Clinker sampling

Alkali Sulfates. Since the silicate phases (C3S and C2S), present in total at up to 85 wt.%, normally dominate clinker samples, all minor phases are significantly concentrated in Residue 2. This includes the important alkali sulfate phases which can (i) affect setting times and final strength, and (ii) be used to assess kiln operating conditions. Since these are normally present at a total of about 0.5 wt.% in clinker, and are often distributed across several Na and K sulfate phases, they are not easily identified in raw clinker XRD patterns. However, their presence may be more easily detected in the XRD pattern of Residue 2. By optimizing the parameters of the alkali sulfates from Residue 2 data, and then constraining them in the on-line analysis system, these phases can be measured at the <0.5wt.% level (Madsen, Scarlett and Storer 2001, unpublished results) even when rapidly collected on-line data is used. 

Taking the clinker sample for microscopical examination has, as yet, no formally accepted procedure and several techniques are currently used, largely dependent on the purpose of the investigation. Because of time constraints during clinker analysis, the clinker sample must necessarily be small and, therefore, the conclusions must be cautiously drawn. A grab sample is preferable to composite samples for most investigations. 

One of the most popular methods involves crushing a random clinker sample of roughly a liter volume (1 to 2 kg) to approximately 2- to 4-mm-diameter par-... 

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. 

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

Photograph 7-58 Belite striations in light blue alite. Multicolored, round belite showing typical lamellae, but somewhat scalloped cross section. Small secondary belite in brightly reflecting ferrite matrix. Clinker sample contains remnants of chrome-magnesia refractory brick. (S A6678)... 

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. 

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."... 

Campbell, D.H., "Microscopical Description of Clinker Sample No. 44ICMA Sample Exchange Program," Proceedings of the 16th International Conference on Cement Microscopy, International Cement Microscopy Association, Richmond, Virginia, 1994a, pp. 377-380. 

In the presence of limestone, the needles have a fibrillar morphology, but they are thinner and are straight, perpendicular to the surface of the grains. The alite paste is similar to the C3S paste. In clinker samples, especially on STEM cross sections, it is more difficult to distinguish between C-S-H needles and ettringite needles. 

When the kiln material is cooled it forms into crystallized clinkers. These are rather large irregular pieces of the solidified cement material. These clinkers are ground and a small amount of gypsum is added (usually about 1.5 to 3%). The gypsum prevents flash setting of the cement and also controls free CaO. This final cement product is sampled, analyzed and stored. The actual commercial cement is usually a hlend of several different cements. This blending ensures a consistent product. 

Aliphatic solvents, alkyllithium compounds and, 14 250-251 Aliphatic sulfonates, 26 145 Aliquot samples, 13 413-415 analysis of, 13 416 Aliskren, 5 158 Alitame, 12 42 24 232 Alite, phase in Portland cement clinker, 5 471, 472t, 473t Alitretinoin, 25 790 Alizarin, color of, 7 331 Alizarin derivatives, 9 337 Alizarin pure Blue B, 4 361t Alkadienes, metathesis of, 26 923 Alkali/alkaline-earth cation recognition,... 

Bensted (B38) described the use of TG in the study of clinkers or unhydrated cements. At 4°Cmin in Nj with cements, losses normally occur at I00-200"C from gypsum or hemihydrate, 400-500°C from CH and 500-800°C from CaCOj. If a normal, open sample cup is used, the losses from conversion of gypsum to hemihydrate and from dehydration of hemihydrate are poorly resolved, making interpretation difficult. Better separation can be achieved by using a sample cup with a top that is closed except for a narrow exit (S32). 

The experimental considerations applying to calcium silicate pastes (Sections 5.1 and 5.2) are equally relevant to cement pastes. Of the methods so far used in attempts to determine the degrees of reaction of the individual clinker phases as a function of time, QXDA (C39,D12,T34,P28) has proved much the most satisfactory. Procedures are essentially as for the analysis of a clinker or unreacted cement (Section 4.3.2), but it is necessary to take account of overlaps with peaks from the hydration products, and especially, with the C-S-H band at 0.27-0.31 nm. The water content of the sample must be known, so that the results can be referred to the weight of anhydrous material. If a sample of the unhydrated cement is available, and its quantitative phase composition has been determined, it may be used as the reference standard for the individual clinker phases in the paste. 

Fig. 7.3 QXDA results for the fractions of the clinker phases reacted in Portland cement pastes. Filled circles Copeland and Kantro (C39), w/c = 0.65. Diamonds Bezjak et al. (B98), sample C2. Vertical lines Osbaeck and Jons (08), range for 7 samples. Open circles Dalziel and Gutteridge (DI2). Open squares Patel et al. (P28), samples cured at 100% RH. Filled squares Tang and Gartner (T34), clinker interground with gypsum.

It should be noted that significantly more cement and hydration phases are known in literature [12]. For example, dicalcium silicate (2 CaO Si02 C2S), an important clinker phase which accounts for approx. 5-10 wt-% of the cement used to prepare the samples, was deliberately left out of the refinement. Although dicalcium silicate could be positively identified in the diffraction patterns of the unhydrated cement, its quantification in the Rietveld refinement was not reliably possible after the samples had been exposed to water and the phase was, therefore, excluded. 

When comparing the influence of the polymers, the most apparent result is the incomplete consumption of clinker phases in the c/PVAc samples, whereas in the c/PVA samples, the clinker phases are consumed in less then four days. It should be noted that the consumption of the clinker phases is the lowest for c/PVAc in pure water. The reason for this is the above mentioned hydrophobic nature of PVAc, which requires alkaline pH values for saponification before the polymer can be dissolved. Thus, the XRD measurements are consistent with the NMR measurements. Additionally, approx. 10% more amorphous material is formed in the case of c/PVAc. This is again a result of the hydrophobic nature of PVAc. As discussed in the NMR section, c/PVAc swells at a lower rate than c/PVA. This limits the access of water to the clinker phases, which hampers the formation of larger crystallite sizes. 

The experiments in POW resemble the conditions of the NMR experiments. Based on the appearance of the samples at the end of the experiments (disintegrated in the case of PVA and rodlike brittle in the case of PVAc) it was postulated that PVA dissolves faster, while PVAc dissolves slower than the cementitious matrix establishes. This is exactly backed up by the XRD measurements in the case of PVA, less than 10% of the clinker phases had hydrolysed at the time the sample disintegrated (8h), while after 48h, the time of full sample saturation, more than 40% of the clinker had reacted in the c/PVAc sample. 

Wachtler and Jannsen [90] studied the material phase composition in the kiln with partial precalcinahon, and without its shut down. In the material from cyclone preheater spurrite, C2F and aluminates CA and and free CaO were found. In the samples also these phases and additionally C AF were present Then the gehlenite appears, C2S and C3A. Appearing of CjA is accompanied with the disappearing of C2F and CA. When C3S appears the samples have already the composition of clinker. 

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