H.F.W. Taylor

Synthesis of normal and anomalous tobermorites

Abstract Tobermorites were made from several starting materials at 105 – 180°C and Ca/(Si + Al) 0.8 – 1.0. Reaction gives in succession C-S-H, normal, mixed and anomalous tobermorites, and finally xonotlite. High C/S ratio (1.0), short time, low temperature, stirring, presence of Al, and if quartz is used, small particle size, all tend to stop it at normal tobermorite. In some cases, this effect is due to promotion of crystal growth of normal tobermorite. Low C/S ratio (0.8), long time, high temperature, no stirring, presence of Al plus alkali, and, if quartz is used, large particle size, all tend to give anomalous tobermorite. However, at 180° C this changes easily into xonotlite if C/S > 0.9.

Calcium silicate hydrate (II) (“C-S-H(II)”)

Abstract This semicrystalline phase, originally named ‘calcium silicate hydrate(II)’ by Taylor (1950), has been studied with X-rays, electron optics, chemical investigation of silicate anion type, infrared spectra, and thermal methods. It is structurally related to jennite (C 9 S 6 H 11 ) and probably also to the fibrous CSH of cement pastes, the three phases forming a sequence of decreasing crystallinity. The specimen studied had approximate composition C 2 SH 3.2 after standing over saturated CaCλ 2 at about 15°C. CSH(II) contains metasilicate chains and pyrosilicate groups and has a disordered layer structure. Much of the water can be lost reversibly without significant change in lattice parameters.

Analyses of the aqueous phase during early C3S hydration

Abstract The concentrations of calcium and silica in solution during the first 4 hours of C 3 S hydration were measured. The results of these analyses indicate that a solid calcium silicate hydrate forms within 30 seconds of the start of hydration and that an equilibrium between the solution and the solid hydrate is rapidly established. A strong dependence of the rate of early hydration on the w:C 3 S ratio was observed, while the dependence on the surface area of the C 3 S was minimal.

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.

An electron microprobe study of a mature cement paste

Abstract A portland cement paste 23 years old, and essentially fully hydrated, was studied by electron probe microanalysis. X-ray images indicated that the shapes of the original, largely polymineralic cement grains, and those of the regions occupied by the individual phases within them, are substantially preserved in the hydrated material. This was shown especially clearly by the Mg and Fe images, probably because these elements do not readily migrate in the alkaline medium. Estimation of individual phase compositions is rendered uncertain because of possible admixture of phases on or below a micrometer scale, but the atomic ratios relative to Ca are, approximately: Mg 0.03, Al 0.08, Si 0.60, S 0.03 and Fe 0.015 (Ca:Si 1.67) for the C-S-H, and Al 0.40, Si 0.33 and Fe 0.27 for the hydrogarnet.

Reactions of tricalcium silicate paste with organic liquids

Abstract Thermoanalytical and other evidence shows that methanol, acetone and some other organic liquids are strongly sorbed by tricalcium silicate pastes, and cannot be completely removed by vacuum drying or heating at temperatures that do not profoundly alter the material. This confirms an observation by Day (1981). When pastes that have been treated with these liquids are heated in nitrogen to 200° to 600°C, carbonate ion is formed; this seriously alters the thermogravimetric curve. Acetone, when sorbed in tricalcium silicate pastes, undergoes condensation reactions at room temperature. These conclusions have implications for the use of organic liquids to stop hydration or in the preparation of polished sections for X-ray microanalysis.

The hydration of tricalcium silicate

SummaryEvidence on the mechanism and products of tricalcium silicate hydration is summarized, and present-day interpretations of that evidence critically discussed, partly with a view to supplying a basis for mathematical modeling of the hydration process. There is general agreement on many, broad features of the reaction and its products, and it should be possible to express many of the proposed hypotheses in mathematical form. Uncertainties nevertheless remain about many questions that are of essential importance if kinetic equations based on an unequivocal understanding of the mechanism are to be formulated. The paper concludes with a list of these questions.

Influence of aluminium on the conversion of calcium silicate hydrate gels into 11 Å tobermorite at 90°C and 120°C

Abstract Mixtures of CaO and colloidal silica with and without γ-Al2O3, CaO and alkali-bearing Al2O3-SiO2 gels, or CaO and clinoptilolite were treated hydrothermally at 90°C or 120°C for 4 hr – 4 weeks. Reaction seemed always to proceed through formation of C-S-H gels to 11 A tobermorite. In the absence of Al, tobermorite crystallized more rapidly at c/S = 1.0 than at C/S = 0.8 but in the presence of Al, it crystallized more rapidly at Ca/(Si + Al) = 0.8 than at Ca/(Si + Al = 1.0. Where the starting materials contained both Al and alkali the tobermorite showed anomalous thermal behaviour similar to that of the natural mineral from Loch Eynort, but where they contained Al but no alkali, the thermal behaviour of the tobermorite was complex.

A trimethylsilylation study of tricalcium silicate pastes

Tricalcium silicate and alite pastes aged from 1 day to 30 years were studied by trimethylsilylation and examination of the resulting derivatives by gas liquid chromatography, gel permeation chromatography and other methods. At ages up to about 6 months, silicate anion polymerization probably occurs predominantly during the formation of the CSH and not by changes within CSH that has already formed. The latter process is extremely slow, and only becomes significant after substantially all the C3S has reacted.

Electron-optical analyses of the phases in a portland cement clinker, with some observations on the calculation of quantitative phase composition

Abstract The four major phases in a typical wet-process clinker have been analyzed by energy-dispersive X-ray analysis in the scanning electron microscope. The contents of minor oxides in the phases were: alite, 2 %; belite, 5 %; aluminate, 12 %; ferrite, 10 %. The composition of the ferrite phase was near to Ca 2 AlFe 0·6 Mg 0·15 Ti 0·05 O 5 , and similar compositions have been observed in other clinkers. A further modification of Yamaguchi and Takagis (1969) modification of the Bogue calculation is used to compute the quantitative phase composition and the results compared with those obtained by other methods. The possibility of using such a method more generally is discussed.