Eric E. Lachowski

XRD, EDX and IR analysis of solid solutions between thaumasite and ettringite

Solid solutions between thaumasite and ettringite were prepared by methods analogous to those well established for the preparation of thaumasite and ettringite. The extent of immiscibility in this system is investigated by varying the Al:Si and SO42−:CO32− ratios in reactant mixtures. The solids produced were analysed by quantitative X-ray diffraction, with Rietveld refinement also providing accurate unit cell dimensions, energy-dispersive X-ray analysis and infrared spectroscopy. The compositional and unit cell variations in the solid solution are discussed. A wide variety of solid solution compositions were produced with both the thaumasite and ettringite structures, but all preparations were considerably diluted by secondary amorphous products.

A multi-method study of C3S hydration

Abstract C3S pastes hydrated at 25°C have been studied using QXRD (to determine uncreacted C3S), TG (to determine CH and water), and trimethylsilylation (to determinemonomeric and dimeric silicate) and the results compared with ones obtained with analytical electron microscopy. Monomeric silicate is accounted for by unreacted C3S. The silicate in the C-S-H formed during the first few days is entirely dimeric, but at later ages dimer and polymer are both present. A new hypothesis for the reaction mechanism is tentatively proposed.

Clinker mineral hydration at reduced relative humidities

Abstract Vapour phase hydration of pure cement clinker minerals at reduced relative humidities is described. This is relevant to modern high performance concrete that may self-desiccate during hydration and is also relevant to the quality of the cement during storage. Both theoretical considerations and experimental data are presented showing that C 3 A can hydrate at lower humidities than either C 3 S or C 2 S. It is suggested that the initiation of hydration during exposure to water vapour is nucleation controlled. When C 3 A hydrates at low humidity, the characteristic hydration product is C 3 AH 6 , hydrogarnet.

Oxygen stoichiometry-Tc correlations in Bi2Sr2CaCu2O8+x

The oxygen content of single-phase Bi2Sr2CaCu2O8+x depends on the annealing temperature and the oxygen partial pressure. The Tc maximum, 87 K, is associated with an excess oxygen content, x, of 0.035+or-0.003, as determined by volumetric analysis and thermogravimetry. This stoichiometry is obtained by, for instance, annealing in air at approximately 820 degrees C or in nitrogen at approximately 400 degrees C. For higher and lower x, Tc decreases. No structural changes associated with this change in oxygen content were observed; variations in Tc appear therefore to be associated with changes in carrier concentration. The rate of change of Tc with x is more than ten times greater than in YBa2Cu3Ox.

Acid attack on pore-reduced cements

Because the durability of high-performance cements is as important as their strength, the performance of pore-reduced cement (PRC) in aggressive media such as sulfuric, hydrochloric and ethanoic acids, was studied and compared with that of ordinary Portland cement (OPC). The effects of exposure to these media on these cements were monitored by periodic visual inspection and sample weighing. Specific interactions with regard to interconnected porosity were addressed and the corrosion products characterized. PRC is less susceptible than OPC against hydrochloric and ethanoic acids. However, sulfuric acid damages PRC and OPC to almost the same extent. It is shown by electron microprobe analysis that the hydrochloric and ethanoic acids quickly penetrate the interior of normal cement pastes by acid leaching of the interconnected porosity. The reduced porosity of PRC reduces the susceptibility to attack by this mechanism. Sulfuric acid exposure causes extensive formation of gypsum in the cement surface regions, which results in mechanical stress and ultimately leads to spalling. Thus fresh surfaces are exposed regularly and therefore the relatively closed microstructure of PRC is no hindrance to this kind of attack.

Investigation of the composition and morphology of individual particles of portland cement paste: 1. CSH gel and calcium hydroxide particles

Abstract This investigation represents an attempt to combine analytical electron microscope analysis of the composition of individual particles separated from hydrated portland cements with a micromorphological examination of the same particles using high-resolution scanning electron microscopy. The particles described here are all referrable to the CSH gel type III category, or to impure calcium hydroxide. Variations in composition turned out to be substantial, not only from one CSH gel particle to another, but between different small regions of the same fragment of gel.

Identification of some of the polysilicate components of trimethylsilylated cement paste

Abstract Trimethylsilyl derivatives from polymerised silicate anions in an eight-year-old cement paste have been fractionated by high-pressure liquid chromatography (hplc) and the fractions examined by thin layer chromatography, mass spectrometry and infrared spectrometry. The hplc separates linear from cyclic species. The major low molecular weight silicate anion in the C-S-H larger than dimer appears to be the linear pentamer. The presence in small quantity, of both linear tetramer and cyclic pentamer has been confirmed and the identification of the two high-temperature gas-liquid chromatography peaks with those species is supported.

Silicon-29 and carbon-13 NMR studies of organosilicon chemistry: X. The structure of Si8O11(OSiMe3)10

Abstract Trimethylsilylation of tetramethylammonium silicate produced a compound of formula C 30 H 90 O 21 Si 18 . NMR studies using the 13 C and 29 Si nuclei have shown that the structure of this compound is related to a double four-membered cage by the replacement of one SiOSi bridge by trimethylsiloxy units.

Trimethylsilylation as a tool for the study of cement pastes (2) quantitative analysis of the silicate fraction of Portland cement pastes

Abstract The trimethylsilyl derivatives of the silicate fractions of three fully hydrated Portland cement pastes have been studied by gas-liquid and gel-permeation chromatography. The pastes had 9–11% of the silica as monomer, 22–30% as dimer and 44–57% as polysilicate. Gel-permeation chromatograms of the polysilicate derivatives all had maxima corresponding to a degree of polymerisation (dp) of about 4 and shoulders at higher values; the weight average dps were 14–17 and although the maximum dps were high, only about 2% of the silica had dps greater than 50. The mean connectivity of the polysilicates was 2.3.

Modelling approach to the prediction of Equilibrium Phase Distribution in Slag-Cement Blends and their Solubility Properties.

Blended cements containing mixtures of granulated blast-furnace slag (BFS) and Portland cement give low permeability matrices with initially favourable leach characteristics. Their retention arises from a combination of physical and chemical effects which include high pH and sorption. It is not practical though, in either laboratory or site-based experimentation, to determine changes in matrix chemistry over long timescales and the development of realistic models for long-term property predictions therefore becomes increasingly important. This paper pursues the development of such a model enabling changes in chemical and mineralogical balances during ageing to be predicted. Phase development is assessed in the system CaO-Al 2 O 3 -SiO 2 -MgO-H 2 O. In the relevant composition range, the phases occurring include crystalline hydrates: portlandite, (Ca(OH) 2 ); gehlenite hydrate, (2CaO.Al 2 O 3 .SiO 2 .8H 2 O); a hydrotalcite-structured phase (nominally 6MgO.Al 2 O 3 .(OH) x .yH 2 O). an AF m type phase, (nominally 4CaO.Al 2 O 3 SO 3 .12H 2 O); and a poorly crysiallised c~lcium silicate hydrogel, C-S-H. All five phases are observed to occur together in slag-cements which are still hydrating. Given, as input, the chemical analyses of both the slag and the cement, and the initial blending proportions, the model predicts the equilibrium distribution between the five components and additionally, the Ca/Si ratio of the C-S-H. The aqueous chemistry in the system is predicted from the calculated phase distribution and appropriate solubility products.