Joseph J. Biernacki

MICROANALYSIS OF ALKALI-ACTIVATED FLY ASH-CH PASTES

Abstract Samples of a Class F fly ash and calcium hydroxide (CH) hydrated in pH 13.2 sodium hydroxide solution were analyzed using backscattered electron, scanning Auger, and X-ray microanalysis. The Class F fly ash, composed mainly of aluminosilicate glass and silica, was reacted for 8, 14, and 78 days at various temperatures. These samples represent both long-term and early-age stages of hydration. Results show that a hydrate product with calcium to silica ratio near 1.4 and katoite are formed. X-ray and scanning Auger microanalysis show evidence of the formation of hydrate product on the surface of both fly ash and CH particles at early ages. This finding suggests a new mechanism to explain prior data that shows that the hydration rates increase with increasing CH–ash content in the starting mixture.

Kinetics of Reaction of Calcium Hydroxide and Fly Ash

In this research, the alkali activated reaction kinetics of a Type-F fly ash with calcium hydroxide (CH) and water were studied at temperatures between 25 and 60 degrees C. Thermogravimetric analysis was used to determine the CH consumption and production of hydrates as a function of hydration temperature and time for various CH/fly ash ratios. Results show that the reaction rate, reaction stoichiometry, and activation energy are dependent on the CH/ash ratio. The reaction rate was also found to be a function of the extent of reaction of both CH and fly ash phases. Various kinetic models were considered, including those proposed by Knudsen and Avrami; these had limited applicability. A model is suggested providing a broader fit to the observed data.

Unified Shrinkage Model for Concrete from Autogenous Shrinkage Test on Paste with and without Ground-Granulated Blast-Furnace Slag

Autogenous shrinkage development was studied as a function of time for cement paste and concrete hydrating under sealed conditions at room temperature. Effects of water-cementitious material ratio (w/cm) (0.35, 0.40, and 0.45), ground-granulated blast-furnace slag (GGBFS) content as a percentage of total cementitious material (0, 30, and 50%) by mass, and aggregate content (40%) by volume on shrinkage development was obtained. Shrinkage measurements started after 10 hours and lasted up to 90 days. Self-desiccation (that is, reduction in pore humidity) was predicted using the HYMOSTRUC model. The effects of w/cm on shrinkage development can be normalized from shrinkage vs. pore humidity curves for portland-cement paste. The aggregate effect on autogenous shrinkage was found to follow a Pickett model developed for drying shrinkage. These results suggest that a unified shrinkage model, which combines autogenous and drying shrinkage, exists. The framework for such a model is presented, which incorporates relative humidity (RH), aggregate content, and restraint factor as major variables. GGBFS initially reduces shrinkage as it behaves as a filler, thus increasing the effective w/cm. While the long-term shrinkage is increased, the major factor is most likely a reduction in pore humidity associated with pozzolanic reactions. Due to a higher internal RH in a 0.45 w/cm system, the pozzolanic effect on autogenous shrinkage is more pronounced at later ages.

Cements in the 21st Century: Challenges, Perspectives, and Opportunities

In a book published in 1906, Richard Meade outlined the history of portland cement up to that point1. Since then there has been great progress in portland cement-based construction materials technologies brought about by advances in the materials science of composites and the development of chemical additives (admixtures) for applications. The resulting functionalities, together with its economy and the sheer abundance of its raw materials, have elevated ordinary portland cement (OPC) concrete to the status of most used synthetic material on Earth. While the 20th century was characterized by the emergence of computer technology, computational science and engineering, and instrumental analysis, the fundamental composition of portland cement has remained surprisingly constant. And, although our understanding of ordinary portland cement (OPC) chemistry has grown tremendously, the intermediate steps in hydration and the nature of calcium silicate hydrate (C-S-H), the major product of OPC hydration, remain clouded in uncertainty. Nonetheless, the century also witnessed great advances in the materials technology of cement despite the uncertain understanding of its most fundamental components. Unfortunately, OPC also has a tremendous consumption-based environmental impact, and concrete made from OPC has a poor strength-to-weight ratio. If these challenges are not addressed, the dominance of OPC could wane over the next 100 years. With this in mind, this paper envisions what the 21st century holds in store for OPC in terms of the driving forces that will shape our continued use of this material. Will a new material replace OPC, and concrete as we know it today, as the preeminent infrastructure construction material?

Microanalytical and Computational Analysis of Class F Fly Ash

A Class F fly ash has been analyzed using synchrotron x-ray diffraction (XKD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) to determine the composition, phase distribution, particle size, and particle morphology. XRD showed the existence of mullite, quartz, Fe 2 O 3 (hematite or maghemite), and CaSO 4 (anhydrite), with the possibility of calcium hydroxide (CH), which was also confirmed using TGA. SEM and x-ray microanalysis indicate four particle types: 1) a mixed aluminosilicate (A-S) phase with variable amounts of calcium, iron, and magnesium; 2) quartz or glassy silica; 3) FeO, Fe 2 O 3 , or an MgO-FeO phase; and 4) Ca(OH) 2 mixed with CaSO 4 . A combination of image analysis and XRD was used to identify and quantify the phase fraction of the major components in the system, including aluminosilicate glass and silica. These were used to construct segmented microstructures suitable for use in multi-scale microstructural simulations. Microanaysis also suggests that the A-S glassy portion of the ash may actually be two separately identifiable glasses or at least bounded by the compositions AS 3 and A 2 S 3 .

