Michael W. Grutzeck

Alkali-activated fly ashes: A cement for the future

The alkali activation of waste materials (especially those coming from industrial and mining activities) has become an important area of research in many laboratories because it is possible to use these materials to synthesize inexpensive and ecologically sound cementlike construction materials. In the present paper, the mechanism of activation of a fly ash (no other solid material was used) with highly alkaline solutions is described. These solutions, made with NaOH, KOH, water glass, etc., have the common characteristic of having a very high OH 2 concentration. The product of the reaction is an amorphous aluminosilicate gel having a structure similar to that of zeolitic precursors. Temperature and time of curing of specimens together with the solution/fly ash ratio are some of the variables that were studied. These variables have been shown to notably influence the development of the mechanical strength of the final product. Mechanical strengths with values in the 60 MPa range were obtained after curing the fly ash at 85 8 C for only 5 h.

Chemical stability of cementitious materials based on metakaolin

The alkali activation of metakaolin is a way of producing high strength cementitious materials. The processing of these materials has been the subject of numerous investigations. The present paper describes the results of a research project initiated to study the stability of these materials when exposed to aggressive solutions. Prisms of mortar made of sand and alkali-activated metakaolin were immersed in deionized water, ASTM sea water, sodium sulfate solution (4.4% wt), and sulfuric acid solution (0.001 M). The prisms were removed from the solutions at 7, 28, 56, 90, 180, and 270 days. Their microstructure was characterized and their physical, mechanical, and microstructural properties were measured. It was observed that the nature of the aggressive solution had little negative effect on the evolution of microstructure and the strength of these materials. It was also found that the 90-day and older samples experienced a slight increase in their flexural strengths with time. This tendency was most pronounced in those samples cured in sodium sulfate solutions. This behavior may be related to the change in microstructure of the cementitious matrix of the mortars cured longer than 90 days. Some of the amorphous material present had crystallized to a zeolite-like material belonging to the faujasite family of zeolites.

The retarding effects of fly ash upon the hydration of cement pastes: The first 24 hours

Abstract Disagreement exists in the literature as to whether or not fly ash accelerates or retards the early hydration of fly-ash blended cements. As an outgrowth of this controversy the effects of two fly ashes, a Class C and a Class F, their leachates and leached fly ash residues upon the first 24 hours of cement hydration were studied. It was found that both fly ashes (“as received and to some degree, leached”) retarded a Type I cement hydration; however the fly-ash leachates did not. The retardation phenomenon is apparently related to the presence and condition of the fly ash surfaces.

Solid state water motions revealed by deuterium relaxation in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-zeolite A.

Deuterium NMR relaxation experiments, low temperature deuterium NMR lineshape analysis, and FTIR spectra are consistent with a new model for solid state jump dynamics of water in (2)H(2)O-synthesized kanemite and (2)H(2)O-hydrated Na(+)-Zeolite A. Exchange occurs between two populations of water: one in which water molecules are directly coordinated to sodium ions and experience C(2) symmetry jumps of their OH bonds, and a population of interstitial water molecules outside the sodium ion coordination sphere that experience tetrahedral jumps of their OH bonds. For both samples the C(2) jump rate is much faster than the tetrahedral jump rate. (2)H NMR relaxation experiments match well with the fast exchange regime of the model over a wide range of temperatures, including room temperature and above. For hydrated Zeolite A, the kinetic activation parameters for the tetrahedral and C(2) symmetry jumps are Delta H tet++=+17 kJ/mol, Delta S tet++=-109 J/(mol K), Delta H C2++=+19 kJ/mol, and Delta S C2++=-20 J/(mol K). For kanemite, Delta H tet++ =+23 kJ/mol, Delta S tet++=-69 J/(mol K), Delta H C2++ =+23 kJ/mol, and Delta S C2++ =-11 J/(mol K).

Self-Generating Zeolite-Cement Composites

Zeolites can be synthesized in mixtures containing 80 wt% Class F fly ash and 20 wt% ordinary Portland cement if they are mixed with a concentrated NaOH solution and cured at temperatures of 60–90° C. Zeolite Y and NaP-type zeolite were grown in situ in a coexisting calcium silicate hydrate matrix. Those samples made with NaOH, which contained the zeolites, had higher compressive and flexural strengths than equivalent samples made with water.

