A new publication titled “Evolution of kaolinite morphology upon exfoliation and dissolution: Evidence for nanoscale layer thinning in metakaolin” was published in Applied Clay Science in March 2022.
When kaolinite is calcined, it transforms into metakaolin, which can dissolve and react under alkaline conditions, making it a potential low-CO2 alternative to Portland cement. The reactivity of kaolinite has been studied in terms of dissolution kinetics, but not much is known about the evolution of clay morphology upon dissolution. Here, we apply quantitative imaging approaches to quantify the extent of morphological changes that occur in dissolving kaolinite and metakaolin at multiple scales. At the micro-scale, we successfully capture in situ exfoliation of clay particles while dissolving in NaOH. We find a noticeable difference in the pattern in which these clays break apart. Raw kaolinite would expand along its length, while layers in metakaolin were not as well defined as in kaolinite. At the nano-scale, when comparing the layer thickness of metakaolin and dissolved metakaolin, an evident thinning of ~20 nm (from 95 nm to 75 nm) is found. These results explain how the dissolution process takes place on these layered structures: by breaking the bonds in-between layers and then dissolving these individual layers leading to a reduction in thickness. These new results pave the way towards a morphological understanding of calcined clay dissolution.
This is the first article from our group’s M.S. candidate Pablo Romero. Congratulations Pablo!
A new publication titled “Impact of Na/Al Ratio on the Extent of Alkali-Activation Reaction: Non-linearity and Diminishing Returns” was published in Frontiers in Chemistry in January 2022.
To address the high CO2 footprint associated with cement production, many alternative, sustainable binders are now gaining worldwide attention, including alkali-activated materials (AAM). The alkali-activation reaction of metakaolin is a fairly complex process involving transformation of one amorphous reactant (precursor metakaolin) into another amorphous product or products (N-A-S-H gel and/or disordered zeolite type phases). In spite of this complexity, researchers in the past 2 decades have gained significant knowledge on the nature of this reaction at multiple scales. Understanding and developing a clear relationship between the alkalinity of the mix and the extent of reaction is of high interest for practical applications. However, detailed and thorough investigations on this important relationship are limited. Here, in this study, we address this gap by systematically investigating a series of alkali-activated materials samples with a wide range of Na/Al ratios (0.5–1.8) using seven different yet complementary analytical techniques (isothermal calorimetry, FTIR, XRD, TGA, 27Al and 23Na NMR, and Raman imaging). Applied in tandem, these tools reveal a clear but non-linear relationship between the Na/Al ratio and the extent of alkali-activation reaction indicating diminishing returns at higher Na/Al ratios, where higher Na/Al ratios cause an increase in the degree of reaction until a certain point at which the increase in Na/Al ratio does not significantly affect the reaction kinetics, but may affect the gel polymerization. These findings could potentially aid decision making for commercial applications of AAMs where alkalinity of the mix is an important parameter for performance as well as safety.
This is the first article from our group’s MS candidate Omar Abdelrahman. Congratulations Omar!
A new publication titled “National and Regional Waste Stream in the United States: Conformance and Disparity” was published in Environmental Research: Infrastructure and Sustainability in November 2021.
Accurate estimation of material classes – paper, food, plastic, yard, metal, and glass waste – present in the municipal solid waste stream is critical for efficient waste management. The generation estimates for these material classes (both composition and quantity) are estimated via two approaches, the material-flow-based estimates and site-specific estimates. In the United States, the U.S. EPA’s material flow-based predictions yield MSW generation estimates for the entire nation, whereas site-specific estimates yield MSW generation estimates on a regional scale, i.e., states and counties. In the past, several studies had indicated that the U.S. EPA’s material-flow-based predictions differ substantially from the aggregated tonnage of MSW managed by waste handling facilities in the United States. However, the material-class-specific factors that led to these discrepancies are not apparent. In this study, we uncover the basis of these discrepancies by comparing national MSW generation estimates with the site-specific MSW general estimates. Specifically, our analysis suggests that the material-flow-based estimates are accurate for food, plastic, and glass material classes. In contrast, we find that the material-flow-based predictions underestimate paper waste disposal by at least 15 million tons annually. Based on these insights, the material-flow-based MSW estimation framework can be refined to yield better MSW generation estimates. A thorough estimation of waste is the key to efficient waste management.
This is the second article from our group’s Ph.D. candidate Vikram Kumar. Congratulations Vikram!
Garg Group warmly welcomes new members who started in Summer and Fall 2021. These are MS candidates: Jacob Doehring, Dhanush Sahasra, Andrew Witte; PhD candidates: Bayezid Baten, Chirayu Kothari, Hyeonseok Jee, Brandy Diggs-McGee; and Postdoc: Dr. Hamza Samouh. Additionally, MS candidate Vikram Kumar successfully completed his MS thesis in Summer 2021 and continues in the group as a new PhD candidate, starting Fall 2021.
Mulitple openings for graduate students (both at MS and PhD level) are available for Fall 2022. Please apply and join us!
Additionally, a postdoc position has also just opened in our group. Please apply before Feb 21, 2022. Job details and application info is in the file below:.
A new publication titled “The Chemical and Physical Origin of Incineration Ash Reactivity in Cementitious Systems” was published in Resources, Conservation and Recycling in October 2021.
