The database of chemical, mineralogical and physical characteristics of North American Fly ashes, assembled by the WFARDDC in North Dakota, was analyzed using multivariate statistics. Prior to the multivariate analysis, the data were rearranged in subgroups containing information on bulk-chemistry, glass chemistry, mineralogy and ASTM physical test results. These groups were analyzed individually. The multivariate technique used was Fuzzy C-Means Cluster Analysis, combined with Non-Linear Mapping. Analysis of the data-set indicates a relation between glass network former and network modifier content. The database shows that a subdivision on the basis of bulk CaO (< 11%; 11–20%; >20%) correlates well with the ASTM C618 Σ(SiO2 +Al2O3 +Fe2O3) and/or specific gravity. Mineralogical data indicate a subdivision into clusters containing varying amounts of mullite, quartz and/or ferrite spinel and a variety of Ca-containing minerals; high CaO ashes usually have high Ca-mineral contents. Of the CaO containing minerals, only portlandite contributed slightly to the compressive strength as defined by ASTM C618. Analysis of glass chemistry reveals smaller differences in absolute amounts of major oxides than would be expected on the basis of bulk chemistry alone. Surprisingly, the total glass content does not contribute significantly to 28 day compressive strength; multiple regression analysis only indicates a significant relation of particle size and specific gravity with the ASTM Pozzolanic Activity Index (portland cement). The Pozzolanic Activity Index with lime seems to be of limited importance in evaluating the performance of fly ashes as mineral admixtures in concrete. On the basis of the statistical analysis, suggestions for selection of important classifying variables are made.

Blending of different types of coals is an economical method of utilizing locally available lower quality coals. Four blends of Wyoming/Oklahoma coal were prepared (100:0, 90:10, 75:25, 0:100) and burned in a laboratory furnace in a diffusion flame of a mixture of propane and nitrogen in air. Flame temperatures ranged from 1419 K for Oklahoma to 1626 K for Wyoming coal. The higher temperatures indicate better boiler utility, more oxidation, less free carbon, more and better quality fly ash. These observations conform well with the SEM evaluations which indicated that as the amount of Wyoming coal increased, the matrix contained densely populated glassy spherical particles. The SEM data on cured paste samples indicated that the Wyoming fly ash showed a better tendency to crystal (presumably ettringite) formation, followed by the blends of 90% Wyoming-10% Oklahoma and 75% Wyoming-25% Oklahoma. The least amount of crystal formation was observed in the fly ash of 100% Oklahoma coal. These effects are extremely pronounced in the early curing stages.

When heated at 750°C for five hours, African laterites show good pozzolanic activity. The kaolin content of the materials affects their pozzolanicity as indicated by lime reactivity. Blended cements containing 20, 30, 40, and 50% calcined laterite admixture were examined.

The rate of hydration was studied from compressive strength up to 90 days of curing and the hydrates formed as measured by DTA and XRD. The burnt laterite addition considerably reduced calcium hydroxide content and contributed to the formation of hydrated gehlenite (C2 ASH8) and gismondine (CASH).

The best compressive streng hs were obtained with blended cements containing 30% calcined laterite. In some cases, there was no more portlandite in binders where the replacement level of cement by burnt laterite was 50% by mass.

Between 20 and 50 per cent of the total iron in low-Ca fly ashes resides in low-substitution magnetite spinel with Curie temperatures in between 565 and 590°C. A TEM study reveals that the spinel consists of aggregates of closely spaced spherules of 10 – 30 nm in diameter, which is in complete agreement with rock magnetic determinations. The low-field magnetic susceptibility correlates extremely well with total iron and fairly well with specific heavy metals. Measurement of the magnetic susceptibility may serve as a rapid tool for the evaluation of the speciation of these heavy metals in fly ash.

Slag as a supplementary cementitious material is known for its latent hydraulic properties. Thus, constant efforts are being directed towards improving its reactivity. This mostly involves the use of alkali salts. The authors present the results of alkali activation of a slag from Hamilton, Ontario, Canada, by means of water glass (Na2SiO3). Distinct improvement in early and late age strength was noted when water glass was used in combination with CH. The microstructure of this activated slag paste at 28 days is described. The microanalytical techniques used included SEM/EDXA, and XRDA.

Red muds are waste materials obtained from the aluminium extraction industry. They consist mainly of clays, aluminium and iron hydrated oxides. Three muds were studied; they differed in chemical and mineralogical compositions. They were converted into reactive pozzolans by calcination in the temperature range 600–800°C for five hours. Pozzolanicity was investigated on calcined red mud-OPC mixes studying strength development and lime consumption as evaluated by DTA. The nature of hydrates formed during hardening was also identified.

