By implementing a carbonated — instead of a motionless — water-centered solution during the cement manufacturing process, an engineering team led by Northwestern University has revealed a new method to retain carbon dioxide (CO2) in the widespread construction material.
Not only does this new technique help confine CO2 from the progressively warming atmosphere, it also delivers cement with uncompromised robustness and durability.
In lab trials, this process achieved a CO2 sequestration efficiency of nearly 45%, indicating that almost half of the CO2 introduced during cement manufacturing was captured and preserved. The scientists expect that their fresh method could help balance out CO2 emissions from the cement and concrete sectors, which account for 8% of global greenhouse gas emissions.
The study was printed in Communications Materials, a magazine issued by Nature Portfolio.
“The cement and concrete industries play a significant role in human-induced CO2 emissions,” stated Northwestern’s Alessandro Rotta Loria, who headed the study. “We are striving to devise methods that diminish CO2 emissions linked to those industries and, eventually, could transform cement and concrete into extensive ‘carbon repositories.’ We haven’t reached that point yet, but we now have a fresh strategy to recycle a portion of the CO2 released as a consequence of cement production in this very same material. Furthermore, our solution is technologically simple enough that it should be relatively straightforward for the industry to adopt.”
“What’s more intriguing, this strategy to expedite and intensify the carbonation of cement-based elements offers the chance to formulate new clinker-based commodities in which CO2 becomes a crucial ingredient,” remarked study coauthor Davide Zampini, chief of global research and development at CEMEX.
Rotta Loria serves as the Louis Berger Assistant Professor of Civil and Environmental Engineering at Northwestern’s McCormick School of Engineering. The study was a partnership between Rotta Loria’s laboratory and CEMEX, a global establishment focused on environmentally-friendly construction.
Drawbacks of previous techniques
An indispensable component of infrastructure, cement is among the most consumed materials worldwide — following just water. In its simplest form, to create cement, individuals blend water, fine components (such as sand), coarse components (like gravel), and cement, which amalgamates all the elements. Since the 1970s, former researchers have examined diverse methods to store CO2 in cement.
“The concept is that cement already responds to CO2,” explained Rotta Loria. “Hence, cement structures inherently soak up CO2. However, the absorbed CO2 was only a tiny segment of the CO2 discharged from making the cement necessary for cement formation.”
Techniques to retain CO2 are classified into two groups: hardened cement carbonation or fresh cement carbonation. In the solid approach, solid cement blocks are situated in compartments where CO2 gas is introduced under high pressures. In the freshly prepared alternative, individuals introduce CO2 gas into the amalgamation of water, cement, and components while cement is being created.
In both methods, a portion of the added CO2 interacts with the cement to form solid calcium carbonate crystals. Despite this, both techniques share show-stopping limitations. They are constrained by low CO2 capture efficiency and high energy usage. What’s even worse is that the resulting cement is often weakened, impairing its usability.
Unwavering robustness
In Northwestern’s recent approach, the researchers exploited the fresh cement carbonation procedure. However, rather than injecting CO2 while mixing all the elements collectively, they initially introduced CO2 gas into water mixed with a small measure of cement powder. After blending this carbonated suspension with the remaining cement and components, they produced cement that actively soaked up CO2 throughout its creation.
“The cement suspension carbonated in our approach possesses a significantly lower viscosity compared to the regular mixture of water, cement, and components customarily used in current methods to carbonate fresh cement,” disclosed Rotta Loria. “Therefore, we can combine it rapidly and benefit from rapid chemical reaction kinetics resulting in calcium carbonate minerals. The outcome is a cement commodity with a considerable concentration of calcium carbonate minerals in contrast to when CO2 is introduced into the fresh cement mixture.”
After assessing their carbonated cement, Rotta Loria and his comrades found that its toughness equaled the endurance of standard cement.
“A customary limitation of carbonation methodologies is that toughness is commonly influenced by chemical responses,” he remarked. “However, based on our trials, we demonstrate that toughness might even be enhanced. We still must further test this, but, at the very least, we can assert that it remains unaltered. Because the robustness is preserved, the applications also remain unchanged. It could be implemented in beams, slabs, pillars, foundations — the full spectrum of applications of cement currently.”
“The results of this research underline that despite being a well-known reaction, there are still opportunities to advance the CO2 absorption by improving our understanding of the mechanisms linked to materials handling,” Zampini remarked.
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