Clinker well burned

Well-burned clinkers are less porous and contain better-crystallized colorless alite and dirty-green to muddy belite. 

Burning too near the discharge end of the kiln, where the temperature change is 1400°C to 1000°C, also produces small alite, and the clinker is usually poorly burned. Alite sizes of less than 15 pm in a 1000 tons-per-day kiln can be indicative of poor burning a 20-pm alite size is typical of poor burning in a 4000 tons-per-day kiln (Ono, 1980c). A well burned clinker (f-CaO < 0.6%) does not have alite crystals under 20 pm (Ono, 1995). 

Poorly burned clinker frequently contains many small belite clusters. If the raw mix contains coarse quartz grains, belite clusters appear even in well-burned clinker, and the alite size has a wide range. 

Ono (1991) listed some of the characteristics of poorly burned clinker free lime greater than 4.5%, tightly packed large free lime nests, belite nests with a surrounding of small alites, high porosity, a loose framework of free lime and alkali aluminate, and a flow pattern of matrix into the free-lime nest. Well-burned clinker was said to contain small free lime and octahedral periclase from dolomite and coarse aluminate and ferrite, resulting from equilibrium crystallization. 

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. 

Flame formation must be favorable to a dense, stable coating on the brick refractory lining in the burning zone of the kiln as well as to a nodular clinker formation with low dust content and correctly developed clinker phases. 

The desirable characteristics of Class H well cement were listed by Arbelaez (1990) free lime levels less than 0.5% with a uniform distribution, CjA less than 6.5%, no weathered clinker, using only the 12.7-to 38.1-mm clinker fraction for the cement, relatively hot burning without production of cannibalistic alite, and avoidance of ragged belite by rapid cooling. 

Relatively large alite crystals, typically corroded well-differentiated matrix Clinker burned under oxidizing conditions and cooled to 1250 C in the kiln (Sylla, 1981)... 

Relatively wide and more numerous belite borders on alite which shows lamellar structure, the latter well-developed upon withdrawal from kiln at temperatures lower than 1200°C Clinker burned under reducing conditions, removed from kiln at1200 C, aircooled. Similar texture when removed at 1150°C and quenched in water (Sylla, 1981)... 

Photograph 7-25 Experimental laboratory burn with raw mix containing marl instead of quartz as a silica source. Resulting belite was well scattered in clinker and, to a minor extent, as nests. 1000°C for 30 min, 1425°C for 10 min. Very rapid temperature change. Average alite size = 20 pm. Clinker courtesy of Joe Garcia, Capitol Cement, San Antonio, Texas. (S A6645)... 

Relatively rapid set of cement Clinker burned and cooled under reducing conditions highly reactive, well-crystallized, more abundant C3A, slowly cooled (Sylla, 1981)... 

A relatively "hard-to-burn" feed from the western U.S., with a very impure dolomitic limestone, has 6.7% >125 pm and an acetic-acid insoluble residue of 9.5% >45 pm, the latter comprised of quartz, feldspar, medium to finely crystalline igneous and metamorphic rock fragments, and an abundance of ferro-magnesian minerals (mainly amphiboles and pyroxenes). = 1.6% and = 4.5%. Belite nests (many with tightly packed crystals), solitary belite, and periclase are abundant in this fine- to medium-crystalline clinker. Nevertheless, a high-compressive strength mortar (44.8 to 48.3 MPa) is made, mainly because of the small alite size and the well-scattered solitary belite. 

The chemical enthalpy of the formation of sulfobelitic clinkers is lower than that of ordinary Portland clinkers and even of belitic clinkers. This is due mainly to a lower overall CaO content in the clinker to be produced, as well as to the fact that a fraction of the needed CaO is introduced in the form of calcium sulfate rather than calcium carbonate. The thermal losses are also reduced because of the lower burning temperature... 

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