The mineralogical composition of the mud is the most important factor affecting its pozzolanicity. Blended cements containing 30% calcined red mud develop significant strengths.

Three samples of fly ashes from pilot-scale tests of gas reburning and sorbent injection (GR-SI) technology were characterized physically, chemically, and mineralogically. Texturally, the samples consist of approximately 97% by weight of silt-size particles. Total chemical analysis showed that Al, Ca, C, Fe, Si, and S were the major elements, making up 56% of the total mass of the sample on average. Approximately 3% of the sample mass consisted of the elements Cl, Mg, P, K, Na, and Ti, and 0.4% consisted of trace elements. Major crystalline compounds found in these samples were lime (CaO), anhydrite (CaSO4), and calcium carbonate (CaCO3). Calculations show that these compounds constituted from 56 to 76% of the mass of the samples. The morphology and chemistry of particles in GR-SI samples were similar to those of particles in conventional coal fly ashes. The particles in the GR-SI samples consisted of fragments and spheres of varying sizes. Most of the particles were calcareous. Silicate and alumino-silicate particles were fewer in number, and iron-rich particles were rare. The EP test indicated that extract concentrations of Ag, As, Ba, Cd, Cr, Pb, and Se were well below the EPA regulatory levels. Predictions of leachate compositions from these types of fly ashes, if disposed of as a landfill at a midwestern U.S. site indicate, that during the first ten years the concentrations of Ca, SO4, Na, B, and OH would remain high. The concentrations of minor constituents (As, Ba, Cd, Cd, Cu, Cr, Fe, Ni, and Se) in the leachate are predicted to be at trace levels.

Cementitious reactions and ettringite formation, which occur when water is added to high-calcium fly ash, to many dry flue gas desulfurization solids, and to two of the residues from the emerging “clean coal” technologies, fluidized bed combustion and limestone injection multiphase burner, have been studied. The parameters varied included water to solid ratio and curing time. Crystalline reactants and products were monitored by X-ray powder diffraction. The amount of ettringite, the principal crystalline cementitious reaction product, was determined after three months of curing. Results are discussed in terms of available Ca, Al and S in each by-product and w/s ratio.

Fluidized bed combustion (FBC) residues from four Iowa power plants were characterized to provide background with respect to chemical, physical, mineralogical and microstructural parameters that might affect their utilization potential. Methodologies used include: bulk chemical analysis; grain size analysis; specific gravity determination; mineralogical analysis by x-ray diffraction; scanning electron microscopy; and thermal analysis.

Chemical analysis of the major components showed the separation of the constituents during combustion. The bottom ash is derived from the calcined and partly sulfated limestone, thus the concentration of calcium and sulfur compounds is greater. The fly ash however is derived mostly from the coal and therefore exhibits higher concentrations of coal ash components such as silica (SiO2), alumina (Al2O3), and ferric oxide (Fe2O3). The alkalis appear to be more concentrated in the fly ash.

The measured particle size distributions of the bulk samples varied greatly, from extremely coarse (mean particle size ˜2000 μm) to fine (mean particle size ˜25 μm). The size distributions also varied in breadth. Specific gravities values recorded ranged from about 2.65 to about 3.05.

X-ray diffraction analyses showed that most of the FBC by-products contain, as easily detectable crystalline components, only quartz, anhydrite and lime, and as is to be expected due to the low combustion temperatures, do not show broad peaks characteristic of glass in conventional fly ashes. Scanning electron microscopy revealed the FBC by-products to be extremely intricate mixtures of particles of complex and variable composition and internal structure.

FBC by-products are shown to be extremely complex mixtures of particles of variable composition and internal structure. However, despite their local variation, useful results can be obtained by overall chemical and physico-chemical analyses of their composition. The exploitable properties of FBC residue include the somewhat cementitious nature and the granularity. However, their heterogeneous nature, lack of pozzolanic properties, and elevated sulfate content may limit their uses, especially in construction.

Acid mine drainage (AMD) is being recognized as a major pollution source to surface water. Heavy trace metals emanating from abandoned mines are continuously being released and contaminating surrounding lakes and streams. The potential for utilizing fly ash and water softening sludge (WSS) as buffering and adsorption media for AMD water was assessed. The results indicated that AMD water treated with fly ash either met or exceeded the U.S. Environmental Protection Agency water quality criteria for effluent standards for total iron, manganese, suspended solids, and pH. The optimum dosage of fly ash and sludge needed for treating the acid mine water from Picher field, an abandoned lead and zinc mine in Oklahoma, has been determined. It was observed that each had better than 90 percent efficiency for removal of heavy metals from the AMD water. The combined use of fly ash and WSS was also investigated, but there was no significant improvement compared to using fly ash alone. In general fly ash had a greater buffering capacity to treat acid mine water than did WSS. Consequently, fly ash can be used to treat AMD water and minimize its environmental impact.

