Mineralogy of Hydrated Cements

Date This project started on 01 August 2004 and ended on 01 January 2007

Status This project is Finished

Authors
University of Aberdeen, UK
Eidgenössische Materialprüfungs und Forschunganstalt, CH
Objectives

The central mechanism by which cement works is the hydration reaction, in which the starting phases react and combine with water to give an increase in solid volume, which fills the space originally occupied by water and bind the cement grains together. The resulting cement paste consists of a fine-grained mass of solids many of which are of low crystallinity.

Therefore characterisation of the number and constitution of hydrated substances present has presented many seemingly intractable problems. Many techniques have been applied which reveal partial structural information but it is often difficult to combine and integrate this knowledge into a consistent picture.

However progress in other fields of inorganic structural materials has rested on developing correlations between, on the one hand, physical properties - normally bulk properties such as strength - and on the other, with phase constitution, amounts of substance and microstructure. But progress in developing such correlations for hydrated cements has been slow, owing in part to the above-mentioned difficulties in quantification of the number, composition, amount and microstructural relationships of the constituent solids and, of course, the coexisting aqueous phase.

About 80 years ago, Bogue wrote a series of equations describing the relationship between clinker raw meal chemical composition and the mineralogy of the finished clinker. These enabled the amounts of minerals to be calculated from a bulk chemical composition. Fundamental to the equations was a precise description of the high temperature equilibrium achieved during clinkering.

Hydrated cements are more complex than cement clinkers. Even more complex is the assemblage of hydrate phases which will result from the hydration of a cementitious system, when supplementary cementing materials (SCMs) and fillers such as slags, fly ashes, natural pozzolans, limestones are included. Nevertheless it is not unrealistic to determine the information needed to predict the phase assemblage from the degree of reaction of the composants.

This project aims to define the compositions and stabilities of the hydrated phase assemblages that are likely to occur over the temperature range 0-50°C and represents a fresh attempt to determine these relationships. If successful, it will initiate a new start to the understanding and eventual control of cement properties.

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