ASSESSMENT OF A SYNCHROTRON X-RAY METHOD FOR QUANTITATIVE ANALYSIS OF CALCIUM HYDROXIDE

Thermogravimetric analysis (TGA) and quantitative X-ray diffraction (QXRD) are widely used to determine the calcium hydroxide (CH) content in cementitious systems containing blends of Portland cement, fly ash, blast furnace slag, silica fume and other pozzolanic and hydraulic materials. These techniques, however, are destructive to cement samples and subject to various forms of error. While precise weight losses can be measured by TGA, extracting information from samples with multiple overlapping thermal events is difficult. And, however, while QXRD can offer easier deconvolution, the accuracy for components below about 5 wt.% is typically poor when a laboratory X-ray source is used. Furthermore, the destructive nature of both techniques prevents using them to study the in situ hydration of a single contiguous sample for kinetic analysis. In an attempt to overcome these problems, the present research evaluated the use of synchrotron X-rays for quantitative analysis of CH. A synchrotron X-ray source was used to develop calibration data for quantification of the amount of CH in mixtures with fly ash. These data were compared to conventional laboratory XRD data for like samples. While both methods were found to offer good quantification, synchrotron XRD (SXRD) provided a broader range of detectability and higher accuracy than laboratory diffraction and removed the subjectivity as compared to TGA analysis. Further, the sealed glass capillaries used with the synchrotron source provided a nondestructive closed, in situ environment for tracking hydrating specimens from zero to any desired age.

Wolff–Kishner reduction reactions using a solar irradiation heat source and a green solvent system

Due to the recognition of the irreversible damage done to the environment through man-made materials, scientists have attempted to transform synthetic procedures into environmentally favorable procedures. Since fossil fuels are used for electrical energy in the USA, the amount of electricity required to complete an experiment has become an environmental concern. Solar parabolic reflectors have been proposed as a means for minimizing the amount of electricity needed to perform chemical reactions. The ability to use the solar reflector as the sole heat source for synthetic reactions is being considered. Another area of environmental concern is the chemical solvent systems involved in synthetic reactions that are not friendly to the environment. The ability to exchange solvent systems for greener solvents is being considered. A comparative study was conducted using an electrical and solar heat source on a series of Wolff–Kishner reduction reactions performed in a green solvent system. The following generalized chemical reaction is representative: where R is a hydrocarbon chain and R′ is a hydrocarbon chain or hydrogen.

Gas-Phase Mixing and Dispersion in a Diffusion Furnace

Gas-phase mixing and dispersion in a typical commercial-scale diffusion furnace was investigated using computational fluid dynamic simulations and experimentation. Five regions were defined within the furnace: (i) entrance volume, (ii) annular volume around the wafer-source stack, (iii) radial volumes between wafer-source pairs, (iv) intermediate volumes between successive wafer carriers, and (v) exit volume. The mixing characteristics within each of these volumes was quantified and appropriate mixing models were defined based on the relative amount of backmixing or gas exchange within and between these volumes. A dispersion-based approach was then used to develop a simplified model describing the transient transport of water vapor (H 2 O) during a typical hydrogen injection cycle. Model parameters were calibrated using experimental data from tracer impulse studies.

Gas Diffusivity Through EPS Foams

A simple multiscale model was developed and used to predict gas diffusivities through expanded polystyrene foam at near standard temperature and pressure conditions. The technique involves measuring gas diffusivities at various length scales then combining them using an electrical analogy for parallel resistances to construct an effective property. A commonly used experimental technique, the continuous flow method, was used to obtain diffusivity data for argon through polystyrene films and foams. Although a simple Fickian mathematical model was able to predict diffusivities through films, a simple ‘coarse’ multiscale model that accounts for the morphological features was developed for the foam.

The Southern Grassroots Biofuels Project: A Participatory Study of Conservationists and Stakeholders From Two Upper Cumberland Counties

Biomass pyrolysis is being developed to convert biomass into renewable energy to reduce fossil fuel dependency, yet little sociological research has been conducted on knowledge and attitudes toward the technology in rural southern communities. Our study involved participatory collaboration with conservationists, farmers and stakeholders in the Tennessee Upper Cumberland to better understand attitudes regarding biomass production and conversion by pyrolysis. We found farmers very knowledgeable of first generation biomass feedstock and fuels but not familiar with pyrolysis. Rural economic growth as a result of supplying residues and feedstock for biofuels production appeared to be the main motivation behind future farmer involvement. Findings from our study indicate that farming communities are willing to partner with scientists if familiarized with the technology and approached with transparency and equality early in the decision making process. We conclude that such collaborative learning is essential when introducing pyrolysis to rural southern communities.