Here at Staffordshire University we have been conducting research into various aspects of cement chemistry.

The areas we have most interest in are ettringite/thaumasite determination (using XRPD and pattern fitting), the hydration of CSA cements and the recycling of industrial wastes as raw materials for the manufacture of low energy cements.

We have had support/funding from the following companies/agencies:

• Building Research Establishment
• Burmah-Castrol
• Forsroc
• Staffordshire University
• Optiroc

Current members of the cement chemistry research group are (in alphabetical order):

• Dr. Craig D. Adam
• Head of Natural Sciences, expertise in XRPD and pattern fitting

• Dr. Jo Bunford
• PhD thesis entitled 'The Formation of Calcium Sulphoaluminate Cements Using Industrial Wastes', looking into recycling of wastes (pfa, gypsum) in low energy cements and the modification of a Bogue style quation for use with CSA cements

• Dr P. Duncan Hywel-Evans
• Chemistry Research Fellow
• Phd thesis entitled 'The Hydration of Calcium Sulphoaluminate Cements'

• Dr. Andrew R. W. Jackson
• Head of Environmental Science, expertise in cement chemistry

and the newest addition to the group

• Mr. Robert Whiting
• Continuing research into ettringite formation

Previous research students include:

• Dr. Stephanie Barnett
• PhD thesis entitled 'XRPD studies of ettringite and related structures'(Currently a postdoctoral researcher at Aberdeen University)

RESEARCH ABSTRACTS

The Formation of Calcium Sulphoaluminate and Related Cements Using Industrial Waste Products

A series of samples was prepared, calcined and analysed in order to test the predictive ability of the Hywel-Evans' Bogue style equation [1]. The results showed that, in most cases, the equation could predict, qualitatively, the mineralogy of a CSA type cements using only the known oxide analysis of the raw materials. Minor adjustments were made in order to improve the predictive ability of the calculation.

Quantitative analysis was performed on a selection of the samples referred to above. The results were in overall agreement with the changes made to the Hywel-Evans' Bogue style equation by the author. This analysis did, however, reveal several issues that required further investigation. These included the formation of more than one C₂S polymorph and solid solution effects that could effect the C₂S , C₄AF and possibly calcium aluminates.

The effect of temperature on the role of formation of C₄A₃S(bar) was studied. The effect of the addition of fluxes/mineralisers to the C₄A₃S(bar) raw materials (before calcination) was also investigated. The results showed that the addition of CaF₂ and CaCl₂ increased the rate of formation of this phase whilst the addition of Fe₂O₃ had little or no effect on the rate of reaction. It was also observed that the addition of B(OH)₃ greatly enhanced the rate at which the C₄A₃S(bar) formed.

A series of CSA tyoe cements were prepared from both laboratory grade materials and industrial wastes. Samples were also prepared with the addition of fluxes/mineralisers (including B(OH)₃). The research showed that it was possible to produce cements at lower temperatured (below the normal 1250-1350^oC) by part replacement of pure materials with by products (in this case, pulveried fuel ash and gypsum). It was laso found that the additions of CaF₂, CaCl₂, ZnO and B(OH)₃ further lowered the formation temeprature of these materials.

Hydration of the CSA type cements allowed the effects of grinding, water:cement ratio and curing to be examined. It was found that the cements had not been ground to a high enough specific surface area, or cured at sufficient relative humidity, to gain the desired strengths (comparable to commercial CSA).

REFERENCES

1. The Hydration of Calcium Sulphoaluminate Cements, P. D. Hywel-Evans, PhD Thesis, Staffordshire University - Oct 1996

We would like to thank FOSROC for their support with this project

This brief abstract will be replaced with that used in the thesis when it has been accepted

X-Ray Powder Diffraction Studies of Ettringite and Related Systems

Ettringite (Ca₆Al₂(SO₄)3(OH)₁₂.26H₂O) and the crystallographically related thaumasite (Ca₃SiSO₄CO₃(OH)₆.12H₂O) are naturally occurring minerals which also occur in hydrated cements. There is a high degree of isomorphous replacement possible within these minerals. Considering the complex nature of cements and the ease with which substitution into the ettringite lattice takes place, it is highly likely that the composition of the ettringite-type phase in a cement system varies markedly. Previously, XRPD identification of these phases has depended on measurement of d-spacings only.

