Sieving clinker

Photograph 9-25 Alite crystal with attached alkali sulfates. Lamellar structure in belite revealed in upper right corner. 30-min maleic acid etch on crushed, sieved clinker. (S A6748)... 

With quickly setting epoxy resins or similar materials, such as cyanoacrylate ester (Super Glue ), and modern semiautomatic grinding and polishing equipment, polished sections can be made within a few minutes, while an alcohol-washed, sieved clinker powder, moimted in refractive-index oil, is studied. 

The bulk density of a clinker, determined under standard conditions by rejecting material passing a 5-mm sieve, pouring the remainder into a conical container, and weighing, is called the litre weight. This quantity, which is typically 1.25-1.35 kg 1 gives some indication of the operating conditions. Its optimum value depends on the composition. 

In this step, 40% of the CO2 is due to fossil fuel combustion to produce the flame, and 50% comes from the reaction. Because of the high temperatures, the powder agglomerates (forms clinkers). Before packaging and distribution, these particles are milled and sieved to the desired size. 

For determination of the phase content of clinker, Chromy (1983) utilized polished sections made from the quartered residue from 0.5 kg of clinker ground to a particle size passing a 1.0-mm sieve. A 20-mm-diam-eter polished section of particles embedded in epoj was prepared. 

Centurione (1993) recommends an initial 15 kg clinker sample, which is then quartered to 2.5 kg and sieved. The sieved fractions are crushed, sieved into 2.4-, 0.6-, and 0.3-mm fractions, and blended. A 50-gram sample is taken for microscopy, XRF, and chemical determination of free lime. 

If the clinker is extremely sandy or dusty, crushing prior to sieving may not be necessary. A random spoonful taken from a well-mixed sample will likely be adequate. 

Other workers prefer to sieve the clinker sample, after which representative portions of arbitrarily... 

The procedure described here is an outline of recommended steps, not to be taken as unalterable, in the production of polished sections of whole clinkers or a sieved fraction of crushed clinkers. The recommended procedure involves the use of epoxy resin, a rotating-wheel grinder/polisher and a tabletop saw. An elapsed time of less than 30 minutes is typical for the proposed procedure by which a virtually flawless polished section is produced. Following are the basic recommended steps ... 

The epoxy-resin procedures described here are intended for single polished sections and polished thin sections of selected sieve fractions of whole or fragmented clinkers, rocks, bricks, ceramics, concrete, and many other materials. The desirable properties of an epoxy-encapsulating and -impregnating medium are ... 

Ono s method of cement kiln evaluation is based on observations of clinker or cement powder mounted in a liquid medium on a glass microscope slide. A polar ized-light microscope (the so called petrographic microscope) is an absolute necessity, and magniflca tions at approximately 400X are recommended. To determine the parameters of the kiln conditions in Ono s method as described in 1995, cement or clinker powder is sieved through a 100 pm screen (approxl mately U.S. Sieve No. 140), and a powder mount is prepared with a liquid of refractive index in the range of 1.705 to 1.715. The principal value of Ono s tech nique is that it can be employed by a competent, well trained microscopist on a small sample of clinker... 

Well-burned clinker with a high VW, volume weight, is difficult in coarse grinding (getting it to pass the 1-2 mm sieve), but soft in fine grinding (<88 microns). VW is the weight of clinker nodules, 5-10 mm diameter, in a liter container. Opti mum VW is approximately 1.35 kg/L. 

With the use of Ono s Method and microscopy of raw feed, clinker, cement, gypsum, and kiln dust, coupled with laboratory burns and sieve analysis of the raw feed, Vanisko (1978) demonstrated the deleterious effect of belite nests in development of mortar strength. He showed that coarse quartz was correlated with numerous large belite nests and, when the raw sand was separately and more finely groimd, mortar strengths jumped to 41 MPa. 

Fortune, J ohansen, and Fimdal (1987) microscopically evaluated the effect of changing the kiln feed fineness from a normal value of 12% retained on the 90-pm sieve to 5-6%, with reductionin the silica modulus (MS) from 3.0 to 2.4. The results were an improvement in kiln fuel consumption, a much better clinker granulometry, smaller alite, and fewer belite nests. 

If a clinker sample is to be subjected to the extraction, a random sample of 1- to 2-mm crushed clinker particles, taken from the same fraction as previously prepared for polished section examination, is further crushed in a mortar and pestle until all the subsample passes a 75- j,m screen (No. 200 mesh). If acement is to be treated, a random sample of approximately 10 grams is sieved to produce the 45- to 75-pm fraction (325 to 200 mesh) particles left on the 75- j,m screen could be further crushed to pass the screen or, perhaps, studied microscopically to determine belite nest percentage. Sieving, however, is an optional step the main benefit is that it provides a uniformly sized powder promoting a relatively uniform level of focus by removing "boulders" that may interfere with examination and particle manipulation. If sieve confaminafion is a likely problem, one can use disposable nylon with the proper mesh opening. 

The sample is made from 5 kg of clinker, crushed in a jaw crusher with a gap of 2 mm and screened on a 150-pm sieve. The fraction larger than 150... 

Chromy (1983), utilizing a 2000-point coimt on 22-mm diameter polished sections of a sieved crushed clinker sample, demonstrated the usefulness of the microscope in determining the mineralogical composition of clinker, the data from which were related mathematically to clinker and raw mix composition, and cement strength. He concluded, "If conversion constants linking the equilibrium clinker composition and strength are determined, it is not necessary to carry out the quantitative phase analyses of the clinker produced. Monitoring the free lime content will suffice."... 

The analytical approach followed two routes. The first was a microscopic study including the use of scanning electron microscopy. By such means, the aggregates were analyzed for their size, shape and mineral composition, and the binder was assessed for its microstiucture, chemical composition, and the mineral composition of relict clinker phases. The second approach was based on the separation of the aggregate from the binder followed by chemical and mineral analysis of the binder and sieve fractioning of the aggregate. 

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