Contributed by Cheng-Wei Lin, Ph.D. candidate; Department of Chemistry and Biochemistry, University of California, Los Angeles; Bu Wang Ph.D.; Department of Civil and Environmental Engineering, University of California, Los Angeles; Richard Kaner, Distinguished Professor; University of California, Los Angeles; and Gaurav Sant, Associate Professor, University of California, Los Angeles
Scientists and engineers at the University of California, Los Angeles (UCLA) are developing an innovative way of embedding carbon dioxide (CO2) into concrete. Specifically, the process secures CO2 produced by power plants, cement plants, and other point-source emitters, and embeds it into 3D-printed building materials and components. The work seeks to mitigate the CO2 impact of cement production [N.B.: upon mixing with sand, stone and water, cement forms a “composite” referred to as ‘concrete’], which currently accounts for nearly 9 percent of anthropogenic CO2 emissions. In light of the ever-increasing demand for concrete worldwide (e.g., in China and India), it is crucial, now more than ever, to address the environmental impact of this ubiquitous building material.
To alleviate the CO2 emissions associated with cement production – the most CO2-intensive component in concrete – we designed a closed-loop process for manufacturing building materials as shown in Figure 1 . First, quarried limestone (CaCO3) is calcined to produce lime (CaO) – a process that releases the mineralized CO2 embedded within it. Second, lime is reacted with water to form portlandite (Ca(OH)2), which is then mixed into slurry with sand, mineral aggregates, water, and performance modifying agents. The slurry can be formed into modular structural elements, such as beams and columns, using advanced shape stabilization methods like 3D printing. Finally, the shaped-stabilized structural elements are reacted with the CO2 released during calcination, or from other point-source emitters (e.g., coal and natural gas power plants) to produce the building components from CO2NCRETETM. This process of re-embedding mineralized CO2 within building materials not only reduces the effective CO2 emissions creating a cementing agent with greatly reduced CO2 impact, but also acts to reduce the impacts of electricity generation using fossil-fuels.
Though a related year-long approach has been attempted recently in Iceland, our team at UCLA was able to accelerate the carbonation process at near-ambient conditions in terms of temperature and pressure, thereby offering new, beneficial routes for the practical and economical use of CO2. In addition, by sourcing lime from industrial alkaline waste streams, a negative life-cycle carbon footprint can be achieved. This technology seeks to re-imagine how we perceive and address the emissions of greenhouse gases (GHGs) associated with process intensive industries today.
Beyond the realization of a new building material, the broader “Carbon Upcycling” effort emphasizes a vital need for technology integration and value creation. While membrane technologies are used for the capture and enrichment of CO2, 3D printing has proven an efficient method to fabricate building components like beams, columns and slabs. But 3D printing has not yet impacted the construction industry despite its aggressive adoption by various industries and even for personal use. Therefore, as a lab scale proof-of-concept, our team at UCLA has 3D-printed a beam several centimeters in length, composed of our new construction material. The Lego-like 3D-printed building blocks offer greater design flexibility and ease in on-site assembly, offering newfound efficiency for construction operations. The present challenge lies in scaling 3D printing building blocks up from centimeters to meters in size, and then to tens of meters as required for practical buildings, roads and bridges.
Our “Carbon Upcycling” team – comprised of an interdisciplinary group of UCLA researchers led by Gaurav Sant, Associate Professor; Henry Samueli, Fellow in Civil and Environmental Engineering; Richard Kaner, Distinguished Professor in Chemistry & Biochemistry and Materials Science & Engineering; Laurent Pilon, Professor in Mechanical & Aerospace Engineering and Bioengineering; J. R. DeShazo, Professor of Public Policy at the Luskin School of Public Affairs; and Mathieu Bauchy, Assistant Professor of Civil & Environmental Engineering – has recently advanced to the semi-finals of the NRG COSIA Carbon XPRIZE competition. This competition challenges and stimulates people to respond to the global issue of CO2 emission. As such, our team is in the midst of transitioning its technology from the laboratory-scale to the pilot-scale by demonstrating the ability to scale up: (1) CO2 separation and enrichment, (2) the carbonation of large volumes of portlandite, and (3) the size of the 3D printed CO2NCRETETM building blocks – all while minimizing the overall consumption of water and electricity.
Our team has made substantial progress so far, and seeks to make transformative contributions to how CO2 management is approached by the construction sector. Indeed, this style of breakthrough advancement can only be realized when a highly motivated team from different disciplines comes together to solve important problems of global and societal relevance. We look forward to bringing sustainable building materials like CO2NCRETETM to fruition, an outcome enabled and promoted by green chemistry at large.
 K. Vance, G. Falzone, I. Pignatelli, M. Bauchy, M. Balonis, G.Sant, “Direct Carbonation of Ca(OH)2 Using Liquid and Supercritical CO2: Implications for Carbon-Neutral Cementation,” Industrial & Engineering Chemistry Research. 2015, 54(36), 8908-8918.
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