The aims of this project were the crystallographic characterisation of ettringite, thaumasite and other related phases, by the X-ray powder diffraction data analysis techniques, full pattern fitting and Rietveld refinement, and the evaluation of these techniques in investigation of ettringite-type phases in cementitious systems.

Initially, several phases with the ettringite structure were synthesised by established methods and analysed by full pattern fitting and Rietveld refinement, using data collected with both laboratory and synchrotron sources of X-rays.

Two solid solutions between ettringite and related phases, believed to be important in cement applications, were investigated using these techniques. These are the solid solution between ettringite and carbonate ettringite and that between ettringite and thaumasite.

In the final stages of the work, cement systems containing ettringite-type phases were investigated using the techniques developed.

Several important developments in the characterisation of ettringite, thaumasite and related phases were achieved.

Rietveld refinement, using high resolution powder diffraction data collected on Station 2.3 at CLRC Daresbury's Synchrotron Radiation Source (SRC), produced refined crystal models for ettringite and thaumasite. By adapting the refined model for ettringite, the Rietveld technique was then used to create novel crystal structure models for the carbonate and iron(III) analogues of ettringite (Ca₆Al₂(CO₃)₃(OH)₁₂.26H₂O and Ca₆Fe₂(SO₄)₃(OH)₁₂.26H₂O, respectively). All of these refined models can also be adapted to produce crystal structure models for other compounds with the ettringite structure and for compounds with intermediate stoichiometries.

Studies of the solid solution series between ettringite and its carbonate analogue showed that a single solid solution phase is produced for samples prepared with up to 60 mole% SO₄ ^2- replaced by CO₃ ^2-. At higher carbonate contents, there are two ettringite type phases, both of which are solid solutions between ettringite and carbonate ettringite.

The solid solution between ettringite and thaumasite has been investigated in depth, for the first time. A discontinuity in the solid solution was identified, as expected since these compounds have different space groups. Solid solutions having the ettringite structure (space group P31c) and thaumasite structure (space group P63, c-axis halved) have been shown to exist.

In the cement systems studied, there were found to be only slightly variations from pure ettringite. The ettringite-type phase in these grouts was identified as ettringite with a possible deficiency in its water content.

In general, the techniques of full pattern fitting and Rietveld refinement have been shown to be useful tools in identification of these compounds in cement systems. Previously, identification has depended upon measurement of d-spacings only. This project has demonstrated that these techniques are able to characterise solid solution effects in these systems, even where there are more than one ettringite/thaumasite-type phases, along with several other related hydrated and anhydrous compounds.

We would like to thank FOSROC for their support with this project

The Hydration of Calcium Sulphoaluminate Cements

A number of cementitious grouts have been examined at a 2.5:1. 0.5:1 and 0.25:1 weight for weight waster to powder ratio. The hydration products from the various mixtures were examined by X-ray powder diffraction, Scanning electron microscopy, EDAX, Magic angle NMR, ICP-AES, compressive strength and thermal profiling techniques. The grouts formed were initially tested at ages of 2 hrs, 1, 7, 14 and 28 days. An IBM PC based computer program was developed to empirically model the results

A number of mechanisms have been hypothesised in an attempt to explain some of the behaviour of the cements used, and hydrates generated by the grouts studied in this thesis. Mechanisms have a;so been proposed to reconcile the contradictory results from different techniques used to examine the hydrates in the grouts

A unique kiln was designed and built to produce laboratory quanitites of specific cements with controlled compositions and thermal histories. A Bogue type equation with controlled compositions was developed to predict the mineral composition of the different types of cement produced in the kiln. A new cement has been designed and prepared based on the proposed hydration mechanisms, to give the greatest hydration rate.

We would like to thank FOSROC for their support with this project

Characterisation and Formation of Ettringite

Other Research in the Division of Natural Sciences

Research is currently being undertaken into the hydrolysis of tyres and coal, fingerprinting of oils for forensic pruposes and organometallics (abstracts from some of the researchers are below). We also have members of staff with expertise in various areas of environmental, organic and inorganic chemistry.

Fingerprinting of Oils for Forensic Purposes

Sign Guestbook View Guestbook