Iodine Waste Forms: Calcium Aluminate Hydrate Analogues

Phase relations in the system 3CaO·AI 2 O 3 -CaSO 4 -CaI 2 -H 2 O in equilibrium with excess water were established by means of room temperature bottle hydration of various bulk chemistries in the system. Starting with end members ettringite (3CaO·Al 2 O 3 ·3CaSO 4 ·32H 2 O) and tetracalcium aluminate monosulfate-12-hydrate (3CaO·Al 2 O 3 -CaSO 4 -12H 2 O), iodine-substituted analogue phases were synthesized which containe increasingly greater percentages of iodine. The iodine-substituted ettringite was found to be unstable whereas the iodine-substituted monosulfate formed readily. SEM, wet chemistry, IR, and x-ray diffraction characterization of the latter phase suggest that its formula is 3CaO·Al 2 O 3 ·Ca(IO 3 ) 2 ·2H 2 O. Cement pellets containing this “Afm” iodine-substituted phase were subjected to a modified MCC-1 static leach test. Although the normalized iodine leach rate was relatively high when compared with AgI encapsulated in portland Type III cement, this same leach rate was approximately equal to the rates that have been reported for Ba(IO 3 ) 2 , Ca(IO 3 ) 2 , and Hg(IO 3 ) 2 in portland cement. The normalized iodine leach rate obtained also was found to be roughly comparable to that given for I-sodalite in cement. Diffusion is indicated as the primary leach mechanism, becoming dominant after the first three days of leaching.

Synthesis of double-layer silicates from recycled glass cullet: A new type of chemical adsorbent

Curbside recycling of glass bottles and jars has been extremely successful. Those glasses that are sorted by color are a marketable commodity; those that are not have no immediate commercial value and must be disposed of in landfills. With proper chemical treatment, however, mixed-glass cullet can be transformed into claylike chemical adsorbents. By mixing ground glass cullet with either alkali hydroxide or alkali carbonate solutions one is able to form a hydrous double-layer silicate known as rhodesite (NaKCa2[Si8O19]·5H2O). Tests of the adsorptive and cation exchange properties of glass cullet derived materials have shown them to have properties comparable to natural clays and zeolites. Whereas natural materials tend to become “sticky” and/or lose their granularity when wet, rhodesite-based adsorbents do not.

The synthesis and characterization of calcium aluminate monoiodide

Abstract The hydrated calcium aluminate AFt and AFm phases are known hosts for a wide variety of chemical species. This characteristic is beneficial to those using portland cement to solidify/encapsulate radioactive waste which more often than not contains a wide variety of elements. In order to investigate the potential of the calcium aluminate hydrates as host phases for selected ions, the following experiments were carried out. Bottle hydration studies (water/solid > 1) were used to investigate the suitability of the AFt and AFm phases as hosts for iodine, one of the more mobile radioactive waste elements. Trial compositions along the AFt and AFm joins in the systems 3CaO·Al2O3CaSO4CaI2H2O were investigated. No stable iodine end-member AFt phase was formed at room temperature. The end-member AFm phase, 3CaO·Al2O3·CaI2·12H2O, was synthesized and was designated monoiodide. Characterization was carried out using chemical analysis, scanning electron microscopy, x-ray diffraction (conventional and high temperature), thermogravimetric analysis and differential thermal analysis. Monoiodide was indexed as hexagonal and thus isostructural with previously described AFm phases. Monoiodide is stable to about 85°C. A loss of approximately four molecules of water occurs between 71° and 101°C. The lower hydrate, tentatively identified as 3CaO·Al2O3·CaI2·8H2O, is stable to approximately 300°C. The latter hydrate was observed to revert to the original hydrate on exposure to the relative humidity in the laboratory.

Characterization of samples of a cement-borehole plug in bedded evaporites from southeastern New Mexico

This report describes the laboratory characterization of a section of an eighteen-year-old cement-based plug emplaced to seal a four-inch (ten-centimeter) borehole in the Salado Formation near Carlsbad, NM. The dominantly halite salt strata contain a horizon rich in potassium-bearing minerals such as langbeinite, in the plug region. Other host rock minerals identified include illite, kainite, magnesite, syngenite and polyhalite. Identified in the plug were: the cement phase calcium silicate hydrate (C-S-H having an intermediate degree of crystallinity), Friedels salt, halite, sylvite and portlandite. The plug, though intact, unfractured on a macroscale, and forming an adequate physical bond with the salt formation, was weak and permeable relative to the surrounding bedded salt. Characterization of the plug and rock was carried out by a combination of measurements: compressive strength, permeability, density and porosity, thermal measurements (DTA, TGA), x-ray diffractometry, SEM and optical (including thin section) microscopy, and energy-dispersive x-ray analysis for chemical composition.

PCT leach tests of hot isostatically pressed (HIPped) zeolitic concretes

Provided that it is implemented properly, cementitious solidification of radwastes represents an attractive alternative to glass-making. The zeolitic mineral assemblages produced by intrinsically safe, low-temperature cementitious reactions are apt to be much more stable in any of this nation`s likely ultimate repository sites than are radwaste-type glasses. Another significant advantage is that it is easier and cheaper to accomplish large-scale solidification with cementitious technologies than it is to attempt to do the same thing with glass melters--especially when the operation must done remotely and the feedstream contains volatiles. This and previous papers in this series, demonstrate that good concretes can be readily converted to good glass-ceramics within hermetically-sealed containers using process temperatures far below those required to make glasses.