Incorporating industrial byproducts and waste in concrete is the key to reducing landfill usage as well as lowering the environmental footprint of cement industry. An emerging industrial byproduct which can partly replace cement is the Municipal Solid Waste Incinerator Ash (MSWI ash: residue that is left after incineration of municipal solid waste in a Waste-to-Energy facility). These ashes are predominantly calcium-rich; however, they also contain additional elements whose speciation is not known. These elements can significantly alter the hydration characteristics of a cementitious system. Our initial foray into cementitious matrices including these ashes, reveals that these ashes can accelerate as well as retard cement hydration. Specifically, Pb, Br, S, Ca, and Cl appear to accelerate cement hydration, whereas Cu, Fe, Al, Ti, Si, K, Zn, and Sr appear to retard cement hydration. Changes in hydration characteristics can have a strong bearing on the physical characteristics of cementitious systems incorporating incineration ashes. Thus, to selectively screen ashes that synergistically enhance the physical characteristics, we introduce a novel “Incineration Ash Coefficient (IAC),” which shows a strong correlation with the compressive strength (R2=0.79) of cement-ash binary mixtures.
This is the first article from our group’s Ph.D. candidate Vikram Kumar. Congratulations Vikram!
Given the growing world population and urban density, management of municipal solid waste is becoming an increasingly difficult issue. One way to approach handling of all this solid waste is to incinerate it for energy as is done in Waste-to-Energy plants. However, the residual ash (bottom and fly ash) post combustion of this waste is unused and often sent to the landfill. There is potential in utilizing this ash for several commercial applications if its chemical composition and mineralogy could be understood in detail.
Garg Group has recently received funding from Advanced Research Projects Agency – Energy (ARPA-E) for a two year project (2021-2023) for investigating the chemistry of these ashes and then identifying composition dependent end uses. The project is titled RADAR-X (Rapid AI-based Dissection of Ashes using Raman and XRF Spectroscopy). This is an interdisciplinary project in collaboration with Prof. Jeffery Roesler, Dr. Brajendra K. Sharma, and Prof. Lav Varshney. This project will build upon the findings from an earlier project on municipal solid waste which was seed funded by the Institute for Sustainability, Energy, and Environment at University of Illinois, Urbana-Champaign. Some more information on this new project can be found here.
We are excited to continue our efforts in this field to make our world a sustainable world!
A new publication titled “Enabling Phase Quantification of Anhydrous Cements via Raman Imaging” was published in Cement and Concrete Research in September 2021.
Quantifying the mineral phase composition of an anhydrous cement is essential in determine/predicting the hydrated phase assemblage which consequently governs the overall performance of hardened concrete. Traditional techniques such as X-ray diffraction, optical microscopy, and electron microscopy are well suited to quantify phases in anhydrous cements but they may have some sample-specific limitations in certain scenarios. Here, we demonstrate Raman imaging as a complementary tool for quantitative phase analysis on 11 different cements. Using sufficient statistics (250,000 spectra per image, 5×5 mm area scans with 10 μm/pixel in each image), we were able to accurately quantify the 4 principal phases (alite, belite, aluminate, and ferrite) as well as (up to) 8 secondary phases (gypsum, anhydrite, bassanite, syngenite, dolomite, calcite, quartz, and portlandite) in a broad variety of cements. These results pave the way for future application of Raman imaging for phase quantification in other complex mixtures and systems.
This is the second article from our group’s Ph.D. candidate Krishna C. Polavaram. Congratulations Krishna!
The first version of G-GAP ’21 was launched in July 2021 where the group spent a day eating and relaxing outdoors. Participation was free for all group members, however, everyone was required to bring a dish for the potluck in lieu of their registration fee. This resulted in a rather extensive buffet-style feast which lifted everyone’s spirits as shown in Figure 1.
Once the attendees were motivated, they were assembled to execute the real purpose of this picnic: creating some fun memories! The group tried making several creative shots but most of them turned out to be not publishable. One of them, where the group attempts to create an “I” on the ground (reported here as Video 1), survived the editorial cut.
Nevertheless, the group will continue to try to generate new content in the meanwhile and will be back next year, in summer 2022. Thanks for reading and watching.
The announcement was made at the 11th Advances in Cement-Based Materials Conference held virtually last week (June 23-25, 2021). This award is given every year to the author(s) of the best-refereed paper published in the previous calendar year in the Bulletin or the Journal of the American Ceramic Society.
This award honors Dr. Stephen Brunauer (1903-1986), a surface scientist and chemist, who is best known for his BET (Brunauer, Emmett, and Teller) paper on “Adsorption of Gases in Multi-Molecular Layers” published in the Journal of the American Chemical Society in 1938. The BET method is one of the most widely used methods for measuring the specific surface area of porous as well as powdered materials. Dr. Brunauer also made significant contributions to our microstructural understanding of cement hydrates.
A new publication titled “High-fidelity and high-resolution phase mapping of granites via confocal Raman imaging” was published in Scientific Reports in April 2021.
Granites are one of the most abundant silicates on Earth’s crust, and they can often be found in concrete mixtures where siliceous aggregates have been used. Understanding the mineral phase composition of these complex rocks is a key requirement to predict their tolerance to long-term radiation in a nuclear power plant. However, obtaining accurate phase maps from traditional petrographic methods as well as newer elemental mapping methods has a series of limitations. Here, we report a methodology that allows direct mineralogical mapping and fingerprinting using Raman spectroscopy and imaging. Our results enable high-resolution and high-fidelity spatial mapping of minerals at the sub-micron scale, opening up pathways to rapidly assess and quantify the mineralogical composition of samples that require minimal sample preparation.
This is the first article from our group’s Ph.D. candidate Krishna C. Polavaram. Congratulations Krishna!