Blends of portland clinker and gypsum plaster exhibit fast setting and early strength development if mixed with water. An excessive expansion of such systems may be controlled by the use of a “sulfate resistant” rather than “ordinary” clinker and by adding condensed silica to the system. The water resistance of such hardened pastes is significantly improved as compared to plain gypsum pastes, mainly due to the formation of the C-S-H-and AFt-phases.

Cementitious materials, together with other materials, are being considered to seal a potential repository at Yucca Mountain. A concern with cementitious materials is the chemical and mineralogic changes that may occur as these materials age while in contact with local ground waters. A combined theoretical and experimental approach was taken to determine the ability to theoretically predict mineralogic changes. The cementitious material selected for study has a relatively low Ca:Si ratio approaching that of the mineral tobermorite. Samples were treated hydrothermally at 200°C with water similar to that obtained from the J-13 well on the Nevada Test Site. Post-test solutions were analyzed for pH as well as dissolved K, Na, Ca, Al, and Si. Solid phases formed during these experiments were characterized by scanning electron microscopy and X-ray diffraction. These findings were compared with predictions made by the geochemical modeling code EQ3NR/EQ6. It was generally found that there was good agreement between predicted and experimental results.

A concrete liner emplaced in 1984 in a shaft at the Waste Isolation Pilot Plant has served as a natural laboratory for observing interactions among concrete, evaporite rocks, and brine. During a routine inspection of the liner in the spring of 1990, discoloration, deposition of secondary salts, wet areas with exposed aggregate grains, softening of paste, surficial spalling, and cracking were observed locally on the concrete surface of the liner. Some construction joints showed apparent leakage of brine from behind the liner, which was nominally 50 cm thick. Seepage brines were nearly saturated relative to CaCl2 and contained lesser amounts of MgCl2 and KCl, and minor NaCl. The liner surface was locally altered to a 1–2 cm friable hygroscopic layer containing little cement paste; concrete cores (7 or 10 cm diameter) through the liner at depths of 248, 254, 255, and 271 m showed similar degrees of alteration at the liner/rock interface. The most profound alteration of concrete was developed in a ˜7 cm zone sub-parallel to and straddling the construction joint cored at a depth of ˜254.5 m. This zone was extensively microfractured, transected aggregate grains, and contained brucite, gypsum, magnesium hydroxychloride hydrate, and locally calcium chloroaluminate instead of the usual phases of hydrated portland cement. Several mechanisms of chemical degradation have been proposed, the most likely being attack by magnesium ions.

WES developed a grout to be used as a cold (non-radioactive) cap or void-fill material between the solidified low-level waste and the cover blocks of near-surface disposal vaults at the U.S. Department of Energy (DOE) Hanford Facility. The project consisted of formulation and evaluation of candidate grout, followed by a physical scale-model test to verify grout performance under project-specific conditions and provide data to verify numerical models of stresses and isotherms inside the Hanford demonstration vault. Evaluation of unhardened grout included segregation, bleed, flow, and working time. For hardened grout, strength, volume stability, thermal heat rise, and geochemical compatibility with surrogate wasteform grout were examined.

The grout was formulated to accommodate unique environmental boundary conditions (vault temperature = 45 °C) and exacting regulatory requirements (mandating less than 0.1% shrinkage with no expansion and no bleeding); and to remain pumpable for a minimum 2 hr. A grout consisting of API Class H cement, an ASTM C 618 Class F fly ash, sodium bentonite clay, and a natural sand from the Hanford area met all performance requirements in laboratory studies.

The long-term integrity of cementitious materials is of interest where cement is used as part of the isolation system in underground workings sited in evaporite rocks. However, the slow rates of cement/fluid interactions at room temperature provide minimal guidance for predicting long-term cement behavior. To accelerate reactions that degrade cement, hydrothermal brine/cement interaction experiments were carried out at temperatures between 100° and 250° C. The pastes used in these experiments were two batches containing 65 (weight) % Class H cement and 35 % fly ash (one with Class C and one Class F, both with 10 mass equivalent % plaster), and one batch of Type K expansive cement, all with NaCl-saturated mix water. The brine used in testing was based on a composite representation of groundwaters from the Rustler formation of southeastern New Mexico, a mixed evaporite/clastic rock sequence. This brine was sufficiently concentrated that its use afforded an opportunity to study several mechanisms likely to degrade cement performance. At the conclusion of each experiment solid products were characterized and the coexisting fluids analyzed. In general, the cement was extensively altered by the brine at all temperatures assessed. In addition to the expected sulfate attack, it was found that magnesium effectively displaced calcium from the CSH gels that impart strength to cementitious materials. Sodium and potassium did not play a role in altering the cement.

