News

A new publication titled “Tracking Spatiotemporal Evolution of Cementitious Carbonation via Raman Imaging” was published in the Journal of Raman Spectroscopy in December 2022.

Carbonation of cement systems is a growing area of interest as it offers a permanent solution to store CO₂. Various analytical techniques like measuring pH changes and calcite content over time have been used to study this dynamic process. However, these methods rely on bulk measurements, which may miss the fine microstructural changes that occur during carbonation. In this work, we report the use of Raman imaging to follow the carbonation process in cement pastes at a micron-scale resolution. Results show that 40% of the sample surface was covered with calcite after 2 weeks of exposure and portlandite content declined from 15% to 5%. These findings suggest that other hydration products such as calcium silicate hydrate and ettringite also undergo carbonation simultaneously along with calcium hydroxide, opening up the possibility of using Raman imaging to understand the nature and kinetics of complex dynamic phenomena.

This is the first article from our group’s M.S. graduate Sonali Srivastava. Congratulations Sonali!

This article can be accessed here.

A new publication titled “Superhydrophobic and Self-Cleaning Aluminum via a Rapid and Controlled Process” was published in ACS Applied Engineering Materials in October 2022.

Engineers have been often inspired by nature in various ways, ranging from the design of structures to the selection of materials. For e.g., lotus leaves exhibit hydrophobic behavior which has been translated to the creation of self-cleaning materials. One construction material of interest is aluminum for light-weight structural applications. Previously, studies have reported creation of superhydrophobic aluminum surfaces. However, most of the processes are not environmentally friendly, are time-consuming, and some are not feasible for large-scale applications. In our most recent paper, we present a rapid and controlled process to create superhydrophobic aluminum for use in external environments. With a 1 hr of fabrication time, we achieve contact angle of 158.06° and a sliding angle of 1.94°. Finally, the surface is durable and resilient when exposed to a range of extreme temperatures (-18°C to 100°C). These results pave the way for implementation of superhydrophobic aluminum surfaces for large-scale structural and construction applications.

This is the first article from our group’s MS candidate Ravi Sharma.

Congratulations Ravi!

The article can be accessed here.

A new publication titled “Ultra-high Gamma Irradiation of Calcium Silicate Hydrates: Impact on Mechanical Properties, Nanostructure, and Atomic Environments” was published in Cement and Concrete Research in August 2022.

Nuclear power plants, a major source of emission-free energy, are closing on the end of their design life, and extending the operating life of these power plants will require extensively studying irradiation effects on each critical part of nuclear power plants. The concrete biological shield is one such critical part, which not only absorbs irradiation but also provides structural support. In this paper, we looked at gamma irradiation effects on calcium silicate hydrate, on micro, nano, and atomic scale on a range of irradiation dosages (from 0 MGy to 189 MGy), based on an extended 80-year design life. XRD reveals that irradiation decreases C-S-H basal spacing (~ 0.6 ± 0.1 Å for 189 MGy), likely through the removal of interlayer water as supported by TGA. The Young’s modulus increased with irradiation, but porosity remained unchanged implying the decrease in basal spacing is the main reason behind the increase in young’s modulus. ¹H NMR data show that irradiation increases the FWHM of the CaO-H cluster peaks indicating some disorder in the local proton CaO-H species. Finally, ²⁹Si NMR data show that the silicate structure mostly stays unaffected, but the chemical shift of minor Q³ silica becomes less negative indicating slight depolymerization of the silicate structure. Overall, the C-S-H gel stiffens upon ultrahigh gamma irradiation affecting the long-term service life of a nuclear powerplant.

This work was led by Aniruddha Baral and performed in collaboration with Oak Ridge National Lab, Columbia University, and Argonne National Lab. Aniruddha graduated with a PhD in summer 2022 and started a postdoc at the University of Sheffield.

Congratulations Aniruddha!

The article can be accessed here.

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!

The article can be accessed here.

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!

The article can be accessed here.

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!

The article can be accessed here.