Clinker Microscopy

One should not, therefore, immediately draw the conclusion that a clinker phase is particularly reactive if its freshly polished surface exhibits a slight etch or stain due to impure polishing vehicles or cleaning solutions. Keeping the etchants at constant temperature is recommended to eliminate that persistent question of temperature effects. Etching andstaining should be consistently timed. 

Use of the hair dryer to warm the surface of a polished section accelerates etching and staining. Therefore, beware of a premature conclusion of high phase reactivity. Delayed etching may inhibit normal coloration and give one a misinterpretation of sluggish phase reactivity. 

Finally, make interpretive generalizations based on the dominant (most common) clinker characteristics, always attempting to he quantitative and systematic. 

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Although it is not clear whether LeChatelier examined cement made by Joseph Aspdin, who patented Portland cement in England in 1824, a few comments on the nature of the Aspdin cement appear relevant to the history of clinker microscopy. 

Also among the many major historical contribu tions in clinker microscopy are the works of Parker and Nurse (1939) Taylor (1943) Gille (1955) Kramer (1960) Nurse, Midgley, and Welch (1961) Midgley (1964) Butt and Timashev (1974) and others. Most of these authors are mentioned again in Chapter 7, Microscopical Interpretation of Clinkers. ... 

McKenzie (1989) studied the relationships between feed particle size distributions and the clinker microscopy, showing that coarsely crystalline clinkers generallyresultfrom coarse inhomogeneous feeds. 

As an economical and rapid method to control the quality of portland cement, the value of routine clinker microscopy should be an inescapable conclusion from the numerous observations and interpretations given on previous pages. Quality control of clinker without microscopy of raw feed, in the writer s opinion, is less than adequate. Profound cause-effect relationships exist between the raw feed/particle size distribution, energy required for grinding and burning, clinker quality, and cement performance. Visually appreciating the characteristics of raw feed via microscopical examination gives additional comprehension to quality control. 

Campbell, D.H., and Galehouse, J.S, "Quantitative Clinker Microscopy with the Light Microscope," Cement, Concrete, and Aggregates, ASTM, Winter 1991, pp. 94-96. 

Gouda, G.R., "Clinker Microstructure by Scanning Electron Microscope," Second Annual Conference on Cement and Clinker Microscopy, Sponsored by Gifford-Hill Co. Inc., General Portland Inc., and Southwestern Portland Cement Company, Dallas, Texas, 1980,19 pp. 

McKenzie, L., "A Case Study on the Effects of Burner Pipe Position and Its Effects on Clinker Microscopy," Proceedings of the 11th International Conference on Cement Microscopy, International Cement Microscopy Association, New Orleans, Louisiana, 1989a, pp. 306-322. 

In 1995, Dr. Campbell established Campbell Petrographic Services, Inc., in Dodgeville, Wisconsin, where he continues to emphasize thin-section microscopy, fortified by X-ray diffraction, chemical analysis, and physical testing. He has written numerous articles on cement and concrete microscopy, as well as both editions of Microscopical Examination and Interpretation of Portland Cement and Clinker. He teaches classes on cement and clinker microscopy at the Portland Cement Association, in addition to having taught in Mexico, Australia, France, and the Philippines. He is active in ASTM, the International Cement Microscopy Association (ICMA), and the Society of Sedimentary Geology. 

The other C, A modification is a disordered, poorly crystalline form, called proto-C,A, which was obtained metastably from simulated clinker liquids, either by rapid cooling or by static crystallization at low temperatures (BIO). It gave an XRD powder pattern with broadened peaks, corresponding to the systematically strong reflections of cubic CjA indexable on the subcell with a 0.39nm. Analytical electron microscopy of individual crystals showed it to be very high in substituents, one preparation, for example, having an Fe/Al ratio of 0.54 (H6). 

The early literature contains many references to the presence in production clinkers of glass, often in substantial proportions. This view was based partly on observations by light microscopy however, this method cannot distinguish glass from crystalline solids of the cubic system unless crystals with distinct faces have been formed, nor from crystalline materials of any kind if the crystals are below a certain size. It was also found that if clinkers believed to contain glass were annealed, their heats of solution in an acid medium increased, and this method was used to obtain approximate estimates of the glass content (LI 3). This evidence, too, is inconclusive, because the same effect would arise from the presence of small or structurally imperfect crystals. 

Neither XRD nor electron or light microscopy indicates that C12A7 is present in any modern clinkers, and when free lime is found, microscopic examination does not suggest that it has formed by precipitation from the liquid. 

Light microscopy can be used to find the causes of unsatisfactory clinker quality or to determine what modifications in composition or plant operation are needed to change the clinker properties in a desired direction. It... 

The methods that have proved effective for quantitative determination of phases in clinkers are based on light microscopy (Section 4.2.1), X-ray diffraction (Section 4.3.2) and calculation from the bulk chemical analysis. The last two of these are applicable also to cements. SEM with image analysis (Section 4.3.1) shows promise, but other methods that have been investigated, such as IR spectroscopy, appear to have little potential. Sections 4.4.2 to 4.4.5 describe a method of calculation from the bulk analysis and Section 4.4.6 compares the results of the various methods. 

The hydrated material has been analysed by X-ray microanalysis and analytical electron microscopy. In a 3-day old paste, that formed in situ from alite or belite did not differ significantly in composition from the corresponding product in pure Portland cement pastes (H4). but at later ages Ca/ Si is lower and Al/Ca higher (R25,R26,T44,U 17,U 18,R42). Ca/Si is typically about 1.55, but the value decreases with age and ratio of pfa to clinker. Uchikawa (U20,U17) reported a value of 1.01 for a 4-year-old paste with 40% replacement of cement by pfa. Several of the studies (R25,T44,U20,U 17) showed that the C-S-H was higher in alkalis if pfa was present, but one cannot tell to what extent potassium or sodium apparently present in the C-S-H has been deposited from the pore solution on drying. For material close to the pfa particles in a 10-year-old mortar. Sato and Furuhashi (S92) found a Ca/Si ratio of 1.1-1.2. 

The basis for rate cements to individual kinds is cement composition based principally on chemical determinations, to which belong insoluble residue and loss on ignition. They are principally linked with cement additions. For quantitative slag content determination from long time the light microscopy is used, and the accuracy of this method is assessed to be 5 % (Fig. 1.6). Lastly also the methods of separation in heavy liquids are recommended, based on the density differences of individual cement components clinker about 3.1 g/cm, slag 2.85 g/... 

Different 38 phases, in the case of low content of belite in clinker, is most convenient to identify using light microscopy. Among others, Metzger [161] applying this method found the presence of phase a. The striations of belite crystals always observed in industrial ehnkers due to polysynthetic twinning, are distinctly differentiate this phase from alite crystals and are formed in the polymorphic transformation process. 

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