New Publication on Machine Learning Enabled Contact Angle Goniometry

A new publication titled “Machine Learning Enabled Orthogonal Camera Goniometry for Accurate and Robust Contact Angle Measurements” was published in Scientific Reports, in January 2023. 

Machine learning enabled dual camera goniometry for contact angle measurements.

Understanding the wetting properties of surfaces is crucial for physical, chemical, and biological processes. However, conventional methods for accurately estimating contact angles, especially on hydrophilic surfaces, can be limited by optical distortions caused by moving droplets. In response, we have developed a new setup that combines Convolutional Neural Networks (CNN) with an automated orthogonal camera goniometer to estimate contact angles with high precision.

Our algorithm was trained on a dataset of 3375 images, including different lighting conditions and various degrees of Gaussian blurring, and was found to be less sensitive to edge effects than existing goniometers. In addition, our method was able to accurately analyze droplets of different colors and chemistries on a range of surfaces. The resulting contact angle measurements from our automated orthogonal camera goniometer exhibited significantly lower average standard deviation (6.7°) and coefficient of variation (14.9%) compared to existing techniques (average standard deviation of 14.6° and coefficient of variation of 29.2%). This demonstrates the reliability and precision of our method for characterizing the wetting properties of non-spherical droplets on heterogeneous surfaces.

This is the first article from our group’s Ph.D. candidate Hossein Kabir. Congratulations Hossein!

The article can be accessed here

New Publication on Tracking Cementitious Carbonation via Raman Imaging

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

Raman imaging of calcium carbonate after specified time of CO2 exposure to Ordinary Portland Cement paste sample.

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.

New Publication on Superhydrophobic and Self-Cleaning Aluminum

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.

Response of superhydrophobic aluminum surface to water jetting

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.

New Publication on Calcium Silicate Hydrates Subject to Irradiation

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.

Effect of Gama Irradiation Dosages on Basal Spacing and Young’s modulus measured using nanoindentation. 

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.

New Publication on Kaolinite Morphology under Dissolution

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.

Kaolinite and metakaolin dissolving under the optical microscope.

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.

Illustration of a kaolinite particle with reduced layer thickness after calcination and dissolution. These results bring clarity about the nanoscale changes in this clay when subjected to dissolution.

This is the first article from our group’s M.S. candidate Pablo Romero. Congratulations Pablo!

The article can be accessed here.

New Publication on Alkali-Activation of Metakaolin

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.

A snapshot of results from 27Al MAS NMR of various AAM mixtures, illustrating a direct effect of the overall Na/Al ratio on the local Al environments.

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.

New Publication on US Waste Streams

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.

An illustration of the spatial distribution of current Waste-to-Energy (WTE) facilities along with the US population density plotted on a common map.

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.

New Publication on Reactivity of Incineration Ashes

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!

The article can be accessed here.

New Publication on Raman Imaging of Anhydrous Cements

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 article can be accessed here.