Recent results on synthesis, crystal chemistry, structure and stability of ettringite*, with specific reference to use of this material in hazardous waste immobilization, are presented. Ettringites with selenate, chromate, borate, sulfite and carbonate replacing sulfate have been synthesized and characterized by XRD for phase purity and structure. In X-ray powder diffractograms, selenate and chromate etringites have the normal trigonal P31cettringite structure, whereas the borate, sulfite and carbonate ettringites can be indexed on a hexagonal unit cell with a halved c parameter. In excess of 95% of the Se and B in solutions spiked with various concentrations of these elements has been removed by precipitation of ettringite. Ettringites appear to be unstable in solutions outside of the approximate pH range 11.0-12.5, and there is a potential for some oxyanion exchange between ettringites and oxyanion-containing solutions. Buffering of pH, and dissolved Ca, Al and sulfate activities by other components of ettringite-based hazardous waste forms, combined with low-reactivity C-S-H matrices, could largely mitigate these concerns.

This paper deals with the hydration products and pore structure of Portland cement (PC) and alkali-phosphorus slag cement (APSC) pastes, and the uptake of metal ions (Sr2+, Co2+, Cd2+, and Cu2+) in pastes which have been hydrated at 150°C for 25 days. Results indicate that the hydration products of PC are crystalline Ca(OH)2 and C2SH(A); for APSC the products are poorly crystallized low-basic CSH(B) and crystalline tobermorite. The PC pastes have a lower total porosity than APSC pastes, but the PC pastes consist mainly of larger pores with r> 1000Å, while the APSC pastes consist mainly of smaller pores with r< 100Å. The two types of paste were immersed for 19 days at room temperature in Sr2+, Co2+, Cd2+ and Cu2+ solutions with concentrations of 100, 200, 500 and 1000 ppm. It was found that all Ca(OH)2, in the PC pastes was dissolved. Except for Sr2+, the uptake of metal ions by PC paste is mainly due to the formation of insoluble hydroxides. The uptake of metal ions by APSC pastes is due to physical adsorption and the formation of some insoluble compounds. The APSC pastes show a stable structure after immersion in these metal ion solutions.

Alkali-activated cementitious materials have considerable potential, with properties ranging from very high early strength to very high long term strength and low porosity. The role of alkalis in activating industrial by-products such as ground granulated (glassy) blast-furnace slag, ultra-fine silica fume or other by-product silicas, glassy fly ashes, and other amorphous materials is discussed. These by-product materials are activated by alkali additions which break the strong silicon oxygen bonds in the silicate or alumino-silicate network, accompanied by the formation of new reaction products. The role of the different components in multi-component activated cements on the reactivity and the nature of the resultant products is discussed. Characterization of starting materials and reaction products by XRD, SEM (including environmental SEM), chemical, and particle characterization techniques has been made. Additional results include investigation of pore solution chemistry as a function of time. Some inferences for long term durability are discussed.

A series of glasses in the system CaO-Al2O3-SiO2 was synthetized and studied with respect to their hydraulic reactivity. Generally, the initial reactivity is greater but the developed maximum strength is lower in glasses yielding a hydrogarnet phase, as compared to those yielding gehlenite hydrate. Another factor that determines initial reactivity appears to be the cooling rate of the glass melt. After longer hydration times the strength of glass cement pastes starts to decline, apparently due to a recrystallization of the hydrates formed initially.

MDF(Macro-Defect-Free ) cement pastes, which consist of portland cement and polyvinyl alcohol/acetate, were prepared by varying the temperature during pressing and drying operations. We then examined the expansion of MDF cement pastes at various constant humidities. There was a large difference in expansion above 60%R.H. between samples prepared varying temperature at which samples were pressed. Samples pressed at 90 °C showed less expansion than samples pressed at 40 °C.

The pore structure of MDF cement pastes before exposure to moisture was measured by nitrogen adsorption, mercury intrusion porosimetry and image analysis. The properties of a matrix containing polyvinyl alcohol/acetate and cemnt hydrates were also investigated by TEM, IR and XPS.

There were not large differences in the result of IR and XPS measurement between the MDF cement pastes prepared at various temperatures. Calcium hydroxide crystal, lying perpendicular to cement particles, were often observed only in the MDF cement pastes pressed at 90 °C which occurs by water absorption, seems to be suppressed by calcium hydroxide crystal.