Belite Size

This parameter is the average of the longest diameters of approximately 10 crystals. Typical belite crystals are seen in Photographs 6-3 through 6-5. In selecting the crystals for measurement one should look for crystals representing the most commonly occurring crystal size. Belite size, in the writer s opinion, is best determined with polished, etched sections or thin sections. 

At a temperature of approximately 1100°C to 1200°C alpha-prime belite forms as small crystals at about 1400°C the crystals change to alpha and exhibit considerable growth. Crystal size of belite, therefore, is primarily dependent on the time maintained above 1400°C—the burning time. 

---

Theisen (1993) described a rapid method of mi croscopical determination of alite and belite size and approximation of visible pore space by recording the number of intercepts along a line of traverse in successive fields of view. The intercept numbers were used with Bogue calculations and related to power consumption (kwh/1) in grinding. Data can be gathered in less than an hour. 

AB = alite birefringence BS = belite size BC = belite color... 

Using alite birefringence and belite size, Ueda and Suzuki (1985) were able to monitor the variable calorific value of coals and make adjustments in the kiln conditions to maintain clinker quality. 

Mor and Perez (1994) presented a critical evaluation of Ono s method (powder mount only) using laboratory heating stages, concluding that the alite size and alite birefringence did not correlate. Correlation was said to be much better with regard to belite size and color. The correspondence between laboratory and industrial kiln microscopy was seriously questioned and differences in environmental conditions, mainly atmospheric composition, were alleged to be responsible. 

Alite crystals, granular, showing strong growth perpendicular to basal pinacoid (0001) due to development of pyramidal faces solely variety concomitant increase in belite size Recrystallization of alite during retention for 120 min at 1600°C melt is low in degree of supersaturation (Maki, Haba, and Takahashi, 1983)... 

Increase in alite and belite sizes, deformed belite, low alite birefringence Dusty, oxidizing divergent flame (Campbell and Weiss, 1987)... 

Belite size increasing, belite abundance decreasing Increasing burning temperature from 1500°C to 1700°C (Suzukawa, Kono, and Fukunaga, 1964)... 

Because the constituent phases of a cement are not equally easy to grind, different particle size fractions differ in composition. Gypsum, and its dehydration products, are concentrated in the finer fractions. Osbaeck and Jons (08) concluded that each 1% of gypsum contributed about 10m kg to the specific surface area in a typical case, some 15% of the total specific surface area is thus due to gypsum. The content of alite decreases, and that of belite increases, with increasing particle size (R12,G30), the contents of aluminate and ferrite phases being little affected. 

Reference Surface of Concrete. The AR concrete s surface, observed by optic microscopy, presents many grains in a homogeneous paste. Most the grain sizes were between 10 and 20 pm some of them are identified by Raman micro-spectroscopy as alite and belite phases (see Fig. la). The most intense peaks of alite and belite are related to the symmetrical stretching mode of the Si-0 bond in the SiO/ unit. Three peaks characterize the alite spectrum at 548, 838 and 880 cm The belite presents several peaks at 371, 416, 533, 552, 840, 853, 889, 945, 973 and 1000 cm All these wavelengths conform to those reported in literature [2,25,26]. 

Ono s doctoral thesis (1963), the most exhaustive study of alite and belite known to the present writer, was concerned with many of the microscopic aspects of phase transformation during production of portland cement clinker. Among his many findings was the fact that alite grows larger with increasing particle size of quartz in the raw feed. 

Kawamura and Mizukami (1969), while investigating the relation between raw feed containing various particle sizes and different Blaines of quartz and feldspar, described belite rings. Ono (1995) stated that belite rings with diameters of 300- to 600-pm develop from coarse silicates (quartz, feldspar, and shale), forming large Type I crystals (40 to 60 pm) which are colorless even in slowly cooled clinkers. 

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. 

Belite—crystal size, optics, morphology and tex ture, recrystallization, gelappster, exclusion of impurity ... 

---