Alite cooling rate

Colorless belite, according to Lee (1983), can occur as very small inclusions in alite and contains very little impurity. Large-crystal, ringlike belite nests (from coarse alkali feldspar) are also colorless because of iron-oxide deficiency. These occurrences of belite, therefore, do not reflect the cooling rate. Consequently, Ono (1978) recommends color observation of roughly 20 pm belite crystals in order to judge the cooling rate. 

Microcrystalline matrix two distinct phases ragged alite (belite coating) and irregular belite prismatic aluminate Slow cooling rate (Fundal, 1980)... 

Photograph 7-90 Dark alkali sulfate in clinker void. Prominently zoned alite. Clearly defined lamellae in relatively small, round belite. Low maximum temperature, long burning time, slow heating rate, slow cooling rate, reducing conditions. (S A6708)... 

Another dopant that may be considered for increasing the reactivity of belite cements is S04 ions (Gies and Knofel, 1987 Stark et al, 1987). Under these conditions the final clinker contains the rather than the a -CjS phase, even if high cooling rates have been employed however, the SO -doped form of yff-dicalcium silicate is much more reactive than its SO -free counterpart. The doped C S typically contains about 3% each of SO3 and AI2O3 in its crystalline lattice. If an SO3-doped belitic clinker that also contains some alite is to be produced, the amoimt of SO3 in the raw meal must not exceed... 

All the effects described above indicate that rapid cooling is desirable the aluminate phase reacts more slowly with water when finely grained and intimately mixed with ferrite, making it easier to control the setting rate (S24), decrease in alite content either from reactions involving the interstitial material or from decomposition is avoided, a higher MgO content can be tolerated, and the clinker is easier to grind. 

Photograph 7-7 Variation in alite crystal sizes clusters of small crystals (14 pm), noncluster crystals (38 pm). Round belite crystals in nest in upper center. High maximum temperature, long burning time, moderately slow heating rate, quickly cooled, 42 MPa. Gas-fired, dry-process kiln, 770 tons/day. (S A6627)... 

Photograph 7-16 Euhedral blue and reddish brown alite round, brown belite with multidirectional lamellae well-differentiated, very finely microcrystalline matrix of aluminate and ferrite. Moderately high maximum temperature, long burning time, moderately slow heating rate, moderately rapidly cooled. Coal-fired, wet-process kiln, 1000 tons/day. Clamshell, clay, iron-ore feed. (S A6636)... 

The average phase composition of Portland cement (ASTM Type I, CSA 10) is -50% alite, C3S -25% belite, P-C2S -12% tricalcium aluminate, C3A -8% ferrite, C4AF > and -3.5% gypsum (Mindness, 1983). The structural order and crystallinity of the cement phases-and hence their hydraulic reactivities-are heavily dependent on the rate of cooling of the clinker ... 

It is generally believed that the rate ofhydration in the first few days of cement compounds in cements proceeds in the order of C3A > C3S > C4AF > C2S. The rate ofhydration of the compounds depends on the crystal size, imperfections, particle size, particle size distribution, the rate of cooling, surface area, the presence of admixtures, the temperature, etc. After ninety days, little or no alite or aluminate phase is detectable. 

---