Cement microscopy is a very valuable technique, used for examining clinker, cement, raw materials, raw feed and coal. Every stage of the cement manufacturing process can be improved through the use of a microscope.
Most cement microscopy is done using a petrographic microscope. Usually the specimen is a polished section of cement clinker examined using reflected light, although it may be a powder mount or a thin section examined using transmitted light.
A scanning electron microscope (SEM) may also be used. The combination of SEM with X-ray microanalysis (=EDX, EDS, EDAX) is very powerful as it enables the analysis of individual crystals or particles.
Details of the history of a clinker can be seen - raw material fineness and homogeneity, clinker composition, temperature profile in the kiln, for example. From this information, the likely performance of the cement can be predicted or the cause of production problems identified such as poor combinability, or low grindability.
Some cement manufacturers use microscopy as a technique for kiln control, with clinker samples being examined continuously. Other manufacturers use it occasionally on an 'as required' basis while some manufacturers never use it at all. (As cement microscopists ourselves, if we may let a little bias creep in here, we would say these cement producers who don't use microscopy are really missing out on making better cement at lower cost.)
Important characteristics the microscopist examines include:
Other clinker mineral characteristics can indicate very slow cooling, reducing conditions, an excess of alkali over sulfate in the clinker and other adverse conditions.
While clinker microscopy is more usually performed using a petrographic microscope, SEM/EDX of clinker, cement and of concrete and mortar is a very powerful technique and is often used to clarify the results of examinations using optical microscopy where the results were uncertain. For more on this, see our book: "Scanning Electron Microscopy of Cement and Concrete".
The International Cement Microscopy Association (ICMA) holds an annual meeting, usually in the USA. The proceedings of the meetings are a valuable source of reference.
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