic journal PNAS Nexus, under the title “Cementing CO2 into CSH: A step toward concrete carbon neutrality.” (Fountain: NCYT de Amazings)
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