The processes by which cement paste transforms from a viscous suspension into a rigid solid must be understood if the performance of concrete and other cement-based materials is to be reliably predicted from the properties of their constituents. While the hydration reactions and mechanisms have not been completely elucidated, the topic is further complicated by a lack of a quantitative description of the anhydrous cement particles. Both the bulk composition of a cement and the spatial distribution of the various phases will influence the temporal properties of a hydrating system. Quantification of the initial cement particles is thus seen as an important step in developing scientifically-based relationships between cement microstructure and resultant properties such as strength and durability. Additionally, such quantification could serve as a valuable quality control technique for the cement production industry, ultimately leading to a new generation of cement and concrete standards.
In recent years, the application of scanning electron microscopy (SEM) to characterizing cement clinker and ground cements has increased. SEM and X-ray microanalysis have been utilized to identify the four major phases in portland cement clinker [1]. Scrivener has applied similar techniques to determine the distribution of silicates and interstitial phases in cement grains [2] and compared the results to the rates of heat release during hydration. Bonen and Diamond have analyzed the same cement clinker ground in both a ball mill and a high pressure roller mill, using SEM and X-ray analysis to classify the predominant phase found in each cement particle [3]. Additionally, the particles were characterized on the basis of aspect ratio and shape factor using image analysis techniques.
Another recent development in the field of cement research is the use of computer modelling to relate microstructure to properties. Often, these models are digital-image-based, with a two or three-dimensional digital image being the basis for the microstructure model [4]. The underlying image structure allows for the efficient computation of properties such as ionic diffusivity or elastic modulus [5]. While simplifications such as using circular particles can be made, these models can accept actual images of cement particles as input. It was therefore of interest to develop techniques to obtain images of cement particles in which each pixel (element) in the image has been classified as a phase of portland cement. This paper details the technique developed to obtain two-dimensional images of the real anhydrous cement particles and provides examples of using these images as input into a computer model of the microstructural development of hydrating cement paste.