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!
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!
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!
A new publication titled “Nanoscale Ordering and Depolymerization of Calcium Silicate Hydrates in the Presence of Alkalis” was published in The Journal of Physical Chemistry C in September 2019.
Sustainable cements like alkali-activated materials often contain non-negligible amounts of alkalis (Na or K) which significantly influence the resulting material’s performance. However, the precise role of these alkalis is not fully understood. In this publication, using a combination of X-ray PDF and NMR, we present evidence on the silicate polymerization and the structure of the CNASH gel. Additionally, we also report novel data on the long-range atomic ordering of a series of 45 synthetic gels.
A new publication titled “Dissolution Kinetics of Calcined Kaolinite and Montmorillonite in Alkaline Conditions: Evidence for Reactive Al(V) Sites” was published in Journal of the American Ceramic Society in July 2019.
Using solid-state Nuclear Magnetic Resonance spectroscopy and Inductively-coupled Plasma – Optical Emission Spectroscopy, we followed the dissolution kinetics of calcined kaolinite and montmorillonite. It was shown that dissolution kinetics are correlated with pozzolanic reactivity and dissolution rates are strongly influenced by the presence of reactive Al(V) sites.
A new publication titled “Symmetry-Induced Stability in Alkali-Doped Calcium Silicate Hydrate” was published in The Journal of Physical Chemistry C in May 2019.
Using first-principles quantum chemistry calculations on the model crystalline phase clinotobermorite, it was shown that there is a strong interplay between the thermodynamic stability of alkali-doped C-S-H and the symmetry of the alkali atoms in the structure. The article can be accessed here.